Fixed fetch abort behaviour for Edge 16+ (improbable-eng#819)

.travis.yml

@@ -26,7 +26,8 @@ env:
     - BROWSER=chrome_52
     - BROWSER=chrome_43
     - BROWSER=chrome_41
-    # Edge does not support aborting fetch requests (documented known limitation in project README)
+    - BROWSER=edge16_win
+    # Edge < 16 does not support aborting fetch requests (documented known limitation in project README)
     - BROWSER=edge15_win DISABLE_ABORT_TESTS=true
     - BROWSER=edge14_win DISABLE_ABORT_TESTS=true
     - BROWSER=edge13_win DISABLE_ABORT_TESTS=true

client/grpc-web/docs/transport.md

@@ -43,7 +43,7 @@ It's great that we have more than one choice when it comes to Web Browsers, howe
 
 * gRPC offers four categories of request: unary, server-streaming, client-streaming and bi-directional. Due to limitations of the Browser HTTP primitives (`fetch` and `XMLHttpRequest`), the HTTP/2-based transports provided by `@improbable-eng/grpc-web` can only support unary and server-streaming requests. Attempts to invoke either client-streaming or bi-directional endpoints will result in failure.
 * Older versions of Safari (<7) and all versions of Internet Explorer do not provide an efficient way to stream data from a server; this will result in the entire response of a gRPC client-stream being buffered into memory which can cause performance and stability issues for end-users. 
-* Microsoft Edge does not propagate the cancellation of requests to the server; which can result in memory/process leaks on your server. Track this issue for status.
+* Microsoft Edge (<16) does not propagate the cancellation of requests to the server; which can result in memory/process leaks on your server. Track [this issue](https://github.com/improbable-eng/grpc-web/issues/125) for status.
 
 Note that the [Socket-based Transports](#socket-based-transports) alleviate the above issues.
 

client/grpc-web/src/transports/http/fetch.ts

@@ -37,7 +37,10 @@ class Fetch implements Transport {
     if (this.cancelled) {
       // If the request was cancelled before the first pump then cancel it here
       this.options.debug && debug("Fetch.pump.cancel at first pump");
-      this.reader.cancel();
+      this.reader.cancel().catch(e => {
+        // This can be ignored. It will likely throw an exception due to the request being aborted
+        this.options.debug && debug("Fetch.pump.reader.cancel exception", e);
+      });
       return;
     }
     this.reader.read()
@@ -67,7 +70,7 @@ class Fetch implements Transport {
       headers: this.metadata.toHeaders(),
       method: "POST",
       body: msgBytes,
-      signal: this.controller && this.controller.signal
+      signal: this.controller && this.controller.signal,
     }).then((res: Response) => {
       this.options.debug && debug("Fetch.response", res);
       this.options.onHeaders(new Metadata(res.headers as any), res.status);
@@ -101,19 +104,27 @@ class Fetch implements Transport {
 
   cancel() {
     if (this.cancelled) {
-      this.options.debug && debug("Fetch.abort.cancel already cancelled");
+      this.options.debug && debug("Fetch.cancel already cancelled");
       return;
     }
     this.cancelled = true;
+
+    if (this.controller) {
+      this.options.debug && debug("Fetch.cancel.controller.abort");
+      this.controller.abort();
+    } else {
+      this.options.debug && debug("Fetch.cancel.missing abort controller");
+    }
+
     if (this.reader) {
       // If the reader has already been received in the pump then it can be cancelled immediately
-      this.options.debug && debug("Fetch.abort.cancel");
-      this.reader.cancel();
+      this.options.debug && debug("Fetch.cancel.reader.cancel");
+      this.reader.cancel().catch(e => {
+        // This can be ignored. It will likely throw an exception due to the request being aborted
+        this.options.debug && debug("Fetch.cancel.reader.cancel exception", e);
+      });
     } else {
-      this.options.debug && debug("Fetch.abort.cancel before reader");
-    }
-    if (this.controller) {
-      this.controller.abort();
+      this.options.debug && debug("Fetch.cancel before reader");
     }
   }
 }

integration_test/browsers.ts

@@ -49,6 +49,7 @@ function browser(browserName, browserVersion, os, osVersion) {
 // Browser versions that should not have any Fetch/XHR differences in functionality to other (tested) versions are
 // commented out.
 const browsers = {
+  edge16_win: browser("edge", "16", "Windows", "10"),
   edge15_win: browser("edge", "15", "Windows", "10"),
   edge14_win: browser("edge", "14", "Windows", "10"),
   edge13_win: browser('edge', "13", 'Windows', "10"),