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// Copyright 2014 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.
// Filter performs filtering on data streams. Sample usage:
// IStream* pre_filter_source;
// ...
// Filter* filter = Filter::Factory(filter_type, size);
// int pre_filter_data_len = filter->stream_buffer_size();
// pre_filter_source->read(filter->stream_buffer(), pre_filter_data_len);
// filter->FlushStreamBuffer(pre_filter_data_len);
// char post_filter_buf[kBufferSize];
// int post_filter_data_len = kBufferSize;
// filter->ReadFilteredData(post_filter_buf, &post_filter_data_len);
// To filter a data stream, the caller first gets filter's stream_buffer_
// through its accessor and fills in stream_buffer_ with pre-filter data, next
// calls FlushStreamBuffer to notify Filter, then calls ReadFilteredData
// repeatedly to get all the filtered data. After all data have been fitlered
// and read out, the caller may fill in stream_buffer_ again. This
// WriteBuffer-Flush-Read cycle is repeated until reaching the end of data
// stream.
// The lifetime of a Filter instance is completely controlled by its caller.
#include <string>
#include <vector>
#include "base/basictypes.h"
#include "base/gtest_prod_util.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "base/time/time.h"
#include "net/base/net_export.h"
class GURL;
namespace net {
class URLRequestContext;
class IOBuffer;
// Define an interface class that allows access to contextual information
// supplied by the owner of this filter. In the case where there are a chain of
// filters, there is only one owner of all the chained filters, and that context
// is passed to the constructor of all those filters. To be clear, the context
// does NOT reflect the position in a chain, or the fact that there are prior
// or later filters in a chain.
class NET_EXPORT_PRIVATE FilterContext {
// Enum to control what histograms are emitted near end-of-life of this
// instance.
enum StatisticSelector {
virtual ~FilterContext();
// What mime type was specified in the header for this data?
// Only makes senses for some types of contexts, and returns false
// when not applicable.
virtual bool GetMimeType(std::string* mime_type) const = 0;
// What URL was used to access this data?
// Return false if gurl is not present.
virtual bool GetURL(GURL* gurl) const = 0;
// What Content-Disposition header came with this data?
// Return false if no header was present.
virtual bool GetContentDisposition(std::string* disposition) const = 0;
// When was this data requested from a server?
virtual base::Time GetRequestTime() const = 0;
// Is data supplied from cache, or fresh across the net?
virtual bool IsCachedContent() const = 0;
// Is this a download?
virtual bool IsDownload() const = 0;
// Was this data flagged as a response to a request with an SDCH dictionary?
virtual bool SdchResponseExpected() const = 0;
// How many bytes were read from the net or cache so far (and potentially
// pushed into a filter for processing)?
virtual int64 GetByteReadCount() const = 0;
// What response code was received with the associated network transaction?
// For example: 200 is ok. 4xx are error codes. etc.
virtual int GetResponseCode() const = 0;
// The URLRequestContext associated with the request.
virtual const URLRequestContext* GetURLRequestContext() const = 0;
// The following method forces the context to emit a specific set of
// statistics as selected by the argument.
virtual void RecordPacketStats(StatisticSelector statistic) const = 0;
// Return values of function ReadFilteredData.
enum FilterStatus {
// Read filtered data successfully
// Read filtered data successfully, and the data in the buffer has been
// consumed by the filter, but more data is needed in order to continue
// filtering. At this point, the caller is free to reuse the filter
// buffer to provide more data.
// Read filtered data successfully, and filter reaches the end of the data
// stream.
// There is an error during filtering.
// Specifies type of filters that can be created.
enum FilterType {
FILTER_TYPE_GZIP_HELPING_SDCH, // Gzip possible, but pass through allowed.
FILTER_TYPE_SDCH_POSSIBLE, // Sdch possible, but pass through allowed.
virtual ~Filter();
// Creates a Filter object.
// Parameters: Filter_types specifies the type of filter created;
// filter_context allows filters to acquire additional details needed for
// construction and operation, such as a specification of requisite input
// buffer size.
// If success, the function returns the pointer to the Filter object created.
// If failed or a filter is not needed, the function returns NULL.
// Note: filter_types is an array of filter types (content encoding types as
// provided in an HTTP header), which will be chained together serially to do
// successive filtering of data. The types in the vector are ordered based on
// encoding order, and the filters are chained to operate in the reverse
// (decoding) order. For example, types[0] = FILTER_TYPE_SDCH,
// types[1] = FILTER_TYPE_GZIP will cause data to first be gunzip filtered,
// and the resulting output from that filter will be sdch decoded.
static Filter* Factory(const std::vector<FilterType>& filter_types,
const FilterContext& filter_context);
// A simpler version of Factory() which creates a single, unchained
// Filter of type FILTER_TYPE_GZIP, or NULL if the filter could not be
// initialized.
static Filter* GZipFactory();
// External call to obtain data from this filter chain. If ther is no
// next_filter_, then it obtains data from this specific filter.
