[DevTools] Add V8InspectorSession::state(), which returns binary (CBOR).

Keep the existing method for compatibility, by converting
to json from CBOR using the inspector_protocol_encoding library,
via a v8 specific interface library that directs routines for
converting between strings and doubles to v8's implementations.

This change also brings in the encoding.h / encoding.cc files from the
upstream inspector_protocol project. The only modification here
are the header guards, and the namespace. I will fix roll.py to
make it so that we pick up future changes.

third_party/inspector_protocol/BUILD.gn is specific to v8, by necessity.
third_party/inspector_protocol/.clang-format is a copy of the upstream
file. If we don't put this, we'll find ourselves auto-formatting the roll,
which is annoying.

Change-Id: I20fa8759164e7a39f8a7c30e0d2a3f8a7e4be227
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1590627
Reviewed-by: Alexei Filippov <alph@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Johannes Henkel <johannes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61187}

include/v8-inspector.h

@@ -132,6 +132,7 @@ class V8_EXPORT V8InspectorSession {
   static bool canDispatchMethod(const StringView& method);
   virtual void dispatchProtocolMessage(const StringView& message) = 0;
   virtual std::unique_ptr<StringBuffer> stateJSON() = 0;
+  virtual std::vector<uint8_t> state() = 0;
   virtual std::vector<std::unique_ptr<protocol::Schema::API::Domain>>
   supportedDomains() = 0;
 

src/inspector/BUILD.gn

@@ -83,6 +83,7 @@ v8_header_set("inspector_test_headers") {
 v8_source_set("inspector") {
   deps = [
     "../..:v8_version",
+    "../../third_party/inspector_protocol:encoding",
   ]
 
   public_deps = [
@@ -130,6 +131,8 @@ v8_source_set("inspector") {
     "v8-heap-profiler-agent-impl.h",
     "v8-inspector-impl.cc",
     "v8-inspector-impl.h",
+    "v8-inspector-protocol-encoding.cc",
+    "v8-inspector-protocol-encoding.h",
     "v8-inspector-session-impl.cc",
     "v8-inspector-session-impl.h",
     "v8-profiler-agent-impl.cc",

src/inspector/DEPS

@@ -13,6 +13,9 @@ include_rules = [
   "+src/v8memory.h",
   "+src/inspector",
   "+src/tracing",
+  "+src/vector.h",
   "+src/debug/debug-interface.h",
   "+src/debug/interface-types.h",
+  "+../../third_party/inspector_protocol/encoding/encoding.h",
+  "+../../third_party/inspector_protocol/encoding/encoding.cc",
 ]

src/inspector/v8-inspector-protocol-encoding.cc

@@ -0,0 +1,46 @@
+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/inspector/v8-inspector-protocol-encoding.h"
+
+#include <cmath>
+#include "../../third_party/inspector_protocol/encoding/encoding.h"
+#include "src/conversions.h"
+#include "src/vector.h"
+
+namespace v8_inspector {
+namespace {
+using IPEStatus = ::v8_inspector_protocol_encoding::Status;
+using ::v8_inspector_protocol_encoding::span;
+
+class Platform : public ::v8_inspector_protocol_encoding::json::Platform {
+ public:
+  bool StrToD(const char* str, double* result) const override {
+    *result = v8::internal::StringToDouble(str, v8::internal::NO_FLAGS);
+    return !std::isnan(*result);
+  }
+  std::unique_ptr<char[]> DToStr(double value) const override {
+    v8::internal::ScopedVector<char> buffer(
+        v8::internal::kDoubleToCStringMinBufferSize);
+    const char* str = v8::internal::DoubleToCString(value, buffer);
+    if (str == nullptr) return nullptr;
+    std::unique_ptr<char[]> result(new char[strlen(str) + 1]);
+    memcpy(result.get(), str, strlen(str) + 1);
+    DCHECK_EQ(0, result[strlen(str)]);
+    return result;
+  }
+};
+}  // namespace
+
+IPEStatus ConvertCBORToJSON(span<uint8_t> cbor, std::vector<uint8_t>* json) {
+  Platform platform;
+  return ConvertCBORToJSON(platform, cbor, json);
+}
+
+IPEStatus ConvertJSONToCBOR(span<uint8_t> json, std::vector<uint8_t>* cbor) {
+  Platform platform;
+  return ConvertJSONToCBOR(platform, json, cbor);
+}
+
+}  // namespace v8_inspector

