http2/hpack/decoder/hpack_string_decoder.h - quiche - Git at Google

 // Copyright 2016 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.

 #ifndef QUICHE_HTTP2_HPACK_DECODER_HPACK_STRING_DECODER_H_
 #define QUICHE_HTTP2_HPACK_DECODER_HPACK_STRING_DECODER_H_

 // HpackStringDecoder decodes strings encoded per the HPACK spec; this does
 // not mean decompressing Huffman encoded strings, just identifying the length,
 // encoding and contents for a listener.

 #include <stddef.h>

 #include <algorithm>
 #include <cstdint>

 #include "net/third_party/quiche/src/http2/decoder/decode_buffer.h"
 #include "net/third_party/quiche/src/http2/decoder/decode_status.h"
 #include "net/third_party/quiche/src/http2/hpack/varint/hpack_varint_decoder.h"
 #include "net/third_party/quiche/src/http2/platform/api/http2_export.h"
 #include "net/third_party/quiche/src/http2/platform/api/http2_logging.h"
 #include "net/third_party/quiche/src/http2/platform/api/http2_macros.h"
 #include "net/third_party/quiche/src/http2/platform/api/http2_string.h"

 namespace http2 {

 // Decodes a single string in an HPACK header entry. The high order bit of
 // the first byte of the length is the H (Huffman) bit indicating whether
 // the value is Huffman encoded, and the remainder of the byte is the first
 // 7 bits of an HPACK varint.
 //
 // Call Start() to begin decoding; if it returns kDecodeInProgress, then call
 // Resume() when more input is available, repeating until kDecodeInProgress is
 // not returned. If kDecodeDone or kDecodeError is returned, then Resume() must
 // not be called until Start() has been called to start decoding a new string.
 class HTTP2_EXPORT_PRIVATE HpackStringDecoder {
  public:
   enum StringDecoderState {
     kStartDecodingLength,
     kDecodingString,
     kResumeDecodingLength,
   };

   template <class Listener>
   DecodeStatus Start(DecodeBuffer* db, Listener* cb) {
     // Fast decode path is used if the string is under 127 bytes and the
     // entire length of the string is in the decode buffer. More than 83% of
     // string lengths are encoded in just one byte.
     if (db->HasData() && (*db->cursor() & 0x7f) != 0x7f) {
       // The string is short.
       uint8_t h_and_prefix = db->DecodeUInt8();
       uint8_t length = h_and_prefix & 0x7f;
       bool huffman_encoded = (h_and_prefix & 0x80) == 0x80;
       cb->OnStringStart(huffman_encoded, length);
       if (length <= db->Remaining()) {
         // Yeah, we've got the whole thing in the decode buffer.
         // Ideally this will be the common case. Note that we don't
         // update any of the member variables in this path.
         cb->OnStringData(db->cursor(), length);
         db->AdvanceCursor(length);
         cb->OnStringEnd();
         return DecodeStatus::kDecodeDone;
       }
       // Not all in the buffer.
       huffman_encoded_ = huffman_encoded;
       remaining_ = length;
       // Call Resume to decode the string body, which is only partially
       // in the decode buffer (or not at all).
       state_ = kDecodingString;
       return Resume(db, cb);
     }
     // Call Resume to decode the string length, which is either not in
     // the decode buffer, or spans multiple bytes.
     state_ = kStartDecodingLength;
     return Resume(db, cb);
   }

   template <class Listener>
   DecodeStatus Resume(DecodeBuffer* db, Listener* cb) {
     DecodeStatus status;
     while (true) {
       switch (state_) {
         case kStartDecodingLength:
           HTTP2_DVLOG(2) << "kStartDecodingLength: db->Remaining="
                          << db->Remaining();
           if (!StartDecodingLength(db, cb, &status)) {
             // The length is split across decode buffers.
             return status;
           }
           // We've finished decoding the length, which spanned one or more
           // bytes. Approximately 17% of strings have a length that is greater
           // than 126 bytes, and thus the length is encoded in more than one
           // byte, and so doesn't get the benefit of the optimization in
           // Start() for single byte lengths. But, we still expect that most
           // of such strings will be contained entirely in a single decode
           // buffer, and hence this fall through skips another trip through the
           // switch above and more importantly skips setting the state_ variable
           // again in those cases where we don't need it.
           HTTP2_FALLTHROUGH;

         case kDecodingString:
           HTTP2_DVLOG(2) << "kDecodingString: db->Remaining=" << db->Remaining()
                          << "    remaining_=" << remaining_;
           return DecodeString(db, cb);

         case kResumeDecodingLength:
           HTTP2_DVLOG(2) << "kResumeDecodingLength: db->Remaining="
                          << db->Remaining();
           if (!ResumeDecodingLength(db, cb, &status)) {
             return status;
           }
       }
     }
   }

   Http2String DebugString() const;

  private:
   static Http2String StateToString(StringDecoderState v);

   // Returns true if the length is fully decoded and the listener wants the
   // decoding to continue, false otherwise; status is set to the status from
   // the varint decoder.
   // If the length is not fully decoded, case state_ is set appropriately
   // for the next call to Resume.
   template <class Listener>
   bool StartDecodingLength(DecodeBuffer* db,
                            Listener* cb,
                            DecodeStatus* status) {
     if (db->Empty()) {
       *status = DecodeStatus::kDecodeInProgress;
       state_ = kStartDecodingLength;
       return false;
     }
     uint8_t h_and_prefix = db->DecodeUInt8();
     huffman_encoded_ = (h_and_prefix & 0x80) == 0x80;
     *status = length_decoder_.Start(h_and_prefix, 7, db);
     if (*status == DecodeStatus::kDecodeDone) {
       OnStringStart(cb, status);
       return true;
     }
     // Set the state to cover the DecodeStatus::kDecodeInProgress case.
     // Won't be needed if the status is kDecodeError.
     state_ = kResumeDecodingLength;
     return false;
   }

   // Returns true if the length is fully decoded and the listener wants the
   // decoding to continue, false otherwise; status is set to the status from
   // the varint decoder; state_ is updated when fully decoded.
   // If the length is not fully decoded, case state_ is set appropriately
   // for the next call to Resume.
   template <class Listener>
   bool ResumeDecodingLength(DecodeBuffer* db,
                             Listener* cb,
                             DecodeStatus* status) {
     DCHECK_EQ(state_, kResumeDecodingLength);
     *status = length_decoder_.Resume(db);
     if (*status == DecodeStatus::kDecodeDone) {
       state_ = kDecodingString;
       OnStringStart(cb, status);
       return true;
     }
     return false;
   }

   // Returns true if the listener wants the decoding to continue, and
   // false otherwise, in which case status set.
   template <class Listener>
   void OnStringStart(Listener* cb, DecodeStatus* status) {
     // TODO(vasilvv): fail explicitly in case of truncation.
     remaining_ = static_cast<size_t>(length_decoder_.value());
     // Make callback so consumer knows what is coming.
     cb->OnStringStart(huffman_encoded_, remaining_);
   }

   // Passes the available portion of the string to the listener, and signals
   // the end of the string when it is reached. Returns kDecodeDone or
   // kDecodeInProgress as appropriate.
   template <class Listener>
   DecodeStatus DecodeString(DecodeBuffer* db, Listener* cb) {
     size_t len = std::min(remaining_, db->Remaining());
     if (len > 0) {
       cb->OnStringData(db->cursor(), len);
       db->AdvanceCursor(len);
       remaining_ -= len;
     }
     if (remaining_ == 0) {
       cb->OnStringEnd();
       return DecodeStatus::kDecodeDone;
     }
     state_ = kDecodingString;
     return DecodeStatus::kDecodeInProgress;
   }

   HpackVarintDecoder length_decoder_;

   // These fields are initialized just to keep ASAN happy about reading
   // them from DebugString().
   size_t remaining_ = 0;
   StringDecoderState state_ = kStartDecodingLength;
   bool huffman_encoded_ = false;
 };

 HTTP2_EXPORT_PRIVATE std::ostream& operator<<(std::ostream& out,
                                               const HpackStringDecoder& v);

 }  // namespace http2
 #endif  // QUICHE_HTTP2_HPACK_DECODER_HPACK_STRING_DECODER_H_
	// Copyright 2016 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.

