First step towards support for being able to interrupt a running Dart Isolate

runtime/bin/dbg_message.cc

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "bin/dbg_connection.h"
+#include "bin/dbg_message.h"
+#include "bin/dartutils.h"
+#include "bin/thread.h"
+#include "bin/utils.h"
+
+#include "platform/globals.h"
+#include "platform/json.h"
+#include "platform/thread.h"
+#include "platform/utils.h"
+
+#include "include/dart_api.h"
+
+bool MessageParser::IsValidMessage() const {
+  if (buf_length_ == 0) {
+    return false;
+  }
+  dart::JSONReader msg_reader(buf_);
+  return msg_reader.EndOfObject() != NULL;
+}
+
+
+int MessageParser::MessageId() const {
+  dart::JSONReader r(buf_);
+  r.Seek("id");
+  if (r.Type() == dart::JSONReader::kInteger) {
+    return atoi(r.ValueChars());
+  } else {
+    return -1;
+  }
+}
+
+
+const char* MessageParser::Params() const {
+  dart::JSONReader r(buf_);
+  r.Seek("params");
+  if (r.Type() == dart::JSONReader::kObject) {
+    return r.ValueChars();
+  } else {
+    return NULL;
+  }
+}
+
+
+intptr_t MessageParser::GetIntParam(const char* name) const {
+  const char* params = Params();
+  ASSERT(params != NULL);
+  dart::JSONReader r(params);
+  r.Seek(name);
+  ASSERT(r.Type() == dart::JSONReader::kInteger);
+  return strtol(r.ValueChars(), NULL, 10);
+}
+
+
+intptr_t MessageParser::GetOptIntParam(const char* name,
+                                       intptr_t default_val) const {
+  const char* params = Params();
+  ASSERT(params != NULL);
+  dart::JSONReader r(params);
+  r.Seek(name);
+  if (r.Type() == dart::JSONReader::kInteger) {
+    return strtol(r.ValueChars(), NULL, 10);
+  } else {
+    return default_val;
+  }
+}
+
+
+static const char* GetStringChars(Dart_Handle str) {
+  ASSERT(Dart_IsString(str));
+  const char* chars;
+  Dart_Handle res = Dart_StringToCString(str, &chars);
+  ASSERT(!Dart_IsError(res));
+  return chars;
+}
+
+
+static int GetIntValue(Dart_Handle int_handle) {
+  int64_t int64_val = -1;
+  ASSERT(Dart_IsInteger(int_handle));
+  Dart_Handle res = Dart_IntegerToInt64(int_handle, &int64_val);
+  ASSERT_NOT_ERROR(res);
+  // TODO(hausner): Range check.
+  return int64_val;
+}
+
+
+char* MessageParser::GetStringParam(const char* name) const {
+  const char* params = Params();
+  ASSERT(params != NULL);
+  dart::JSONReader pr(params);
+  pr.Seek(name);
+  if (pr.Type() != dart::JSONReader::kString) {
+    return NULL;
+  }
+  intptr_t buflen = pr.ValueLen() + 1;
+  char* param_chars = reinterpret_cast<char*>(malloc(buflen));
+  pr.GetValueChars(param_chars, buflen);
+  // TODO(hausner): Decode escape sequences.
+  return param_chars;
+}
+
+
+static void FormatEncodedString(dart::TextBuffer* buf, Dart_Handle str) {
+  intptr_t str_len = 0;
+  Dart_Handle res = Dart_StringLength(str, &str_len);
+  ASSERT_NOT_ERROR(res);
+  uint32_t* codepoints =
+      reinterpret_cast<uint32_t*>(malloc(str_len * sizeof(uint32_t)));
+  ASSERT(codepoints != NULL);
+  intptr_t actual_len = str_len;
+  res = Dart_StringGet32(str, codepoints, &actual_len);
+  ASSERT_NOT_ERROR(res);
+  ASSERT(str_len == actual_len);
+  buf->AddChar('\"');
+  for (int i = 0; i < str_len; i++) {
+    buf->AddEscapedChar(codepoints[i]);
+  }
+  buf->AddChar('\"');
+  free(codepoints);
+}
+
+
+static void FormatErrorMsg(dart::TextBuffer* buf, Dart_Handle err) {
+  // TODO(hausner): Turn message into Dart string and
+  // properly encode the message.
