Bring some sanity to request parsing and error handling (#2335)

* Update docs/request.md
* Bring some sanity to request parsing and error handling

- The browser can do JSON parsing itself. Let's defer to that where
  possible. (A few IE hacks are required here, though.)
- Don't propagate any error that occurs before `deserialize`/`extract`.
- Allow sending raw array buffers/blobs/etc. to `deserialize`.
- Align behavior more closely with the XHR spec.
- Send the more useful parsed response to `deserialize`, not the less
  useful string response.

request/request.js

@@ -79,7 +79,7 @@ module.exports = function($window, Promise) {
 			}
 			if (args.withCredentials) xhr.withCredentials = args.withCredentials
 			if (args.timeout) xhr.timeout = args.timeout
-			if (args.responseType) xhr.responseType = args.responseType
+			xhr.responseType = args.responseType || (typeof args.extract === "function" ? "" : "json")
 
 			for (var key in args.headers) {
 				if ({}.hasOwnProperty.call(args.headers, key)) {
@@ -96,19 +96,38 @@ module.exports = function($window, Promise) {
 				if (xhr.readyState === 4) {
 					try {
 						var success = (xhr.status >= 200 && xhr.status < 300) || xhr.status === 304 || (/^file:\/\//i).test(url)
-						var response = xhr.responseText
+						// When the response type isn't "" or "text",
+						// `xhr.responseText` is the wrong thing to use.
+						// Browsers do the right thing and throw here, and we
+						// should honor that and do the right thing by
+						// preferring `xhr.response` where possible/practical.
+						var response = xhr.response, message
+
+						if (response == null) {
+							try {
+								response = xhr.responseText
+								// Note: this snippet is intentionally *after*
+								// `xhr.responseText` is accessed, since the
+								// above will throw in modern browsers (thus
+								// skipping the rest of this section). It's an
+								// IE hack to detect and work around the lack of
+								// native `responseType: "json"` support there.
+								if (typeof args.extract !== "function" && xhr.responseType === "json") response = JSON.parse(response)
+							}
+							catch (e) { response = null }
+						}
+
 						if (typeof args.extract === "function") {
 							response = args.extract(xhr, args)
 							success = true
 						} else if (typeof args.deserialize === "function") {
 							response = args.deserialize(response)
-						} else {
-							try {response = response ? JSON.parse(response) : null}
-							catch (e) {throw new Error("Invalid JSON: " + response)}
 						}
 						if (success) resolve(response)
 						else {
-							var error = new Error(xhr.responseText)
+							try { message = xhr.responseText }
+							catch (e) { message = response }
+							var error = new Error(message)
 							error.code = xhr.status
 							error.response = response
 							reject(error)

request/tests/test-request.js

@@ -290,7 +290,7 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "GET", url: "/item", deserialize: deserialize}).then(function(data) {
-				o(data).equals("{\"test\":123}")
+				o(data).deepEquals({test: 123})
 			}).then(done)
 		})
 		o("deserialize parameter works in POST", function(done) {
@@ -304,12 +304,12 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "POST", url: "/item", deserialize: deserialize}).then(function(data) {
-				o(data).equals("{\"test\":123}")
+				o(data).deepEquals({test: 123})
 			}).then(done)
 		})
 		o("extract parameter works in GET", function(done) {
 			var extract = function() {
-				return JSON.stringify({test: 123})
+				return {test: 123}
 			}
 
 			mock.$defineRoutes({
@@ -318,12 +318,12 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "GET", url: "/item", extract: extract}).then(function(data) {
-				o(data).equals("{\"test\":123}")
+				o(data).deepEquals({test: 123})
 			}).then(done)
 		})
 		o("extract parameter works in POST", function(done) {
 			var extract = function() {
-				return JSON.stringify({test: 123})
+				return {test: 123}
 			}
 
 			mock.$defineRoutes({
@@ -332,7 +332,7 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "POST", url: "/item", extract: extract}).then(function(data) {
-				o(data).equals("{\"test\":123}")
+				o(data).deepEquals({test: 123})
 			}).then(done)
 		})
 		o("ignores deserialize if extract is defined", function(done) {
@@ -545,7 +545,8 @@ o.spec("xhr", function() {
 			})
 			xhr({method: "GET", url: "/item"}).catch(function(e) {
 				o(e instanceof Error).equals(true)
-				o(e.message).equals(JSON.stringify({error: "error"}))
+				o(e.message).equals("[object Object]")
+				o(e.response).deepEquals({error: "error"})
 				o(e.code).equals(500)
 			}).then(done)
 		})
@@ -568,7 +569,8 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "GET", url: "/item"}).catch(function(e) {
-				o(e.message).equals("Invalid JSON: error")
+				o(e.message).equals("null")
+				o(e.response).equals(null)
 			}).then(done)
 		})
 		o("triggers all branched catches upon rejection", function(done) {