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third_party/sqlite/src/src/recover.c

Index: third_party/sqlite/src/src/recover.c
diff --git a/third_party/sqlite/src/src/recover.c b/third_party/sqlite/src/src/recover.c
new file mode 100644
index 0000000000000000000000000000000000000000..c996d536b4735be1ee9ed531896094746c7de034
--- /dev/null
+++ b/third_party/sqlite/src/src/recover.c
@@ -0,0 +1,2164 @@
+/*
+** 2012 Jan 11
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+*/
+/* TODO(shess): THIS MODULE IS STILL EXPERIMENTAL.  DO NOT USE IT. */
+/* Implements a virtual table "recover" which can be used to recover
+ * data from a corrupt table.  The table is walked manually, with
+ * corrupt items skipped.  Additionally, any errors while reading will
+ * be skipped.
+ *
+ * Given a table with this definition:
+ *
+ * CREATE TABLE Stuff (
+ *   name TEXT PRIMARY KEY,
+ *   value TEXT NOT NULL
+ * );
+ *
+ * to recover the data from teh table, you could do something like:
+ *
+ * -- Attach another database, the original is not trustworthy.
+ * ATTACH DATABASE '/tmp/db.db' AS rdb;
+ * -- Create a new version of the table.
+ * CREATE TABLE rdb.Stuff (
+ *   name TEXT PRIMARY KEY,
+ *   value TEXT NOT NULL
+ * );
+ * -- This will read the original table's data.
+ * CREATE VIRTUAL TABLE temp.recover_Stuff using recover(
+ *   main.Stuff,
+ *   name TEXT STRICT NOT NULL,  -- only real TEXT data allowed
+ *   value TEXT STRICT NOT NULL
+ * );
+ * -- Corruption means the UNIQUE constraint may no longer hold for
+ * -- Stuff, so either OR REPLACE or OR IGNORE must be used.
+ * INSERT OR REPLACE INTO rdb.Stuff (rowid, name, value )
+ *   SELECT rowid, name, value FROM temp.recover_Stuff;
+ * DROP TABLE temp.recover_Stuff;
+ * DETACH DATABASE rdb;
+ * -- Move db.db to replace original db in filesystem.
+ *
+ *
+ * Usage
+ *
+ * Given the goal of dealing with corruption, it would not be safe to
+ * create a recovery table in the database being recovered.  So
+ * recovery tables must be created in the temp database.  They are not
+ * appropriate to persist, in any case.  [As a bonus, sqlite_master
+ * tables can be recovered.  Perhaps more cute than useful, though.]
+ *
+ * The parameters are a specifier for the table to read, and a column
+ * definition for each bit of data stored in that table.  The named
+ * table must be convertable to a root page number by reading the
+ * sqlite_master table.  Bare table names are assumed to be in
+ * database 0 ("main"), other databases can be specified in db.table
+ * fashion.
+ *
+ * Column definitions are similar to BUT NOT THE SAME AS those
+ * provided to CREATE statements:
+ *  column-def: column-name [type-name [STRICT] [NOT NULL]]
+ *  type-name: (ANY|ROWID|INTEGER|FLOAT|NUMERIC|TEXT|BLOB)
+ *
+ * Only those exact type names are accepted, there is no type
+ * intuition.  The only constraints accepted are STRICT (see below)
+ * and NOT NULL.  Anything unexpected will cause the create to fail.
+ *
+ * ANY is a convenience to indicate that manifest typing is desired.
+ * It is equivalent to not specifying a type at all.  The results for
+ * such columns will have the type of the data's storage.  The exposed
+ * schema will contain no type for that column.
+ *
+ * ROWID is used for columns representing aliases to the rowid
+ * (INTEGER PRIMARY KEY, with or without AUTOINCREMENT), to make the
+ * concept explicit.  Such columns are actually stored as NULL, so
+ * they cannot be simply ignored.  The exposed schema will be INTEGER
+ * for that column.
+ *
+ * NOT NULL causes rows with a NULL in that column to be skipped.  It
+ * also adds NOT NULL to the column in the exposed schema.  If the
+ * table has ever had columns added using ALTER TABLE, then those
+ * columns implicitly contain NULL for rows which have not been
+ * updated.  [Workaround using COALESCE() in your SELECT statement.]
+ *
+ * The created table is read-only, with no indices.  Any SELECT will
+ * be a full-table scan, returning each valid row read from the
+ * storage of the backing table.  The rowid will be the rowid of the
+ * row from the backing table.  "Valid" means:
+ * - The cell metadata for the row is well-formed.  Mainly this means that
+ *   the cell header info describes a payload of the size indicated by
+ *   the cell's payload size.
+ * - The cell does not run off the page.
+ * - The cell does not overlap any other cell on the page.
+ * - The cell contains doesn't contain too many columns.
+ * - The types of the serialized data match the indicated types (see below).
+ *
+ *
+ * Type affinity versus type storage.
+ *
+ * http://www.sqlite.org/datatype3.html describes SQLite's type
+ * affinity system.  The system provides for automated coercion of
+ * types in certain cases, transparently enough that many developers
+ * do not realize that it is happening.  Importantly, it implies that
+ * the raw data stored in the database may not have the obvious type.
+ *
+ * Differences between the stored data types and the expected data
+ * types may be a signal of corruption.  This module makes some
+ * allowances for automatic coercion.  It is important to be concious
+ * of the difference between the schema exposed by the module, and the
+ * data types read from storage.  The following table describes how
+ * the module interprets things:
+ *
+ * type     schema   data                     STRICT
+ * ----     ------   ----                     ------
+ * ANY      <none>   any                      any
+ * ROWID    INTEGER  n/a                      n/a
+ * INTEGER  INTEGER  integer                  integer
+ * FLOAT    FLOAT    integer or float         float
+ * NUMERIC  NUMERIC  integer, float, or text  integer or float
+ * TEXT     TEXT     text or blob             text
+ * BLOB     BLOB     blob                     blob
+ *
+ * type is the type provided to the recover module, schema is the
+ * schema exposed by the module, data is the acceptable types of data
+ * decoded from storage, and STRICT is a modification of that.
+ *
+ * A very loose recovery system might use ANY for all columns, then
+ * use the appropriate sqlite3_column_*() calls to coerce to expected
+ * types.  This doesn't provide much protection if a page from a
+ * different table with the same column count is linked into an
+ * inappropriate btree.
+ *
+ * A very tight recovery system might use STRICT to enforce typing on
+ * all columns, preferring to skip rows which are valid at the storage
+ * level but don't contain the right types.  Note that FLOAT STRICT is
+ * almost certainly not appropriate, since integral values are
+ * transparently stored as integers, when that is more efficient.
+ *
+ * Another option is to use ANY for all columns and inspect each
+ * result manually (using sqlite3_column_*).  This should only be
+ * necessary in cases where developers have used manifest typing (test
+ * to make sure before you decide that you aren't using manifest
+ * typing!).
+ *
+ *
+ * Caveats
+ *
+ * Leaf pages not referenced by interior nodes will not be found.
+ *
+ * Leaf pages referenced from interior nodes of other tables will not
+ * be resolved.
+ *
+ * Rows referencing invalid overflow pages will be skipped.
+ *
+ * SQlite rows have a header which describes how to interpret the rest
+ * of the payload.  The header can be valid in cases where the rest of
+ * the record is actually corrupt (in the sense that the data is not
+ * the intended data).  This can especially happen WRT overflow pages,
+ * as lack of atomic updates between pages is the primary form of
+ * corruption I have seen in the wild.
+ */
+/* The implementation is via a series of cursors.  The cursor
+ * implementations follow the pattern:
+ *
+ * // Creates the cursor using various initialization info.
+ * int cursorCreate(...);
+ *
+ * // Returns 1 if there is no more data, 0 otherwise.
+ * int cursorEOF(Cursor *pCursor);
+ *
+ * // Various accessors can be used if not at EOF.
+ *
+ * // Move to the next item.
+ * int cursorNext(Cursor *pCursor);
+ *
+ * // Destroy the memory associated with the cursor.
+ * void cursorDestroy(Cursor *pCursor);
+ *
+ * References in the following are to sections at
+ * http://www.sqlite.org/fileformat2.html .
+ *
+ * RecoverLeafCursor iterates the records in a leaf table node
+ * described in section 1.5 "B-tree Pages".  When the node is
+ * exhausted, an interior cursor is used to get the next leaf node,
+ * and iteration continues there.
+ *
+ * RecoverInteriorCursor iterates the child pages in an interior table
+ * node described in section 1.5 "B-tree Pages".  When the node is
+ * exhausted, a parent interior cursor is used to get the next
+ * interior node at the same level, and iteration continues there.
+ *
+ * Together these record the path from the leaf level to the root of
+ * the tree.  Iteration happens from the leaves rather than the root
+ * both for efficiency and putting the special case at the front of
+ * the list is easier to implement.
+ *
+ * RecoverCursor uses a RecoverLeafCursor to iterate the rows of a
+ * table, returning results via the SQLite virtual table interface.
+ */
+/* TODO(shess): It might be useful to allow DEFAULT in types to
+ * specify what to do for NULL when an ALTER TABLE case comes up.
+ * Unfortunately, simply adding it to the exposed schema and using
+ * sqlite3_result_null() does not cause the default to be generate.
+ * Handling it ourselves seems hard, unfortunately.
+ */
+
+#include <assert.h>
+#include <ctype.h>
+#include <stdio.h>
+#include <string.h>
+
+/* Internal SQLite things that are used:
+ * u32, u64, i64 types.
+ * Btree, Pager, and DbPage structs.
+ * DbPage.pData, .pPager, and .pgno
+ * sqlite3 struct.
+ * sqlite3BtreePager() and sqlite3BtreeGetPageSize()
+ * sqlite3PagerAcquire() and sqlite3PagerUnref()
+ * getVarint().
