Add support for async/await using Babel

For proof-of-concept, this patch converts a couple of `Promise` returning methods to use `async` instead.
Please note that the `generic` build, based on this patch, has been successfully testing in IE11 (i.e. the viewer loads and nothing is obviously broken).

Being able to use modern JavaScript features like `async`/`await` is a huge plus, but there's one (obvious) side-effect: The size of the built files will increase slightly (unless `SKIP_BABEL == true`). That's unavoidable, but seems like a small price to pay in the grand scheme of things.

Finally, note that the `chromium` build target was changed to no longer skip Babel translation, since the Chrome extension still supports version `49` of the browser (where native `async` support isn't available).

src/core/evaluator.js

@@ -131,19 +131,17 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
     this.options = options || DefaultPartialEvaluatorOptions;
     this.pdfFunctionFactory = pdfFunctionFactory;
 
-    this.fetchBuiltInCMap = (name) => {
+    this.fetchBuiltInCMap = async (name) => {
       if (this.builtInCMapCache.has(name)) {
-        return Promise.resolve(this.builtInCMapCache.get(name));
+        return this.builtInCMapCache.get(name);
       }
-      return this.handler.sendWithPromise('FetchBuiltInCMap', {
-        name,
-      }).then((data) => {
-        if (data.compressionType !== CMapCompressionType.NONE) {
-          // Given the size of uncompressed CMaps, only cache compressed ones.
-          this.builtInCMapCache.set(name, data);
-        }
-        return data;
-      });
+      const data = await this.handler.sendWithPromise('FetchBuiltInCMap',
+                                                      { name, });
+      if (data.compressionType !== CMapCompressionType.NONE) {
+        // Given the size of uncompressed CMaps, only cache compressed ones.
+        this.builtInCMapCache.set(name, data);
+      }
+      return data;
     };
   }
 

src/core/obj.js

@@ -1497,29 +1497,23 @@ var XRef = (function XRefClosure() {
       return xrefEntry;
     },
 
-    fetchIfRefAsync: function XRef_fetchIfRefAsync(obj, suppressEncryption) {
+    async fetchIfRefAsync(obj, suppressEncryption) {
       if (!isRef(obj)) {
-        return Promise.resolve(obj);
+        return obj;
       }
       return this.fetchAsync(obj, suppressEncryption);
     },
 
-    fetchAsync: function XRef_fetchAsync(ref, suppressEncryption) {
-      var streamManager = this.stream.manager;
-      var xref = this;
-      return new Promise(function tryFetch(resolve, reject) {
-        try {
-          resolve(xref.fetch(ref, suppressEncryption));
-        } catch (e) {
-          if (e instanceof MissingDataException) {
-            streamManager.requestRange(e.begin, e.end).then(function () {
-              tryFetch(resolve, reject);
-            }, reject);
-            return;
-          }
-          reject(e);
+    async fetchAsync(ref, suppressEncryption) {
+      try {
+        return this.fetch(ref, suppressEncryption);
+      } catch (ex) {
+        if (!(ex instanceof MissingDataException)) {
+          throw ex;
         }
-      });
+        await this.pdfManager.requestRange(ex.begin, ex.end);
+        return this.fetchAsync(ref, suppressEncryption);
+      }
     },
 
     getCatalogObj: function XRef_getCatalogObj() {

src/core/pdf_manager.js

@@ -72,7 +72,7 @@ class BasePdfManager {
     return this.pdfDocument.cleanup();
   }
 
-  ensure(obj, prop, args) {
+  async ensure(obj, prop, args) {
     unreachable('Abstract method `ensure` called');
   }
 
@@ -111,15 +111,12 @@ class LocalPdfManager extends BasePdfManager {
     this._loadedStreamPromise = Promise.resolve(stream);
   }
 
-  ensure(obj, prop, args) {
-    return new Promise(function(resolve) {
-      const value = obj[prop];
-      if (typeof value === 'function') {
-        resolve(value.apply(obj, args));
-      } else {
-        resolve(value);
-      }
-    });
+  async ensure(obj, prop, args) {
+    const value = obj[prop];
+    if (typeof value === 'function') {
+      return value.apply(obj, args);
+    }
+    return value;
   }
 
   requestRange(begin, end) {
@@ -155,30 +152,20 @@ class NetworkPdfManager extends BasePdfManager {
     this.pdfDocument = new PDFDocument(this, this.streamManager.getStream());
   }
 