+  ASSERT(Dart_IsError(err));
+  const char* msg = Dart_GetError(err);
+  buf->Printf("\"%s\"", msg);
+}
+
+
+static void FormatTextualValue(dart::TextBuffer* buf, Dart_Handle object) {
+  Dart_Handle text;
+  if (Dart_IsNull(object)) {
+    text = Dart_Null();
+  } else {
+    Dart_ExceptionPauseInfo savedState = Dart_GetExceptionPauseInfo();
+
+    // TODO(hausner): Check whether recursive/reentrant pauses on exceptions
+    // should be prevented in Debugger::SignalExceptionThrown() instead.
+    if (savedState != kNoPauseOnExceptions) {
+      Dart_Handle res = Dart_SetExceptionPauseInfo(kNoPauseOnExceptions);
+      ASSERT_NOT_ERROR(res);
+    }
+
+    text = Dart_ToString(object);
+
+    if (savedState != kNoPauseOnExceptions) {
+      Dart_Handle res = Dart_SetExceptionPauseInfo(savedState);
+      ASSERT_NOT_ERROR(res);
+    }
+  }
+  buf->Printf("\"text\":");
+  if (Dart_IsNull(text)) {
+    buf->Printf("null");
+  } else if (Dart_IsError(text)) {
+    FormatErrorMsg(buf, text);
+  } else {
+    FormatEncodedString(buf, text);
+  }
+}
+
+
+static void FormatValue(dart::TextBuffer* buf, Dart_Handle object) {
+  if (Dart_IsInteger(object)) {
+    buf->Printf("\"kind\":\"integer\",");
+  } else if (Dart_IsString(object)) {
+    buf->Printf("\"kind\":\"string\",");
+  } else if (Dart_IsBoolean(object)) {
+    buf->Printf("\"kind\":\"boolean\",");
+  } else if (Dart_IsList(object)) {
+    intptr_t len = 0;
+    Dart_Handle res = Dart_ListLength(object, &len);
+    ASSERT_NOT_ERROR(res);
+    buf->Printf("\"kind\":\"list\",\"length\":%"Pd",", len);
+  } else {
+    buf->Printf("\"kind\":\"object\",");
+  }
+  FormatTextualValue(buf, object);
+}
+
+
+static void FormatValueObj(dart::TextBuffer* buf, Dart_Handle object) {
+  buf->Printf("{");
+  FormatValue(buf, object);
+  buf->Printf("}");
+}
+
+
+static void FormatRemoteObj(dart::TextBuffer* buf, Dart_Handle object) {
+  intptr_t obj_id = Dart_CacheObject(object);
+  ASSERT(obj_id >= 0);
+  buf->Printf("{\"objectId\":%"Pd",", obj_id);
+  FormatValue(buf, object);
+  buf->Printf("}");
+}
+
+
+static void FormatNamedValue(dart::TextBuffer* buf,
+                             Dart_Handle object_name,
+                             Dart_Handle object) {
+  ASSERT(Dart_IsString(object_name));
+  buf->Printf("{\"name\":\"%s\",", GetStringChars(object_name));
+  buf->Printf("\"value\":");
+  FormatRemoteObj(buf, object);
+  buf->Printf("}");
+}
+
+
+static void FormatNamedValueList(dart::TextBuffer* buf,
+                                 Dart_Handle obj_list) {
+  ASSERT(Dart_IsList(obj_list));
+  intptr_t list_length = 0;
+  Dart_Handle res = Dart_ListLength(obj_list, &list_length);
+  ASSERT_NOT_ERROR(res);
+  ASSERT(list_length % 2 == 0);
+  buf->Printf("[");
+  for (int i = 0; i + 1 < list_length; i += 2) {
+    Dart_Handle name_handle = Dart_ListGetAt(obj_list, i);
+    ASSERT_NOT_ERROR(name_handle);
+    Dart_Handle value_handle = Dart_ListGetAt(obj_list, i + 1);
+    ASSERT_NOT_ERROR(value_handle);
+    if (i > 0) {
+      buf->Printf(",");
+    }
+    FormatNamedValue(buf, name_handle, value_handle);
+  }
+  buf->Printf("]");
+}
+
+
+static const char* FormatClassProps(dart::TextBuffer* buf,
+                                    intptr_t cls_id) {
+  Dart_Handle name, static_fields;
+  intptr_t super_id = -1;
+  intptr_t library_id = -1;
+  Dart_Handle res =
+      Dart_GetClassInfo(cls_id, &name, &library_id, &super_id, &static_fields);
+  RETURN_IF_ERROR(res);
+  RETURN_IF_ERROR(name);
+  buf->Printf("{\"name\":\"%s\",", GetStringChars(name));
+  if (super_id > 0) {
+    buf->Printf("\"superclassId\":%"Pd",", super_id);
+  }
+  buf->Printf("\"libraryId\":%"Pd",", library_id);
+  RETURN_IF_ERROR(static_fields);
+  buf->Printf("\"fields\":");
+  FormatNamedValueList(buf, static_fields);
+  buf->Printf("}");
+  return NULL;
+}
+
+
+static const char* FormatLibraryProps(dart::TextBuffer* buf,
+                                      intptr_t lib_id) {
+  Dart_Handle url = Dart_GetLibraryURL(lib_id);
+  RETURN_IF_ERROR(url);
+  buf->Printf("{\"url\":");
+  FormatEncodedString(buf, url);
+
+  // Whether debugging is enabled.