+ */
+#include "sqliteInt.h"
+
+/* For debugging. */
+#if 0
+#define FNENTRY() fprintf(stderr, "In %s\n", __FUNCTION__)
+#else
+#define FNENTRY()
+#endif
+
+/* Generic constants and helper functions. */
+
+static const unsigned char kTableLeafPage = 0x0D;
+static const unsigned char kTableInteriorPage = 0x05;
+
+/* From section 1.5. */
+static const unsigned kiPageTypeOffset = 0;
+static const unsigned kiPageFreeBlockOffset = 1;
+static const unsigned kiPageCellCountOffset = 3;
+static const unsigned kiPageCellContentOffset = 5;
+static const unsigned kiPageFragmentedBytesOffset = 7;
+static const unsigned knPageLeafHeaderBytes = 8;
+/* Interior pages contain an additional field. */
+static const unsigned kiPageRightChildOffset = 8;
+static const unsigned kiPageInteriorHeaderBytes = 12;
+
+/* Accepted types are specified by a mask. */
+#define MASK_ROWID (1<<0)
+#define MASK_INTEGER (1<<1)
+#define MASK_FLOAT (1<<2)
+#define MASK_TEXT (1<<3)
+#define MASK_BLOB (1<<4)
+#define MASK_NULL (1<<5)
+
+/* Helpers to decode fixed-size fields. */
+static u32 decodeUnsigned16(const unsigned char *pData){
+  return (pData[0]<<8) + pData[1];
+}
+static u32 decodeUnsigned32(const unsigned char *pData){
+  return (decodeUnsigned16(pData)<<16) + decodeUnsigned16(pData+2);
+}
+static i64 decodeSigned(const unsigned char *pData, unsigned nBytes){
+  i64 r = (char)(*pData);
+  while( --nBytes ){
+    r <<= 8;
+    r += *(++pData);
+  }
+  return r;
+}
+/* Derived from vdbeaux.c, sqlite3VdbeSerialGet(), case 7. */
+/* TODO(shess): Determine if swapMixedEndianFloat() applies. */
+static double decodeFloat64(const unsigned char *pData){
+#if !defined(NDEBUG)
+  static const u64 t1 = ((u64)0x3ff00000)<<32;
+  static const double r1 = 1.0;
+  u64 t2 = t1;
+  assert( sizeof(r1)==sizeof(t2) && memcmp(&r1, &t2, sizeof(r1))==0 );
+#endif
+  i64 x = decodeSigned(pData, 8);
+  double d;
+  memcpy(&d, &x, sizeof(x));
+  return d;
+}
+
+/* Return true if a varint can safely be read from pData/nData. */
+/* TODO(shess): DbPage points into the middle of a buffer which
+ * contains the page data before DbPage.  So code should always be
+ * able to read a small number of varints safely.  Consider whether to
+ * trust that or not.
+ */
+static int checkVarint(const unsigned char *pData, unsigned nData){
+  unsigned i;
+
+  /* In the worst case the decoder takes all 8 bits of the 9th byte. */
+  if( nData>=9 ){
+    return 1;
+  }
+
+  /* Look for a high-bit-clear byte in what's left. */
+  for( i=0; i<nData; ++i ){
+    if( !(pData[i]&0x80) ){
+      return 1;
+    }
+  }
+
+  /* Cannot decode in the space given. */
+  return 0;
+}
+
+/* Return 1 if n varints can be read from pData/nData. */
+static int checkVarints(const unsigned char *pData, unsigned nData,
+                        unsigned n){
+  unsigned nCur = 0;   /* Byte offset within current varint. */
+  unsigned nFound = 0; /* Number of varints found. */
+  unsigned i;
+
+  /* In the worst case the decoder takes all 8 bits of the 9th byte. */
+  if( nData>=9*n ){
+    return 1;
+  }
+
+  for( i=0; nFound<n && i<nData; ++i ){
+    nCur++;
+    if( nCur==9 || !(pData[i]&0x80) ){
+      nFound++;
+      nCur = 0;
+    }
+  }
+
+  return nFound==n;
+}
+
+/* ctype and str[n]casecmp() can be affected by locale (eg, tr_TR).
+ * These versions consider only the ASCII space.
+ */
+/* TODO(shess): It may be reasonable to just remove the need for these
+ * entirely.  The module could require "TEXT STRICT NOT NULL", not
+ * "Text Strict Not Null" or whatever the developer felt like typing
+ * that day.  Handling corrupt data is a PERFECT place to be pedantic.
+ */
+static int ascii_isspace(char c){
+  /* From fts3_expr.c */
+  return c==' ' || c=='\t' || c=='\n' || c=='\r' || c=='\v' || c=='\f';
+}
+static int ascii_isalnum(int x){
+  /* From fts3_tokenizer1.c */
+  return (x>='0' && x<='9') || (x>='A' && x<='Z') || (x>='a' && x<='z');
+}
+static int ascii_tolower(int x){
+  /* From fts3_tokenizer1.c */
+  return (x>='A' && x<='Z') ? x-'A'+'a' : x;
+}
+/* TODO(shess): Consider sqlite3_strnicmp() */
+static int ascii_strncasecmp(const char *s1, const char *s2, size_t n){
+  const unsigned char *us1 = (const unsigned char *)s1;
+  const unsigned char *us2 = (const unsigned char *)s2;
+  while( *us1 && *us2 && n && ascii_tolower(*us1)==ascii_tolower(*us2) ){
+    us1++, us2++, n--;
+  }
+  return n ? ascii_tolower(*us1)-ascii_tolower(*us2) : 0;
+}
+static int ascii_strcasecmp(const char *s1, const char *s2){
+  /* If s2 is equal through strlen(s1), will exit while() due to s1's
+   * trailing NUL, and return NUL-s2[strlen(s1)].
+   */
+  return ascii_strncasecmp(s1, s2, strlen(s1)+1);
+}
+
+/* For some reason I kept making mistakes with offset calculations. */
+static const unsigned char *PageData(DbPage *pPage, unsigned iOffset){
+  assert( iOffset<=pPage->nPageSize );
+  return (unsigned char *)pPage->pData + iOffset;
+}
+
+/* The first page in the file contains a file header in the first 100
+ * bytes.  The page's header information comes after that.  Note that
+ * the offsets in the page's header information are relative to the
+ * beginning of the page, NOT the end of the page header.
+ */
+static const unsigned char *PageHeader(DbPage *pPage){
+  if( pPage->pgno==1 ){
+    const unsigned nDatabaseHeader = 100;
+    return PageData(pPage, nDatabaseHeader);
+  }else{
+    return PageData(pPage, 0);
+  }
+}
+
+/* Helper to fetch the pager and page size for the named database. */
+static int GetPager(sqlite3 *db, const char *zName,
+                    Pager **pPager, unsigned *pnPageSize){
+  Btree *pBt = NULL;
+  int i;
+  for( i=0; i<db->nDb; ++i ){
+    if( ascii_strcasecmp(db->aDb[i].zName, zName)==0 ){
+      pBt = db->aDb[i].pBt;
+      break;
+    }
+  }
+  if( !pBt ){
+    return SQLITE_ERROR;
+  }
+
+  *pPager = sqlite3BtreePager(pBt);
+  *pnPageSize = sqlite3BtreeGetPageSize(pBt) - sqlite3BtreeGetReserve(pBt);
+  return SQLITE_OK;
+}
+
+/* iSerialType is a type read from a record header.  See "2.1 Record Format".
+ */
+
+/* Storage size of iSerialType in bytes.  My interpretation of SQLite
+ * documentation is that text and blob fields can have 32-bit length.
+ * Values past 2^31-12 will need more than 32 bits to encode, which is
+ * why iSerialType is u64.
+ */
+static u32 SerialTypeLength(u64 iSerialType){
+  switch( iSerialType ){
+    case 0 : return 0;  /* NULL */
+    case 1 : return 1;  /* Various integers. */
+    case 2 : return 2;
+    case 3 : return 3;
+    case 4 : return 4;
+    case 5 : return 6;
+    case 6 : return 8;
+    case 7 : return 8;  /* 64-bit float. */
+    case 8 : return 0;  /* Constant 0. */
+    case 9 : return 0;  /* Constant 1. */
+    case 10 : case 11 : assert( !"RESERVED TYPE"); return 0;
+  }
+  return (u32)((iSerialType>>1) - 6);
+}
+
+/* True if iSerialType refers to a blob. */
+static int SerialTypeIsBlob(u64 iSerialType){
+  assert( iSerialType>=12 );
+  return (iSerialType%2)==0;
+}
+
+/* Returns true if the serialized type represented by iSerialType is
+ * compatible with the given type mask.
+ */
+static int SerialTypeIsCompatible(u64 iSerialType, unsigned char mask){
+  switch( iSerialType ){
+    case 0  : return (mask&MASK_NULL)!=0;
+    case 1  : return (mask&MASK_INTEGER)!=0;
+    case 2  : return (mask&MASK_INTEGER)!=0;
+    case 3  : return (mask&MASK_INTEGER)!=0;
+    case 4  : return (mask&MASK_INTEGER)!=0;
+    case 5  : return (mask&MASK_INTEGER)!=0;
+    case 6  : return (mask&MASK_INTEGER)!=0;
+    case 7  : return (mask&MASK_FLOAT)!=0;
+    case 8  : return (mask&MASK_INTEGER)!=0;
+    case 9  : return (mask&MASK_INTEGER)!=0;
+    case 10 : assert( !"RESERVED TYPE"); return 0;
+    case 11 : assert( !"RESERVED TYPE"); return 0;
+  }
+  return (mask&(SerialTypeIsBlob(iSerialType) ? MASK_BLOB : MASK_TEXT));
+}
+
+/* Versions of strdup() with return values appropriate for
+ * sqlite3_free().  malloc.c has sqlite3DbStrDup()/NDup(), but those
+ * need sqlite3DbFree(), which seems intrusive.
+ */
+static char *sqlite3_strndup(const char *z, unsigned n){
+  char *zNew;
+
+  if( z==NULL ){
+    return NULL;
+  }
+
+  zNew = sqlite3_malloc(n+1);
+  if( zNew!=NULL ){
+    memcpy(zNew, z, n);
+    zNew[n] = '\0';
+  }
+  return zNew;
+}
+static char *sqlite3_strdup(const char *z){
+  if( z==NULL ){
+    return NULL;
+  }
+  return sqlite3_strndup(z, strlen(z));
+}
+
+/* Fetch the page number of zTable in zDb from sqlite_master in zDb,
+ * and put it in *piRootPage.
+ */
+static int getRootPage(sqlite3 *db, const char *zDb, const char *zTable,
+                       u32 *piRootPage){
+  char *zSql;  /* SQL selecting root page of named element. */
+  sqlite3_stmt *pStmt;
+  int rc;
+
+  if( strcmp(zTable, "sqlite_master")==0 ){
+    *piRootPage = 1;
+    return SQLITE_OK;
+  }
+
+  zSql = sqlite3_mprintf("SELECT rootpage FROM %s.sqlite_master "
+                         "WHERE type = 'table' AND tbl_name = %Q",
+                         zDb, zTable);
+  if( !zSql ){
+    return SQLITE_NOMEM;
+  }
+
+  rc = sqlite3_prepare_v2(db, zSql, -1, &pStmt, 0);
+  sqlite3_free(zSql);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+
+  /* Require a result. */
+  rc = sqlite3_step(pStmt);
+  if( rc==SQLITE_DONE ){
+    rc = SQLITE_CORRUPT;
+  }else if( rc==SQLITE_ROW ){
+    *piRootPage = sqlite3_column_int(pStmt, 0);
+
+    /* Require only one result. */
+    rc = sqlite3_step(pStmt);
+    if( rc==SQLITE_DONE ){
+      rc = SQLITE_OK;
+    }else if( rc==SQLITE_ROW ){
+      rc = SQLITE_CORRUPT;
+    }
+  }
+  sqlite3_finalize(pStmt);
+  return rc;
+}
+
+static int getEncoding(sqlite3 *db, const char *zDb, int* piEncoding){
+  sqlite3_stmt *pStmt;
+  int rc;
+  char *zSql = sqlite3_mprintf("PRAGMA %s.encoding", zDb);
+  if( !zSql ){
+    return SQLITE_NOMEM;
+  }
+
+  rc = sqlite3_prepare_v2(db, zSql, -1, &pStmt, 0);
+  sqlite3_free(zSql);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+
+  /* Require a result. */
+  rc = sqlite3_step(pStmt);
+  if( rc==SQLITE_DONE ){
+    /* This case should not be possible. */
+    rc = SQLITE_CORRUPT;
+  }else if( rc==SQLITE_ROW ){
+    if( sqlite3_column_type(pStmt, 0)==SQLITE_TEXT ){
+      const char* z = (const char *)sqlite3_column_text(pStmt, 0);
+      /* These strings match the literals in pragma.c. */
+      if( !strcmp(z, "UTF-16le") ){
+        *piEncoding = SQLITE_UTF16LE;
+      }else if( !strcmp(z, "UTF-16be") ){
+        *piEncoding = SQLITE_UTF16BE;
+      }else if( !strcmp(z, "UTF-8") ){
+        *piEncoding = SQLITE_UTF8;
+      }else{
+        /* This case should not be possible. */
+        *piEncoding = SQLITE_UTF8;
+      }
+    }else{
+      /* This case should not be possible. */
+      *piEncoding = SQLITE_UTF8;
+    }
+
+    /* Require only one result. */
+    rc = sqlite3_step(pStmt);
+    if( rc==SQLITE_DONE ){
+      rc = SQLITE_OK;
+    }else if( rc==SQLITE_ROW ){
+      /* This case should not be possible. */
+      rc = SQLITE_CORRUPT;
+    }
+  }
+  sqlite3_finalize(pStmt);
+  return rc;
+}
+
+/* Cursor for iterating interior nodes.  Interior page cells contain a
+ * child page number and a rowid.  The child page contains items left
+ * of the rowid (less than).  The rightmost page of the subtree is
+ * stored in the page header.
+ *
+ * interiorCursorDestroy - release all resources associated with the
+ *                         cursor and any parent cursors.
+ * interiorCursorCreate - create a cursor with the given parent and page.
+ * interiorCursorEOF - returns true if neither the cursor nor the
+ *                     parent cursors can return any more data.
+ * interiorCursorNextPage - fetch the next child page from the cursor.
+ *
+ * Logically, interiorCursorNextPage() returns the next child page
+ * number from the page the cursor is currently reading, calling the
+ * parent cursor as necessary to get new pages to read, until done.
+ * SQLITE_ROW if a page is returned, SQLITE_DONE if out of pages,
+ * error otherwise.  Unfortunately, if the table is corrupted
+ * unexpected pages can be returned.  If any unexpected page is found,
+ * leaf or otherwise, it is returned to the caller for processing,
+ * with the interior cursor left empty.  The next call to
+ * interiorCursorNextPage() will recurse to the parent cursor until an
+ * interior page to iterate is returned.
+ *
+ * Note that while interiorCursorNextPage() will refuse to follow
+ * loops, it does not keep track of pages returned for purposes of
+ * preventing duplication.
+ *
+ * Note that interiorCursorEOF() could return false (not at EOF), and
+ * interiorCursorNextPage() could still return SQLITE_DONE.  This
+ * could happen if there are more cells to iterate in an interior
+ * page, but those cells refer to invalid pages.
+ */
+typedef struct RecoverInteriorCursor RecoverInteriorCursor;
+struct RecoverInteriorCursor {
+  RecoverInteriorCursor *pParent; /* Parent node to this node. */
+  DbPage *pPage;                  /* Reference to leaf page. */
+  unsigned nPageSize;             /* Size of page. */
+  unsigned nChildren;             /* Number of children on the page. */
+  unsigned iChild;                /* Index of next child to return. */
+};
+
+static void interiorCursorDestroy(RecoverInteriorCursor *pCursor){
+  /* Destroy all the cursors to the root. */
+  while( pCursor ){
+    RecoverInteriorCursor *p = pCursor;
+    pCursor = pCursor->pParent;
+
+    if( p->pPage ){
+      sqlite3PagerUnref(p->pPage);
+      p->pPage = NULL;
+    }
+
+    memset(p, 0xA5, sizeof(*p));
+    sqlite3_free(p);
+  }
+}
+
+/* Internal helper.  Reset storage in preparation for iterating pPage. */
+static void interiorCursorSetPage(RecoverInteriorCursor *pCursor,
+                                  DbPage *pPage){
+  const unsigned knMinCellLength = 2 + 4 + 1;
+  unsigned nMaxChildren;
+  assert( PageHeader(pPage)[kiPageTypeOffset]==kTableInteriorPage );
+
+  if( pCursor->pPage ){
+    sqlite3PagerUnref(pCursor->pPage);
+    pCursor->pPage = NULL;
+  }
+  pCursor->pPage = pPage;
+  pCursor->iChild = 0;
+
+  /* A child for each cell, plus one in the header. */
+  pCursor->nChildren = decodeUnsigned16(PageHeader(pPage) +
+                                        kiPageCellCountOffset) + 1;
+
+  /* Each child requires a 16-bit offset from an array after the header,
+   * and each child contains a 32-bit page number and at least a varint
+   * (min size of one byte).  The final child page is in the header.  So
+   * the maximum value for nChildren is:
+   *   (nPageSize - kiPageInteriorHeaderBytes) /
+   *      (sizeof(uint16) + sizeof(uint32) + 1) + 1
+   */
+  /* TODO(shess): This count is very unlikely to be corrupted in
+   * isolation, so seeing this could signal to skip the page.  OTOH, I
+   * can't offhand think of how to get here unless this or the page-type
+   * byte is corrupted.  Could be an overflow page, but it would require
+   * a very large database.
+   */
+  nMaxChildren =
+      (pCursor->nPageSize - kiPageInteriorHeaderBytes) / knMinCellLength + 1;
+  if (pCursor->nChildren > nMaxChildren) {
+    pCursor->nChildren = nMaxChildren;
+  }
+}
+
+static int interiorCursorCreate(RecoverInteriorCursor *pParent,
+                                DbPage *pPage, int nPageSize,
+                                RecoverInteriorCursor **ppCursor){
+  RecoverInteriorCursor *pCursor =
+    sqlite3_malloc(sizeof(RecoverInteriorCursor));
+  if( !pCursor ){
+    return SQLITE_NOMEM;
+  }
+
+  memset(pCursor, 0, sizeof(*pCursor));
+  pCursor->pParent = pParent;
+  pCursor->nPageSize = nPageSize;
+  interiorCursorSetPage(pCursor, pPage);
+  *ppCursor = pCursor;
+  return SQLITE_OK;
+}
+
+/* Internal helper.  Return the child page number at iChild. */
+static unsigned interiorCursorChildPage(RecoverInteriorCursor *pCursor){
+  const unsigned char *pPageHeader;  /* Header of the current page. */
+  const unsigned char *pCellOffsets; /* Offset to page's cell offsets. */
+  unsigned iCellOffset;              /* Offset of target cell. */
+
+  assert( pCursor->iChild<pCursor->nChildren );
+
+  /* Rightmost child is in the header. */
+  pPageHeader = PageHeader(pCursor->pPage);
+  if( pCursor->iChild==pCursor->nChildren-1 ){
+    return decodeUnsigned32(pPageHeader + kiPageRightChildOffset);
+  }
+
+  /* Each cell is a 4-byte integer page number and a varint rowid
+   * which is greater than the rowid of items in that sub-tree (this
+   * module ignores ordering). The offset is from the beginning of the
+   * page, not from the page header.
+   */
+  pCellOffsets = pPageHeader + kiPageInteriorHeaderBytes;
+  iCellOffset = decodeUnsigned16(pCellOffsets + pCursor->iChild*2);
+  if( iCellOffset<=pCursor->nPageSize-4 ){
+    return decodeUnsigned32(PageData(pCursor->pPage, iCellOffset));
+  }
+
+  /* TODO(shess): Check for cell overlaps?  Cells require 4 bytes plus
+   * a varint.  Check could be identical to leaf check (or even a
+   * shared helper testing for "Cells starting in this range"?).
+   */
+
+  /* If the offset is broken, return an invalid page number. */
+  return 0;
+}
+
+static int interiorCursorEOF(RecoverInteriorCursor *pCursor){
+  /* Find a parent with remaining children.  EOF if none found. */
+  while( pCursor && pCursor->iChild>=pCursor->nChildren ){
+    pCursor = pCursor->pParent;
+  }
+  return pCursor==NULL;
+}
+
+/* Internal helper.  Used to detect if iPage would cause a loop. */
+static int interiorCursorPageInUse(RecoverInteriorCursor *pCursor,
+                                   unsigned iPage){
+  /* Find any parent using the indicated page. */
+  while( pCursor && pCursor->pPage->pgno!=iPage ){
+    pCursor = pCursor->pParent;
+  }
+  return pCursor!=NULL;
+}
+
+/* Get the next page from the interior cursor at *ppCursor.  Returns
+ * SQLITE_ROW with the page in *ppPage, or SQLITE_DONE if out of
+ * pages, or the error SQLite returned.
+ *
+ * If the tree is uneven, then when the cursor attempts to get a new
+ * interior page from the parent cursor, it may get a non-interior
+ * page.  In that case, the new page is returned, and *ppCursor is
+ * updated to point to the parent cursor (this cursor is freed).
+ */
+/* TODO(shess): I've tried to avoid recursion in most of this code,
+ * but this case is more challenging because the recursive call is in
+ * the middle of operation.  One option for converting it without
+ * adding memory management would be to retain the head pointer and
+ * use a helper to "back up" as needed.  Another option would be to
+ * reverse the list during traversal.
+ */
+static int interiorCursorNextPage(RecoverInteriorCursor **ppCursor,
+                                  DbPage **ppPage){
+  RecoverInteriorCursor *pCursor = *ppCursor;
+  while( 1 ){
+    int rc;
+    const unsigned char *pPageHeader;  /* Header of found page. */
+
+    /* Find a valid child page which isn't on the stack. */
+    while( pCursor->iChild<pCursor->nChildren ){
+      const unsigned iPage = interiorCursorChildPage(pCursor);
+      pCursor->iChild++;
+      if( interiorCursorPageInUse(pCursor, iPage) ){
+        fprintf(stderr, "Loop detected at %d\n", iPage);
+      }else{
+        int rc = sqlite3PagerAcquire(pCursor->pPage->pPager, iPage, ppPage, 0);
+        if( rc==SQLITE_OK ){
+          return SQLITE_ROW;
+        }
+      }
+    }
+
+    /* This page has no more children.  Get next page from parent. */
+    if( !pCursor->pParent ){
+      return SQLITE_DONE;
+    }
+    rc = interiorCursorNextPage(&pCursor->pParent, ppPage);
+    if( rc!=SQLITE_ROW ){
+      return rc;
+    }
+
+    /* If a non-interior page is received, that either means that the
+     * tree is uneven, or that a child was re-used (say as an overflow
+     * page).  Remove this cursor and let the caller handle the page.
