Completely rewrite the PpdProvider/PpdCache to use the SCS backend. Along the way, clean it up a l…

chromeos/printing/ppd_cache.cc

Index: chromeos/printing/ppd_cache.cc
diff --git a/chromeos/printing/ppd_cache.cc b/chromeos/printing/ppd_cache.cc
index 2674d50fb96957295f7047c32a2281ccfcdae8ff..44abfd9565168c4122bf1cf794be57929bea3c7b 100644
--- a/chromeos/printing/ppd_cache.cc
+++ b/chromeos/printing/ppd_cache.cc
@@ -7,6 +7,7 @@
 #include <utility>
 #include <vector>
 
+#include "base/bind.h"
 #include "base/files/file_util.h"
 #include "base/json/json_parser.h"
 #include "base/json/json_writer.h"
@@ -14,9 +15,11 @@
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/synchronization/lock.h"
+#include "base/threading/sequenced_task_runner_handle.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/time/time.h"
 #include "base/values.h"
+#include "chromeos/printing/printing_constants.h"
 #include "crypto/sha2.h"
 #include "net/base/io_buffer.h"
 #include "net/filter/gzip_header.h"
@@ -25,274 +28,138 @@ namespace chromeos {
 namespace printing {
 namespace {
 
-// Name of the file we use to cache the list of available printer drivers from
-// QuirksServer.  This file resides in the cache directory.
-const char kAvailablePrintersFilename[] = "all_printers.json";
-
-// Return true if it looks like contents is already gzipped, false otherwise.
-bool IsGZipped(const std::string& contents) {
-  const char* ignored;
-  net::GZipHeader header;
-  return header.ReadMore(contents.data(), contents.size(), &ignored) ==
-         net::GZipHeader::COMPLETE_HEADER;
-}
-
 class PpdCacheImpl : public PpdCache {
  public:
   PpdCacheImpl(const base::FilePath& cache_base_dir,
-               const PpdCache::Options& options)
-      : cache_base_dir_(cache_base_dir),
-        available_printers_file_(
-            cache_base_dir.Append(kAvailablePrintersFilename)),
-        options_(options) {}
-  ~PpdCacheImpl() override {}
+               const scoped_refptr<base::SequencedTaskRunner>& disk_task_runner)
+      : cache_base_dir_(cache_base_dir), disk_task_runner_(disk_task_runner) {}
 
   // Public API functions.
-  base::Optional<base::FilePath> Find(
-      const Printer::PpdReference& reference) const override {
-    base::AutoLock l(lock_);
-    base::ThreadRestrictions::AssertIOAllowed();
-    base::Optional<base::FilePath> ret;
+  void Find(const std::string& key, const FindCallback& cb) override {
+    // Ensure the cache lives until the op is over.
+    AddRef();
+    ++inflight_ops_;
+    disk_task_runner_->PostTask(
+        FROM_HERE, base::Bind(&PpdCacheImpl::FindImpl, this, key,
+                              base::SequencedTaskRunnerHandle::Get(), cb));
+  }
 
-    // We can't know here if we have a gzipped or un-gzipped version, so just
-    // look for both.
-    base::FilePath contents_path_base = GetCachePathBase(reference);
-    for (const std::string& extension : {".ppd", ".ppd.gz"}) {
-      base::FilePath contents_path = contents_path_base.AddExtension(extension);
-      if (base::PathExists(contents_path)) {
-        ret = contents_path;
-        break;
-      }
-    }
-    return ret;
+  // Store the given contents at the given key.  If cb is non-null, it will
+  // be invoked on completion.
+  void Store(const std::string& key,
+             const std::string& contents,
+             const base::Callback<void()>& cb) override {
+    AddRef();
+    ++inflight_ops_;
+    disk_task_runner_->PostTask(
+        FROM_HERE, base::Bind(&PpdCacheImpl::StoreImpl, this, key, contents,
+                              base::SequencedTaskRunnerHandle::Get(), cb));
   }
 