	#ifndef QUICHE_HTTP2_HPACK_DECODER_HPACK_STRING_DECODER_H_
	#define QUICHE_HTTP2_HPACK_DECODER_HPACK_STRING_DECODER_H_

	// HpackStringDecoder decodes strings encoded per the HPACK spec; this does
	// not mean decompressing Huffman encoded strings, just identifying the length,
	// encoding and contents for a listener.

	#include <stddef.h>

	#include <algorithm>
	#include <cstdint>

	#include "net/third_party/quiche/src/http2/decoder/decode_buffer.h"
	#include "net/third_party/quiche/src/http2/decoder/decode_status.h"
	#include "net/third_party/quiche/src/http2/hpack/varint/hpack_varint_decoder.h"
	#include "net/third_party/quiche/src/http2/platform/api/http2_export.h"
	#include "net/third_party/quiche/src/http2/platform/api/http2_logging.h"
	#include "net/third_party/quiche/src/http2/platform/api/http2_macros.h"
	#include "net/third_party/quiche/src/http2/platform/api/http2_string.h"

	namespace http2 {

	// Decodes a single string in an HPACK header entry. The high order bit of
	// the first byte of the length is the H (Huffman) bit indicating whether
	// the value is Huffman encoded, and the remainder of the byte is the first
	// 7 bits of an HPACK varint.
	//
	// Call Start() to begin decoding; if it returns kDecodeInProgress, then call
	// Resume() when more input is available, repeating until kDecodeInProgress is
	// not returned. If kDecodeDone or kDecodeError is returned, then Resume() must
	// not be called until Start() has been called to start decoding a new string.
	class HTTP2_EXPORT_PRIVATE HpackStringDecoder {
	public:
	enum StringDecoderState {
	kStartDecodingLength,
	kDecodingString,
	kResumeDecodingLength,
	};

	template <class Listener>
	DecodeStatus Start(DecodeBuffer* db, Listener* cb) {
	// Fast decode path is used if the string is under 127 bytes and the
	// entire length of the string is in the decode buffer. More than 83% of
	// string lengths are encoded in just one byte.
	if (db->HasData() && (*db->cursor() & 0x7f) != 0x7f) {
	// The string is short.
	uint8_t h_and_prefix = db->DecodeUInt8();
	uint8_t length = h_and_prefix & 0x7f;
	bool huffman_encoded = (h_and_prefix & 0x80) == 0x80;
	cb->OnStringStart(huffman_encoded, length);
	if (length <= db->Remaining()) {
	// Yeah, we've got the whole thing in the decode buffer.
	// Ideally this will be the common case. Note that we don't
	// update any of the member variables in this path.
	cb->OnStringData(db->cursor(), length);
	db->AdvanceCursor(length);
	cb->OnStringEnd();
	return DecodeStatus::kDecodeDone;
	}
	// Not all in the buffer.
	huffman_encoded_ = huffman_encoded;
	remaining_ = length;
	// Call Resume to decode the string body, which is only partially
	// in the decode buffer (or not at all).
	state_ = kDecodingString;
	return Resume(db, cb);
	}
	// Call Resume to decode the string length, which is either not in
	// the decode buffer, or spans multiple bytes.
	state_ = kStartDecodingLength;
	return Resume(db, cb);
	}

	template <class Listener>
	DecodeStatus Resume(DecodeBuffer* db, Listener* cb) {
	DecodeStatus status;
	while (true) {
	switch (state_) {
	case kStartDecodingLength:
	HTTP2_DVLOG(2) << "kStartDecodingLength: db->Remaining="
	<< db->Remaining();
	if (!StartDecodingLength(db, cb, &status)) {
	// The length is split across decode buffers.
	return status;
	}
	// We've finished decoding the length, which spanned one or more
	// bytes. Approximately 17% of strings have a length that is greater
	// than 126 bytes, and thus the length is encoded in more than one
	// byte, and so doesn't get the benefit of the optimization in
	// Start() for single byte lengths. But, we still expect that most
	// of such strings will be contained entirely in a single decode
	// buffer, and hence this fall through skips another trip through the
	// switch above and more importantly skips setting the state_ variable
	// again in those cases where we don't need it.
	HTTP2_FALLTHROUGH;

