Add an HTTP client based on Curl.

pkg/http/lib/src/curl_client.dart

+// 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.
+
+library curl_client;
+
+import 'dart:io';
+
+import 'base_client.dart';
+import 'base_request.dart';
+import 'streamed_response.dart';
+import 'utils.dart';
+
+/// A drop-in replacement for [Client] that uses the `curl` command-line utility
+/// rather than [dart:io] to make requests. This class will only exist
+/// temporarily until [dart:io] natively supports requests over HTTPS.
+class CurlClient extends BaseClient {
+  /// The path to the `curl` executable to run. By default, this will look up
+  /// `curl` on the system path.
+  final String executable;
+
+  /// Creates a new [CurlClient] with [executable] as the path to the `curl`
+  /// executable. By default, this will look up `curl` on the system path.
+  CurlClient([String executable])
+    : executable = executable == null ? "curl" : executable;
+
+  /// Sends a request via `curl` and returns the response.
+  Future<StreamedResponse> send(BaseRequest request) {
+    var requestStream = request.finalize();
+    return withTempDir((tempDir) {
+      var headerFile = new Path(tempDir).append("curl-headers").toNativePath();
+      var arguments = _argumentsForRequest(request, headerFile);
+      var process;
+      return Process.start("curl", arguments).chain((process_) {
+        process = process_;
+        if (requestStream.closed) {
+          process.stdin.close();
+        } else {
+          requestStream.pipe(process.stdin);
+        }
+
+        return _waitForHeaders(process, expectBody: request.method != "HEAD");
+      }).chain((_) => new File(headerFile).readAsLines())
+        .transform((lines) => _buildResponse(process, lines));
+    });
+  }
+
+  /// Returns the list of arguments to `curl` necessary for performing
+  /// [request]. [headerFile] is the path to the file where the response headers
+  /// should be stored.
+  List<String> _argumentsForRequest(BaseRequest request, String headerFile) {
+    var arguments = ["--dump-header", headerFile];
+    if (request.method == 'HEAD') {
+      arguments.add("--head");
+    } else {
+      arguments.add("--request");
+      arguments.add(request.method);
+    }
+    if (request.followRedirects) {
+      arguments.add("--location");
+      arguments.add("--max-redirs");
+      arguments.add(request.maxRedirects.toString());
+    }
+    if (request.contentLength != 0)  {
+      arguments.add("--data-binary");
+      arguments.add("@-");
+    }
+
+    // Override the headers automatically added by curl. We want to make it
+    // behave as much like the dart:io client as possible.
+    var headers = {
+      'accept': '',
+      'user-agent': ''
+    };
+    mapAddAll(headers, request.headers);
+    if (request.contentLength < 0) {
+      headers['content-length'] = '';
+      headers['transfer-encoding'] = 'chunked';
+    } else if (request.contentLength > 0) {
+      headers['content-length'] = request.contentLength.toString();
+    }
+
+    headers.forEach((name, value) {
+      arguments.add("--header");
+      arguments.add("$name: $value");
+    });
+    arguments.add(request.url.toString());
+
+    return arguments;
+  }
+
+  /// Returns a [Future] that completes once the `curl` [process] has finished
+  /// receiving the response headers. [expectBody] indicates that the server is
+  /// expected to send a response body (which is not the case for HEAD
+  /// requests).
+  Future _waitForHeaders(Process process, {bool expectBody}) {
+    var exitCompleter = new Completer<int>();
+    var exitFuture = exitCompleter.future;
+    process.onExit = (exitCode) {
+      if (exitCode == 0) {
+        exitCompleter.complete(0);
+        return;
+      }
+
+      chainToCompleter(consumeInputStream(process.stderr)
+            .transform((stderrBytes) {
+        var message = new String.fromCharCodes(stderrBytes);
+        if (exitCode == 47) {
+          throw new RedirectLimitExceededException(message);
+        } else {
+          throw new HttpException(message);
+        }
+      }), exitCompleter);
+    };
+
+    // If there's not going to be a response body (e.g. for HEAD requests), curl
+    // prints the headers to stdout instead of the body. We want to wait until
+    // all the headers are received to read them from the header file.
+    if (!expectBody) {
+      return Futures.wait([
+        consumeInputStream(process.stdout),
+        exitFuture
+      ]);
+    }
+
+    var completer = new Completer();
+    resetCallbacks() {
+      process.stdout.onData = null;
+      process.stdout.onError = null;
+      process.stdout.onClosed = null;
+    }
+    process.stdout.onData = () {
+      // TODO(nweiz): If an error happens after the body data starts being
+      // received, it should be piped through Response.stream once issue
+      // 3657 is fixed.
+      exitFuture.handleException((e) => true);
+      resetCallbacks();
+      completer.complete(null);
+    };
+    process.stdout.onError = (e) {
+      resetCallbacks();
+      completer.completeException(e);
+    };
+    process.stdout.onClosed = () {
+      resetCallbacks();
+      chainToCompleter(exitFuture, completer);
+    };
+    return completer.future;
+  }
+
+  /// Returns a [StreamedResponse] from the response data printed by the `curl`
+  /// [process]. [lines] are the headers that `curl` wrote to a file.
+  StreamedResponse _buildResponse(Process process, List<String> lines) {
+    // When curl follows redirects, it prints the redirect headers as well as
+    // the headers of the final request. Each block is separated by a blank
+    // line. We just care about the last block. There is one trailing empty
+    // line, though, which we don't want to consider a separator.
+    var lastBlank = lines.lastIndexOf("", lines.length - 2);
+    if (lastBlank != -1) lines.removeRange(0, lastBlank + 1);
+
+    var statusParts = lines.removeAt(0).split(" ");
+    var status = int.parse(statusParts[1]);
+    var isRedirect = status >= 300 && status < 400;
+    var reasonPhrase =
+        Strings.join(" ", statusParts.getRange(2, statusParts.length - 2));
+    var headers = <String>{};
+    for (var line in lines) {
+      if (line.isEmpty) continue;
+      var split = split1(line, ":");
+      headers[split[0].toLowerCase()] = split[1].trim();
+    }
+    var responseStream = process.stdout;
+    if (responseStream.closed) {
+      responseStream = new ListInputStream();
+      responseStream.markEndOfStream();
+    }
+    var contentLength = -1;
+    if (headers.containsKey('content-length')) {
+      contentLength = int.parse(headers['content-length']);
+    }
+
+    return new StreamedResponse(responseStream, status, contentLength,
+        headers: headers,
+        isRedirect: isRedirect,
+        reasonPhrase: reasonPhrase);
+  }
+}