Simple PMP reader to parse Picasa's metadata

webkit/fileapi/media/picasa/pmp_column_reader.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "webkit/fileapi/media/picasa/pmp_column_reader.h"
+
+#include <cstring>
+
+#include "base/files/file_path.h"
+#include "base/logging.h"
+#include "webkit/fileapi/media/picasa/pmp_constants.h"
+
+namespace fileapi {
+
+PmpColumnReader::PmpColumnReader(std::string column_name)
+    : column_name_(column_name),
+      data_(NULL),
+      length_(0),
+      rows_(0),
+      strings_(),
+      fieldsize_(0) { }
+
+PmpColumnReader::~PmpColumnReader() { }
+
+bool PmpColumnReader::ReadFromMemory(uint32* rows_read, const uint8* data,
+                                     const size_t len) {
+  if(len < kPmpHeaderSize || data == NULL) {

[vandebo (ex-Chrome), 2013/03/27 00:06:19]

nit: omit {}'s here.

[tommycli, 2013/03/27 19:34:30]

Done.

+    return false;
+  }
+
+  length_ = len;
+  data_.reset(new uint8[length_]);
+  std::copy(data, data + length_, data_.get());
+
+  return ParseData(rows_read);
+}
+
+bool PmpColumnReader::ReadString(const uint32 row, std::string* target) const {

[vandebo (ex-Chrome), 2013/03/27 00:06:19]

const std::string*

[tommycli, 2013/03/27 19:34:30]

I use operator= on it.

+  DCHECK(data_.get() != NULL);
+  DCHECK(length_ > kPmpHeaderSize);
+
+  if(row < rows_) {

[vandebo (ex-Chrome), 2013/03/27 00:06:19]

Check the field type?

[tommycli, 2013/03/27 19:34:30]

Done.

+    *target = strings_[row];
+    return true;
+  } else {
+    return false;
+  }
+}
+
+bool PmpColumnReader::ReadUInt32(const uint32 row, uint32* target) const {
+  return ReadPrimitive<uint32>(row, target);
+}
+
+bool PmpColumnReader::ReadDouble64(const uint32 row, double* target) const {
+  return ReadPrimitive<double>(row, target);
+}
+
+bool PmpColumnReader::ReadUInt8(const uint32 row, uint8* target) const {
+  return ReadPrimitive<uint8>(row, target);
+}
+
+bool PmpColumnReader::ReadUInt64(const uint32 row, uint64* target) const {
+  return ReadPrimitive<uint64>(row, target);
+}
+
+template<class T>
+bool PmpColumnReader::ReadPrimitive(uint32 row, T* target) const {
+  DCHECK(data_.get() != NULL);
+  DCHECK(length_ > kPmpHeaderSize);
+
+  if(sizeof(T) != fieldsize_) {
+    return false;
+  }
+
+  if(row < rows_) {
+    *target = *(reinterpret_cast<T*>(
+        data_.get() + kPmpHeaderSize + row*fieldsize_));
+    return true;
+  } else {
+    return false;
+  }
+}
+
+bool PmpColumnReader::ParseData(uint32* rows_read) {
+  DCHECK(data_.get() != NULL);
+  DCHECK(length_ >= kPmpHeaderSize);
+
+  // Check all magic bytes.
+  if (memcmp(kPmpMagicO0S4, data_.get(), 4) != 0||
+      memcmp(kPmpMagicO6S2, data_.get() + 6, 2) != 0 ||
+      memcmp(kPmpMagicO8S4, data_.get() + 8, 4) != 0 ||
+      memcmp(kPmpMagicO14S2, data_.get() + 14, 2) != 0) {
+    return false;
+  }
+
+  // Verify row field type matches.
+  if (data_[kPmpFieldTypeFirstOffset] != data_[kPmpFieldTypeSecondOffset]) {
+    return false;
+  }
+
+  // Read the field type and number of rows expected.
+  uint16 field_type = data_[kPmpFieldTypeFirstOffset];
+  rows_ = *(reinterpret_cast<uint32*>(&data_[kPmpRowCountOffset]));
+
+  bool parse_success = false;
+
+  switch (field_type) {
+    case kPmpFieldTypeString:
+      parse_success = IndexStrings();
+      break;
+    case kPmpFieldTypeUInt32:
+      parse_success = SetAndValidateFieldsize<uint32>();
+      break;
+    case kPmpFieldTypeDouble64:
+      parse_success = SetAndValidateFieldsize<double>();
+      break;
+    case kPmpFieldTypeUInt8:
+      parse_success = SetAndValidateFieldsize<uint8>();
+      break;
+    case kPmpFieldTypeUInt64:
+      parse_success = SetAndValidateFieldsize<uint64>();
+      break;
+    default:
+      parse_success = false;
+      break;
+  }
+
+  if(parse_success) {
+    // Set the number of rows read. Though it's not valid unless we return true.
+    if(rows_read != NULL) {
+      *rows_read = rows_;
+    }
+    return true;
+  }
+
+  return false;
+}
+
+bool PmpColumnReader::IndexStrings() {
+  DCHECK(data_.get() != NULL);
+  DCHECK(length_ >= kPmpHeaderSize);
+
+  strings_.clear();
+  strings_.reserve(rows_);
+
+  size_t bytes_parsed = kPmpHeaderSize;
+  const uint8* itr = data_.get() + kPmpHeaderSize;
+
+  while (strings_.size() < rows_) {
+    const uint8* ptr_to_str_end = static_cast<const uint8*>(
+        memchr(itr, '\0', length_ - bytes_parsed));
+
+    // Fail if cannot find null termination. String runs on past file end.
+    if(ptr_to_str_end == NULL) return false;
+
+    // Length of string. (+1 to include the termination character).
+    ptrdiff_t len_bytes = ptr_to_str_end - itr + 1;
+
+    strings_.push_back(reinterpret_cast<const char*>(itr));
+    itr += len_bytes;
+    bytes_parsed += len_bytes;
+  }
+
+  // This means the file has more bytes at the end we haven't parsed.
+  if(bytes_parsed != length_) return false;

[vandebo (ex-Chrome), 2013/03/27 00:06:19]

return false on next line.

[tommycli, 2013/03/27 19:34:30]

Done.

+
+  return true;
+}
+
+template<class T>
+bool PmpColumnReader::SetAndValidateFieldsize() {
+  unsigned long calculated_n_rows = (length_ - kPmpHeaderSize) / sizeof(T);
+
+  if(calculated_n_rows == rows_) {
+    fieldsize_ = sizeof(T);
+    return true;
+  }
+
+  return false;
+}
+
+}  // namespace