	case kDecodingString:
	HTTP2_DVLOG(2) << "kDecodingString: db->Remaining=" << db->Remaining()
	<< " remaining_=" << remaining_;
	return DecodeString(db, cb);

	case kResumeDecodingLength:
	HTTP2_DVLOG(2) << "kResumeDecodingLength: db->Remaining="
	<< db->Remaining();
	if (!ResumeDecodingLength(db, cb, &status)) {
	return status;
	}
	}
	}
	}

	Http2String DebugString() const;

	private:
	static Http2String StateToString(StringDecoderState v);

	// Returns true if the length is fully decoded and the listener wants the
	// decoding to continue, false otherwise; status is set to the status from
	// the varint decoder.
	// If the length is not fully decoded, case state_ is set appropriately
	// for the next call to Resume.
	template <class Listener>
	bool StartDecodingLength(DecodeBuffer* db,
	Listener* cb,
	DecodeStatus* status) {
	if (db->Empty()) {
	*status = DecodeStatus::kDecodeInProgress;
	state_ = kStartDecodingLength;
	return false;
	}
	uint8_t h_and_prefix = db->DecodeUInt8();
	huffman_encoded_ = (h_and_prefix & 0x80) == 0x80;
	*status = length_decoder_.Start(h_and_prefix, 7, db);
	if (*status == DecodeStatus::kDecodeDone) {
	OnStringStart(cb, status);
	return true;
	}
	// Set the state to cover the DecodeStatus::kDecodeInProgress case.
	// Won't be needed if the status is kDecodeError.
	state_ = kResumeDecodingLength;
	return false;
	}

	// Returns true if the length is fully decoded and the listener wants the
	// decoding to continue, false otherwise; status is set to the status from
	// the varint decoder; state_ is updated when fully decoded.
	// If the length is not fully decoded, case state_ is set appropriately
	// for the next call to Resume.
	template <class Listener>
	bool ResumeDecodingLength(DecodeBuffer* db,
	Listener* cb,
	DecodeStatus* status) {
	DCHECK_EQ(state_, kResumeDecodingLength);
	*status = length_decoder_.Resume(db);
	if (*status == DecodeStatus::kDecodeDone) {
	state_ = kDecodingString;
	OnStringStart(cb, status);
	return true;
	}
	return false;
	}

	// Returns true if the listener wants the decoding to continue, and
	// false otherwise, in which case status set.
	template <class Listener>
	void OnStringStart(Listener* cb, DecodeStatus* status) {
	// TODO(vasilvv): fail explicitly in case of truncation.
	remaining_ = static_cast<size_t>(length_decoder_.value());
	// Make callback so consumer knows what is coming.
	cb->OnStringStart(huffman_encoded_, remaining_);
	}

	// Passes the available portion of the string to the listener, and signals
	// the end of the string when it is reached. Returns kDecodeDone or
	// kDecodeInProgress as appropriate.
	template <class Listener>
	DecodeStatus DecodeString(DecodeBuffer* db, Listener* cb) {
	size_t len = std::min(remaining_, db->Remaining());
	if (len > 0) {
	cb->OnStringData(db->cursor(), len);
	db->AdvanceCursor(len);
	remaining_ -= len;
	}
	if (remaining_ == 0) {
	cb->OnStringEnd();
	return DecodeStatus::kDecodeDone;
	}
	state_ = kDecodingString;
	return DecodeStatus::kDecodeInProgress;
	}

	HpackVarintDecoder length_decoder_;

	// These fields are initialized just to keep ASAN happy about reading
	// them from DebugString().
	size_t remaining_ = 0;
	StringDecoderState state_ = kStartDecodingLength;
	bool huffman_encoded_ = false;
	};

	HTTP2_EXPORT_PRIVATE std::ostream& operator<<(std::ostream& out,
	const HpackStringDecoder& v);

	} // namespace http2
	#endif // QUICHE_HTTP2_HPACK_DECODER_HPACK_STRING_DECODER_H_