-  ensure(obj, prop, args) {
-    return new Promise((resolve, reject) => {
-      let ensureHelper = () => {
-        try {
-          const value = obj[prop];
-          let result;
-          if (typeof value === 'function') {
-            result = value.apply(obj, args);
-          } else {
-            result = value;
-          }
-          resolve(result);
-        } catch (ex) {
-          if (!(ex instanceof MissingDataException)) {
-            reject(ex);
-            return;
-          }
-          this.streamManager.requestRange(ex.begin, ex.end)
-            .then(ensureHelper, reject);
-        }
-      };
-
-      ensureHelper();
-    });
+  async ensure(obj, prop, args) {
+    try {
+      const value = obj[prop];
+      if (typeof value === 'function') {
+        return value.apply(obj, args);
+      }
+      return value;
+    } catch (ex) {
+      if (!(ex instanceof MissingDataException)) {
+        throw ex;
+      }
+      await this.requestRange(ex.begin, ex.end);
+      return this.ensure(obj, prop, args);
+    }
   }
 
   requestRange(begin, end) {

src/display/fetch_stream.js

@@ -152,23 +152,21 @@ class PDFFetchStreamReader {
     return this._isStreamingSupported;
   }
 
-  read() {
-    return this._headersCapability.promise.then(() => {
-      return this._reader.read().then(({ value, done, }) => {
-        if (done) {
-          return Promise.resolve({ value, done, });
-        }
-        this._loaded += value.byteLength;
-        if (this.onProgress) {
-          this.onProgress({
-            loaded: this._loaded,
-            total: this._contentLength,
-          });
-        }
-        let buffer = new Uint8Array(value).buffer;
-        return Promise.resolve({ value: buffer, done: false, });
+  async read() {
+    await this._headersCapability.promise;
+    const { value, done, } = await this._reader.read();
+    if (done) {
+      return { value, done, };
+    }
+    this._loaded += value.byteLength;
+    if (this.onProgress) {
+      this.onProgress({
+        loaded: this._loaded,
+        total: this._contentLength,
       });
-    });
+    }
+    let buffer = new Uint8Array(value).buffer;
+    return { value: buffer, done: false, };
   }
 
   cancel(reason) {
@@ -223,20 +221,18 @@ class PDFFetchStreamRangeReader {
     return this._isStreamingSupported;
   }
 
-  read() {
-    return this._readCapability.promise.then(() => {
-      return this._reader.read().then(({ value, done, }) => {
-        if (done) {
-          return Promise.resolve({ value, done, });
-        }
-        this._loaded += value.byteLength;
-        if (this.onProgress) {
-          this.onProgress({ loaded: this._loaded, });
-        }
-        let buffer = new Uint8Array(value).buffer;
-        return Promise.resolve({ value: buffer, done: false, });
-      });
-    });
+  async read() {
+    await this._readCapability.promise;
+    const { value, done, } = await this._reader.read();
+    if (done) {
+      return { value, done, };
+    }
+    this._loaded += value.byteLength;
+    if (this.onProgress) {
+      this.onProgress({ loaded: this._loaded, });
+    }
+    let buffer = new Uint8Array(value).buffer;
+    return { value: buffer, done: false, };
   }
 
   cancel(reason) {

src/display/network.js

@@ -453,16 +453,16 @@ PDFNetworkStreamFullRequestReader.prototype = {
     return this._headersReceivedCapability.promise;
   },
 
-  read: function PDFNetworkStreamFullRequestReader_read() {
+  async read() {
     if (this._storedError) {
-      return Promise.reject(this._storedError);
+      throw this._storedError;
     }
     if (this._cachedChunks.length > 0) {
       var chunk = this._cachedChunks.shift();
-      return Promise.resolve({ value: chunk, done: false, });
+      return { value: chunk, done: false, };
     }
     if (this._done) {
-      return Promise.resolve({ value: undefined, done: true, });
+      return { value: undefined, done: true, };
     }
     var requestCapability = createPromiseCapability();
     this._requests.push(requestCapability);
@@ -534,14 +534,14 @@ PDFNetworkStreamRangeRequestReader.prototype = {
     return false; // TODO allow progressive range bytes loading
   },
 
-  read: function PDFNetworkStreamRangeRequestReader_read() {
+  async read() {
     if (this._queuedChunk !== null) {
       var chunk = this._queuedChunk;
       this._queuedChunk = null;
-      return Promise.resolve({ value: chunk, done: false, });
+      return { value: chunk, done: false, };
     }
     if (this._done) {
-      return Promise.resolve({ value: undefined, done: true, });
+      return { value: undefined, done: true, };
     }
     var requestCapability = createPromiseCapability();
     this._requests.push(requestCapability);

src/display/node_stream.js

@@ -131,31 +131,30 @@ class BaseFullReader {
     return this._isStreamingSupported;
   }
 