src/inspector/v8-inspector-protocol-encoding.h

@@ -0,0 +1,22 @@
+// Copyright 2019 the V8 project 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 V8_INSPECTOR_V8_INSPECTOR_PROTOCOL_ENCODING_H_
+#define V8_INSPECTOR_V8_INSPECTOR_PROTOCOL_ENCODING_H_
+
+#include "../../third_party/inspector_protocol/encoding/encoding.h"
+
+namespace v8_inspector {
+
+::v8_inspector_protocol_encoding::Status ConvertCBORToJSON(
+    ::v8_inspector_protocol_encoding::span<uint8_t> cbor,
+    std::vector<uint8_t>* json);
+
+::v8_inspector_protocol_encoding::Status ConvertJSONToCBOR(
+    ::v8_inspector_protocol_encoding::span<uint8_t> json,
+    std::vector<uint8_t>* cbor);
+
+}  // namespace v8_inspector
+
+#endif  // V8_INSPECTOR_V8_INSPECTOR_PROTOCOL_ENCODING_H_

src/inspector/v8-inspector-session-impl.cc

@@ -4,6 +4,8 @@
 
 #include "src/inspector/v8-inspector-session-impl.h"
 
+#include "src/base/logging.h"
+#include "src/base/macros.h"
 #include "src/inspector/injected-script.h"
 #include "src/inspector/inspected-context.h"
 #include "src/inspector/protocol/Protocol.h"
@@ -15,11 +17,16 @@
 #include "src/inspector/v8-debugger.h"
 #include "src/inspector/v8-heap-profiler-agent-impl.h"
 #include "src/inspector/v8-inspector-impl.h"
+#include "src/inspector/v8-inspector-protocol-encoding.h"
 #include "src/inspector/v8-profiler-agent-impl.h"
 #include "src/inspector/v8-runtime-agent-impl.h"
 #include "src/inspector/v8-schema-agent-impl.h"
 
 namespace v8_inspector {
+namespace {
+using ::v8_inspector_protocol_encoding::SpanFrom;
+using IPEStatus = ::v8_inspector_protocol_encoding::Status;
+}  // namespace
 
 // static
 bool V8InspectorSession::canDispatchMethod(const StringView& method) {
@@ -355,8 +362,17 @@ void V8InspectorSessionImpl::dispatchProtocolMessage(
 }
 
 std::unique_ptr<StringBuffer> V8InspectorSessionImpl::stateJSON() {
-  String16 json = m_state->toJSONString();
-  return StringBufferImpl::adopt(json);
+  std::vector<uint8_t> json;
+  IPEStatus status = ConvertCBORToJSON(SpanFrom(state()), &json);
+  DCHECK(status.ok());
+  USE(status);
+  return v8::base::make_unique<BinaryStringBuffer>(std::move(json));
+}
+
+std::vector<uint8_t> V8InspectorSessionImpl::state() {
+  std::vector<uint8_t> out;
+  m_state->writeBinary(&out);
+  return out;
 }
 
 std::vector<std::unique_ptr<protocol::Schema::API::Domain>>

src/inspector/v8-inspector-session-impl.h

@@ -65,6 +65,7 @@ class V8InspectorSessionImpl : public V8InspectorSession,
   // V8InspectorSession implementation.
   void dispatchProtocolMessage(const StringView& message) override;
   std::unique_ptr<StringBuffer> stateJSON() override;
+  std::vector<uint8_t> state() override;
   std::vector<std::unique_ptr<protocol::Schema::API::Domain>> supportedDomains()
       override;
   void addInspectedObject(