+  bool is_debuggable = false;
+  Dart_Handle res = Dart_GetLibraryDebuggable(lib_id, &is_debuggable);
+  RETURN_IF_ERROR(res);
+  buf->Printf(",\"debuggingEnabled\":%s",
+              is_debuggable ? "\"true\"" : "\"false\"");
+
+  // Imports and prefixes.
+  Dart_Handle import_list = Dart_GetLibraryImports(lib_id);
+  RETURN_IF_ERROR(import_list);
+  ASSERT(Dart_IsList(import_list));
+  intptr_t list_length = 0;
+  res = Dart_ListLength(import_list, &list_length);
+  RETURN_IF_ERROR(res);
+  buf->Printf(",\"imports\":[");
+  for (int i = 0; i + 1 < list_length; i += 2) {
+    Dart_Handle lib_id = Dart_ListGetAt(import_list, i + 1);
+    ASSERT_NOT_ERROR(lib_id);
+    buf->Printf("%s{\"libraryId\":%d,",
+                (i > 0) ? ",": "",
+                GetIntValue(lib_id));
+
+    Dart_Handle name = Dart_ListGetAt(import_list, i);
+    ASSERT_NOT_ERROR(name);
+    buf->Printf("\"prefix\":\"%s\"}",
+                Dart_IsNull(name) ? "" : GetStringChars(name));
+  }
+  buf->Printf("],");
+
+  // Global variables in the library.
+  Dart_Handle global_vars = Dart_GetLibraryFields(lib_id);
+  RETURN_IF_ERROR(global_vars);
+  buf->Printf("\"globals\":");
+  FormatNamedValueList(buf, global_vars);
+  buf->Printf("}");
+  return NULL;
+}
+
+
+static const char* FormatObjProps(dart::TextBuffer* buf,
+                                  Dart_Handle object) {
+  intptr_t class_id;
+  if (Dart_IsNull(object)) {
+    buf->Printf("{\"classId\":-1,\"fields\":[]}");
+    return NULL;
+  }
+  Dart_Handle res = Dart_GetObjClassId(object, &class_id);
+  RETURN_IF_ERROR(res);
+  buf->Printf("{\"classId\": %"Pd",", class_id);
+  buf->Printf("\"kind\":\"object\",\"fields\":");
+  Dart_Handle fields = Dart_GetInstanceFields(object);
+  RETURN_IF_ERROR(fields);
+  FormatNamedValueList(buf, fields);
+  buf->Printf("}");
+  return NULL;
+}
+
+
+static const char* FormatListSlice(dart::TextBuffer* buf,
+                                   Dart_Handle list,
+                                   intptr_t list_length,
+                                   intptr_t index,
+                                   intptr_t slice_length) {
+  intptr_t end_index = index + slice_length;
+  ASSERT(end_index <= list_length);
+  buf->Printf("{\"index\":%"Pd",", index);
+  buf->Printf("\"length\":%"Pd",", slice_length);
+  buf->Printf("\"elements\":[");
+  for (intptr_t i = index; i < end_index; i++) {
+    Dart_Handle value = Dart_ListGetAt(list, i);
+    if (i > index) {
+      buf->Printf(",");
+    }
+    FormatValueObj(buf, value);
+  }
+  buf->Printf("]}");
+  return NULL;
+}
+
+
+static void FormatCallFrames(dart::TextBuffer* msg, Dart_StackTrace trace) {
+  intptr_t trace_len = 0;
+  Dart_Handle res = Dart_StackTraceLength(trace, &trace_len);
+  ASSERT_NOT_ERROR(res);
+  msg->Printf("\"callFrames\" : [ ");
+  for (int i = 0; i < trace_len; i++) {
+    Dart_ActivationFrame frame;
+    res = Dart_GetActivationFrame(trace, i, &frame);
+    ASSERT_NOT_ERROR(res);
+    Dart_Handle func_name;
+    Dart_Handle script_url;
+    intptr_t line_number = 0;
+    intptr_t library_id = 0;
+    res = Dart_ActivationFrameInfo(
+        frame, &func_name, &script_url, &line_number, &library_id);
+    ASSERT_NOT_ERROR(res);
+    ASSERT(Dart_IsString(func_name));
+    msg->Printf("%s{\"functionName\":", (i > 0) ? "," : "");
+    FormatEncodedString(msg, func_name);
+    msg->Printf(",\"libraryId\": %"Pd",", library_id);
+
+    ASSERT(Dart_IsString(script_url));
+    msg->Printf("\"location\": { \"url\":");
