lib/src/http.dart - pub - Git at Google

 // 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.

 /// Helpers for dealing with HTTP.
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:math' as math;

 import 'package:http/http.dart' as http;
 import 'package:http_retry/http_retry.dart';
 import 'package:pool/pool.dart';
 import 'package:stack_trace/stack_trace.dart';

 import 'command.dart';
 import 'io.dart';
 import 'log.dart' as log;
 import 'oauth2.dart' as oauth2;
 import 'package.dart';
 import 'sdk.dart';
 import 'utils.dart';

 /// Headers and field names that should be censored in the log output.
 const _censoredFields = ['refresh_token', 'authorization'];

 /// Headers required for pub.dartlang.org API requests.
 ///
 /// The Accept header tells pub.dartlang.org which version of the API we're
 /// expecting, so it can either serve that version or give us a 406 error if
 /// it's not supported.
 const pubApiHeaders = {'Accept': 'application/vnd.pub.v2+json'};

 /// A unique ID to identify this particular invocation of pub.
 final _sessionId = createUuid();

 /// An HTTP client that transforms 40* errors and socket exceptions into more
 /// user-friendly error messages.
 class _PubHttpClient extends http.BaseClient {
   final _requestStopwatches = <http.BaseRequest, Stopwatch>{};

   http.Client _inner;

   _PubHttpClient([http.Client inner]) : _inner = inner ?? http.Client();

   @override
   Future<http.StreamedResponse> send(http.BaseRequest request) async {
     if (_shouldAddMetadata(request)) {
       request.headers['X-Pub-OS'] = Platform.operatingSystem;
       request.headers['X-Pub-Command'] = PubCommand.command;
       request.headers['X-Pub-Session-ID'] = _sessionId;

       var environment = Platform.environment['PUB_ENVIRONMENT'];
       if (environment != null) {
         request.headers['X-Pub-Environment'] = environment;
       }

       var type = Zone.current[#_dependencyType];
       if (type != null) request.headers['X-Pub-Reason'] = type.toString();
     }

     _requestStopwatches[request] = Stopwatch()..start();
     request.headers[HttpHeaders.userAgentHeader] = 'Dart pub ${sdk.version}';
     _logRequest(request);

     final streamedResponse = await _inner.send(request);

     _logResponse(streamedResponse);

     return streamedResponse;
   }

   /// Whether extra metadata headers should be added to [request].
   bool _shouldAddMetadata(http.BaseRequest request) {
     if (runningFromTest && Platform.environment.containsKey('PUB_HOSTED_URL')) {
       if (request.url.origin != Platform.environment['PUB_HOSTED_URL']) {
         return false;
       }
     } else {
       if (request.url.origin != 'https://pub.dartlang.org') return false;
     }

     if (Platform.environment.containsKey('CI') &&
         Platform.environment['CI'] != 'false') {
       return false;
     }

     return true;
   }

   /// Logs the fact that [request] was sent, and information about it.
   void _logRequest(http.BaseRequest request) {
     var requestLog = StringBuffer();
     requestLog.writeln('HTTP ${request.method} ${request.url}');
     request.headers
         .forEach((name, value) => requestLog.writeln(_logField(name, value)));

     if (request.method == 'POST') {
       var contentTypeString = request.headers[HttpHeaders.contentTypeHeader];
       var contentType = ContentType.parse(contentTypeString ?? '');
       if (request is http.MultipartRequest) {
         requestLog.writeln();
         requestLog.writeln('Body fields:');
         request.fields.forEach(
             (name, value) => requestLog.writeln(_logField(name, value)));

         // TODO(nweiz): make MultipartRequest.files readable, and log them?
       } else if (request is http.Request) {
         if (contentType.value == 'application/x-www-form-urlencoded') {
           requestLog.writeln();
           requestLog.writeln('Body fields:');
           request.bodyFields.forEach(
               (name, value) => requestLog.writeln(_logField(name, value)));
         } else if (contentType.value == 'text/plain' ||
             contentType.value == 'application/json') {
           requestLog.write(request.body);
         }
       }
     }

     log.io(requestLog.toString().trim());
   }

   /// Logs the fact that [response] was received, and information about it.
   void _logResponse(http.StreamedResponse response) {
     // TODO(nweiz): Fork the response stream and log the response body. Be
     // careful not to log OAuth2 private data, though.

     var responseLog = StringBuffer();
     var request = response.request;
     var stopwatch = _requestStopwatches.remove(request)..stop();
     responseLog.writeln('HTTP response ${response.statusCode} '
         '${response.reasonPhrase} for ${request.method} ${request.url}');
     responseLog.writeln('took ${stopwatch.elapsed}');
     response.headers
         .forEach((name, value) => responseLog.writeln(_logField(name, value)));

     log.io(responseLog.toString().trim());
   }

   /// Returns a log-formatted string for the HTTP field or header with the given
   /// [name] and [value].
   String _logField(String name, String value) {
     if (_censoredFields.contains(name.toLowerCase())) {
       return '$name: <censored>';
     } else {
       return '$name: $value';
     }
   }

   @override
   void close() => _inner.close();
 }

 /// The [_PubHttpClient] wrapped by [httpClient].
 final _pubClient = _PubHttpClient();

 /// A set of all hostnames for which we've printed a message indicating that
 /// we're waiting for them to come back up.
 final _retriedHosts = <String>{};

 /// Intercepts all requests and throws exceptions if the response was not
 /// considered successful.
 class _ThrowingClient extends http.BaseClient {
   final http.Client _inner;

   _ThrowingClient(this._inner);

   @override
   Future<http.StreamedResponse> send(http.BaseRequest request) async {
     http.StreamedResponse streamedResponse;
     try {
       streamedResponse = await _inner.send(request);
     } on SocketException catch (error, stackTraceOrNull) {
       // Work around issue 23008.
       var stackTrace = stackTraceOrNull ?? Chain.current();

       if (error.osError == null) rethrow;

       // Handle error codes known to be related to DNS or SSL issues. While it
       // is tempting to handle these error codes before retrying, saving time
       // for the end-user, it is known that DNS lookups can fail intermittently
       // in some cloud environments. Furthermore, since these error codes are
       // platform-specific (undocumented) and essentially cargo-culted along
       // skipping retries may lead to intermittent issues that could be fixed
       // with a retry. Failing to retry intermittent issues is likely to cause
       // customers to wrap pub in a retry loop which will not improve the
       // end-user experience.
       if (error.osError.errorCode == 8 ||
           error.osError.errorCode == -2 ||
           error.osError.errorCode == -5 ||
           error.osError.errorCode == 11001 ||
           error.osError.errorCode == 11004) {
         fail('Could not resolve URL "${request.url.origin}".', error,
             stackTrace);
       } else if (error.osError.errorCode == -12276) {
         fail(
             'Unable to validate SSL certificate for '
             '"${request.url.origin}".',
             error,
             stackTrace);
       } else {
         rethrow;
       }
     }

     var status = streamedResponse.statusCode;
     // 401 responses should be handled by the OAuth2 client. It's very
     // unlikely that they'll be returned by non-OAuth2 requests. We also want
     // to pass along 400 responses from the token endpoint.
     var tokenRequest = streamedResponse.request.url == oauth2.tokenEndpoint;
     if (status < 400 || status == 401 || (status == 400 && tokenRequest)) {
       return streamedResponse;
     }

     if (status == 406 && request.headers['Accept'] == pubApiHeaders['Accept']) {
       fail('Pub ${sdk.version} is incompatible with the current version of '
           '${request.url.host}.\n'
           'Upgrade pub to the latest version and try again.');
     }

     if (status == 500 &&
         (request.url.host == 'pub.dartlang.org' ||
             request.url.host == 'storage.googleapis.com')) {
       fail('HTTP error 500: Internal Server Error at ${request.url}.\n'
           'This is likely a transient error. Please try again later.');
     }

