Implement FileImporter (#57)

Author: nex3

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.0.0-beta.14
+
+* Support `FileImporter`s.
+
 ## 1.0.0-beta.13
 
 * Report a better error message for an empty `CompileRequest.Input.path`.

bin/dart_sass_embedded.dart

@@ -12,7 +12,8 @@ import 'package:sass_embedded/src/dispatcher.dart';
 import 'package:sass_embedded/src/embedded_sass.pb.dart';
 import 'package:sass_embedded/src/function_registry.dart';
 import 'package:sass_embedded/src/host_callable.dart';
-import 'package:sass_embedded/src/importer.dart';
+import 'package:sass_embedded/src/importer/file.dart';
+import 'package:sass_embedded/src/importer/host.dart';
 import 'package:sass_embedded/src/logger.dart';
 import 'package:sass_embedded/src/util/length_delimited_transformer.dart';
 import 'package:sass_embedded/src/utils.dart';
@@ -125,7 +126,7 @@ void main(List<String> args) {
   });
 }
 
-/// Converts [importer] into an [Importer].
+/// Converts [importer] into a [sass.Importer].
 sass.Importer? _decodeImporter(
     Dispatcher dispatcher,
     InboundMessage_CompileRequest request,
@@ -135,10 +136,10 @@ sass.Importer? _decodeImporter(
       return sass.FilesystemImporter(importer.path);
 
     case InboundMessage_CompileRequest_Importer_Importer.importerId:
-      return Importer(dispatcher, request.id, importer.importerId);
+      return HostImporter(dispatcher, request.id, importer.importerId);
 
     case InboundMessage_CompileRequest_Importer_Importer.fileImporterId:
-      throw "CompileRequest.Importer.fileImporterId is not yet supported";
+      return FileImporter(dispatcher, request.id, importer.fileImporterId);
 
     case InboundMessage_CompileRequest_Importer_Importer.notSet:
       return null;

lib/src/dispatcher.dart

@@ -80,6 +80,11 @@ class Dispatcher {
             _dispatchResponse(response.id, response);
             break;
 
+          case InboundMessage_Message.fileImportResponse:
+            var response = message.fileImportResponse;
+            _dispatchResponse(response.id, response);
+            break;
+
           case InboundMessage_Message.functionCallResponse:
             var response = message.functionCallResponse;
             _dispatchResponse(response.id, response);
@@ -131,6 +136,11 @@ class Dispatcher {
       _sendRequest<InboundMessage_ImportResponse>(
           OutboundMessage()..importRequest = request);
 
+  Future<InboundMessage_FileImportResponse> sendFileImportRequest(
+          OutboundMessage_FileImportRequest request) =>
+      _sendRequest<InboundMessage_FileImportResponse>(
+          OutboundMessage()..fileImportRequest = request);
+
   Future<InboundMessage_FunctionCallResponse> sendFunctionCallRequest(
           OutboundMessage_FunctionCallRequest request) =>
       _sendRequest<InboundMessage_FunctionCallResponse>(
@@ -165,8 +175,12 @@ class Dispatcher {
   /// Throws an error if there's no outstanding request with the given [id] or
   /// if that request is expecting a different type of response.
   void _dispatchResponse<T extends GeneratedMessage>(int id, T response) {
-    var completer =
-        id < _outstandingRequests.length ? _outstandingRequests[id] : null;
+    Completer<GeneratedMessage>? completer;
+    if (id < _outstandingRequests.length) {
+      completer = _outstandingRequests[id];
+      _outstandingRequests[id] = null;
+    }
+
     if (completer == null) {
       throw paramsError(
           "Response ID $id doesn't match any outstanding requests.");