+    FormatEncodedString(msg, script_url);
+    msg->Printf(",\"lineNumber\":%"Pd"},", line_number);
+
+    Dart_Handle locals = Dart_GetLocalVariables(frame);
+    ASSERT_NOT_ERROR(locals);
+    msg->Printf("\"locals\":");
+    FormatNamedValueList(msg, locals);
+    msg->Printf("}");
+  }
+  msg->Printf("]");
+}
+
+
+typedef bool (*CommandHandler)(DbgMessage* msg);
+
+struct JSONDebuggerCommand {
+  const char* cmd_string;
+  CommandHandler handler_function;
+};
+
+
+static JSONDebuggerCommand debugger_commands[] = {
+  { "resume", DbgMessage::HandleResumeCmd },
+  { "stepInto", DbgMessage::HandleStepIntoCmd },
+  { "stepOut", DbgMessage::HandleStepOutCmd },
+  { "stepOver", DbgMessage::HandleStepOverCmd },
+  { "getLibraries", DbgMessage::HandleGetLibrariesCmd },
+  { "getClassProperties", DbgMessage::HandleGetClassPropsCmd },
+  { "getLibraryProperties", DbgMessage::HandleGetLibPropsCmd },
+  { "setLibraryProperties", DbgMessage::HandleSetLibPropsCmd },
+  { "getObjectProperties", DbgMessage::HandleGetObjPropsCmd },
+  { "getListElements", DbgMessage::HandleGetListCmd },
+  { "getGlobalVariables", DbgMessage::HandleGetGlobalsCmd },
+  { "getScriptURLs", DbgMessage::HandleGetScriptURLsCmd },
+  { "getScriptSource", DbgMessage::HandleGetSourceCmd },
+  { "getStackTrace", DbgMessage::HandleGetStackTraceCmd },
+  { "setBreakpoint", DbgMessage::HandleSetBpCmd },
+  { "setPauseOnException", DbgMessage::HandlePauseOnExcCmd },
+  { "removeBreakpoint", DbgMessage::HandleRemBpCmd },
+  { NULL, NULL }
+};
+
+
+bool DbgMessage::HandleMessage() {
+  // Dispatch to the appropriate handler for the command.
+  int max_index = (sizeof(debugger_commands) / sizeof(JSONDebuggerCommand));
+  ASSERT(cmd_idx_ < max_index);
+  return (*debugger_commands[cmd_idx_].handler_function)(this);
+}
+
+
+void DbgMessage::SendReply(dart::TextBuffer* reply) {
+  DebuggerConnectionHandler::SendMsg(debug_fd(), reply);
+}
+
+
+void DbgMessage::SendErrorReply(int msg_id, const char* err_msg) {
+  DebuggerConnectionHandler::SendError(debug_fd(), msg_id, err_msg);
+}
+
+
+bool DbgMessage::HandleResumeCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  dart::TextBuffer msg(64);
+  msg.Printf("{ \"id\": %d }", msg_id);
+  in_msg->SendReply(&msg);
+  return true;
+}
+
+
+bool DbgMessage::HandleStepIntoCmd(DbgMessage* in_msg) {
+  Dart_Handle res = Dart_SetStepInto();
+  ASSERT_NOT_ERROR(res);
+  return HandleResumeCmd(in_msg);
+}
+
+
+bool DbgMessage::HandleStepOutCmd(DbgMessage* in_msg) {
+  Dart_Handle res = Dart_SetStepOut();
+  ASSERT_NOT_ERROR(res);
+  return HandleResumeCmd(in_msg);
+}
+
+
+bool DbgMessage::HandleStepOverCmd(DbgMessage* in_msg) {
+  Dart_Handle res = Dart_SetStepOver();
+  ASSERT_NOT_ERROR(res);
+  return HandleResumeCmd(in_msg);
+}
+
+
+bool DbgMessage::HandleGetLibrariesCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  dart::TextBuffer msg(64);
+  msg.Printf("{ \"id\": %d, \"result\": { \"libraries\": [", msg_id);
+  Dart_Handle lib_ids = Dart_GetLibraryIds();
+  ASSERT_NOT_ERROR(lib_ids);
+  intptr_t num_libs;
+  Dart_Handle res = Dart_ListLength(lib_ids, &num_libs);
+  ASSERT_NOT_ERROR(res);
+  for (int i = 0; i < num_libs; i++) {
+    Dart_Handle lib_id_handle = Dart_ListGetAt(lib_ids, i);
+    ASSERT(Dart_IsInteger(lib_id_handle));
+    int lib_id = GetIntValue(lib_id_handle);
+    Dart_Handle lib_url = Dart_GetLibraryURL(lib_id);
+    ASSERT_NOT_ERROR(lib_url);
+    ASSERT(Dart_IsString(lib_url));
+    msg.Printf("%s{\"id\":%d,\"url\":", (i == 0) ? "" : ", ", lib_id);