     throw PubHttpException(await http.Response.fromStream(streamedResponse));
   }

   @override
   void close() => _inner.close();
 }

 /// The HTTP client to use for all HTTP requests.
 final httpClient = _ThrottleClient(
     16,
     _ThrowingClient(RetryClient(_pubClient,
         retries: math.max(
           1, // Having less than 1 retry is **always** wrong.
           int.tryParse(Platform.environment['PUB_MAX_HTTP_RETRIES'] ?? '') ?? 7,
         ),
         when: (response) =>
             const [500, 502, 503, 504].contains(response.statusCode),
         whenError: (error, stackTrace) {
           if (error is! IOException) return false;

           var chain = Chain.forTrace(stackTrace);
           log.io('HTTP error:\n$error\n\n${chain.terse}');
           return true;
         },
         delay: (retryCount) {
           if (retryCount < 3) {
             // Retry quickly a couple times in case of a short transient error.
             //
             // Add a random delay to avoid retrying a bunch of parallel requests
             // all at the same time.
             return Duration(milliseconds: 500) * math.pow(1.5, retryCount) +
                 Duration(milliseconds: random.nextInt(500));
           } else {
             // If the error persists, wait a long time. This works around issues
             // where an AppEngine instance will go down and need to be rebooted,
             // which takes about a minute.
             return Duration(seconds: 30);
           }
         },
         onRetry: (request, response, retryCount) {
           log.io('Retry #${retryCount + 1} for '
               '${request.method} ${request.url}...');
           if (retryCount != 3) return;
           if (!_retriedHosts.add(request.url.host)) return;
           log.message(
               'It looks like ${request.url.host} is having some trouble.\n'
               'Pub will wait for a while before trying to connect again.');
         })));

 /// The underlying HTTP client wrapped by [httpClient].
 http.Client get innerHttpClient => _pubClient._inner;
 set innerHttpClient(http.Client client) => _pubClient._inner = client;

 /// Runs [callback] in a zone where all HTTP requests sent to `pub.dartlang.org`
 /// will indicate the [type] of the relationship between the root package and
 /// the package being requested.
 ///
 /// If [type] is [DependencyType.none], no extra metadata is added.
 Future<T> withDependencyType<T>(
     DependencyType type, Future<T> Function() callback) {
   if (type == DependencyType.none) return callback();
   return runZoned(callback, zoneValues: {#_dependencyType: type});
 }

 /// Handles a successful JSON-formatted response from pub.dartlang.org.
 ///
 /// These responses are expected to be of the form `{"success": {"message":
 /// "some message"}}`. If the format is correct, the message will be printed;
 /// otherwise an error will be raised.
 void handleJsonSuccess(http.Response response) {
   var parsed = parseJsonResponse(response);
   if (parsed['success'] is! Map ||
       !parsed['success'].containsKey('message') ||
       parsed['success']['message'] is! String) {
     invalidServerResponse(response);
   }
   log.message(log.green(parsed['success']['message']));
 }

 /// Handles an unsuccessful JSON-formatted response from pub.dartlang.org.
 ///
 /// These responses are expected to be of the form `{"error": {"message": "some
 /// message"}}`. If the format is correct, the message will be raised as an
 /// error; otherwise an [invalidServerResponse] error will be raised.
 void handleJsonError(http.Response response) {
   var errorMap = parseJsonResponse(response);
   if (errorMap['error'] is! Map ||
       !errorMap['error'].containsKey('message') ||
       errorMap['error']['message'] is! String) {
     invalidServerResponse(response);
   }
   fail(log.red(errorMap['error']['message']));
 }

 /// Parses a response body, assuming it's JSON-formatted.
 ///
 /// Throws a user-friendly error if the response body is invalid JSON, or if
 /// it's not a map.
 Map parseJsonResponse(http.Response response) {
   Object value;
   try {
     value = jsonDecode(response.body);
   } on FormatException {
     invalidServerResponse(response);
   }
   if (value is! Map) invalidServerResponse(response);
   return value;
 }