lib/src/importer/base.dart

@@ -0,0 +1,45 @@
+// Copyright 2021 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:meta/meta.dart';
+import 'package:sass_api/sass_api.dart' as sass;
+
+import '../dispatcher.dart';
+import '../embedded_sass.pb.dart' hide SourceSpan;
+import '../utils.dart';
+
+/// An abstract base class for importers that communicate with the host in some
+/// way.
+abstract class ImporterBase extends sass.Importer {
+  /// The [Dispatcher] to which to send requests.
+  @protected
+  final Dispatcher dispatcher;
+
+  ImporterBase(this.dispatcher);
+
+  /// Parses [url] as a [Uri] and throws an error if it's invalid or relative
+  /// (including root-relative).
+  ///
+  /// The [field] name is used in the error message if one is thrown.
+  @protected
+  Uri parseAbsoluteUrl(String field, String url) {
+    Uri parsedUrl;
+    try {
+      parsedUrl = Uri.parse(url);
+    } on FormatException catch (error) {
+      sendAndThrow(paramsError("$field is invalid: $error"));
+    }
+
+    if (parsedUrl.scheme.isNotEmpty) return parsedUrl;
+    sendAndThrow(paramsError('$field must be absolute, was "$parsedUrl"'));
+  }
+
+  /// Sends [error] to the remote endpoint, and also throws it so that the Sass
+  /// compilation fails.
+  @protected
+  Never sendAndThrow(ProtocolError error) {
+    dispatcher.sendError(error);
+    throw "Protocol error: ${error.message}";
+  }
+}

lib/src/importer/file.dart

@@ -0,0 +1,66 @@
+// Copyright 2021 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:cli';
+
+import 'package:sass_api/sass_api.dart' as sass;
+
+import '../dispatcher.dart';
+import '../embedded_sass.pb.dart' hide SourceSpan;
+import '../utils.dart';
+import 'base.dart';
+
+/// A filesystem importer to use for most implementation details of
+/// [FileImporter].
+///
+/// This allows us to avoid duplicating logic between the two importers.
+final _filesystemImporter = sass.FilesystemImporter('.');
+
+/// An importer that asks the host to resolve imports in a simplified,
+/// file-system-centric way.
+class FileImporter extends ImporterBase {
+  /// The ID of the compilation in which this importer is used.
+  final int _compilationId;
+
+  /// The host-provided ID of the importer to invoke.
+  final int _importerId;
+
+  FileImporter(Dispatcher dispatcher, this._compilationId, this._importerId)
+      : super(dispatcher);
+
+  Uri? canonicalize(Uri url) {
+    if (url.scheme == 'file') return _filesystemImporter.canonicalize(url);
+
+    return waitFor(() async {
+      var response = await dispatcher
+          .sendFileImportRequest(OutboundMessage_FileImportRequest()
+            ..compilationId = _compilationId
+            ..importerId = _importerId
+            ..url = url.toString()
+            ..fromImport = fromImport);
+
+      switch (response.whichResult()) {
+        case InboundMessage_FileImportResponse_Result.fileUrl:
+          var url =
+              parseAbsoluteUrl("FileImportResponse.file_url", response.fileUrl);
+          if (url.scheme != 'file') {
+            sendAndThrow(paramsError(
+                'FileImportResponse.file_url must be a file: URL, was "$url"'));
+          }
+
+          return _filesystemImporter.canonicalize(url);
+
+        case InboundMessage_FileImportResponse_Result.error:
+          throw response.error;
+
+        case InboundMessage_FileImportResponse_Result.notSet:
+          return null;
+      }
+    }());
+  }
+
+  sass.ImporterResult? load(Uri url) => _filesystemImporter.load(url);
+
+  String toString() => "FileImporter";
+}

lib/src/importer.dart renamed to lib/src/importer/host.dart

@@ -6,26 +6,25 @@ import 'dart:cli';
 
 import 'package:sass_api/sass_api.dart' as sass;
 
-import 'dispatcher.dart';
-import 'embedded_sass.pb.dart' hide SourceSpan;
-import 'utils.dart';
+import '../dispatcher.dart';
+import '../embedded_sass.pb.dart' hide SourceSpan;
+import '../utils.dart';
+import 'base.dart';
 