third_party/inspector_protocol/.clang-format

@@ -0,0 +1,36 @@
+# Defines the Chromium style for automatic reformatting.
+# http://clang.llvm.org/docs/ClangFormatStyleOptions.html
+BasedOnStyle: Chromium
+# This defaults to 'Auto'. Explicitly set it for a while, so that
+# 'vector<vector<int> >' in existing files gets formatted to
+# 'vector<vector<int>>'. ('Auto' means that clang-format will only use
+# 'int>>' if the file already contains at least one such instance.)
+Standard: Cpp11
+
+# Make sure code like:
+# IPC_BEGIN_MESSAGE_MAP()
+#   IPC_MESSAGE_HANDLER(WidgetHostViewHost_Update, OnUpdate)
+# IPC_END_MESSAGE_MAP()
+# gets correctly indented.
+MacroBlockBegin: "^\
+BEGIN_MSG_MAP|\
+BEGIN_MSG_MAP_EX|\
+BEGIN_SAFE_MSG_MAP_EX|\
+CR_BEGIN_MSG_MAP_EX|\
+IPC_BEGIN_MESSAGE_MAP|\
+IPC_BEGIN_MESSAGE_MAP_WITH_PARAM|\
+IPC_PROTOBUF_MESSAGE_TRAITS_BEGIN|\
+IPC_STRUCT_BEGIN|\
+IPC_STRUCT_BEGIN_WITH_PARENT|\
+IPC_STRUCT_TRAITS_BEGIN|\
+POLPARAMS_BEGIN|\
+PPAPI_BEGIN_MESSAGE_MAP$"
+MacroBlockEnd: "^\
+CR_END_MSG_MAP|\
+END_MSG_MAP|\
+IPC_END_MESSAGE_MAP|\
+IPC_PROTOBUF_MESSAGE_TRAITS_END|\
+IPC_STRUCT_END|\
+IPC_STRUCT_TRAITS_END|\
+POLPARAMS_END|\
+PPAPI_END_MESSAGE_MAP$"

third_party/inspector_protocol/BUILD.gn

@@ -0,0 +1,10 @@
+# Copyright 2019 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+static_library("encoding") {
+  sources = [
+    "encoding/encoding.cc",
+    "encoding/encoding.h",
+  ]
+}