+     */
+    pPageHeader = PageHeader(*ppPage);
+    if( pPageHeader[kiPageTypeOffset]!=kTableInteriorPage ){
+      *ppCursor = pCursor->pParent;
+      pCursor->pParent = NULL;
+      interiorCursorDestroy(pCursor);
+      return SQLITE_ROW;
+    }
+
+    /* Iterate the new page. */
+    interiorCursorSetPage(pCursor, *ppPage);
+    *ppPage = NULL;
+  }
+
+  assert(NULL);  /* NOTREACHED() */
+  return SQLITE_CORRUPT;
+}
+
+/* Large rows are spilled to overflow pages.  The row's main page
+ * stores the overflow page number after the local payload, with a
+ * linked list forward from there as necessary.  overflowMaybeCreate()
+ * and overflowGetSegment() provide an abstraction for accessing such
+ * data while centralizing the code.
+ *
+ * overflowDestroy - releases all resources associated with the structure.
+ * overflowMaybeCreate - create the overflow structure if it is needed
+ *                       to represent the given record.  See function comment.
+ * overflowGetSegment - fetch a segment from the record, accounting
+ *                      for overflow pages.  Segments which are not
+ *                      entirely contained with a page are constructed
+ *                      into a buffer which is returned.  See function comment.
+ */
+typedef struct RecoverOverflow RecoverOverflow;
+struct RecoverOverflow {
+  RecoverOverflow *pNextOverflow;
+  DbPage *pPage;
+  unsigned nPageSize;
+};
+
+static void overflowDestroy(RecoverOverflow *pOverflow){
+  while( pOverflow ){
+    RecoverOverflow *p = pOverflow;
+    pOverflow = p->pNextOverflow;
+
+    if( p->pPage ){
+      sqlite3PagerUnref(p->pPage);
+      p->pPage = NULL;
+    }
+
+    memset(p, 0xA5, sizeof(*p));
+    sqlite3_free(p);
+  }
+}
+
+/* Internal helper.  Used to detect if iPage would cause a loop. */
+static int overflowPageInUse(RecoverOverflow *pOverflow, unsigned iPage){
+  while( pOverflow && pOverflow->pPage->pgno!=iPage ){
+    pOverflow = pOverflow->pNextOverflow;
+  }
+  return pOverflow!=NULL;
+}
+
+/* Setup to access an nRecordBytes record beginning at iRecordOffset
+ * in pPage.  If nRecordBytes can be satisfied entirely from pPage,
+ * then no overflow pages are needed an *pnLocalRecordBytes is set to
+ * nRecordBytes.  Otherwise, *ppOverflow is set to the head of a list
+ * of overflow pages, and *pnLocalRecordBytes is set to the number of
+ * bytes local to pPage.
+ *
+ * overflowGetSegment() will do the right thing regardless of whether
+ * those values are set to be in-page or not.
+ */
+static int overflowMaybeCreate(DbPage *pPage, unsigned nPageSize,
+                               unsigned iRecordOffset, unsigned nRecordBytes,
+                               unsigned *pnLocalRecordBytes,
+                               RecoverOverflow **ppOverflow){
+  unsigned nLocalRecordBytes;  /* Record bytes in the leaf page. */
+  unsigned iNextPage;          /* Next page number for record data. */
+  unsigned nBytes;             /* Maximum record bytes as of current page. */
+  int rc;
+  RecoverOverflow *pFirstOverflow;  /* First in linked list of pages. */
+  RecoverOverflow *pLastOverflow;   /* End of linked list. */
+
+  /* Calculations from the "Table B-Tree Leaf Cell" part of section
+   * 1.5 of http://www.sqlite.org/fileformat2.html .  maxLocal and
+   * minLocal to match naming in btree.c.
+   */
+  const unsigned maxLocal = nPageSize - 35;
+  const unsigned minLocal = ((nPageSize-12)*32/255)-23;  /* m */
+
+  /* Always fit anything smaller than maxLocal. */
+  if( nRecordBytes<=maxLocal ){
+    *pnLocalRecordBytes = nRecordBytes;
+    *ppOverflow = NULL;
+    return SQLITE_OK;
+  }
+
+  /* Calculate the remainder after accounting for minLocal on the leaf
+   * page and what packs evenly into overflow pages.  If the remainder
+   * does not fit into maxLocal, then a partially-full overflow page
+   * will be required in any case, so store as little as possible locally.
+   */
+  nLocalRecordBytes = minLocal+((nRecordBytes-minLocal)%(nPageSize-4));
+  if( maxLocal<nLocalRecordBytes ){
+    nLocalRecordBytes = minLocal;
+  }
+
+  /* Don't read off the end of the page. */
+  if( iRecordOffset+nLocalRecordBytes+4>nPageSize ){
+    return SQLITE_CORRUPT;
+  }
+
+  /* First overflow page number is after the local bytes. */
+  iNextPage =
+      decodeUnsigned32(PageData(pPage, iRecordOffset + nLocalRecordBytes));
+  nBytes = nLocalRecordBytes;
+
+  /* While there are more pages to read, and more bytes are needed,
+   * get another page.
+   */
+  pFirstOverflow = pLastOverflow = NULL;
+  rc = SQLITE_OK;
+  while( iNextPage && nBytes<nRecordBytes ){
+    RecoverOverflow *pOverflow;  /* New overflow page for the list. */
+
+    rc = sqlite3PagerAcquire(pPage->pPager, iNextPage, &pPage, 0);
+    if( rc!=SQLITE_OK ){
+      break;
+    }
+
+    pOverflow = sqlite3_malloc(sizeof(RecoverOverflow));
+    if( !pOverflow ){
+      sqlite3PagerUnref(pPage);
+      rc = SQLITE_NOMEM;
+      break;
+    }
+    memset(pOverflow, 0, sizeof(*pOverflow));
+    pOverflow->pPage = pPage;
+    pOverflow->nPageSize = nPageSize;
+
+    if( !pFirstOverflow ){
+      pFirstOverflow = pOverflow;
+    }else{
+      pLastOverflow->pNextOverflow = pOverflow;
+    }
+    pLastOverflow = pOverflow;
+
+    iNextPage = decodeUnsigned32(pPage->pData);
+    nBytes += nPageSize-4;
+
+    /* Avoid loops. */
+    if( overflowPageInUse(pFirstOverflow, iNextPage) ){
+      fprintf(stderr, "Overflow loop detected at %d\n", iNextPage);
+      rc = SQLITE_CORRUPT;
+      break;
+    }
+  }
+
+  /* If there were not enough pages, or too many, things are corrupt.
+   * Not having enough pages is an obvious problem, all the data
+   * cannot be read.  Too many pages means that the contents of the
+   * row between the main page and the overflow page(s) is
+   * inconsistent (most likely one or more of the overflow pages does
+   * not really belong to this row).
+   */
+  if( rc==SQLITE_OK && (nBytes<nRecordBytes || iNextPage) ){
+    rc = SQLITE_CORRUPT;
+  }
+
+  if( rc==SQLITE_OK ){
+    *ppOverflow = pFirstOverflow;
+    *pnLocalRecordBytes = nLocalRecordBytes;
+  }else if( pFirstOverflow ){
+    overflowDestroy(pFirstOverflow);
+  }
+  return rc;
+}
+
+/* Use in concert with overflowMaybeCreate() to efficiently read parts
+ * of a potentially-overflowing record.  pPage and iRecordOffset are
+ * the values passed into overflowMaybeCreate(), nLocalRecordBytes and
+ * pOverflow are the values returned by that call.
+ *
+ * On SQLITE_OK, *ppBase points to nRequestBytes of data at
+ * iRequestOffset within the record.  If the data exists contiguously
+ * in a page, a direct pointer is returned, otherwise a buffer from
+ * sqlite3_malloc() is returned with the data.  *pbFree is set true if
+ * sqlite3_free() should be called on *ppBase.
+ */
+/* Operation of this function is subtle.  At any time, pPage is the
+ * current page, with iRecordOffset and nLocalRecordBytes being record
+ * data within pPage, and pOverflow being the overflow page after
+ * pPage.  This allows the code to handle both the initial leaf page
+ * and overflow pages consistently by adjusting the values
+ * appropriately.
+ */
+static int overflowGetSegment(DbPage *pPage, unsigned iRecordOffset,
+                              unsigned nLocalRecordBytes,
+                              RecoverOverflow *pOverflow,
+                              unsigned iRequestOffset, unsigned nRequestBytes,
+                              unsigned char **ppBase, int *pbFree){
+  unsigned nBase;         /* Amount of data currently collected. */
+  unsigned char *pBase;   /* Buffer to collect record data into. */
+
+  /* Skip to the page containing the start of the data. */
+  while( iRequestOffset>=nLocalRecordBytes && pOverflow ){
+    /* Factor out current page's contribution. */
+    iRequestOffset -= nLocalRecordBytes;
+
+    /* Move forward to the next page in the list. */
+    pPage = pOverflow->pPage;
+    iRecordOffset = 4;
+    nLocalRecordBytes = pOverflow->nPageSize - iRecordOffset;
+    pOverflow = pOverflow->pNextOverflow;
+  }
+
+  /* If the requested data is entirely within this page, return a
+   * pointer into the page.
+   */
+  if( iRequestOffset+nRequestBytes<=nLocalRecordBytes ){
+    /* TODO(shess): "assignment discards qualifiers from pointer target type"
+     * Having ppBase be const makes sense, but sqlite3_free() takes non-const.
+     */
+    *ppBase = (unsigned char *)PageData(pPage, iRecordOffset + iRequestOffset);
+    *pbFree = 0;
+    return SQLITE_OK;
+  }
+
+  /* The data range would require additional pages. */
+  if( !pOverflow ){
+    /* Should never happen, the range is outside the nRecordBytes
+     * passed to overflowMaybeCreate().
+     */
+    assert(NULL);  /* NOTREACHED */
+    return SQLITE_ERROR;
+  }
+
+  /* Get a buffer to construct into. */
+  nBase = 0;
+  pBase = sqlite3_malloc(nRequestBytes);
+  if( !pBase ){
+    return SQLITE_NOMEM;
+  }
+  while( nBase<nRequestBytes ){
+    /* Copy over data present on this page. */
+    unsigned nCopyBytes = nRequestBytes - nBase;
+    if( nLocalRecordBytes-iRequestOffset<nCopyBytes ){
+      nCopyBytes = nLocalRecordBytes - iRequestOffset;
+    }
+    memcpy(pBase + nBase, PageData(pPage, iRecordOffset + iRequestOffset),
+           nCopyBytes);
+    nBase += nCopyBytes;
+
+    if( pOverflow ){
+      /* Copy from start of record data in future pages. */
+      iRequestOffset = 0;
+
+      /* Move forward to the next page in the list.  Should match
+       * first while() loop.
