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

net/http2/decoder/http2_structure_decoder.h

Index: net/http2/decoder/http2_structure_decoder.h
diff --git a/net/http2/decoder/http2_structure_decoder.h b/net/http2/decoder/http2_structure_decoder.h
new file mode 100644
index 0000000000000000000000000000000000000000..8665e96cb21f8607cc31fe4509a5131fb396b294
--- /dev/null
+++ b/net/http2/decoder/http2_structure_decoder.h
@@ -0,0 +1,129 @@
+// 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_DECODER_HTTP2_STRUCTURE_DECODER_H_
+#define NET_HTTP2_DECODER_HTTP2_STRUCTURE_DECODER_H_
+
+// Http2StructureDecoder is a class for decoding the fixed size structures in
+// the HTTP/2 spec, defined in net/http2/http2_structures.h. This class
+// is in aid of deciding whether to keep the SlowDecode methods which I
+// (jamessynge) now think may not be worth their complexity. In particular,
+// if most transport buffers are large, so it is rare that a structure is
+// split across buffer boundaries, than the cost of buffering upon
+// those rare occurrences is small, which then simplifies the callers.
+
+#include "base/logging.h"
+#include "net/base/net_export.h"
+#include "net/http2/decoder/decode_buffer.h"
+#include "net/http2/decoder/decode_http2_structures.h"
+#include "net/http2/decoder/decode_status.h"
+#include "net/http2/http2_structures.h"
+
+namespace net {
+namespace test {
+class Http2StructureDecoderPeer;
+}  // namespace test
+
+class NET_EXPORT_PRIVATE Http2StructureDecoder {
+ public:
+  // The caller needs to keep track of whether to call Start or Resume.
+  //
+  // Start has an optimization for the case where the DecodeBuffer holds the
+  // entire encoded structure; in that case it decodes into *out and returns
+  // true, and does NOT touch the data members of the Http2StructureDecoder
+  // instance because the caller won't be calling Resume later.
+  //
+  // However, if the DecodeBuffer is too small to hold the entire encoded
+  // structure, Start copies the available bytes into the Http2StructureDecoder
+  // instance, and returns false to indicate that it has not been able to
+  // complete the decoding.
+  //
+  template <class S>
+  bool Start(S* out, DecodeBuffer* db) {
+    static_assert(S::EncodedSize() <= sizeof buffer_, "buffer_ is too small");
+    DVLOG(2) << __func__ << "@" << this << ": db->Remaining=" << db->Remaining()
+             << "; EncodedSize=" << S::EncodedSize();
+    if (db->Remaining() >= S::EncodedSize()) {
+      DoDecode(out, db);
+      return true;
+    }
+    IncompleteStart(db, S::EncodedSize());
+    return false;
+  }
+
+  template <class S>
+  bool Resume(S* out, DecodeBuffer* db) {
+    DVLOG(2) << __func__ << "@" << this << ": offset_=" << offset_
+             << "; db->Remaining=" << db->Remaining();
+    if (ResumeFillingBuffer(db, S::EncodedSize())) {
+      // We have the whole thing now.
+      DVLOG(2) << __func__ << "@" << this << "    offset_=" << offset_
+               << "    Ready to decode from buffer_.";
+      DecodeBuffer buffer_db(buffer_, S::EncodedSize());
+      DoDecode(out, &buffer_db);
+      return true;
+    }
+    DCHECK_LT(offset_, S::EncodedSize());
+    return false;
+  }
+
+  // A second pair of Start and Resume, where the caller has a variable,
+  // |remaining_payload| that is both tested for sufficiency and updated
+  // during decoding. Note that the decode buffer may extend beyond the
+  // remaining payload because the buffer may include padding.
+  template <class S>
+  DecodeStatus Start(S* out, DecodeBuffer* db, uint32_t* remaining_payload) {
+    static_assert(S::EncodedSize() <= sizeof buffer_, "buffer_ is too small");
+    DVLOG(2) << __func__ << "@" << this
+             << ": *remaining_payload=" << *remaining_payload
+             << "; db->Remaining=" << db->Remaining()
+             << "; EncodedSize=" << S::EncodedSize();
+    if (db->MinLengthRemaining(*remaining_payload) >= S::EncodedSize()) {
+      DoDecode(out, db);
+      *remaining_payload -= S::EncodedSize();
+      return DecodeStatus::kDecodeDone;
+    }
+    return IncompleteStart(db, remaining_payload, S::EncodedSize());
+  }
+
+  template <class S>
+  bool Resume(S* out, DecodeBuffer* db, uint32_t* remaining_payload) {
+    DVLOG(3) << __func__ << "@" << this << ": offset_=" << offset_
+             << "; *remaining_payload=" << *remaining_payload
+             << "; db->Remaining=" << db->Remaining()
+             << "; EncodedSize=" << S::EncodedSize();
+    if (ResumeFillingBuffer(db, remaining_payload, S::EncodedSize())) {
+      // We have the whole thing now.
+      DVLOG(2) << __func__ << "@" << this << ": offset_=" << offset_
+               << "; Ready to decode from buffer_.";
+      DecodeBuffer buffer_db(buffer_, S::EncodedSize());
+      DoDecode(out, &buffer_db);
+      return true;
+    }
+    DCHECK_LT(offset_, S::EncodedSize());
+    return false;
+  }
+
+  uint32_t offset() const { return offset_; }
+
+ private:
+  friend class test::Http2StructureDecoderPeer;
+
+  uint32_t IncompleteStart(DecodeBuffer* db, uint32_t target_size);
+  DecodeStatus IncompleteStart(DecodeBuffer* db,
+                               uint32_t* remaining_payload,
+                               uint32_t target_size);
+
+  bool ResumeFillingBuffer(DecodeBuffer* db, uint32_t target_size);
+  bool ResumeFillingBuffer(DecodeBuffer* db,
+                           uint32_t* remaining_payload,
+                           uint32_t target_size);
+
+  uint32_t offset_;
+  char buffer_[Http2FrameHeader::EncodedSize()];
+};
+
+}  // namespace net
+
+#endif  // NET_HTTP2_DECODER_HTTP2_STRUCTURE_DECODER_H_