third_party/inspector_protocol/encoding/encoding.h

@@ -0,0 +1,504 @@
+// Copyright 2019 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 V8_INSPECTOR_PROTOCOL_ENCODING_ENCODING_H_
+#define V8_INSPECTOR_PROTOCOL_ENCODING_ENCODING_H_
+
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace v8_inspector_protocol_encoding {
+// =============================================================================
+// span - sequence of bytes
+// =============================================================================
+
+// This template is similar to std::span, which will be included in C++20.  Like
+// std::span it uses ptrdiff_t, which is signed (and thus a bit annoying
+// sometimes when comparing with size_t), but other than this it's much simpler.
+template <typename T>
+class span {
+ public:
+  using index_type = std::ptrdiff_t;
+
+  span() : data_(nullptr), size_(0) {}
+  span(const T* data, index_type size) : data_(data), size_(size) {}
+
+  const T* data() const { return data_; }
+
+  const T* begin() const { return data_; }
+  const T* end() const { return data_ + size_; }
+
+  const T& operator[](index_type idx) const { return data_[idx]; }
+
+  span<T> subspan(index_type offset, index_type count) const {
+    return span(data_ + offset, count);
+  }
+
+  span<T> subspan(index_type offset) const {
+    return span(data_ + offset, size_ - offset);
+  }
+
+  bool empty() const { return size_ == 0; }
+
+  index_type size() const { return size_; }
+  index_type size_bytes() const { return size_ * sizeof(T); }
+
+ private:
+  const T* data_;
+  index_type size_;
+};
+
+template <typename T>
+span<T> SpanFrom(const std::vector<T>& v) {
+  return span<T>(v.data(), v.size());
+}
+
+template <size_t N>
+span<uint8_t> SpanFrom(const char (&str)[N]) {
+  return span<uint8_t>(reinterpret_cast<const uint8_t*>(str), N - 1);
+}
+
+inline span<uint8_t> SpanFrom(const char* str) {
+  return str ? span<uint8_t>(reinterpret_cast<const uint8_t*>(str), strlen(str))
+             : span<uint8_t>();
+}
+
+inline span<uint8_t> SpanFrom(const std::string& v) {
+  return span<uint8_t>(reinterpret_cast<const uint8_t*>(v.data()), v.size());
+}
+
+// =============================================================================
+// Status and Error codes
+// =============================================================================
+enum class Error {
+  OK = 0,
+  // JSON parsing errors - json_parser.{h,cc}.
+  JSON_PARSER_UNPROCESSED_INPUT_REMAINS = 0x01,
+  JSON_PARSER_STACK_LIMIT_EXCEEDED = 0x02,
+  JSON_PARSER_NO_INPUT = 0x03,
+  JSON_PARSER_INVALID_TOKEN = 0x04,
+  JSON_PARSER_INVALID_NUMBER = 0x05,
+  JSON_PARSER_INVALID_STRING = 0x06,
+  JSON_PARSER_UNEXPECTED_ARRAY_END = 0x07,
+  JSON_PARSER_COMMA_OR_ARRAY_END_EXPECTED = 0x08,
+  JSON_PARSER_STRING_LITERAL_EXPECTED = 0x09,
+  JSON_PARSER_COLON_EXPECTED = 0x0a,
+  JSON_PARSER_UNEXPECTED_MAP_END = 0x0b,
+  JSON_PARSER_COMMA_OR_MAP_END_EXPECTED = 0x0c,
+  JSON_PARSER_VALUE_EXPECTED = 0x0d,
+
+  CBOR_INVALID_INT32 = 0x0e,
+  CBOR_INVALID_DOUBLE = 0x0f,
+  CBOR_INVALID_ENVELOPE = 0x10,
+  CBOR_INVALID_STRING8 = 0x11,
+  CBOR_INVALID_STRING16 = 0x12,
+  CBOR_INVALID_BINARY = 0x13,
+  CBOR_UNSUPPORTED_VALUE = 0x14,
+  CBOR_NO_INPUT = 0x15,
+  CBOR_INVALID_START_BYTE = 0x16,
+  CBOR_UNEXPECTED_EOF_EXPECTED_VALUE = 0x17,
+  CBOR_UNEXPECTED_EOF_IN_ARRAY = 0x18,
+  CBOR_UNEXPECTED_EOF_IN_MAP = 0x19,
+  CBOR_INVALID_MAP_KEY = 0x1a,
+  CBOR_STACK_LIMIT_EXCEEDED = 0x1b,
+  CBOR_TRAILING_JUNK = 0x1c,
+  CBOR_MAP_START_EXPECTED = 0x1d,
+  CBOR_MAP_STOP_EXPECTED = 0x1e,
+  CBOR_ENVELOPE_SIZE_LIMIT_EXCEEDED = 0x1f,
+};
+
+// A status value with position that can be copied. The default status
+// is OK. Usually, error status values should come with a valid position.
+struct Status {
+  static constexpr std::ptrdiff_t npos() { return -1; }
+
+  bool ok() const { return error == Error::OK; }
+
+  Error error = Error::OK;
+  std::ptrdiff_t pos = npos();
+  Status(Error error, std::ptrdiff_t pos) : error(error), pos(pos) {}
+  Status() = default;
+