-  base::Optional<base::FilePath> Store(
-      const Printer::PpdReference& reference,
-      const std::string& ppd_contents) override {
-    base::ThreadRestrictions::AssertIOAllowed();
-    base::AutoLock l(lock_);
-    if (!EnsureCacheDirectoryExists()) {
-      return base::nullopt;
-    }
-    base::Optional<base::FilePath> ret;
-    base::FilePath contents_path =
-        GetCachePathBase(reference).AddExtension(".ppd");
-    if (IsGZipped(ppd_contents)) {
-      contents_path = contents_path.AddExtension(".gz");
-    }
-    if (base::WriteFile(contents_path, ppd_contents.data(),
-                        ppd_contents.size()) ==
-        static_cast<int>(ppd_contents.size())) {
-      ret = contents_path;
-    } else {
-      LOG(ERROR) << "Failed to write " << contents_path.LossyDisplayName();
-      // Try to clean up the file, as it may have partial contents.  Note that
-      // DeleteFile(nonexistant file) should return true, so failure here means
-      // something is exceptionally hosed.
-      if (!base::DeleteFile(contents_path, false)) {
-        LOG(ERROR) << "Failed to cleanup partially-written file "
-                   << contents_path.LossyDisplayName();
-        return ret;
-      }
+  bool Idle() const override { return inflight_ops_ == 0; }
+
+ private:
+  ~PpdCacheImpl() override {}
+
+  // If the cache doesn't already exist, create it.
+  void MaybeCreateCache() {
+    if (!base::PathExists(cache_base_dir_)) {
+      base::CreateDirectory(cache_base_dir_);
     }
-    return ret;
   }
 
-  base::Optional<PpdProvider::AvailablePrintersMap> FindAvailablePrinters()
-      override {
+  // Find implementation, runs on the i/o thread.
+  void FindImpl(const std::string& key,
+                const scoped_refptr<base::SequencedTaskRunner>& callback_runner,
+                const FindCallback& cb) {
     base::ThreadRestrictions::AssertIOAllowed();
-    base::AutoLock l(lock_);
-    if (available_printers_ != nullptr &&
-        base::Time::Now() - available_printers_timestamp_ <
-            options_.max_available_list_staleness) {
-      // Satisfy from memory cache.
-      return *available_printers_;
-    }
-    std::string buf;
-    if (!MaybeReadAvailablePrintersCache(&buf)) {
-      // Disk cache miss.
-      return base::nullopt;
-    }
-    auto dict = base::DictionaryValue::From(base::JSONReader::Read(buf));
-    if (dict == nullptr) {
-      LOG(ERROR) << "Failed to deserialize available printers cache";
-      return base::nullopt;
-    }
-    // Note if we got here, we've already set available_printers_timestamp_ to
-    // the mtime of the file we read from.
-    available_printers_ = base::MakeUnique<PpdProvider::AvailablePrintersMap>();
-    const base::ListValue* models;
-    std::string model;
-    for (base::DictionaryValue::Iterator it(*dict); !it.IsAtEnd();
-         it.Advance()) {
-      auto& out = (*available_printers_)[it.key()];
-      if (!it.value().GetAsList(&models)) {
-        LOG(ERROR) << "Skipping malformed printer make: " << it.key();
-        continue;
-      }
-      for (const auto& model_value : *models) {
-        if (model_value->GetAsString(&model)) {
-          out.push_back(model);
-        } else {
-          LOG(ERROR) << "Skipping malformed printer model in: " << it.key()
-                     << ".  Expected a string, found a "
-                     << base::Value::GetTypeName(model_value->GetType());
+    FindResult result;
+    result.success = false;
+    MaybeCreateCache();
+    base::File file(FilePathForKey(key),
+                    base::File::FLAG_OPEN | base::File::FLAG_READ);
+
+    if (file.IsValid()) {
+      int64_t len = file.GetLength();
+      if (len >= static_cast<int64_t>(crypto::kSHA256Length) &&
+          len <= static_cast<int64_t>(kMaxPpdSizeBytes) +
+                     static_cast<int64_t>(crypto::kSHA256Length)) {
+        std::unique_ptr<char[]> buf(new char[len]);
+        if (file.ReadAtCurrentPos(buf.get(), len) == len) {
+          base::StringPiece contents(buf.get(), len - crypto::kSHA256Length);
+          base::StringPiece checksum(buf.get() + len - crypto::kSHA256Length,
+                                     crypto::kSHA256Length);
+          if (crypto::SHA256HashString(contents) == checksum) {
+            base::File::Info info;
+            if (file.GetInfo(&info)) {
+              result.success = true;
+              result.age = base::Time::Now() - info.last_modified;
+              contents.CopyToString(&result.contents);
+            }
+          } else {
+            LOG(ERROR) << "Bad checksum for cache key " << key;
+          }
         }
       }
     }
-    return *available_printers_;
-  }
-
-  // Note we throw up our hands and fail (gracefully) to store if we encounter
-  // non-unicode things in the strings of |available_printers|.  Since these
-  // strings come from a source we control, being less paranoid about these
-  // values seems reasonable.
-  void StoreAvailablePrinters(std::unique_ptr<PpdProvider::AvailablePrintersMap>
-                                  available_printers) override {
-    base::ThreadRestrictions::AssertIOAllowed();
-    base::AutoLock l(lock_);
-    if (!EnsureCacheDirectoryExists()) {
-      return;
-    }
-    available_printers_ = std::move(available_printers);
-    available_printers_timestamp_ = base::Time::Now();
-    // Convert the map to Values, in preparation for jsonification.
-    base::DictionaryValue top_level;
-    for (const auto& entry : *available_printers_) {
-      auto printers = base::MakeUnique<base::ListValue>();
-      printers->AppendStrings(entry.second);
-      top_level.Set(entry.first, std::move(printers));
-    }
-    std::string contents;
-    if (!base::JSONWriter::Write(top_level, &contents)) {
-      LOG(ERROR) << "Failed to generate JSON";
-      return;
-    }
-    if (contents.size() > options_.max_available_list_cached_size) {
-      LOG(ERROR) << "Serialized available printers list too large (size is "
-                 << contents.size() << " bytes)";
-      return;
-    }
-    if (base::WriteFile(available_printers_file_, contents.data(),
-                        contents.size()) != static_cast<int>(contents.size())) {
-      LOG(ERROR) << "Failed to write available printers cache to "
-                 << available_printers_file_.MaybeAsASCII();
-    }
+    callback_runner->PostTask(FROM_HERE,
+                              base::Bind(&PpdCacheImpl::ReplyAndRelease, this,
+                                         base::Bind(cb, result)));
   }
 