+       */
+      pPage = pOverflow->pPage;
+      iRecordOffset = 4;
+      nLocalRecordBytes = pOverflow->nPageSize - iRecordOffset;
+      pOverflow = pOverflow->pNextOverflow;
+    }else if( nBase<nRequestBytes ){
+      /* Ran out of overflow pages with data left to deliver.  Not
+       * possible if the requested range fits within nRecordBytes
+       * passed to overflowMaybeCreate() when creating pOverflow.
+       */
+      assert(NULL);  /* NOTREACHED */
+      sqlite3_free(pBase);
+      return SQLITE_ERROR;
+    }
+  }
+  assert( nBase==nRequestBytes );
+  *ppBase = pBase;
+  *pbFree = 1;
+  return SQLITE_OK;
+}
+
+/* Primary structure for iterating the contents of a table.
+ *
+ * leafCursorDestroy - release all resources associated with the cursor.
+ * leafCursorCreate - create a cursor to iterate items from tree at
+ *                    the provided root page.
+ * leafCursorNextValidCell - get the cursor ready to access data from
+ *                           the next valid cell in the table.
+ * leafCursorCellRowid - get the current cell's rowid.
+ * leafCursorCellColumns - get current cell's column count.
+ * leafCursorCellColInfo - get type and data for a column in current cell.
+ *
+ * leafCursorNextValidCell skips cells which fail simple integrity
+ * checks, such as overlapping other cells, or being located at
+ * impossible offsets, or where header data doesn't correctly describe
+ * payload data.  Returns SQLITE_ROW if a valid cell is found,
+ * SQLITE_DONE if all pages in the tree were exhausted.
+ *
+ * leafCursorCellColInfo() accounts for overflow pages in the style of
+ * overflowGetSegment().
+ */
+typedef struct RecoverLeafCursor RecoverLeafCursor;
+struct RecoverLeafCursor {
+  RecoverInteriorCursor *pParent;  /* Parent node to this node. */
+  DbPage *pPage;                   /* Reference to leaf page. */
+  unsigned nPageSize;              /* Size of pPage. */
+  unsigned nCells;                 /* Number of cells in pPage. */
+  unsigned iCell;                  /* Current cell. */
+
+  /* Info parsed from data in iCell. */
+  i64 iRowid;                      /* rowid parsed. */
+  unsigned nRecordCols;            /* how many items in the record. */
+  u64 iRecordOffset;               /* offset to record data. */
+  /* TODO(shess): nRecordBytes and nRecordHeaderBytes are used in
+   * leafCursorCellColInfo() to prevent buffer overruns.
+   * leafCursorCellDecode() already verified that the cell is valid, so
+   * those checks should be redundant.
+   */
+  u64 nRecordBytes;                /* Size of record data. */
+  unsigned nLocalRecordBytes;      /* Amount of record data in-page. */
+  unsigned nRecordHeaderBytes;     /* Size of record header data. */
+  unsigned char *pRecordHeader;    /* Pointer to record header data. */
+  int bFreeRecordHeader;           /* True if record header requires free. */
+  RecoverOverflow *pOverflow;      /* Cell overflow info, if needed. */
+};
+
+/* Internal helper shared between next-page and create-cursor.  If
+ * pPage is a leaf page, it will be stored in the cursor and state
+ * initialized for reading cells.
+ *
+ * If pPage is an interior page, a new parent cursor is created and
+ * injected on the stack.  This is necessary to handle trees with
+ * uneven depth, but also is used during initial setup.
+ *
+ * If pPage is not a table page at all, it is discarded.
+ *
+ * If SQLITE_OK is returned, the caller no longer owns pPage,
+ * otherwise the caller is responsible for discarding it.
+ */
+static int leafCursorLoadPage(RecoverLeafCursor *pCursor, DbPage *pPage){
+  const unsigned char *pPageHeader;  /* Header of *pPage */
+
+  /* Release the current page. */
+  if( pCursor->pPage ){
+    sqlite3PagerUnref(pCursor->pPage);
+    pCursor->pPage = NULL;
+    pCursor->iCell = pCursor->nCells = 0;
+  }
+
+  /* If the page is an unexpected interior node, inject a new stack
+   * layer and try again from there.
+   */
+  pPageHeader = PageHeader(pPage);
+  if( pPageHeader[kiPageTypeOffset]==kTableInteriorPage ){
+    RecoverInteriorCursor *pParent;
+    int rc = interiorCursorCreate(pCursor->pParent, pPage, pCursor->nPageSize,
+                                  &pParent);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+    pCursor->pParent = pParent;
+    return SQLITE_OK;
+  }
+
+  /* Not a leaf page, skip it. */
+  if( pPageHeader[kiPageTypeOffset]!=kTableLeafPage ){
+    sqlite3PagerUnref(pPage);
+    return SQLITE_OK;
+  }
+
+  /* Take ownership of the page and start decoding. */
+  pCursor->pPage = pPage;
+  pCursor->iCell = 0;
+  pCursor->nCells = decodeUnsigned16(pPageHeader + kiPageCellCountOffset);
+  return SQLITE_OK;
+}
+
+/* Get the next leaf-level page in the tree.  Returns SQLITE_ROW when
+ * a leaf page is found, SQLITE_DONE when no more leaves exist, or any
+ * error which occurred.
+ */
+static int leafCursorNextPage(RecoverLeafCursor *pCursor){
+  if( !pCursor->pParent ){
+    return SQLITE_DONE;
+  }
+
+  /* Repeatedly load the parent's next child page until a leaf is found. */
+  do {
+    DbPage *pNextPage;
+    int rc = interiorCursorNextPage(&pCursor->pParent, &pNextPage);
+    if( rc!=SQLITE_ROW ){
+      assert( rc==SQLITE_DONE );
+      return rc;
+    }
+
+    rc = leafCursorLoadPage(pCursor, pNextPage);
+    if( rc!=SQLITE_OK ){
+      sqlite3PagerUnref(pNextPage);
+      return rc;
+    }
+  } while( !pCursor->pPage );
+
+  return SQLITE_ROW;
+}
+
+static void leafCursorDestroyCellData(RecoverLeafCursor *pCursor){
+  if( pCursor->bFreeRecordHeader ){
+    sqlite3_free(pCursor->pRecordHeader);
+  }
+  pCursor->bFreeRecordHeader = 0;
+  pCursor->pRecordHeader = NULL;
+
+  if( pCursor->pOverflow ){
+    overflowDestroy(pCursor->pOverflow);
+    pCursor->pOverflow = NULL;
+  }
+}
+
+static void leafCursorDestroy(RecoverLeafCursor *pCursor){
+  leafCursorDestroyCellData(pCursor);
+
+  if( pCursor->pParent ){
+    interiorCursorDestroy(pCursor->pParent);
+    pCursor->pParent = NULL;
+  }
+
+  if( pCursor->pPage ){
+    sqlite3PagerUnref(pCursor->pPage);
+    pCursor->pPage = NULL;
+  }
+
+  memset(pCursor, 0xA5, sizeof(*pCursor));
+  sqlite3_free(pCursor);
+}
+
+/* Create a cursor to iterate the rows from the leaf pages of a table
+ * rooted at iRootPage.
+ */
+/* TODO(shess): recoverOpen() calls this to setup the cursor, and I
+ * think that recoverFilter() may make a hard assumption that the
+ * cursor returned will turn up at least one valid cell.
+ *
+ * The cases I can think of which break this assumption are:
+ * - pPage is a valid leaf page with no valid cells.
+ * - pPage is a valid interior page with no valid leaves.
+ * - pPage is a valid interior page who's leaves contain no valid cells.
+ * - pPage is not a valid leaf or interior page.
+ */
+static int leafCursorCreate(Pager *pPager, unsigned nPageSize,
+                            u32 iRootPage, RecoverLeafCursor **ppCursor){
+  DbPage *pPage;               /* Reference to page at iRootPage. */
+  RecoverLeafCursor *pCursor;  /* Leaf cursor being constructed. */
+  int rc;
+
+  /* Start out with the root page. */
+  rc = sqlite3PagerAcquire(pPager, iRootPage, &pPage, 0);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+
+  pCursor = sqlite3_malloc(sizeof(RecoverLeafCursor));
+  if( !pCursor ){
+    sqlite3PagerUnref(pPage);
+    return SQLITE_NOMEM;
+  }
+  memset(pCursor, 0, sizeof(*pCursor));
+
+  pCursor->nPageSize = nPageSize;
+
+  rc = leafCursorLoadPage(pCursor, pPage);
+  if( rc!=SQLITE_OK ){
+    sqlite3PagerUnref(pPage);
+    leafCursorDestroy(pCursor);
+    return rc;
+  }
+
+  /* pPage wasn't a leaf page, find the next leaf page. */
+  if( !pCursor->pPage ){
+    rc = leafCursorNextPage(pCursor);
+    if( rc!=SQLITE_DONE && rc!=SQLITE_ROW ){
+      leafCursorDestroy(pCursor);
+      return rc;
+    }
+  }
+
+  *ppCursor = pCursor;
+  return SQLITE_OK;
+}
+
+/* Useful for setting breakpoints. */
+static int ValidateError(){
+  return SQLITE_ERROR;
+}
+
+/* Setup the cursor for reading the information from cell iCell. */
+static int leafCursorCellDecode(RecoverLeafCursor *pCursor){
+  const unsigned char *pPageHeader;  /* Header of current page. */
+  const unsigned char *pPageEnd;     /* Byte after end of current page. */
+  const unsigned char *pCellOffsets; /* Pointer to page's cell offsets. */
+  unsigned iCellOffset;              /* Offset of current cell (iCell). */
+  const unsigned char *pCell;        /* Pointer to data at iCellOffset. */
+  unsigned nCellMaxBytes;            /* Maximum local size of iCell. */
+  unsigned iEndOffset;               /* End of iCell's in-page data. */
+  u64 nRecordBytes;                  /* Expected size of cell, w/overflow. */
+  u64 iRowid;                        /* iCell's rowid (in table). */
+  unsigned nRead;                    /* Amount of cell read. */
+  unsigned nRecordHeaderRead;        /* Header data read. */
+  u64 nRecordHeaderBytes;            /* Header size expected. */
+  unsigned nRecordCols;              /* Columns read from header. */
+  u64 nRecordColBytes;               /* Bytes in payload for those columns. */
+  unsigned i;
+  int rc;
+
+  assert( pCursor->iCell<pCursor->nCells );
+
+  leafCursorDestroyCellData(pCursor);
+
+  /* Find the offset to the row. */
+  pPageHeader = PageHeader(pCursor->pPage);
+  pCellOffsets = pPageHeader + knPageLeafHeaderBytes;
+  pPageEnd = PageData(pCursor->pPage, pCursor->nPageSize);
+  if( pCellOffsets + pCursor->iCell*2 + 2 > pPageEnd ){
+    return ValidateError();
+  }
+  iCellOffset = decodeUnsigned16(pCellOffsets + pCursor->iCell*2);
+  if( iCellOffset>=pCursor->nPageSize ){
+    return ValidateError();
+  }
+
+  pCell = PageData(pCursor->pPage, iCellOffset);
+  nCellMaxBytes = pCursor->nPageSize - iCellOffset;
+
+  /* B-tree leaf cells lead with varint record size, varint rowid and
+   * varint header size.
