exclude aborted requests and matrix errors when creating connectionerror

- throw an AbortError when aborting is detected
 - don't turn AbortError's into a ConnectionError
 - also consider the string "aborted" an AbortError for unit tests
 - unit tests like to reject the request with a MatrixError,
   so exclude those too

spec/integ/matrix-client-opts.spec.js

@@ -3,6 +3,7 @@ import HttpBackend from "matrix-mock-request";
 import {MatrixClient} from "../../src/matrix";
 import {MatrixScheduler} from "../../src/scheduler";
 import {MemoryStore} from "../../src/store/memory";
+import {MatrixError} from "../../src/http-api";
 
 describe("MatrixClient opts", function() {
     const baseUrl = "http://localhost.or.something";
@@ -132,10 +133,10 @@ describe("MatrixClient opts", function() {
         });
 
         it("shouldn't retry sending events", function(done) {
-            httpBackend.when("PUT", "/txn1").fail(500, {
+            httpBackend.when("PUT", "/txn1").fail(500, new MatrixError({
                 errcode: "M_SOMETHING",
                 error: "Ruh roh",
-            });
+            }));
             client.sendTextMessage("!foo:bar", "a body", "txn1").then(function(res) {
                 expect(false).toBe(true, "sendTextMessage resolved but shouldn't");
             }, function(err) {

src/http-api.js

@@ -276,6 +276,9 @@ MatrixHttpApi.prototype = {
                         callbacks.clearTimeout(xhr.timeout_timer);
                         var resp;
                         try {
+                            if (xhr.status === 0) {
+                                throw new AbortError();
+                            }
                             if (!xhr.responseText) {
                                 throw new Error('No response body.');
                             }
@@ -790,11 +793,16 @@ const requestCallback = function(
 
     return function(err, response, body) {
         if (err) {
+            // the unit tests use matrix-mock-request, which throw the string "aborted" when aborting a request.
+            // See https://github.com/matrix-org/matrix-mock-request/blob/3276d0263a561b5b8326b47bae720578a2c7473a/src/index.js#L48
+            const aborted = err.name === "AbortError" || err === "aborted";
+            if (!aborted && !(err instanceof MatrixError)) {
                 // browser-request just throws normal Error objects,
                 // not `TypeError`s like fetch does. So just assume any
                 // error is due to the connection.
                 err = new ConnectionError("request failed", err);
             }
+        }
         if (!err) {
             try {
                 if (response.statusCode >= 400) {
@@ -930,3 +938,13 @@ export class ConnectionError extends Error {
         return this._cause;
     }
 }
+
+export class AbortError extends Error {
+    constructor() {
+        super("Operation aborted");
+    }
+
+    get name() {
+        return "AbortError";
+    }
+}