FilterStatus ReadData(char* dest_buffer, int* dest_len);
// Returns a pointer to the stream_buffer_.
IOBuffer* stream_buffer() const { return stream_buffer_.get(); }
// Returns the maximum size of stream_buffer_ in number of chars.
int stream_buffer_size() const { return stream_buffer_size_; }
// Returns the total number of chars remaining in stream_buffer_ to be
// filtered.
// If the function returns 0 then all data has been filtered, and the caller
// is safe to copy new data into stream_buffer_.
int stream_data_len() const { return stream_data_len_; }
// Flushes stream_buffer_ for next round of filtering. After copying data to
// stream_buffer_, the caller should call this function to notify Filter to
// start filtering. Then after this function is called, the caller can get
// post-filtered data using ReadFilteredData. The caller must not write to
// stream_buffer_ and call this function again before stream_buffer_ is
// emptied out by ReadFilteredData.
// The input stream_data_len is the length (in number of chars) of valid
// data in stream_buffer_. It can not be greater than stream_buffer_size_.
// The function returns true if success, and false otherwise.
bool FlushStreamBuffer(int stream_data_len);
// Translate the text of a filter name (from Content-Encoding header) into a
// FilterType.
static FilterType ConvertEncodingToType(const std::string& filter_type);
// Given a array of encoding_types, try to do some error recovery adjustment
// to the list. This includes handling known bugs in the Apache server (where
// redundant gzip encoding is specified), as well as issues regarding SDCH
// encoding, where various proxies and anti-virus products modify or strip the
// encodings. These fixups require context, which includes whether this
// response was made to an SDCH request (i.e., an available dictionary was
// advertised in the GET), as well as the mime type of the content.
static void FixupEncodingTypes(const FilterContext& filter_context,
std::vector<FilterType>* encoding_types);
friend class GZipUnitTest;
friend class SdchFilterChainingTest;
// Filters the data stored in stream_buffer_ and writes the output into the
// dest_buffer passed in.
// Upon entry, *dest_len is the total size (in number of chars) of the
// destination buffer. Upon exit, *dest_len is the actual number of chars
// written into the destination buffer.
// This function will fail if there is no pre-filter data in the
// stream_buffer_. On the other hand, *dest_len can be 0 upon successful
// return. For example, a decoding filter may process some pre-filter data
// but not produce output yet.
virtual FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len) = 0;
// Copy pre-filter data directly to destination buffer without decoding.
FilterStatus CopyOut(char* dest_buffer, int* dest_len);
FilterStatus last_status() const { return last_status_; }
// Buffer to hold the data to be filtered (the input queue).
scoped_refptr<IOBuffer> stream_buffer_;
// Maximum size of stream_buffer_ in number of chars.
int stream_buffer_size_;
// Pointer to the next data in stream_buffer_ to be filtered.
char* next_stream_data_;
// Total number of remaining chars in stream_buffer_ to be filtered.
int stream_data_len_;
// Allocates and initializes stream_buffer_ and stream_buffer_size_.
void InitBuffer(int size);
// A factory helper for creating filters for within a chain of potentially
// multiple encodings. If a chain of filters is created, then this may be
// called multiple times during the filter creation process. In most simple
// cases, this is only called once. Returns NULL and cleans up (deleting
// filter_list) if a new filter can't be constructed.
static Filter* PrependNewFilter(FilterType type_id,
const FilterContext& filter_context,
int buffer_size,
Filter* filter_list);
// Helper methods for PrependNewFilter. If initialization is successful,
// they return a fully initialized Filter. Otherwise, return NULL.
static Filter* InitGZipFilter(FilterType type_id, int buffer_size);
static Filter* InitSdchFilter(FilterType type_id,
const FilterContext& filter_context,
int buffer_size);
// Helper function to empty our output into the next filter's input.
void PushDataIntoNextFilter();
// Constructs a filter with an internal buffer of the given size.
// Only meant to be called by unit tests that need to control the buffer size.
static Filter* FactoryForTests(const std::vector<FilterType>& filter_types,
const FilterContext& filter_context,
int buffer_size);
// An optional filter to process output from this filter.
scoped_ptr<Filter> next_filter_;
// Remember what status or local filter last returned so we can better handle
// chained filters.
FilterStatus last_status_;
} // namespace net