 /// An importer that asks the host to resolve imports.
-class Importer extends sass.Importer {
-  /// The [Dispatcher] to which to send requests.
-  final Dispatcher _dispatcher;
-
+class HostImporter extends ImporterBase {
   /// The ID of the compilation in which this importer is used.
   final int _compilationId;
 
   /// The host-provided ID of the importer to invoke.
   final int _importerId;
 
-  Importer(this._dispatcher, this._compilationId, this._importerId);
+  HostImporter(Dispatcher dispatcher, this._compilationId, this._importerId)
+      : super(dispatcher);
 
   Uri? canonicalize(Uri url) {
     return waitFor(() async {
-      var response = await _dispatcher
+      var response = await dispatcher
           .sendCanonicalizeRequest(OutboundMessage_CanonicalizeRequest()
             ..compilationId = _compilationId
             ..importerId = _importerId
@@ -34,7 +33,7 @@ class Importer extends sass.Importer {
 
       switch (response.whichResult()) {
         case InboundMessage_CanonicalizeResponse_Result.url:
-          return _parseAbsoluteUrl("CanonicalizeResponse.url", response.url);
+          return parseAbsoluteUrl("CanonicalizeResponse.url", response.url);
 
         case InboundMessage_CanonicalizeResponse_Result.error:
           throw response.error;
@@ -48,7 +47,7 @@ class Importer extends sass.Importer {
   sass.ImporterResult load(Uri url) {
     return waitFor(() async {
       var response =
-          await _dispatcher.sendImportRequest(OutboundMessage_ImportRequest()
+          await dispatcher.sendImportRequest(OutboundMessage_ImportRequest()
             ..compilationId = _compilationId
             ..importerId = _importerId
             ..url = url.toString());
@@ -58,41 +57,18 @@ class Importer extends sass.Importer {
           return sass.ImporterResult(response.success.contents,
               sourceMapUrl: response.success.sourceMapUrl.isEmpty
                   ? null
-                  : _parseAbsoluteUrl("ImportResponse.success.source_map_url",
+                  : parseAbsoluteUrl("ImportResponse.success.source_map_url",
                       response.success.sourceMapUrl),
               syntax: syntaxToSyntax(response.success.syntax));
 
         case InboundMessage_ImportResponse_Result.error:
           throw response.error;
 
         case InboundMessage_ImportResponse_Result.notSet:
-          _sendAndThrow(mandatoryError("ImportResponse.result"));
+          sendAndThrow(mandatoryError("ImportResponse.result"));
       }
     }());
   }
 
-  /// Parses [url] as a [Uri] and throws an error if it's invalid or relative
-  /// (including root-relative).
-  ///
-  /// The [field] name is used in the error message if one is thrown.
-  Uri _parseAbsoluteUrl(String field, String url) {
-    Uri parsedUrl;
-    try {
-      parsedUrl = Uri.parse(url);
-    } on FormatException catch (error) {
-      _sendAndThrow(paramsError("$field is invalid: $error"));
-    }
-
-    if (parsedUrl.scheme.isNotEmpty) return parsedUrl;
-    _sendAndThrow(paramsError('$field must be absolute, was "$parsedUrl"'));
-  }
-
-  /// Sends [error] to the remote endpoint, and also throws it so that the Sass
-  /// compilation fails.
-  Never _sendAndThrow(ProtocolError error) {
-    _dispatcher.sendError(error);
-    throw "Protocol error: ${error.message}";
-  }
-
   String toString() => "HostImporter";
 }

pubspec.yaml

@@ -1,7 +1,6 @@
 name: sass_embedded
-version: 1.0.0-beta.13
+version: 1.0.0-beta.14
 description: An implementation of the Sass embedded protocol using Dart Sass.
-author: Sass Team
 homepage: https://github.com/sass/dart-sass-embedded
 
 environment: