Revert of Add new HTTP/2 and HPACK decoder in net/http2/.

net/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 NET_HTTP2_HPACK_DECODER_HPACK_STRING_DECODER_H_
-#define NET_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 <string>
-
-#include "base/logging.h"
-#include "base/macros.h"
-#include "net/base/net_export.h"
-#include "net/http2/decoder/decode_buffer.h"
-#include "net/http2/decoder/decode_status.h"
-#include "net/http2/hpack/decoder/hpack_varint_decoder.h"
-
-namespace net {
-
-// 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.
-//
-// There are 3 variants of Start in this class, participants in a performance
-// experiment. Perflab experiments show it is generally fastest to call
-// StartSpecialCaseShort rather than StartOnly (~9% slower) or
-// StartAndDecodeLength (~10% slower).
-class NET_EXPORT_PRIVATE HpackStringDecoder {
- public:
-  enum StringDecoderState {
-    kStartDecodingLength,
-    kDecodingString,
-    kResumeDecodingLength,
-  };
-
-  // TODO(jamessynge): Get rid of all but one of the Start and Resume methods
-  // after all of the HPACK decoder is checked in and has been perf tested.
-  template <class Listener>
-  DecodeStatus Start(DecodeBuffer* db, Listener* cb) {
-    return StartSpecialCaseShort(db, cb);
-  }
-
-  template <class Listener>
-  DecodeStatus StartOnly(DecodeBuffer* db, Listener* cb) {
-    state_ = kStartDecodingLength;
-    return Resume(db, cb);
-  }
-
-  template <class Listener>
-  DecodeStatus StartAndDecodeLength(DecodeBuffer* db, Listener* cb) {
-    DecodeStatus status;
-    if (StartDecodingLength(db, cb, &status)) {
-      state_ = kDecodingString;
-      return DecodeString(db, cb);
-    }
-    return status;
-  }
-
-  template <class Listener>
-  DecodeStatus StartSpecialCaseShort(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:
-          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.
-
-        // FALLTHROUGH_INTENDED
-
-        case kDecodingString:
-          DVLOG(2) << "kDecodingString: db->Remaining=" << db->Remaining()
-                   << "    remaining_=" << remaining_;
-          return DecodeString(db, cb);
-
-        case kResumeDecodingLength:
-          DVLOG(2) << "kResumeDecodingLength: db->Remaining="
-                   << db->Remaining();
-          if (!ResumeDecodingLength(db, cb, &status)) {
-            return status;
-          }
-      }
-    }
-  }
-
-  std::string DebugString() const;
-
- private:
-  static std::string 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, 0x7f, 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) {
-    remaining_ = length_decoder_.value();
-    // Make callback so consumer knows what is coming.
-    cb->OnStringStart(huffman_encoded_, remaining_);
-    return;
-  }
-
-  // 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;
-};
-
-NET_EXPORT_PRIVATE std::ostream& operator<<(std::ostream& out,
-                                            const HpackStringDecoder& v);
-
-}  // namespace net
-#endif  // NET_HTTP2_HPACK_DECODER_HPACK_STRING_DECODER_H_