+  // Returns a 7 bit US-ASCII string, either "OK" or an error message
+  // that includes the position.
+  std::string ToASCIIString() const;
+
+ private:
+  std::string ToASCIIString(const char* msg) const;
+};
+
+// Handler interface for parser events emitted by a streaming parser.
+// See cbor::NewCBOREncoder, cbor::ParseCBOR, json::NewJSONEncoder,
+// json::ParseJSON.
+class StreamingParserHandler {
+ public:
+  virtual ~StreamingParserHandler() = default;
+  virtual void HandleMapBegin() = 0;
+  virtual void HandleMapEnd() = 0;
+  virtual void HandleArrayBegin() = 0;
+  virtual void HandleArrayEnd() = 0;
+  virtual void HandleString8(span<uint8_t> chars) = 0;
+  virtual void HandleString16(span<uint16_t> chars) = 0;
+  virtual void HandleBinary(span<uint8_t> bytes) = 0;
+  virtual void HandleDouble(double value) = 0;
+  virtual void HandleInt32(int32_t value) = 0;
+  virtual void HandleBool(bool value) = 0;
+  virtual void HandleNull() = 0;
+
+  // The parser may send one error even after other events have already
+  // been received. Client code is reponsible to then discard the
+  // already processed events.
+  // |error| must be an eror, as in, |error.is_ok()| can't be true.
+  virtual void HandleError(Status error) = 0;
+};
+
+namespace cbor {
+// The binary encoding for the inspector protocol follows the CBOR specification
+// (RFC 7049). Additional constraints:
+// - Only indefinite length maps and arrays are supported.
+// - Maps and arrays are wrapped with an envelope, that is, a
+//   CBOR tag with value 24 followed by a byte string specifying
+//   the byte length of the enclosed map / array. The byte string
+//   must use a 32 bit wide length.
+// - At the top level, a message must be an indefinite length map
+//   wrapped by an envelope.
+// - Maximal size for messages is 2^32 (4 GB).
+// - For scalars, we support only the int32_t range, encoded as
+//   UNSIGNED/NEGATIVE (major types 0 / 1).
+// - UTF16 strings, including with unbalanced surrogate pairs, are encoded
+//   as CBOR BYTE_STRING (major type 2). For such strings, the number of
+//   bytes encoded must be even.
+// - UTF8 strings (major type 3) are supported.
+// - 7 bit US-ASCII strings must always be encoded as UTF8 strings, never
+//   as UTF16 strings.
+// - Arbitrary byte arrays, in the inspector protocol called 'binary',
+//   are encoded as BYTE_STRING (major type 2), prefixed with a byte
+//   indicating base64 when rendered as JSON.
+
+// =============================================================================
+// Detecting CBOR content
+// =============================================================================
+
+// The first byte for an envelope, which we use for wrapping dictionaries
+// and arrays; and the byte that indicates a byte string with 32 bit length.
+// These two bytes start an envelope, and thereby also any CBOR message
+// produced or consumed by this protocol. See also |EnvelopeEncoder| below.
+uint8_t InitialByteForEnvelope();
+uint8_t InitialByteFor32BitLengthByteString();
+
+// Checks whether |msg| is a cbor message.
+bool IsCBORMessage(span<uint8_t> msg);
+
+// =============================================================================
+// Encoding individual CBOR items
+// =============================================================================
+
+// Some constants for CBOR tokens that only take a single byte on the wire.
+uint8_t EncodeTrue();
+uint8_t EncodeFalse();
+uint8_t EncodeNull();
+uint8_t EncodeIndefiniteLengthArrayStart();
+uint8_t EncodeIndefiniteLengthMapStart();
+uint8_t EncodeStop();
+
+// Encodes |value| as |UNSIGNED| (major type 0) iff >= 0, or |NEGATIVE|
+// (major type 1) iff < 0.
+void EncodeInt32(int32_t value, std::vector<uint8_t>* out);
+void EncodeInt32(int32_t value, std::string* out);
+
+// Encodes a UTF16 string as a BYTE_STRING (major type 2). Each utf16
+// character in |in| is emitted with most significant byte first,
+// appending to |out|.
+void EncodeString16(span<uint16_t> in, std::vector<uint8_t>* out);
+void EncodeString16(span<uint16_t> in, std::string* out);
+