+   */
+  /* TODO(shess): The smallest page size is 512 bytes, which has an m
+   * of 39.  Three varints need at most 27 bytes to encode.  I think.
+   */
+  if( !checkVarints(pCell, nCellMaxBytes, 3) ){
+    return ValidateError();
+  }
+
+  nRead = getVarint(pCell, &nRecordBytes);
+  assert( iCellOffset+nRead<=pCursor->nPageSize );
+  pCursor->nRecordBytes = nRecordBytes;
+
+  nRead += getVarint(pCell + nRead, &iRowid);
+  assert( iCellOffset+nRead<=pCursor->nPageSize );
+  pCursor->iRowid = (i64)iRowid;
+
+  pCursor->iRecordOffset = iCellOffset + nRead;
+
+  /* Start overflow setup here because nLocalRecordBytes is needed to
+   * check cell overlap.
+   */
+  rc = overflowMaybeCreate(pCursor->pPage, pCursor->nPageSize,
+                           pCursor->iRecordOffset, pCursor->nRecordBytes,
+                           &pCursor->nLocalRecordBytes,
+                           &pCursor->pOverflow);
+  if( rc!=SQLITE_OK ){
+    return ValidateError();
+  }
+
+  /* Check that no other cell starts within this cell. */
+  iEndOffset = pCursor->iRecordOffset + pCursor->nLocalRecordBytes;
+  for( i=0; i<pCursor->nCells && pCellOffsets + i*2 + 2 <= pPageEnd; ++i ){
+    const unsigned iOtherOffset = decodeUnsigned16(pCellOffsets + i*2);
+    if( iOtherOffset>iCellOffset && iOtherOffset<iEndOffset ){
+      return ValidateError();
+    }
+  }
+
+  nRecordHeaderRead = getVarint(pCell + nRead, &nRecordHeaderBytes);
+  assert( nRecordHeaderBytes<=nRecordBytes );
+  pCursor->nRecordHeaderBytes = nRecordHeaderBytes;
+
+  /* Large headers could overflow if pages are small. */
+  rc = overflowGetSegment(pCursor->pPage,
+                          pCursor->iRecordOffset, pCursor->nLocalRecordBytes,
+                          pCursor->pOverflow, 0, nRecordHeaderBytes,
+                          &pCursor->pRecordHeader, &pCursor->bFreeRecordHeader);
+  if( rc!=SQLITE_OK ){
+    return ValidateError();
+  }
+
+  /* Tally up the column count and size of data. */
+  nRecordCols = 0;
+  nRecordColBytes = 0;
+  while( nRecordHeaderRead<nRecordHeaderBytes ){
+    u64 iSerialType;  /* Type descriptor for current column. */
+    if( !checkVarint(pCursor->pRecordHeader + nRecordHeaderRead,
+                     nRecordHeaderBytes - nRecordHeaderRead) ){
+      return ValidateError();
+    }
+    nRecordHeaderRead += getVarint(pCursor->pRecordHeader + nRecordHeaderRead,
+                                   &iSerialType);
+    if( iSerialType==10 || iSerialType==11 ){
+      return ValidateError();
+    }
+    nRecordColBytes += SerialTypeLength(iSerialType);
+    nRecordCols++;
+  }
+  pCursor->nRecordCols = nRecordCols;
+
+  /* Parsing the header used as many bytes as expected. */
+  if( nRecordHeaderRead!=nRecordHeaderBytes ){
+    return ValidateError();
+  }
+
+  /* Calculated record is size of expected record. */
+  if( nRecordHeaderBytes+nRecordColBytes!=nRecordBytes ){
+    return ValidateError();
+  }
+
+  return SQLITE_OK;
+}
+
+static i64 leafCursorCellRowid(RecoverLeafCursor *pCursor){
+  return pCursor->iRowid;
+}
+
+static unsigned leafCursorCellColumns(RecoverLeafCursor *pCursor){
+  return pCursor->nRecordCols;
+}
+
+/* Get the column info for the cell.  Pass NULL for ppBase to prevent
+ * retrieving the data segment.  If *pbFree is true, *ppBase must be
+ * freed by the caller using sqlite3_free().
+ */
+static int leafCursorCellColInfo(RecoverLeafCursor *pCursor,
+                                 unsigned iCol, u64 *piColType,
+                                 unsigned char **ppBase, int *pbFree){
+  const unsigned char *pRecordHeader;  /* Current cell's header. */
+  u64 nRecordHeaderBytes;              /* Bytes in pRecordHeader. */
+  unsigned nRead;                      /* Bytes read from header. */
+  u64 iColEndOffset;                   /* Offset to end of column in cell. */
+  unsigned nColsSkipped;               /* Count columns as procesed. */
+  u64 iSerialType;                     /* Type descriptor for current column. */
+
+  /* Implicit NULL for columns past the end.  This case happens when
+   * rows have not been updated since an ALTER TABLE added columns.
+   * It is more convenient to address here than in callers.
+   */
+  if( iCol>=pCursor->nRecordCols ){
+    *piColType = 0;
+    if( ppBase ){
+      *ppBase = 0;
+      *pbFree = 0;
+    }
+    return SQLITE_OK;
+  }
+
+  /* Must be able to decode header size. */
+  pRecordHeader = pCursor->pRecordHeader;
+  if( !checkVarint(pRecordHeader, pCursor->nRecordHeaderBytes) ){
+    return SQLITE_CORRUPT;
+  }
+
+  /* Rather than caching the header size and how many bytes it took,
+   * decode it every time.
+   */
+  nRead = getVarint(pRecordHeader, &nRecordHeaderBytes);
+  assert( nRecordHeaderBytes==pCursor->nRecordHeaderBytes );
+
+  /* Scan forward to the indicated column.  Scans to _after_ column
+   * for later range checking.
+   */
+  /* TODO(shess): This could get expensive for very wide tables.  An
+   * array of iSerialType could be built in leafCursorCellDecode(), but
+   * the number of columns is dynamic per row, so it would add memory
+   * management complexity.  Enough info to efficiently forward
+   * iterate could be kept, if all clients forward iterate
+   * (recoverColumn() may not).
+   */
+  iColEndOffset = 0;
+  nColsSkipped = 0;
+  while( nColsSkipped<=iCol && nRead<nRecordHeaderBytes ){
+    if( !checkVarint(pRecordHeader + nRead, nRecordHeaderBytes - nRead) ){
+      return SQLITE_CORRUPT;
+    }
+    nRead += getVarint(pRecordHeader + nRead, &iSerialType);
+    iColEndOffset += SerialTypeLength(iSerialType);
+    nColsSkipped++;
+  }
+
+  /* Column's data extends past record's end. */
+  if( nRecordHeaderBytes+iColEndOffset>pCursor->nRecordBytes ){
+    return SQLITE_CORRUPT;
+  }
+
+  *piColType = iSerialType;
+  if( ppBase ){
+    const u32 nColBytes = SerialTypeLength(iSerialType);
+
+    /* Offset from start of record to beginning of column. */
+    const unsigned iColOffset = nRecordHeaderBytes+iColEndOffset-nColBytes;
+
+    return overflowGetSegment(pCursor->pPage, pCursor->iRecordOffset,
+                              pCursor->nLocalRecordBytes, pCursor->pOverflow,
+                              iColOffset, nColBytes, ppBase, pbFree);
+  }
+  return SQLITE_OK;
+}
+
+static int leafCursorNextValidCell(RecoverLeafCursor *pCursor){
+  while( 1 ){
+    int rc;
+
+    /* Move to the next cell. */
+    pCursor->iCell++;
+
+    /* No more cells, get the next leaf. */
+    if( pCursor->iCell>=pCursor->nCells ){
+      rc = leafCursorNextPage(pCursor);
+      if( rc!=SQLITE_ROW ){
+        return rc;
+      }
+      assert( pCursor->iCell==0 );
+    }
+
+    /* If the cell is valid, indicate that a row is available. */
+    rc = leafCursorCellDecode(pCursor);
+    if( rc==SQLITE_OK ){
+      return SQLITE_ROW;
+    }
+
+    /* Iterate until done or a valid row is found. */
+    /* TODO(shess): Remove debugging output. */
+    fprintf(stderr, "Skipping invalid cell\n");
+  }
+  return SQLITE_ERROR;
+}
+
+typedef struct Recover Recover;
+struct Recover {
+  sqlite3_vtab base;
+  sqlite3 *db;                /* Host database connection */
+  char *zDb;                  /* Database containing target table */
+  char *zTable;               /* Target table */
+  unsigned nCols;             /* Number of columns in target table */
+  unsigned char *pTypes;      /* Types of columns in target table */
+};
+
+/* Internal helper for deleting the module. */
+static void recoverRelease(Recover *pRecover){
+  sqlite3_free(pRecover->zDb);
+  sqlite3_free(pRecover->zTable);
+  sqlite3_free(pRecover->pTypes);
+  memset(pRecover, 0xA5, sizeof(*pRecover));
+  sqlite3_free(pRecover);
+}
+
+/* Helper function for initializing the module.  Forward-declared so
+ * recoverCreate() and recoverConnect() can see it.
+ */
+static int recoverInit(
+  sqlite3 *, void *, int, const char *const*, sqlite3_vtab **, char **
+);
+
+static int recoverCreate(
+  sqlite3 *db,
+  void *pAux,
+  int argc, const char *const*argv,
+  sqlite3_vtab **ppVtab,
+  char **pzErr
+){
+  FNENTRY();
+  return recoverInit(db, pAux, argc, argv, ppVtab, pzErr);
+}
+
+/* This should never be called. */
+static int recoverConnect(
+  sqlite3 *db,
+  void *pAux,
+  int argc, const char *const*argv,
+  sqlite3_vtab **ppVtab,
+  char **pzErr
+){
+  FNENTRY();
+  return recoverInit(db, pAux, argc, argv, ppVtab, pzErr);
+}
+
+/* No indices supported. */
+static int recoverBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo){
+  FNENTRY();
+  return SQLITE_OK;
+}
+
+/* Logically, this should never be called. */
+static int recoverDisconnect(sqlite3_vtab *pVtab){
+  FNENTRY();
+  recoverRelease((Recover*)pVtab);
+  return SQLITE_OK;
+}
+
+static int recoverDestroy(sqlite3_vtab *pVtab){
+  FNENTRY();
+  recoverRelease((Recover*)pVtab);
+  return SQLITE_OK;
+}
+
+typedef struct RecoverCursor RecoverCursor;
+struct RecoverCursor {
+  sqlite3_vtab_cursor base;
+  RecoverLeafCursor *pLeafCursor;
+  int iEncoding;
+  int bEOF;
+};
+
+static int recoverOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
+  Recover *pRecover = (Recover*)pVTab;
+  u32 iRootPage;                   /* Root page of the backing table. */
+  int iEncoding;                   /* UTF encoding for backing database. */
+  unsigned nPageSize;              /* Size of pages in backing database. */
+  Pager *pPager;                   /* Backing database pager. */
+  RecoverLeafCursor *pLeafCursor;  /* Cursor to read table's leaf pages. */
+  RecoverCursor *pCursor;          /* Cursor to read rows from leaves. */
+  int rc;
+
+  FNENTRY();
+
+  iRootPage = 0;
+  rc = getRootPage(pRecover->db, pRecover->zDb, pRecover->zTable,
+                   &iRootPage);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+
+  iEncoding = 0;
+  rc = getEncoding(pRecover->db, pRecover->zDb, &iEncoding);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+
+  rc = GetPager(pRecover->db, pRecover->zDb, &pPager, &nPageSize);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+
+  rc = leafCursorCreate(pPager, nPageSize, iRootPage, &pLeafCursor);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+
+  pCursor = sqlite3_malloc(sizeof(RecoverCursor));
+  if( !pCursor ){
+    leafCursorDestroy(pLeafCursor);
+    return SQLITE_NOMEM;
+  }
+  memset(pCursor, 0, sizeof(*pCursor));
+  pCursor->base.pVtab = pVTab;
+  pCursor->pLeafCursor = pLeafCursor;
+  pCursor->iEncoding = iEncoding;
+
+  /* If no leaf pages were found, empty result set. */
+  /* TODO(shess): leafCursorNextValidCell() would return SQLITE_ROW or
+   * SQLITE_DONE to indicate whether there is further data to consider.