 /// Throws an error describing an invalid response from the server.
 void invalidServerResponse(http.Response response) =>
     fail(log.red('Invalid server response:\n${response.body}'));

 /// Exception thrown when an HTTP operation fails.
 class PubHttpException implements Exception {
   final http.Response response;

   const PubHttpException(this.response);

   @override
   String toString() => 'HTTP error ${response.statusCode}: '
       '${response.reasonPhrase}';
 }

 /// A middleware client that throttles the number of concurrent requests.
 ///
 /// As long as the number of requests is within the limit, this works just like
 /// a normal client. If a request is made beyond the limit, the underlying HTTP
 /// request won't be sent until other requests have completed.
 class _ThrottleClient extends http.BaseClient {
   final Pool _pool;
   final http.Client _inner;

   /// Creates a new client that allows no more than [maxActiveRequests]
   /// concurrent requests.
   ///
   /// If [inner] is passed, it's used as the inner client for sending HTTP
   /// requests. It defaults to `new http.Client()`.
   _ThrottleClient(int maxActiveRequests, this._inner)
       : _pool = Pool(maxActiveRequests);

   @override
   Future<http.StreamedResponse> send(http.BaseRequest request) async {
     var resource = await _pool.request();

     http.StreamedResponse response;
     try {
       response = await _inner.send(request);
     } catch (_) {
       resource.release();
       rethrow;
     }

     var stream = response.stream.transform(
         StreamTransformer<List<int>, List<int>>.fromHandlers(
             handleDone: (sink) {
       resource.release();
       sink.close();
     }));
     return http.StreamedResponse(stream, response.statusCode,
         contentLength: response.contentLength,
         request: response.request,
         headers: response.headers,
         isRedirect: response.isRedirect,
         persistentConnection: response.persistentConnection,
         reasonPhrase: response.reasonPhrase);
   }

   @override
   void close() => _inner.close();
 }
	// 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.

	/// Helpers for dealing with HTTP.
	import 'dart:async';
	import 'dart:convert';
	import 'dart:io';
	import 'dart:math' as math;

	import 'package:http/http.dart' as http;
	import 'package:http_retry/http_retry.dart';
	import 'package:pool/pool.dart';
	import 'package:stack_trace/stack_trace.dart';

	import 'command.dart';
	import 'io.dart';
	import 'log.dart' as log;
	import 'oauth2.dart' as oauth2;
	import 'package.dart';
	import 'sdk.dart';
	import 'utils.dart';

	/// Headers and field names that should be censored in the log output.
	const _censoredFields = ['refresh_token', 'authorization'];

	/// Headers required for pub.dartlang.org API requests.
	///
	/// The Accept header tells pub.dartlang.org which version of the API we're
	/// expecting, so it can either serve that version or give us a 406 error if
	/// it's not supported.
	const pubApiHeaders = {'Accept': 'application/vnd.pub.v2+json'};

	/// A unique ID to identify this particular invocation of pub.
	final _sessionId = createUuid();

	/// An HTTP client that transforms 40* errors and socket exceptions into more
	/// user-friendly error messages.
	class _PubHttpClient extends http.BaseClient {
	final _requestStopwatches = <http.BaseRequest, Stopwatch>{};

	http.Client _inner;

	_PubHttpClient([http.Client inner]) : _inner = inner ?? http.Client();

	@override
	Future<http.StreamedResponse> send(http.BaseRequest request) async {
	if (_shouldAddMetadata(request)) {
	request.headers['X-Pub-OS'] = Platform.operatingSystem;
	request.headers['X-Pub-Command'] = PubCommand.command;
	request.headers['X-Pub-Session-ID'] = _sessionId;

	var environment = Platform.environment['PUB_ENVIRONMENT'];
	if (environment != null) {
	request.headers['X-Pub-Environment'] = environment;
	}

	var type = Zone.current[#_dependencyType];
	if (type != null) request.headers['X-Pub-Reason'] = type.toString();
	}