+// Encodes a UTF8 string |in| as STRING (major type 3).
+void EncodeString8(span<uint8_t> in, std::vector<uint8_t>* out);
+void EncodeString8(span<uint8_t> in, std::string* out);
+
+// Encodes the given |latin1| string as STRING8.
+// If any non-ASCII character is present, it will be represented
+// as a 2 byte UTF8 sequence.
+void EncodeFromLatin1(span<uint8_t> latin1, std::vector<uint8_t>* out);
+void EncodeFromLatin1(span<uint8_t> latin1, std::string* out);
+
+// Encodes the given |utf16| string as STRING8 if it's entirely US-ASCII.
+// Otherwise, encodes as STRING16.
+void EncodeFromUTF16(span<uint16_t> utf16, std::vector<uint8_t>* out);
+void EncodeFromUTF16(span<uint16_t> utf16, std::string* out);
+
+// Encodes arbitrary binary data in |in| as a BYTE_STRING (major type 2) with
+// definitive length, prefixed with tag 22 indicating expected conversion to
+// base64 (see RFC 7049, Table 3 and Section 2.4.4.2).
+void EncodeBinary(span<uint8_t> in, std::vector<uint8_t>* out);
+void EncodeBinary(span<uint8_t> in, std::string* out);
+
+// Encodes / decodes a double as Major type 7 (SIMPLE_VALUE),
+// with additional info = 27, followed by 8 bytes in big endian.
+void EncodeDouble(double value, std::vector<uint8_t>* out);
+void EncodeDouble(double value, std::string* out);
+
+// =============================================================================
+// cbor::EnvelopeEncoder - for wrapping submessages
+// =============================================================================
+
+// An envelope indicates the byte length of a wrapped item.
+// We use this for maps and array, which allows the decoder
+// to skip such (nested) values whole sale.
+// It's implemented as a CBOR tag (major type 6) with additional
+// info = 24, followed by a byte string with a 32 bit length value;
+// so the maximal structure that we can wrap is 2^32 bits long.
+// See also: https://tools.ietf.org/html/rfc7049#section-2.4.4.1
+class EnvelopeEncoder {
+ public:
+  // Emits the envelope start bytes and records the position for the
+  // byte size in |byte_size_pos_|. Also emits empty bytes for the
+  // byte sisze so that encoding can continue.
+  void EncodeStart(std::vector<uint8_t>* out);
+  void EncodeStart(std::string* out);
+  // This records the current size in |out| at position byte_size_pos_.
+  // Returns true iff successful.
+  bool EncodeStop(std::vector<uint8_t>* out);
+  bool EncodeStop(std::string* out);
+
+ private:
+  std::size_t byte_size_pos_ = 0;
+};
+
+// =============================================================================
+// cbor::NewCBOREncoder - for encoding from a streaming parser
+// =============================================================================
+
+// This can be used to convert to CBOR, by passing the return value to a parser
+// that drives it. The handler will encode into |out|, and iff an error occurs
+// it will set |status| to an error and clear |out|. Otherwise, |status.ok()|
+// will be |true|.
+std::unique_ptr<StreamingParserHandler> NewCBOREncoder(
+    std::vector<uint8_t>* out,
+    Status* status);
+std::unique_ptr<StreamingParserHandler> NewCBOREncoder(std::string* out,
+                                                       Status* status);
+
+// =============================================================================
+// cbor::CBORTokenizer - for parsing individual CBOR items
+// =============================================================================
+
+// Tags for the tokens within a CBOR message that CBORTokenizer understands.
+// Note that this is not the same terminology as the CBOR spec (RFC 7049),
+// but rather, our adaptation. For instance, we lump unsigned and signed
+// major type into INT32 here (and disallow values outside the int32_t range).
+enum class CBORTokenTag {
+  // Encountered an error in the structure of the message. Consult
+  // status() for details.
+  ERROR_VALUE,
+  // Booleans and NULL.
+  TRUE_VALUE,
+  FALSE_VALUE,
+  NULL_VALUE,
+  // An int32_t (signed 32 bit integer).
+  INT32,
+  // A double (64 bit floating point).