+    FormatEncodedString(&msg, lib_url);
+    msg.Printf("}");
+  }
+  msg.Printf("]}}");
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleGetClassPropsCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  intptr_t cls_id = msg_parser.GetIntParam("classId");
+  dart::TextBuffer msg(64);
+  msg.Printf("{\"id\":%d, \"result\":", msg_id);
+  const char* err = FormatClassProps(&msg, cls_id);
+  if (err != NULL) {
+    in_msg->SendErrorReply(msg_id, err);
+    return false;
+  }
+  msg.Printf("}");
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleGetLibPropsCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  intptr_t lib_id = msg_parser.GetIntParam("libraryId");
+  dart::TextBuffer msg(64);
+  msg.Printf("{\"id\":%d, \"result\":", msg_id);
+  const char* err = FormatLibraryProps(&msg, lib_id);
+  if (err != NULL) {
+    in_msg->SendErrorReply(msg_id, err);
+    return false;
+  }
+  msg.Printf("}");
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleSetLibPropsCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  intptr_t lib_id = msg_parser.GetIntParam("libraryId");
+  const char* enable_request = msg_parser.GetStringParam("debuggingEnabled");
+  bool enable;
+  if (strcmp(enable_request, "true") == 0) {
+    enable = true;
+  } else if (strcmp(enable_request, "false") == 0) {
+    enable = false;
+  } else {
+    in_msg->SendErrorReply(msg_id, "illegal argument for 'debuggingEnabled'");
+    return false;
+  }
+  Dart_Handle res = Dart_SetLibraryDebuggable(lib_id, enable);
+  if (Dart_IsError(res)) {
+    in_msg->SendErrorReply(msg_id, Dart_GetError(res));
+    return false;
+  }
+  bool enabled = false;
+  res = Dart_GetLibraryDebuggable(lib_id, &enabled);
+  if (Dart_IsError(res)) {
+    in_msg->SendErrorReply(msg_id, Dart_GetError(res));
+    return false;
+  }
+  dart::TextBuffer msg(64);
+  msg.Printf("{\"id\":%d, \"result\": {\"debuggingEnabled\": \"%s\"}}",
+             msg_id,
+             enabled ? "true" : "false");
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleGetObjPropsCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  intptr_t obj_id = msg_parser.GetIntParam("objectId");
+  Dart_Handle obj = Dart_GetCachedObject(obj_id);
+  if (Dart_IsError(obj)) {
+    in_msg->SendErrorReply(msg_id, Dart_GetError(obj));
+    return false;
+  }
+  dart::TextBuffer msg(64);
+  msg.Printf("{\"id\":%d, \"result\":", msg_id);
+  const char* err = FormatObjProps(&msg, obj);
+  if (err != NULL) {
+    in_msg->SendErrorReply(msg_id, err);
+    return false;
+  }
+  msg.Printf("}");
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleGetListCmd(DbgMessage* in_msg) {
+  const intptr_t kDefaultSliceLength = 100;
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  intptr_t obj_id = msg_parser.GetIntParam("objectId");
+  Dart_Handle list = Dart_GetCachedObject(obj_id);
+  if (Dart_IsError(list)) {
+    in_msg->SendErrorReply(msg_id, Dart_GetError(list));
+    return false;
+  }
+  if (!Dart_IsList(list)) {
+    in_msg->SendErrorReply(msg_id, "object is not a list");
+    return false;
+  }
+  intptr_t list_length = 0;
+  Dart_Handle res = Dart_ListLength(list, &list_length);
+  if (Dart_IsError(res)) {
+    in_msg->SendErrorReply(msg_id, Dart_GetError(res));
+    return false;
+  }
+
+  intptr_t index = msg_parser.GetIntParam("index");
+  if (index < 0) {
+    index = 0;
+  } else if (index > list_length) {
+    index = list_length;
+  }
+
+  // If no slice length is given, get only one element. If slice length
+  // is given as 0, get entire list.