- private:
-  // Create the cache directory if it doesn't already exist.  Returns true
-  // on success.
-  bool EnsureCacheDirectoryExists() {
-    if (base::PathExists(cache_base_dir_) ||
-        base::CreateDirectory(cache_base_dir_)) {
-      return true;
+  // If |cb| is non-null, invoke it on this thread, then decrement the refcount.
+  void ReplyAndRelease(const base::Callback<void()>& cb) {
+    if (!cb.is_null()) {
+      cb.Run();
     }
-    LOG(ERROR) << "Failed to create ppd cache directory "
-               << cache_base_dir_.MaybeAsASCII();
-    return false;
+    --inflight_ops_;
+    Release();
+    // Object may be destroyed here, so no further access to object data
+    // allowed.
   }
 
-  // Get the file path at which we expect to find a PPD if it's cached.
-  //
-  // This is, ultimately, just a hash function.  It's extremely infrequently
-  // used (called once when trying to look up information on a printer or store
-  // a PPD), and should be stable, as changing the function will make previously
-  // cached entries unfindable, causing resolve logic to be reinvoked
-  // unnecessarily.
-  //
-  // There's also a faint possibility that a bad actor might try to do something
-  // nefarious by intentionally causing a cache collision that makes the wrong
-  // PPD be used for a printer.  There's no obvious attack vector, but
-  // there's also no real cost to being paranoid here, so we use SHA-256 as the
-  // underlying hash function, and inject fixed field prefixes to prevent
-  // field-substitution spoofing.  This also buys us hash function stability at
-  // the same time.
-  //
-  // Also, care should be taken to preserve the existing hash values if new
-  // fields are added to PpdReference -- that is, if a new field F is added
-  // to PpdReference,  a PpdReference with a default F value should hash to
-  // the same thing as a PpdReference that predates the addition of F to the
-  // structure.
-  //
-  // Note this function expects that the caller will append ".ppd", or ".ppd.gz"
-  // to the output as needed.
-  base::FilePath GetCachePathBase(const Printer::PpdReference& ref) const {
-    std::vector<std::string> pieces;
-    if (!ref.user_supplied_ppd_url.empty()) {
-      pieces.push_back("user_supplied_ppd_url:");
-      pieces.push_back(ref.user_supplied_ppd_url);
-    } else if (!ref.effective_manufacturer.empty() &&
-               !ref.effective_model.empty()) {
-      pieces.push_back("manufacturer:");
-      pieces.push_back(ref.effective_manufacturer);
-      pieces.push_back("model:");
-      pieces.push_back(ref.effective_model);
+  // Store implementation, runs on the i/o thread.
+  void StoreImpl(
+      const std::string& key,
+      const std::string& contents,
+      const scoped_refptr<base::SequencedTaskRunner>& callback_runner,
+      const base::Callback<void()> cb) {
+    base::ThreadRestrictions::AssertIOAllowed();
+    MaybeCreateCache();
+    if (contents.size() > kMaxPpdSizeBytes) {
+      LOG(ERROR) << "Ignoring attempt to cache large object";
     } else {
-      NOTREACHED() << "PpdCache hashing empty PpdReference";
-    }
-    // The separator here is not needed, but makes debug output more readable.
-    std::string full_key = base::JoinString(pieces, "|");
-    std::string hashed_key = crypto::SHA256HashString(full_key);
-    std::string ascii_hash =
-        base::HexEncode(hashed_key.data(), hashed_key.size());
-    VLOG(3) << "PPD Cache key is " << full_key << " which hashes to "
-            << ascii_hash;
-
-    return cache_base_dir_.Append(ascii_hash);
-  }
-
-  // Try to read the available printers cache.  Returns true on success.  On
-  // success, |buf| will contain the contents of the file, otherwise it will be
-  // cleared.
-  bool MaybeReadAvailablePrintersCache(std::string* buf) {
-    buf->clear();
-
-    base::File cache_file(available_printers_file_,
-                          base::File::FLAG_OPEN | base::File::FLAG_READ);
-    base::File::Info info;
-    if (cache_file.IsValid() && cache_file.GetInfo(&info) &&
-        (base::Time::Now() - info.last_modified <=
-         options_.max_available_list_staleness)) {
-      // We have a file that's recent enough to use.
-      if (!base::ReadFileToStringWithMaxSize(
-              available_printers_file_, buf,
-              options_.max_available_list_cached_size)) {
-        LOG(ERROR) << "Failed to read printer cache from "
-                   << available_printers_file_.MaybeAsASCII();
-        buf->clear();
-        return false;
+      auto path = FilePathForKey(key);
+      base::File file(path,
+                      base::File::FLAG_CREATE_ALWAYS | base::File::FLAG_WRITE);
+      std::string checksum = crypto::SHA256HashString(contents);
+      if (!file.IsValid() ||
+          file.WriteAtCurrentPos(contents.data(), contents.size()) !=
+              static_cast<int>(contents.size()) ||
+          file.WriteAtCurrentPos(checksum.data(), checksum.size()) !=
+              static_cast<int>(checksum.size())) {
+        LOG(ERROR) << "Failed to create ppd cache file";
+        file.Close();
+        if (!base::DeleteFile(path, false)) {
+          LOG(ERROR) << "Failed to cleanup failed creation.";
+        }
       }
-      available_printers_timestamp_ = info.last_modified;
-      return true;
     }
-    // Either we don't have an openable file, or it's too old.
-    //
-    // If we have an invalid file and it's not valid for reasons other than
-    // NOT_FOUND, that's unexpected and worth logging.  Otherwise this is
-    // a normal cache miss.
-    if (!cache_file.IsValid() &&
-        cache_file.error_details() != base::File::FILE_ERROR_NOT_FOUND) {
-      LOG(ERROR) << "Unexpected result when attempting to open printer cache: "
-                 << base::File::ErrorToString(cache_file.error_details());
-    }
-    return false;
+    callback_runner->PostTask(
+        FROM_HERE, base::Bind(&PpdCacheImpl::ReplyAndRelease, this, cb));
   }
 
-  // In-memory copy of the available printers map, null if we don't have an
-  // in-memory copy yet.  Filled in the first time the map is fetched from
-  // disk or stored.
-  std::unique_ptr<PpdProvider::AvailablePrintersMap> available_printers_;
-  // Timestamp for the in-memory copy of the cache.  (The on-disk version uses
-  // the file mtime).
-  base::Time available_printers_timestamp_;
+  // Return the (full) path to the file we expect to find the given key at.
+  base::FilePath FilePathForKey(const std::string& key) {
+    std::string hashed_key = crypto::SHA256HashString(key);
+    return cache_base_dir_.Append(
+        base::HexEncode(hashed_key.data(), hashed_key.size()));
+  }
 
-  const base::FilePath cache_base_dir_;
-  const base::FilePath available_printers_file_;
-  const PpdCache::Options options_;
+  int inflight_ops_ = 0;
 
-  mutable base::Lock lock_;
+  base::FilePath cache_base_dir_;
+  scoped_refptr<base::SequencedTaskRunner> disk_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(PpdCacheImpl);
 };
@@ -300,9 +167,11 @@ class PpdCacheImpl : public PpdCache {
 }  // namespace
 
 // static
-std::unique_ptr<PpdCache> PpdCache::Create(const base::FilePath& cache_base_dir,
-                                           const PpdCache::Options& options) {
-  return base::MakeUnique<PpdCacheImpl>(cache_base_dir, options);
+scoped_refptr<PpdCache> PpdCache::Create(
+    const base::FilePath& cache_base_dir,
+    scoped_refptr<base::SequencedTaskRunner> disk_task_runner) {
+  return scoped_refptr<PpdCache>(
+      new PpdCacheImpl(cache_base_dir, disk_task_runner));
 }
 
 }  // namespace printing