Emulate shelf messaging (#54)

Author: donny-dont

lib/src/message.dart

@@ -0,0 +1,198 @@
+// Copyright (c) 2017, 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.
+
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:collection/collection.dart';
+import 'package:http_parser/http_parser.dart';
+
+import 'body.dart';
+import 'http_unmodifiable_map.dart';
+import 'utils.dart';
+
+/// Retrieves the [Body] contained in the [message].
+///
+/// This is meant for internal use by `http` so the message body is accessible
+/// for subclasses of [Message] but hidden elsewhere.
+Body getBody(Message message) => message._body;
+
+/// Represents logic shared between [Request] and [Response].
+abstract class Message {
+  /// The HTTP headers.
+  ///
+  /// This is immutable. A copy of this with new headers can be created using
+  /// [change].
+  final Map<String, String> headers;
+
+  /// Extra context that can be used by middleware and handlers.
+  ///
+  /// For requests, this is used to pass data to inner middleware and handlers;
+  /// for responses, it's used to pass data to outer middleware and handlers.
+  ///
+  /// Context properties that are used by a particular package should begin with
+  /// that package's name followed by a period. For example, if there was a
+  /// package `foo` which contained a middleware `bar` and it wanted to take
+  /// a context property, its property would be `"foo.bar"`.
+  ///
+  /// This is immutable. A copy of this with new context values can be created
+  /// using [change].
+  final Map<String, Object> context;
+
+  /// The streaming body of the message.
+  ///
+  /// This can be read via [read] or [readAsString].
+  final Body _body;
+
+  /// Creates a new [Message].
+  ///
+  /// [body] is the message body. It may be either a [String], a [List<int>], a
+  /// [Stream<List<int>>], or `null` to indicate no body. If it's a [String],
+  /// [encoding] is used to encode it to a [Stream<List<int>>]. It defaults to
+  /// UTF-8.
+  ///
+  /// If [headers] is `null`, it's treated as empty.
+  ///
+  /// If [encoding] is passed, the "encoding" field of the Content-Type header
+  /// in [headers] will be set appropriately. If there is no existing
+  /// Content-Type header, it will be set to "application/octet-stream".
+  Message(body,
+      {Encoding encoding,
+      Map<String, String> headers,
+      Map<String, Object> context})
+      : this._(new Body(body, encoding), headers, context);
+
+  Message._(Body body, Map<String, String> headers, Map<String, Object> context)
+      : _body = body,
+        headers = new HttpUnmodifiableMap<String>(_adjustHeaders(headers, body),
+            ignoreKeyCase: true),
+        context =
+            new HttpUnmodifiableMap<Object>(context, ignoreKeyCase: false);
+
+  /// If `true`, the stream returned by [read] won't emit any bytes.
+  ///
+  /// This may have false negatives, but it won't have false positives.
+  bool get isEmpty => _body.contentLength == 0;
+
+  /// The contents of the content-length field in [headers].
+  ///
+  /// If not set, `null`.
+  int get contentLength {
+    if (_contentLengthCache != null) return _contentLengthCache;
+    if (!headers.containsKey('content-length')) return null;
+    _contentLengthCache = int.parse(headers['content-length']);
+    return _contentLengthCache;
+  }
+  int _contentLengthCache;
+
+  /// The MIME type declared in [headers].
+  ///
+  /// This is parsed from the Content-Type header in [headers]. It contains only
+  /// the MIME type, without any Content-Type parameters.
+  ///
+  /// If [headers] doesn't have a Content-Type header, this will be `null`.
+  String get mimeType {
+    var contentType = _contentType;
+    if (contentType == null) return null;
+    return contentType.mimeType;
+  }
+
+  /// The encoding of the body returned by [read].
+  ///
+  /// This is parsed from the "charset" parameter of the Content-Type header in
+  /// [headers].
+  ///
+  /// If [headers] doesn't have a Content-Type header or it specifies an
+  /// encoding that [dart:convert] doesn't support, this will be `null`.
+  Encoding get encoding {
+    var contentType = _contentType;
+    if (contentType == null) return null;
+    if (!contentType.parameters.containsKey('charset')) return null;
+    return Encoding.getByName(contentType.parameters['charset']);
+  }
+
+  /// The parsed version of the Content-Type header in [headers].
+  ///
+  /// This is cached for efficient access.
+  MediaType get _contentType {
+    if (_contentTypeCache != null) return _contentTypeCache;
+    if (!headers.containsKey('content-type')) return null;
+    _contentTypeCache = new MediaType.parse(headers['content-type']);
+    return _contentTypeCache;
+  }
+  MediaType _contentTypeCache;
+
+  /// Returns the message body as byte chunks.
+  ///
+  /// Throws a [StateError] if [read] or [readAsString] has already been called.
+  Stream<List<int>> read() => _body.read();
+
+  /// Returns the message body as a string.
+  ///
+  /// If [encoding] is passed, that's used to decode the body. Otherwise the
+  /// encoding is taken from the Content-Type header. If that doesn't exist or
+  /// doesn't have a "charset" parameter, UTF-8 is used.
+  ///
+  /// Throws a [StateError] if [read] or [readAsString] has already been called.
+  Future<String> readAsString([Encoding encoding]) {
+    encoding ??= this.encoding ?? UTF8;
+    return encoding.decodeStream(read());
+  }
+
+  /// Creates a copy of this by copying existing values and applying specified
+  /// changes.
+  Message change(
+      {Map<String, String> headers, Map<String, Object> context, body});
+}
+
+/// Adds information about encoding to [headers].
+///
+/// Returns a new map without modifying [headers].
+Map<String, String> _adjustHeaders(Map<String, String> headers, Body body) {
+  var sameEncoding = _sameEncoding(headers, body);
+  if (sameEncoding) {
+    if (body.contentLength == null ||
+        getHeader(headers, 'content-length') == body.contentLength.toString()) {
+      return headers ?? const HttpUnmodifiableMap.empty();
+    } else if (body.contentLength == 0 &&
+        (headers == null || headers.isEmpty)) {
+      return const HttpUnmodifiableMap.empty();
+    }
+  }
+
+  var newHeaders = headers == null
+      ? new CaseInsensitiveMap<String>()
+      : new CaseInsensitiveMap<String>.from(headers);
+
+  if (!sameEncoding) {
+    if (newHeaders['content-type'] == null) {
+      newHeaders['content-type'] =
+          'application/octet-stream; charset=${body.encoding.name}';
+    } else {
+      var contentType = new MediaType.parse(newHeaders['content-type'])
+          .change(parameters: {'charset': body.encoding.name});
+      newHeaders['content-type'] = contentType.toString();
+    }
+  }
+
+  if (body.contentLength != null) {
+    var coding = newHeaders['transfer-encoding'];
+    if (coding == null || equalsIgnoreAsciiCase(coding, 'identity')) {
+      newHeaders['content-length'] = body.contentLength.toString();
+    }
+  }
+
+  return newHeaders;
+}
+
+/// Returns whether [headers] declares the same encoding as [body].
+bool _sameEncoding(Map<String, String> headers, Body body) {
+  if (body.encoding == null) return true;
+
+  var contentType = getHeader(headers, 'content-type');
+  if (contentType == null) return false;
+
+  var charset = new MediaType.parse(contentType).parameters['charset'];
+  return Encoding.getByName(charset) == body.encoding;
+}