+  intptr_t slice_length = msg_parser.GetOptIntParam("length", 1);
+  if (slice_length == 0) {
+    slice_length = list_length - index;
+  }
+  if ((index + slice_length) > list_length) {
+    slice_length = list_length - index;
+  }
+  ASSERT(slice_length >= 0);
+  if (slice_length > kDefaultSliceLength) {
+    slice_length = kDefaultSliceLength;
+  }
+  dart::TextBuffer msg(64);
+  msg.Printf("{\"id\":%d, \"result\":", msg_id);
+  if (slice_length == 1) {
+    Dart_Handle value = Dart_ListGetAt(list, index);
+    FormatRemoteObj(&msg, value);
+  } else {
+    FormatListSlice(&msg, list, list_length, index, slice_length);
+  }
+  msg.Printf("}");
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleGetGlobalsCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  intptr_t lib_id = msg_parser.GetIntParam("libraryId");
+  dart::TextBuffer msg(64);
+  msg.Printf("{\"id\":%d, \"result\": { \"globals\":", msg_id);
+  Dart_Handle globals = Dart_GetGlobalVariables(lib_id);
+  ASSERT_NOT_ERROR(globals);
+  FormatNamedValueList(&msg, globals);
+  msg.Printf("}}");
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleGetScriptURLsCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  dart::TextBuffer msg(64);
+  intptr_t lib_id = msg_parser.GetIntParam("libraryId");
+  Dart_Handle lib_url = Dart_GetLibraryURL(lib_id);
+  ASSERT_NOT_ERROR(lib_url);
+  Dart_Handle urls = Dart_GetScriptURLs(lib_url);
+  if (Dart_IsError(urls)) {
+    in_msg->SendErrorReply(msg_id, Dart_GetError(urls));
+    return false;
+  }
+  ASSERT(Dart_IsList(urls));
+  intptr_t num_urls = 0;
+  Dart_ListLength(urls, &num_urls);
+  msg.Printf("{ \"id\": %d, ", msg_id);
+  msg.Printf("\"result\": { \"urls\": [");
+  for (int i = 0; i < num_urls; i++) {
+    Dart_Handle script_url = Dart_ListGetAt(urls, i);
+    if (i > 0) {
+      msg.Printf(",");
+    }
+    FormatEncodedString(&msg, script_url);
+  }
+  msg.Printf("]}}");
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleGetSourceCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  dart::TextBuffer msg(64);
+  intptr_t lib_id = msg_parser.GetIntParam("libraryId");
+  char* url_chars = msg_parser.GetStringParam("url");
+  ASSERT(url_chars != NULL);
+  Dart_Handle url = Dart_NewString(url_chars);
+  ASSERT_NOT_ERROR(url);
+  free(url_chars);
+  url_chars = NULL;
+  Dart_Handle source = Dart_ScriptGetSource(lib_id, url);
+  if (Dart_IsError(source)) {
+    in_msg->SendErrorReply(msg_id, Dart_GetError(source));
+    return false;
+  }
+  msg.Printf("{ \"id\": %d, ", msg_id);
+  msg.Printf("\"result\": { \"text\": ");
+  FormatEncodedString(&msg, source);
+  msg.Printf("}}");
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleGetStackTraceCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  Dart_StackTrace trace;
+  Dart_Handle res = Dart_GetStackTrace(&trace);
+  ASSERT_NOT_ERROR(res);
+  dart::TextBuffer msg(128);
+  msg.Printf("{ \"id\": %d, \"result\": {", msg_id);
+  FormatCallFrames(&msg, trace);
+  msg.Printf("}}");
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleSetBpCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  char* url_chars = msg_parser.GetStringParam("url");
+  ASSERT(url_chars != NULL);
+  Dart_Handle url = Dart_NewString(url_chars);
+  ASSERT_NOT_ERROR(url);
+  free(url_chars);
+  url_chars = NULL;
+  intptr_t line_number = msg_parser.GetIntParam("line");
+  Dart_Handle bp_id = Dart_SetBreakpoint(url, line_number);
+  if (Dart_IsError(bp_id)) {
+    in_msg->SendErrorReply(msg_id, Dart_GetError(bp_id));
+    return false;
+  }
+  ASSERT(Dart_IsInteger(bp_id));
+  uint64_t bp_id_value;
+  Dart_Handle res = Dart_IntegerToUint64(bp_id, &bp_id_value);
+  ASSERT_NOT_ERROR(res);
+  dart::TextBuffer msg(64);
+  msg.Printf("{ \"id\": %d, \"result\": { \"breakpointId\": %"Pu64" }}",
+             msg_id, bp_id_value);
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandlePauseOnExcCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  char* exc_chars = msg_parser.GetStringParam("exceptions");