+  DOUBLE,
+  // A UTF8 string.
+  STRING8,
+  // A UTF16 string.
+  STRING16,
+  // A binary string.
+  BINARY,
+  // Starts an indefinite length map; after the map start we expect
+  // alternating keys and values, followed by STOP.
+  MAP_START,
+  // Starts an indefinite length array; after the array start we
+  // expect values, followed by STOP.
+  ARRAY_START,
+  // Ends a map or an array.
+  STOP,
+  // An envelope indicator, wrapping a map or array.
+  // Internally this carries the byte length of the wrapped
+  // map or array. While CBORTokenizer::Next() will read / skip the entire
+  // envelope, CBORTokenizer::EnterEnvelope() reads the tokens
+  // inside of it.
+  ENVELOPE,
+  // We've reached the end there is nothing else to read.
+  DONE,
+};
+
+// The major types from RFC 7049 Section 2.1.
+enum class MajorType {
+  UNSIGNED = 0,
+  NEGATIVE = 1,
+  BYTE_STRING = 2,
+  STRING = 3,
+  ARRAY = 4,
+  MAP = 5,
+  TAG = 6,
+  SIMPLE_VALUE = 7
+};
+
+// CBORTokenizer segments a CBOR message, presenting the tokens therein as
+// numbers, strings, etc. This is not a complete CBOR parser, but makes it much
+// easier to implement one (e.g. ParseCBOR, above). It can also be used to parse
+// messages partially.
+class CBORTokenizer {
+ public:
+  explicit CBORTokenizer(span<uint8_t> bytes);
+  ~CBORTokenizer();
+
+  // Identifies the current token that we're looking at,
+  // or ERROR_VALUE (in which ase ::Status() has details)
+  // or DONE (if we're past the last token).
+  CBORTokenTag TokenTag() const;
+
+  // Advances to the next token.
+  void Next();
+  // Can only be called if TokenTag() == CBORTokenTag::ENVELOPE.
+  // While Next() would skip past the entire envelope / what it's
+  // wrapping, EnterEnvelope positions the cursor inside of the envelope,
+  // letting the client explore the nested structure.
+  void EnterEnvelope();
+
+  // If TokenTag() is CBORTokenTag::ERROR_VALUE, then Status().error describes
+  // the error more precisely; otherwise it'll be set to Error::OK.
+  // In either case, Status().pos is the current position.
+  struct Status Status() const;
+
+  // The following methods retrieve the token values. They can only
+  // be called if TokenTag() matches.
+
+  // To be called only if ::TokenTag() == CBORTokenTag::INT32.
+  int32_t GetInt32() const;
+
+  // To be called only if ::TokenTag() == CBORTokenTag::DOUBLE.
+  double GetDouble() const;
+
+  // To be called only if ::TokenTag() == CBORTokenTag::STRING8.
+  span<uint8_t> GetString8() const;
+
+  // Wire representation for STRING16 is low byte first (little endian).
+  // To be called only if ::TokenTag() == CBORTokenTag::STRING16.
+  span<uint8_t> GetString16WireRep() const;
+
+  // To be called only if ::TokenTag() == CBORTokenTag::BINARY.
+  span<uint8_t> GetBinary() const;
+
+  // To be called only if ::TokenTag() == CBORTokenTag::ENVELOPE.
+  span<uint8_t> GetEnvelopeContents() const;
+
+ private:
+  void ReadNextToken(bool enter_envelope);
+  void SetToken(CBORTokenTag token, std::ptrdiff_t token_byte_length);
+  void SetError(Error error);
+
+  span<uint8_t> bytes_;
+  CBORTokenTag token_tag_;
+  struct Status status_;
+  std::ptrdiff_t token_byte_length_;
+  MajorType token_start_type_;
+  uint64_t token_start_internal_value_;
+};
+
+// =============================================================================
+// cbor::ParseCBOR - for receiving streaming parser events for CBOR messages
+// =============================================================================
+
+// Parses a CBOR encoded message from |bytes|, sending events to
+// |out|. If an error occurs, sends |out->HandleError|, and parsing stops.
+// The client is responsible for discarding the already received information in
+// that case.
+void ParseCBOR(span<uint8_t> bytes, StreamingParserHandler* out);
+
+// =============================================================================
+// cbor::AppendString8EntryToMap - for limited in-place editing of messages
+// =============================================================================
