gecko-dev/netwerk/cache/nsCacheMetaData.cpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "nsCacheMetaData.h"
#include "nsICacheEntryDescriptor.h"

const char* nsCacheMetaData::GetElement(const char* key) {
  const char* data = mBuffer;
  const char* limit = mBuffer + mMetaSize;

  while (data < limit) {
    // Point to the value part
    const char* value = data + strlen(data) + 1;
    MOZ_ASSERT(value < limit, "Cache Metadata corrupted");
    if (strcmp(data, key) == 0) return value;

    // Skip value part
    data = value + strlen(value) + 1;
  }
  MOZ_ASSERT(data == limit, "Metadata corrupted");
  return nullptr;
}

nsresult nsCacheMetaData::SetElement(const char* key, const char* value) {
  const uint32_t keySize = strlen(key) + 1;
  char* pos = (char*)GetElement(key);

  if (!value) {
    // No value means remove the key/value pair completely, if existing
    if (pos) {
      uint32_t oldValueSize = strlen(pos) + 1;
      uint32_t offset = pos - mBuffer;
      uint32_t remainder = mMetaSize - (offset + oldValueSize);

      memmove(pos - keySize, pos + oldValueSize, remainder);
      mMetaSize -= keySize + oldValueSize;
    }
    return NS_OK;
  }

  const uint32_t valueSize = strlen(value) + 1;
  uint32_t newSize = mMetaSize + valueSize;
  if (pos) {
    const uint32_t oldValueSize = strlen(pos) + 1;
    const uint32_t offset = pos - mBuffer;
    const uint32_t remainder = mMetaSize - (offset + oldValueSize);

    // Update the value in place
    newSize -= oldValueSize;
    nsresult rv = EnsureBuffer(newSize);
    NS_ENSURE_SUCCESS(rv, rv);

    // Move the remainder to the right place
    pos = mBuffer + offset;
    memmove(pos + valueSize, pos + oldValueSize, remainder);
  } else {
    // allocate new meta data element
    newSize += keySize;
    nsresult rv = EnsureBuffer(newSize);
    NS_ENSURE_SUCCESS(rv, rv);

    // Add after last element
    pos = mBuffer + mMetaSize;
    memcpy(pos, key, keySize);
    pos += keySize;
  }

  // Update value
  memcpy(pos, value, valueSize);
  mMetaSize = newSize;

  return NS_OK;
}

nsresult nsCacheMetaData::FlattenMetaData(char* buffer, uint32_t bufSize) {
  if (mMetaSize > bufSize) {
    NS_ERROR("buffer size too small for meta data.");
    return NS_ERROR_OUT_OF_MEMORY;
  }

  memcpy(buffer, mBuffer, mMetaSize);
  return NS_OK;
}

nsresult nsCacheMetaData::UnflattenMetaData(const char* data, uint32_t size) {
  if (data && size) {
    // Check if the metadata ends with a zero byte.
    if (data[size - 1] != '\0') {
      NS_ERROR("Cache MetaData is not null terminated");
      return NS_ERROR_ILLEGAL_VALUE;
    }
    // Check that there are an even number of zero bytes
    // to match the pattern { key \0 value \0 }
    bool odd = false;
    for (uint32_t i = 0; i < size; i++) {
      if (data[i] == '\0') odd = !odd;
    }
    if (odd) {
      NS_ERROR("Cache MetaData is malformed");
      return NS_ERROR_ILLEGAL_VALUE;
    }

    nsresult rv = EnsureBuffer(size);
    NS_ENSURE_SUCCESS(rv, rv);

    memcpy(mBuffer, data, size);
    mMetaSize = size;
  }
  return NS_OK;
}

nsresult nsCacheMetaData::VisitElements(nsICacheMetaDataVisitor* visitor) {
  const char* data = mBuffer;
  const char* limit = mBuffer + mMetaSize;

  while (data < limit) {
    const char* key = data;
    // Skip key part
    data += strlen(data) + 1;
    MOZ_ASSERT(data < limit, "Metadata corrupted");
    bool keepGoing;
    nsresult rv = visitor->VisitMetaDataElement(key, data, &keepGoing);
    if (NS_FAILED(rv) || !keepGoing) return NS_OK;

    // Skip value part
    data += strlen(data) + 1;
  }
  MOZ_ASSERT(data == limit, "Metadata corrupted");
  return NS_OK;
}

nsresult nsCacheMetaData::EnsureBuffer(uint32_t bufSize) {
  if (mBufferSize < bufSize) {
    char* buf = (char*)realloc(mBuffer, bufSize);
    if (!buf) {
      return NS_ERROR_OUT_OF_MEMORY;
    }
    mBuffer = buf;
    mBufferSize = bufSize;
  }
  return NS_OK;
}