+  Dart_ExceptionPauseInfo info = kNoPauseOnExceptions;
+  if (strcmp(exc_chars, "none") == 0) {
+    info = kNoPauseOnExceptions;
+  } else if (strcmp(exc_chars, "all") == 0) {
+    info = kPauseOnAllExceptions;
+  } else if (strcmp(exc_chars, "unhandled") == 0) {
+    info = kPauseOnUnhandledExceptions;
+  } else {
+    in_msg->SendErrorReply(msg_id, "illegal value for parameter 'exceptions'");
+    return false;
+  }
+  Dart_Handle res = Dart_SetExceptionPauseInfo(info);
+  ASSERT_NOT_ERROR(res);
+  dart::TextBuffer msg(32);
+  msg.Printf("{ \"id\": %d }", msg_id);
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+bool DbgMessage::HandleRemBpCmd(DbgMessage* in_msg) {
+  ASSERT(in_msg != NULL);
+  MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
+  int msg_id = msg_parser.MessageId();
+  int bpt_id = msg_parser.GetIntParam("breakpointId");
+  Dart_Handle res = Dart_RemoveBreakpoint(bpt_id);
+  if (Dart_IsError(res)) {
+    in_msg->SendErrorReply(msg_id, Dart_GetError(res));
+    return false;
+  }
+  dart::TextBuffer msg(32);
+  msg.Printf("{ \"id\": %d }", msg_id);
+  in_msg->SendReply(&msg);
+  return false;
+}
+
+
+void DbgMessageQueue::AddMessage(int32_t cmd_idx,
+                                 const char* start,
+                                 const char* end,
+                                 int debug_fd) {
+  if ((end > start) && ((end - start) < kMaxUint32)) {
+    MonitorLocker ml(&msg_queue_lock_);
+    DbgMessage* msg = new DbgMessage(cmd_idx, start, end, debug_fd);
+    if (msglist_head_ == NULL) {
+      ASSERT(msglist_tail_ == NULL);
+      msglist_head_ = msg;
+      msglist_tail_ = msg;
+      ml.Notify();
+    } else {
+      ASSERT(msglist_tail_ != NULL);
+      msglist_tail_->set_next(msg);
+      msglist_tail_ = msg;
+    }
+  }
+}
+
+
+void DbgMessageQueue::HandleMessages() {
+  bool resume_requested = false;
+  MonitorLocker ml(&msg_queue_lock_);
+  is_running_ = false;
+  while (!resume_requested) {
+    while (msglist_head_ == NULL) {
+      ASSERT(msglist_tail_ == NULL);
+      dart::Monitor::WaitResult res = ml.Wait();  // Wait for debugger commands.
+      ASSERT(res == dart::Monitor::kNotified);
+    }
+    while (msglist_head_ != NULL && !resume_requested) {
+      ASSERT(msglist_tail_ != NULL);
+      DbgMessage* msg = msglist_head_;
+      msglist_head_ = msglist_head_->next();
+      resume_requested = msg->HandleMessage();
+      delete msg;
+    }
+    if (msglist_head_ == NULL) {
+      msglist_tail_ = NULL;
+    }
+  }
+  is_running_ = true;
+}
+
+
+void DbgMessageQueue::QueueOutputMsg(dart::TextBuffer* msg) {
+  queued_output_messages_.Printf("%s", msg->buf());
+}
+
+
+void DbgMessageQueue::SendQueuedMsgs() {
+  if (queued_output_messages_.length() > 0) {
+    DebuggerConnectionHandler::BroadcastMsg(&queued_output_messages_);
+    queued_output_messages_.Clear();
+  }
+}
+
+
+void DbgMessageQueue::SendBreakpointEvent(Dart_StackTrace trace) {
+  dart::TextBuffer msg(128);
+  msg.Printf("{ \"event\": \"paused\", \"params\": { ");
+  msg.Printf("\"reason\": \"breakpoint\", ");
+  FormatCallFrames(&msg, trace);
+  msg.Printf("}}");
+  DebuggerConnectionHandler::BroadcastMsg(&msg);
+}
+
+
+void DbgMessageQueue::SendExceptionEvent(Dart_Handle exception,
+                                         Dart_StackTrace stack_trace) {
+  intptr_t exception_id = Dart_CacheObject(exception);
+  ASSERT(exception_id >= 0);
+  dart::TextBuffer msg(128);
+  msg.Printf("{ \"event\": \"paused\", \"params\": {");
+  msg.Printf("\"reason\": \"exception\", ");
+  msg.Printf("\"exception\":");
+  FormatRemoteObj(&msg, exception);
+  msg.Printf(", ");
+  FormatCallFrames(&msg, stack_trace);
+  msg.Printf("}}");
+  DebuggerConnectionHandler::BroadcastMsg(&msg);
+}
+
+
+// TODO(asiva): Get rid of this static variable one we have a means
+// for associating an isolate with a debugger message queue object.
+static DbgMessageQueue* message_queue = NULL;
+
+
+void DbgMessageQueue::Initialize() {
+  // TODO(asiva): Need to setup a message queue when an Isolate is created.
+  // For now we use a static message queue object as we are only supporting
+  // debugging of a single isolate.
+  message_queue = new DbgMessageQueue();
+
+  // Setup handlers for isolate events, breakpoints, exceptions and
+  // delayed breakpoints.
+  Dart_SetIsolateEventHandler(IsolateEventHandler);
+  Dart_SetBreakpointHandler(BreakpointHandler);
+  Dart_SetBreakpointResolvedHandler(BptResolvedHandler);
+  Dart_SetExceptionThrownHandler(ExceptionThrownHandler);
+}
+
+
+int32_t DbgMessageQueue::LookupIsolateCommand(const char* buf,
+                                              int32_t buflen) {
+  // Check if we have a isolate specific debugger command.
+  int32_t i = 0;
+  while (debugger_commands[i].cmd_string != NULL) {
+    if (strncmp(buf, debugger_commands[i].cmd_string, buflen) == 0) {
+      return i;
+    }
+    i++;
+  }
+  return kInvalidCommand;
+}
+
+
+DbgMessageQueue* DbgMessageQueue::GetIsolateMessageQueue(Dart_Isolate isolate) {
+  // TODO(asiva): Return a message queue corresponding to the isolate.
+  // For now we use a static message queue object as we are only supporting
+  // debugging of a single isolate.
+  return message_queue;
+}
+
+
+void DbgMessageQueue::BptResolvedHandler(intptr_t bp_id,
+                                         Dart_Handle url,
+                                         intptr_t line_number) {
+  Dart_EnterScope();
+  dart::TextBuffer msg(128);
+  msg.Printf("{ \"event\": \"breakpointResolved\", \"params\": {");
+  msg.Printf("\"breakpointId\": %"Pd", \"url\":", bp_id);
+  FormatEncodedString(&msg, url);
+  msg.Printf(",\"line\": %"Pd" }}", line_number);
+  DbgMessageQueue* msg_queue = GetIsolateMessageQueue(Dart_CurrentIsolate());
+  ASSERT(msg_queue != NULL);
+  msg_queue->QueueOutputMsg(&msg);
+  Dart_ExitScope();
+}
+
+
+void DbgMessageQueue::BreakpointHandler(Dart_Breakpoint bpt,
+                                        Dart_StackTrace trace) {
+  DebuggerConnectionHandler::WaitForConnection();
+  Dart_EnterScope();
+  DbgMessageQueue* msg_queue = GetIsolateMessageQueue(Dart_CurrentIsolate());
+  ASSERT(msg_queue != NULL);
+  msg_queue->SendQueuedMsgs();
+  msg_queue->SendBreakpointEvent(trace);
+  msg_queue->HandleMessages();
+  Dart_ExitScope();
+}
+
+
+void DbgMessageQueue::ExceptionThrownHandler(Dart_Handle exception,
+                                             Dart_StackTrace stack_trace) {
+  DebuggerConnectionHandler::WaitForConnection();
+  Dart_EnterScope();
+  DbgMessageQueue* msg_queue = GetIsolateMessageQueue(Dart_CurrentIsolate());
+  ASSERT(msg_queue != NULL);
+  msg_queue->SendQueuedMsgs();
+  msg_queue->SendExceptionEvent(exception, stack_trace);
+  msg_queue->HandleMessages();
+  Dart_ExitScope();
+}
+
+
+void DbgMessageQueue::IsolateEventHandler(Dart_Isolate isolate,
+                                          Dart_IsolateEvent kind) {
+  DebuggerConnectionHandler::WaitForConnection();
+#if 0
+  if (kind == kCreated) {
+    printf("Isolate created %p\n", isolate);
+  } else if (kind == kInterrupted) {
+    printf("Isolate interrupted %p\n", isolate);
+  } else if (kind == kShutdown) {
+    printf("Isolate shutdown %p\n", isolate);
+  }
+#endif
+}