+   */
+  pCursor->bEOF = (pLeafCursor->pPage==NULL);
+
+  *ppCursor = (sqlite3_vtab_cursor*)pCursor;
+  return SQLITE_OK;
+}
+
+static int recoverClose(sqlite3_vtab_cursor *cur){
+  RecoverCursor *pCursor = (RecoverCursor*)cur;
+  FNENTRY();
+  if( pCursor->pLeafCursor ){
+    leafCursorDestroy(pCursor->pLeafCursor);
+    pCursor->pLeafCursor = NULL;
+  }
+  memset(pCursor, 0xA5, sizeof(*pCursor));
+  sqlite3_free(cur);
+  return SQLITE_OK;
+}
+
+/* Helpful place to set a breakpoint. */
+static int RecoverInvalidCell(){
+  return SQLITE_ERROR;
+}
+
+/* Returns SQLITE_OK if the cell has an appropriate number of columns
+ * with the appropriate types of data.
+ */
+static int recoverValidateLeafCell(Recover *pRecover, RecoverCursor *pCursor){
+  unsigned i;
+
+  /* If the row's storage has too many columns, skip it. */
+  if( leafCursorCellColumns(pCursor->pLeafCursor)>pRecover->nCols ){
+    return RecoverInvalidCell();
+  }
+
+  /* Skip rows with unexpected types. */
+  for( i=0; i<pRecover->nCols; ++i ){
+    u64 iType;  /* Storage type of column i. */
+    int rc;
+
+    /* ROWID alias. */
+    if( (pRecover->pTypes[i]&MASK_ROWID) ){
+      continue;
+    }
+
+    rc = leafCursorCellColInfo(pCursor->pLeafCursor, i, &iType, NULL, NULL);
+    assert( rc==SQLITE_OK );
+    if( rc!=SQLITE_OK || !SerialTypeIsCompatible(iType, pRecover->pTypes[i]) ){
+      return RecoverInvalidCell();
+    }
+  }
+
+  return SQLITE_OK;
+}
+
+static int recoverNext(sqlite3_vtab_cursor *pVtabCursor){
+  RecoverCursor *pCursor = (RecoverCursor*)pVtabCursor;
+  Recover *pRecover = (Recover*)pCursor->base.pVtab;
+  int rc;
+
+  FNENTRY();
+
+  /* Scan forward to the next cell with valid storage, then check that
+   * the stored data matches the schema.
+   */
+  while( (rc = leafCursorNextValidCell(pCursor->pLeafCursor))==SQLITE_ROW ){
+    if( recoverValidateLeafCell(pRecover, pCursor)==SQLITE_OK ){
+      return SQLITE_OK;
+    }
+  }
+
+  if( rc==SQLITE_DONE ){
+    pCursor->bEOF = 1;
+    return SQLITE_OK;
+  }
+
+  assert( rc!=SQLITE_OK );
+  return rc;
+}
+
+static int recoverFilter(
+  sqlite3_vtab_cursor *pVtabCursor,
+  int idxNum, const char *idxStr,
+  int argc, sqlite3_value **argv
+){
+  RecoverCursor *pCursor = (RecoverCursor*)pVtabCursor;
+  Recover *pRecover = (Recover*)pCursor->base.pVtab;
+  int rc;
+
+  FNENTRY();
+
+  /* There were no valid leaf pages in the table. */
+  if( pCursor->bEOF ){
+    return SQLITE_OK;
+  }
+
+  /* Load the first cell, and iterate forward if it's not valid.  If no cells at
+   * all are valid, recoverNext() sets bEOF and returns appropriately.
+   */
+  rc = leafCursorCellDecode(pCursor->pLeafCursor);
+  if( rc!=SQLITE_OK || recoverValidateLeafCell(pRecover, pCursor)!=SQLITE_OK ){
+    return recoverNext(pVtabCursor);
+  }
+
+  return SQLITE_OK;
+}
+
+static int recoverEof(sqlite3_vtab_cursor *pVtabCursor){
+  RecoverCursor *pCursor = (RecoverCursor*)pVtabCursor;
+  FNENTRY();
+  return pCursor->bEOF;
+}
+
+static int recoverColumn(sqlite3_vtab_cursor *cur, sqlite3_context *ctx, int i){
+  RecoverCursor *pCursor = (RecoverCursor*)cur;
+  Recover *pRecover = (Recover*)pCursor->base.pVtab;
+  u64 iColType;             /* Storage type of column i. */
+  unsigned char *pColData;  /* Column i's data. */
+  int shouldFree;           /* Non-zero if pColData should be freed. */
+  int rc;
+
+  FNENTRY();
+
+  if( i>=pRecover->nCols ){
+    return SQLITE_ERROR;
+  }
+
+  /* ROWID alias. */
+  if( (pRecover->pTypes[i]&MASK_ROWID) ){
+    sqlite3_result_int64(ctx, leafCursorCellRowid(pCursor->pLeafCursor));
+    return SQLITE_OK;
+  }
+
+  pColData = NULL;
+  shouldFree = 0;
+  rc = leafCursorCellColInfo(pCursor->pLeafCursor, i, &iColType,
+                             &pColData, &shouldFree);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+  /* recoverValidateLeafCell() should guarantee that this will never
+   * occur.
+   */
+  if( !SerialTypeIsCompatible(iColType, pRecover->pTypes[i]) ){
+    if( shouldFree ){
+      sqlite3_free(pColData);
+    }
+    return SQLITE_ERROR;
+  }
+
+  switch( iColType ){
+    case 0 : sqlite3_result_null(ctx); break;
+    case 1 : sqlite3_result_int64(ctx, decodeSigned(pColData, 1)); break;
+    case 2 : sqlite3_result_int64(ctx, decodeSigned(pColData, 2)); break;
+    case 3 : sqlite3_result_int64(ctx, decodeSigned(pColData, 3)); break;
+    case 4 : sqlite3_result_int64(ctx, decodeSigned(pColData, 4)); break;
+    case 5 : sqlite3_result_int64(ctx, decodeSigned(pColData, 6)); break;
+    case 6 : sqlite3_result_int64(ctx, decodeSigned(pColData, 8)); break;
+    case 7 : sqlite3_result_double(ctx, decodeFloat64(pColData)); break;
+    case 8 : sqlite3_result_int(ctx, 0); break;
+    case 9 : sqlite3_result_int(ctx, 1); break;
+    case 10 : assert( iColType!=10 ); break;
+    case 11 : assert( iColType!=11 ); break;
+
+    default : {
+      u32 l = SerialTypeLength(iColType);
+
+      /* If pColData was already allocated, arrange to pass ownership. */
+      sqlite3_destructor_type pFn = SQLITE_TRANSIENT;
+      if( shouldFree ){
+        pFn = sqlite3_free;
+        shouldFree = 0;
+      }
+
+      if( SerialTypeIsBlob(iColType) ){
+        sqlite3_result_blob(ctx, pColData, l, pFn);
+      }else{
+        if( pCursor->iEncoding==SQLITE_UTF16LE ){
+          sqlite3_result_text16le(ctx, (const void*)pColData, l, pFn);
+        }else if( pCursor->iEncoding==SQLITE_UTF16BE ){
+          sqlite3_result_text16be(ctx, (const void*)pColData, l, pFn);
+        }else{
+          sqlite3_result_text(ctx, (const char*)pColData, l, pFn);
+        }
+      }
+    } break;
+  }
+  if( shouldFree ){
+    sqlite3_free(pColData);
+  }
+  return SQLITE_OK;
+}
+
+static int recoverRowid(sqlite3_vtab_cursor *pVtabCursor, sqlite_int64 *pRowid){
+  RecoverCursor *pCursor = (RecoverCursor*)pVtabCursor;
+  FNENTRY();
+  *pRowid = leafCursorCellRowid(pCursor->pLeafCursor);
+  return SQLITE_OK;
+}
+
+static sqlite3_module recoverModule = {
+  0,                         /* iVersion */
+  recoverCreate,             /* xCreate - create a table */
+  recoverConnect,            /* xConnect - connect to an existing table */
+  recoverBestIndex,          /* xBestIndex - Determine search strategy */
+  recoverDisconnect,         /* xDisconnect - Disconnect from a table */
+  recoverDestroy,            /* xDestroy - Drop a table */
+  recoverOpen,               /* xOpen - open a cursor */
+  recoverClose,              /* xClose - close a cursor */
+  recoverFilter,             /* xFilter - configure scan constraints */
+  recoverNext,               /* xNext - advance a cursor */
+  recoverEof,                /* xEof */
+  recoverColumn,             /* xColumn - read data */
+  recoverRowid,              /* xRowid - read data */
+  0,                         /* xUpdate - write data */
+  0,                         /* xBegin - begin transaction */
+  0,                         /* xSync - sync transaction */
+  0,                         /* xCommit - commit transaction */
+  0,                         /* xRollback - rollback transaction */
+  0,                         /* xFindFunction - function overloading */
+  0,                         /* xRename - rename the table */
+};
+
+int recoverVtableInit(sqlite3 *db){
+  return sqlite3_create_module_v2(db, "recover", &recoverModule, NULL, 0);
+}
+
+/* This section of code is for parsing the create input and
+ * initializing the module.
+ */
+
+/* Find the next word in zText and place the endpoints in pzWord*.
+ * Returns true if the word is non-empty.  "Word" is defined as
+ * ASCII alphanumeric plus '_' at this time.