-  read() {
-    return this._readCapability.promise.then(() => {
-      if (this._done) {
-        return Promise.resolve({ value: undefined, done: true, });
-      }
-      if (this._storedError) {
-        return Promise.reject(this._storedError);
-      }
+  async read() {
+    await this._readCapability.promise;
+    if (this._done) {
+      return { value: undefined, done: true, };
+    }
+    if (this._storedError) {
+      throw this._storedError;
+    }
 
-      let chunk = this._readableStream.read();
-      if (chunk === null) {
-        this._readCapability = createPromiseCapability();
-        return this.read();
-      }
-      this._loaded += chunk.length;
-      if (this.onProgress) {
-        this.onProgress({
-          loaded: this._loaded,
-          total: this._contentLength,
-        });
-      }
-      // Ensure that `read()` method returns ArrayBuffer.
-      let buffer = new Uint8Array(chunk).buffer;
-      return Promise.resolve({ value: buffer, done: false, });
-    });
+    let chunk = this._readableStream.read();
+    if (chunk === null) {
+      this._readCapability = createPromiseCapability();
+      return this.read();
+    }
+    this._loaded += chunk.length;
+    if (this.onProgress) {
+      this.onProgress({
+        loaded: this._loaded,
+        total: this._contentLength,
+      });
+    }
+    // Ensure that `read()` method returns ArrayBuffer.
+    let buffer = new Uint8Array(chunk).buffer;
+    return { value: buffer, done: false, };
   }
 
   cancel(reason) {
@@ -220,28 +219,27 @@ class BaseRangeReader {
     return this._isStreamingSupported;
   }
 
-  read() {
-    return this._readCapability.promise.then(() => {
-      if (this._done) {
-        return Promise.resolve({ value: undefined, done: true, });
-      }
-      if (this._storedError) {
-        return Promise.reject(this._storedError);
-      }
+  async read() {
+    await this._readCapability.promise;
+    if (this._done) {
+      return { value: undefined, done: true, };
+    }
+    if (this._storedError) {
+      throw this._storedError;
+    }
 
-      let chunk = this._readableStream.read();
-      if (chunk === null) {
-        this._readCapability = createPromiseCapability();
-        return this.read();
-      }
-      this._loaded += chunk.length;
-      if (this.onProgress) {
-        this.onProgress({ loaded: this._loaded, });
-      }
-      // Ensure that `read()` method returns ArrayBuffer.
-      let buffer = new Uint8Array(chunk).buffer;
-      return Promise.resolve({ value: buffer, done: false, });
-    });
+    let chunk = this._readableStream.read();
+    if (chunk === null) {
+      this._readCapability = createPromiseCapability();
+      return this.read();
+    }
+    this._loaded += chunk.length;
+    if (this.onProgress) {
+      this.onProgress({ loaded: this._loaded, });
+    }
+    // Ensure that `read()` method returns ArrayBuffer.
+    let buffer = new Uint8Array(chunk).buffer;
+    return { value: buffer, done: false, };
   }
 
   cancel(reason) {

src/display/transport_stream.js

@@ -160,13 +160,13 @@ var PDFDataTransportStream = (function PDFDataTransportStreamClosure() {
       return this._stream._contentLength;
     },
 
-    read: function PDFDataTransportStreamReader_read() {
+    async read() {
       if (this._queuedChunks.length > 0) {
         var chunk = this._queuedChunks.shift();
-        return Promise.resolve({ value: chunk, done: false, });
+        return { value: chunk, done: false, };
       }
       if (this._done) {
-        return Promise.resolve({ value: undefined, done: true, });
+        return { value: undefined, done: true, };
       }
       var requestCapability = createPromiseCapability();
       this._requests.push(requestCapability);
@@ -216,14 +216,14 @@ var PDFDataTransportStream = (function PDFDataTransportStreamClosure() {
       return false;
     },
 
-    read: function PDFDataTransportStreamRangeReader_read() {
+    async read() {
       if (this._queuedChunk) {
         let chunk = this._queuedChunk;
         this._queuedChunk = null;
-        return Promise.resolve({ value: chunk, done: false, });
+        return { value: chunk, done: false, };
       }
       if (this._done) {
-        return Promise.resolve({ value: undefined, done: true, });
+        return { value: undefined, done: true, };
       }
       var requestCapability = createPromiseCapability();
       this._requests.push(requestCapability);

src/shared/message_handler.js

@@ -18,13 +18,11 @@ import {
   ReadableStream, UnexpectedResponseException, UnknownErrorException
 } from './util';
 
-function resolveCall(fn, args, thisArg = null) {
+async function resolveCall(fn, args, thisArg = null) {
   if (!fn) {
-    return Promise.resolve(undefined);
+    return;
   }
-  return new Promise((resolve, reject) => {
-    resolve(fn.apply(thisArg, args));
-  });
+  return fn.apply(thisArg, args);
 }
 
 function wrapReason(reason) {