	_requestStopwatches[request] = Stopwatch()..start();
	request.headers[HttpHeaders.userAgentHeader] = 'Dart pub ${sdk.version}';
	_logRequest(request);

	final streamedResponse = await _inner.send(request);

	_logResponse(streamedResponse);

	return streamedResponse;
	}

	/// Whether extra metadata headers should be added to [request].
	bool _shouldAddMetadata(http.BaseRequest request) {
	if (runningFromTest && Platform.environment.containsKey('PUB_HOSTED_URL')) {
	if (request.url.origin != Platform.environment['PUB_HOSTED_URL']) {
	return false;
	}
	} else {
	if (request.url.origin != 'https://pub.dartlang.org') return false;
	}

	if (Platform.environment.containsKey('CI') &&
	Platform.environment['CI'] != 'false') {
	return false;
	}

	return true;
	}

	/// Logs the fact that [request] was sent, and information about it.
	void _logRequest(http.BaseRequest request) {
	var requestLog = StringBuffer();
	requestLog.writeln('HTTP ${request.method} ${request.url}');
	request.headers
	.forEach((name, value) => requestLog.writeln(_logField(name, value)));

	if (request.method == 'POST') {
	var contentTypeString = request.headers[HttpHeaders.contentTypeHeader];
	var contentType = ContentType.parse(contentTypeString ?? '');
	if (request is http.MultipartRequest) {
	requestLog.writeln();
	requestLog.writeln('Body fields:');
	request.fields.forEach(
	(name, value) => requestLog.writeln(_logField(name, value)));

	// TODO(nweiz): make MultipartRequest.files readable, and log them?
	} else if (request is http.Request) {
	if (contentType.value == 'application/x-www-form-urlencoded') {
	requestLog.writeln();
	requestLog.writeln('Body fields:');
	request.bodyFields.forEach(
	(name, value) => requestLog.writeln(_logField(name, value)));
	} else if (contentType.value == 'text/plain' \|\|
	contentType.value == 'application/json') {
	requestLog.write(request.body);
	}
	}
	}

	log.io(requestLog.toString().trim());
	}

	/// Logs the fact that [response] was received, and information about it.
	void _logResponse(http.StreamedResponse response) {
	// TODO(nweiz): Fork the response stream and log the response body. Be
	// careful not to log OAuth2 private data, though.

	var responseLog = StringBuffer();
	var request = response.request;
	var stopwatch = _requestStopwatches.remove(request)..stop();
	responseLog.writeln('HTTP response ${response.statusCode} '
	'${response.reasonPhrase} for ${request.method} ${request.url}');
	responseLog.writeln('took ${stopwatch.elapsed}');
	response.headers
	.forEach((name, value) => responseLog.writeln(_logField(name, value)));

	log.io(responseLog.toString().trim());
	}

	/// Returns a log-formatted string for the HTTP field or header with the given
	/// [name] and [value].
	String _logField(String name, String value) {
	if (_censoredFields.contains(name.toLowerCase())) {
	return '$name: <censored>';
	} else {
	return '$name: $value';
	}
	}

	@override
	void close() => _inner.close();
	}

	/// The [_PubHttpClient] wrapped by [httpClient].
	final _pubClient = _PubHttpClient();

	/// A set of all hostnames for which we've printed a message indicating that
	/// we're waiting for them to come back up.
	final _retriedHosts = <String>{};

	/// Intercepts all requests and throws exceptions if the response was not
	/// considered successful.
	class _ThrowingClient extends http.BaseClient {
	final http.Client _inner;

	_ThrowingClient(this._inner);

	@override
	Future<http.StreamedResponse> send(http.BaseRequest request) async {
	http.StreamedResponse streamedResponse;
	try {
	streamedResponse = await _inner.send(request);
	} on SocketException catch (error, stackTraceOrNull) {
	// Work around issue 23008.
	var stackTrace = stackTraceOrNull ?? Chain.current();

	if (error.osError == null) rethrow;

	// Handle error codes known to be related to DNS or SSL issues. While it
	// is tempting to handle these error codes before retrying, saving time
	// for the end-user, it is known that DNS lookups can fail intermittently
	// in some cloud environments. Furthermore, since these error codes are
	// platform-specific (undocumented) and essentially cargo-culted along
	// skipping retries may lead to intermittent issues that could be fixed
	// with a retry. Failing to retry intermittent issues is likely to cause
	// customers to wrap pub in a retry loop which will not improve the
	// end-user experience.
	if (error.osError.errorCode == 8 \|\|
	error.osError.errorCode == -2 \|\|
	error.osError.errorCode == -5 \|\|
	error.osError.errorCode == 11001 \|\|
	error.osError.errorCode == 11004) {
	fail('Could not resolve URL "${request.url.origin}".', error,
	stackTrace);
	} else if (error.osError.errorCode == -12276) {
	fail(
	'Unable to validate SSL certificate for '
	'"${request.url.origin}".',
	error,
	stackTrace);
	} else {
	rethrow;
	}
	}

	var status = streamedResponse.statusCode;
	// 401 responses should be handled by the OAuth2 client. It's very
	// unlikely that they'll be returned by non-OAuth2 requests. We also want
	// to pass along 400 responses from the token endpoint.
	var tokenRequest = streamedResponse.request.url == oauth2.tokenEndpoint;
	if (status < 400 \|\| status == 401 \|\| (status == 400 && tokenRequest)) {
	return streamedResponse;
	}

	if (status == 406 && request.headers['Accept'] == pubApiHeaders['Accept']) {
	fail('Pub ${sdk.version} is incompatible with the current version of '
	'${request.url.host}.\n'
	'Upgrade pub to the latest version and try again.');
	}

	if (status == 500 &&
	(request.url.host == 'pub.dartlang.org' \|\|
	request.url.host == 'storage.googleapis.com')) {
	fail('HTTP error 500: Internal Server Error at ${request.url}.\n'
	'This is likely a transient error. Please try again later.');
	}

	throw PubHttpException(await http.Response.fromStream(streamedResponse));
	}

	@override
	void close() => _inner.close();
	}

	/// The HTTP client to use for all HTTP requests.
	final httpClient = _ThrottleClient(
	16,
	_ThrowingClient(RetryClient(_pubClient,
	retries: math.max(
	1, // Having less than 1 retry is always wrong.
	int.tryParse(Platform.environment['PUB_MAX_HTTP_RETRIES'] ?? '') ?? 7,
	),
	when: (response) =>
	const [500, 502, 503, 504].contains(response.statusCode),
	whenError: (error, stackTrace) {
	if (error is! IOException) return false;

	var chain = Chain.forTrace(stackTrace);
	log.io('HTTP error:\n$error\n\n${chain.terse}');
	return true;
	},
	delay: (retryCount) {
	if (retryCount < 3) {
	// Retry quickly a couple times in case of a short transient error.
	//
	// Add a random delay to avoid retrying a bunch of parallel requests
	// all at the same time.
	return Duration(milliseconds: 500) * math.pow(1.5, retryCount) +
	Duration(milliseconds: random.nextInt(500));
	} else {
	// If the error persists, wait a long time. This works around issues
	// where an AppEngine instance will go down and need to be rebooted,
	// which takes about a minute.
	return Duration(seconds: 30);
	}
	},
	onRetry: (request, response, retryCount) {
	log.io('Retry #${retryCount + 1} for '
	'${request.method} ${request.url}...');
	if (retryCount != 3) return;
	if (!_retriedHosts.add(request.url.host)) return;
	log.message(
	'It looks like ${request.url.host} is having some trouble.\n'
	'Pub will wait for a while before trying to connect again.');
	})));

	/// The underlying HTTP client wrapped by [httpClient].
	http.Client get innerHttpClient => _pubClient._inner;
	set innerHttpClient(http.Client client) => _pubClient._inner = client;

	/// Runs [callback] in a zone where all HTTP requests sent to `pub.dartlang.org`
	/// will indicate the [type] of the relationship between the root package and
	/// the package being requested.
	///
	/// If [type] is [DependencyType.none], no extra metadata is added.
	Future<T> withDependencyType<T>(
	DependencyType type, Future<T> Function() callback) {
	if (type == DependencyType.none) return callback();
	return runZoned(callback, zoneValues: {#_dependencyType: type});
	}

	/// Handles a successful JSON-formatted response from pub.dartlang.org.
	///
	/// These responses are expected to be of the form `{"success": {"message":
	/// "some message"}}`. If the format is correct, the message will be printed;
	/// otherwise an error will be raised.
	void handleJsonSuccess(http.Response response) {
	var parsed = parseJsonResponse(response);
	if (parsed['success'] is! Map \|\|
	!parsed['success'].containsKey('message') \|\|
	parsed['success']['message'] is! String) {
	invalidServerResponse(response);
	}
	log.message(log.green(parsed['success']['message']));
	}

	/// Handles an unsuccessful JSON-formatted response from pub.dartlang.org.
	///
	/// These responses are expected to be of the form `{"error": {"message": "some
	/// message"}}`. If the format is correct, the message will be raised as an
	/// error; otherwise an [invalidServerResponse] error will be raised.
	void handleJsonError(http.Response response) {
	var errorMap = parseJsonResponse(response);
	if (errorMap['error'] is! Map \|\|
	!errorMap['error'].containsKey('message') \|\|
	errorMap['error']['message'] is! String) {
	invalidServerResponse(response);
	}
	fail(log.red(errorMap['error']['message']));
	}

	/// Parses a response body, assuming it's JSON-formatted.
	///
	/// Throws a user-friendly error if the response body is invalid JSON, or if
	/// it's not a map.
	Map parseJsonResponse(http.Response response) {
	Object value;
	try {
	value = jsonDecode(response.body);
	} on FormatException {
	invalidServerResponse(response);
	}
	if (value is! Map) invalidServerResponse(response);
	return value;
	}

	/// Throws an error describing an invalid response from the server.
	void invalidServerResponse(http.Response response) =>
	fail(log.red('Invalid server response:\n${response.body}'));

	/// Exception thrown when an HTTP operation fails.
	class PubHttpException implements Exception {
	final http.Response response;

	const PubHttpException(this.response);

	@override
	String toString() => 'HTTP error ${response.statusCode}: '
	'${response.reasonPhrase}';
	}

	/// A middleware client that throttles the number of concurrent requests.
	///
	/// As long as the number of requests is within the limit, this works just like
	/// a normal client. If a request is made beyond the limit, the underlying HTTP
	/// request won't be sent until other requests have completed.
	class _ThrottleClient extends http.BaseClient {
	final Pool _pool;
	final http.Client _inner;

	/// Creates a new client that allows no more than [maxActiveRequests]
	/// concurrent requests.
	///
	/// If [inner] is passed, it's used as the inner client for sending HTTP
	/// requests. It defaults to `new http.Client()`.
	_ThrottleClient(int maxActiveRequests, this._inner)
	: _pool = Pool(maxActiveRequests);

	@override
	Future<http.StreamedResponse> send(http.BaseRequest request) async {
	var resource = await _pool.request();

	http.StreamedResponse response;
	try {
	response = await _inner.send(request);
	} catch (_) {
	resource.release();
	rethrow;
	}

	var stream = response.stream.transform(
	StreamTransformer<List<int>, List<int>>.fromHandlers(
	handleDone: (sink) {
	resource.release();
	sink.close();
	}));
	return http.StreamedResponse(stream, response.statusCode,
	contentLength: response.contentLength,
	request: response.request,
	headers: response.headers,
	isRedirect: response.isRedirect,
	persistentConnection: response.persistentConnection,
	reasonPhrase: response.reasonPhrase);
	}

	@override
	void close() => _inner.close();
	}