+ */
+static int findWord(const char *zText,
+                    const char **pzWordStart, const char **pzWordEnd){
+  int r;
+  while( ascii_isspace(*zText) ){
+    zText++;
+  }
+  *pzWordStart = zText;
+  while( ascii_isalnum(*zText) || *zText=='_' ){
+    zText++;
+  }
+  r = zText>*pzWordStart;  /* In case pzWordStart==pzWordEnd */
+  *pzWordEnd = zText;
+  return r;
+}
+
+/* Return true if the next word in zText is zWord, also setting
+ * *pzContinue to the character after the word.
+ */
+static int expectWord(const char *zText, const char *zWord,
+                      const char **pzContinue){
+  const char *zWordStart, *zWordEnd;
+  if( findWord(zText, &zWordStart, &zWordEnd) &&
+      ascii_strncasecmp(zWord, zWordStart, zWordEnd - zWordStart)==0 ){
+    *pzContinue = zWordEnd;
+    return 1;
+  }
+  return 0;
+}
+
+/* Parse the name and type information out of parameter.  In case of
+ * success, *pzNameStart/End contain the name of the column,
+ * *pzTypeStart/End contain the top-level type, and *pTypeMask has the
+ * type mask to use for the column.
+ */
+static int findNameAndType(const char *parameter,
+                           const char **pzNameStart, const char **pzNameEnd,
+                           const char **pzTypeStart, const char **pzTypeEnd,
+                           unsigned char *pTypeMask){
+  unsigned nNameLen;   /* Length of found name. */
+  const char *zEnd;    /* Current end of parsed column information. */
+  int bNotNull;        /* Non-zero if NULL is not allowed for name. */
+  int bStrict;         /* Non-zero if column requires exact type match. */
+  const char *zDummy;  /* Dummy parameter, result unused. */
+  unsigned i;
+
+  /* strictMask is used for STRICT, strictMask|otherMask if STRICT is
+   * not supplied.  zReplace provides an alternate type to expose to
+   * the caller.
+   */
+  static struct {
+    const char *zName;
+    unsigned char strictMask;
+    unsigned char otherMask;
+    const char *zReplace;
+  } kTypeInfo[] = {
+    { "ANY",
+      MASK_INTEGER | MASK_FLOAT | MASK_BLOB | MASK_TEXT | MASK_NULL,
+      0, "",
+    },
+    { "ROWID",   MASK_INTEGER | MASK_ROWID,             0, "INTEGER", },
+    { "INTEGER", MASK_INTEGER | MASK_NULL,              0, NULL, },
+    { "FLOAT",   MASK_FLOAT | MASK_NULL,                MASK_INTEGER, NULL, },
+    { "NUMERIC", MASK_INTEGER | MASK_FLOAT | MASK_NULL, MASK_TEXT, NULL, },
+    { "TEXT",    MASK_TEXT | MASK_NULL,                 MASK_BLOB, NULL, },
+    { "BLOB",    MASK_BLOB | MASK_NULL,                 0, NULL, },
+  };
+
+  if( !findWord(parameter, pzNameStart, pzNameEnd) ){
+    return SQLITE_MISUSE;
+  }
+
+  /* Manifest typing, accept any storage type. */
+  if( !findWord(*pzNameEnd, pzTypeStart, pzTypeEnd) ){
+    *pzTypeEnd = *pzTypeStart = "";
+    *pTypeMask = MASK_INTEGER | MASK_FLOAT | MASK_BLOB | MASK_TEXT | MASK_NULL;
+    return SQLITE_OK;
+  }
+
+  nNameLen = *pzTypeEnd - *pzTypeStart;
+  for( i=0; i<ArraySize(kTypeInfo); ++i ){
+    if( ascii_strncasecmp(kTypeInfo[i].zName, *pzTypeStart, nNameLen)==0 ){
+      break;
+    }
+  }
+  if( i==ArraySize(kTypeInfo) ){
+    return SQLITE_MISUSE;
+  }
+
+  zEnd = *pzTypeEnd;
+  bStrict = 0;
+  if( expectWord(zEnd, "STRICT", &zEnd) ){
+    /* TODO(shess): Ick.  But I don't want another single-purpose
+     * flag, either.
+     */
+    if( kTypeInfo[i].zReplace && !kTypeInfo[i].zReplace[0] ){
+      return SQLITE_MISUSE;
+    }
+    bStrict = 1;
+  }
+
+  bNotNull = 0;
+  if( expectWord(zEnd, "NOT", &zEnd) ){
+    if( expectWord(zEnd, "NULL", &zEnd) ){
+      bNotNull = 1;
+    }else{
+      /* Anything other than NULL after NOT is an error. */
+      return SQLITE_MISUSE;
+    }
+  }
+
+  /* Anything else is an error. */
+  if( findWord(zEnd, &zDummy, &zDummy) ){
+    return SQLITE_MISUSE;
+  }
+
+  *pTypeMask = kTypeInfo[i].strictMask;
+  if( !bStrict ){
+    *pTypeMask |= kTypeInfo[i].otherMask;
+  }
+  if( bNotNull ){
+    *pTypeMask &= ~MASK_NULL;
+  }
+  if( kTypeInfo[i].zReplace ){
+    *pzTypeStart = kTypeInfo[i].zReplace;
+    *pzTypeEnd = *pzTypeStart + strlen(*pzTypeStart);
+  }
+  return SQLITE_OK;
+}
+
+/* Parse the arguments, placing type masks in *pTypes and the exposed
+ * schema in *pzCreateSql (for sqlite3_declare_vtab).
+ */
+static int ParseColumnsAndGenerateCreate(unsigned nCols,
+                                         const char *const *pCols,
+                                         char **pzCreateSql,
+                                         unsigned char *pTypes,
+                                         char **pzErr){
+  unsigned i;
+  char *zCreateSql = sqlite3_mprintf("CREATE TABLE x(");
+  if( !zCreateSql ){
+    return SQLITE_NOMEM;
+  }
+
+  for( i=0; i<nCols; i++ ){
+    const char *zSep = (i < nCols - 1 ? ", " : ")");
+    const char *zNotNull = "";
+    const char *zNameStart, *zNameEnd;
+    const char *zTypeStart, *zTypeEnd;
+    int rc = findNameAndType(pCols[i],
+                             &zNameStart, &zNameEnd,
+                             &zTypeStart, &zTypeEnd,
+                             &pTypes[i]);
+    if( rc!=SQLITE_OK ){
+      *pzErr = sqlite3_mprintf("unable to parse column %d", i);
+      sqlite3_free(zCreateSql);
+      return rc;
+    }
+
+    if( !(pTypes[i]&MASK_NULL) ){
+      zNotNull = " NOT NULL";
+    }
+
+    /* Add name and type to the create statement. */
+    zCreateSql = sqlite3_mprintf("%z%.*s %.*s%s%s",
+                                 zCreateSql,
+                                 zNameEnd - zNameStart, zNameStart,
+                                 zTypeEnd - zTypeStart, zTypeStart,
+                                 zNotNull, zSep);
+    if( !zCreateSql ){
+      return SQLITE_NOMEM;
+    }
+  }
+
+  *pzCreateSql = zCreateSql;
+  return SQLITE_OK;
+}
+
+/* Helper function for initializing the module. */
+/* argv[0] module name
+ * argv[1] db name for virtual table
+ * argv[2] virtual table name
+ * argv[3] backing table name
+ * argv[4] columns
+ */
+/* TODO(shess): Since connect isn't supported, could inline into
+ * recoverCreate().
+ */
+/* TODO(shess): Explore cases where it would make sense to set *pzErr. */
+static int recoverInit(
+  sqlite3 *db,                        /* Database connection */
+  void *pAux,                         /* unused */
+  int argc, const char *const*argv,   /* Parameters to CREATE TABLE statement */
+  sqlite3_vtab **ppVtab,              /* OUT: New virtual table */
+  char **pzErr                        /* OUT: Error message, if any */
+){
+  const unsigned kTypeCol = 4;  /* First argument with column type info. */
+  Recover *pRecover;            /* Virtual table structure being created. */
+  char *zDot;                   /* Any dot found in "db.table" backing. */
+  u32 iRootPage;                /* Root page of backing table. */
+  char *zCreateSql;             /* Schema of created virtual table. */
+  int rc;
+
+  /* Require to be in the temp database. */
+  if( ascii_strcasecmp(argv[1], "temp")!=0 ){
+    *pzErr = sqlite3_mprintf("recover table must be in temp database");
+    return SQLITE_MISUSE;
+  }
+
+  /* Need the backing table and at least one column. */
+  if( argc<=kTypeCol ){
+    *pzErr = sqlite3_mprintf("no columns specified");
+    return SQLITE_MISUSE;
+  }
+
+  pRecover = sqlite3_malloc(sizeof(Recover));
+  if( !pRecover ){
+    return SQLITE_NOMEM;
+  }
+  memset(pRecover, 0, sizeof(*pRecover));
+  pRecover->base.pModule = &recoverModule;
+  pRecover->db = db;
+
+  /* Parse out db.table, assuming main if no dot. */
+  zDot = strchr(argv[3], '.');
+  if( !zDot ){
+    pRecover->zDb = sqlite3_strdup(db->aDb[0].zName);
+    pRecover->zTable = sqlite3_strdup(argv[3]);
+  }else if( zDot>argv[3] && zDot[1]!='\0' ){
+    pRecover->zDb = sqlite3_strndup(argv[3], zDot - argv[3]);
+    pRecover->zTable = sqlite3_strdup(zDot + 1);
+  }else{
+    /* ".table" or "db." not allowed. */
+    *pzErr = sqlite3_mprintf("ill-formed table specifier");
+    recoverRelease(pRecover);
+    return SQLITE_ERROR;
+  }
+
+  pRecover->nCols = argc - kTypeCol;
+  pRecover->pTypes = sqlite3_malloc(pRecover->nCols);
+  if( !pRecover->zDb || !pRecover->zTable || !pRecover->pTypes ){
+    recoverRelease(pRecover);
+    return SQLITE_NOMEM;
+  }
+
+  /* Require the backing table to exist. */
+  /* TODO(shess): Be more pedantic about the form of the descriptor
+   * string.  This already fails for poorly-formed strings, simply
+   * because there won't be a root page, but it would make more sense
+   * to be explicit.
+   */
+  rc = getRootPage(pRecover->db, pRecover->zDb, pRecover->zTable, &iRootPage);
+  if( rc!=SQLITE_OK ){
+    *pzErr = sqlite3_mprintf("unable to find backing table");
+    recoverRelease(pRecover);
+    return rc;
+  }
+
+  /* Parse the column definitions. */
+  rc = ParseColumnsAndGenerateCreate(pRecover->nCols, argv + kTypeCol,
+                                     &zCreateSql, pRecover->pTypes, pzErr);
+  if( rc!=SQLITE_OK ){
+    recoverRelease(pRecover);
+    return rc;
+  }
+
+  rc = sqlite3_declare_vtab(db, zCreateSql);
+  sqlite3_free(zCreateSql);
+  if( rc!=SQLITE_OK ){
+    recoverRelease(pRecover);
+    return rc;
+  }
+
+  *ppVtab = (sqlite3_vtab *)pRecover;
+  return SQLITE_OK;
+}