+
+// Modifies the |cbor| message by appending a new key/value entry at the end
+// of the map. Patches up the envelope size; Status.ok() iff successful.
+// If not successful, |cbor| may be corrupted after this call.
+Status AppendString8EntryToCBORMap(span<uint8_t> string8_key,
+                                   span<uint8_t> string8_value,
+                                   std::vector<uint8_t>* cbor);
+Status AppendString8EntryToCBORMap(span<uint8_t> string8_key,
+                                   span<uint8_t> string8_value,
+                                   std::string* cbor);
+
+namespace internals {  // Exposed only for writing tests.
+int8_t ReadTokenStart(span<uint8_t> bytes,
+                      cbor::MajorType* type,
+                      uint64_t* value);
+
+void WriteTokenStart(cbor::MajorType type,
+                     uint64_t value,
+                     std::vector<uint8_t>* encoded);
+void WriteTokenStart(cbor::MajorType type,
+                     uint64_t value,
+                     std::string* encoded);
+}  // namespace internals
+}  // namespace cbor
+
+namespace json {
+// Client code must provide an instance. Implementation should delegate
+// to whatever is appropriate.
+class Platform {
+ public:
+  virtual ~Platform() = default;
+  // Parses |str| into |result|. Returns false iff there are
+  // leftover characters or parsing errors.
+  virtual bool StrToD(const char* str, double* result) const = 0;
+
+  // Prints |value| in a format suitable for JSON.
+  virtual std::unique_ptr<char[]> DToStr(double value) const = 0;
+};
+
+// =============================================================================
+// json::NewJSONEncoder - for encoding streaming parser events as JSON
+// =============================================================================
+
+// Returns a handler object which will write ascii characters to |out|.
+// |status->ok()| will be false iff the handler routine HandleError() is called.
+// In that case, we'll stop emitting output.
+// Except for calling the HandleError routine at any time, the client
+// code must call the Handle* methods in an order in which they'd occur
+// in valid JSON; otherwise we may crash (the code uses assert).
+std::unique_ptr<StreamingParserHandler> NewJSONEncoder(
+    const Platform* platform,
+    std::vector<uint8_t>* out,
+    Status* status);
+std::unique_ptr<StreamingParserHandler> NewJSONEncoder(const Platform* platform,
+                                                       std::string* out,
+                                                       Status* status);
+
+// =============================================================================
+// json::ParseJSON - for receiving streaming parser events for JSON
+// =============================================================================
+
+void ParseJSON(const Platform& platform,
+               span<uint8_t> chars,
+               StreamingParserHandler* handler);
+void ParseJSON(const Platform& platform,
+               span<uint16_t> chars,
+               StreamingParserHandler* handler);
+
+// =============================================================================
+// json::ConvertCBORToJSON, json::ConvertJSONToCBOR - for transcoding
+// =============================================================================
+Status ConvertCBORToJSON(const Platform& platform,
+                         span<uint8_t> cbor,
+                         std::string* json);
+Status ConvertCBORToJSON(const Platform& platform,
+                         span<uint8_t> cbor,
+                         std::vector<uint8_t>* json);
+Status ConvertJSONToCBOR(const Platform& platform,
+                         span<uint8_t> json,
+                         std::vector<uint8_t>* cbor);
+Status ConvertJSONToCBOR(const Platform& platform,
+                         span<uint8_t> json,
+                         std::string* cbor);
+}  // namespace json
+}  // namespace v8_inspector_protocol_encoding
+
+#endif  // V8_INSPECTOR_PROTOCOL_ENCODING_ENCODING_H_