improve error output on invalid JSON

More descriptive error message and shows the URL of the file in question:

> Unexpected token '/' at 1:1 in http://localhost:6767/invalid

index.js

@@ -17,6 +17,7 @@ var unzipResponse = require('unzip-response');
 var createErrorClass = require('create-error-class');
 var nodeStatusCodes = require('node-status-codes');
 var isPlainObj = require('is-plain-obj');
+var parseJson = require('parse-json');
 
 function requestAsEventEmitter(opts) {
 	opts = opts || {};
@@ -90,8 +91,9 @@ function asCallback(opts, cb) {
 
 			if (opts.json && statusCode !== 204) {
 				try {
-					data = JSON.parse(data);
+					data = parseJson(data);
 				} catch (e) {
+					e.fileName = urlLib.format(opts);
 					err = new got.ParseError(e, opts);
 				}
 			}

package.json

@@ -49,6 +49,7 @@
     "lowercase-keys": "^1.0.0",
     "node-status-codes": "^1.0.0",
     "object-assign": "^3.0.0",
+    "parse-json": "^2.1.0",
     "pinkie-promise": "^1.0.0",
     "prepend-http": "^1.0.0",
     "read-all-stream": "^3.0.0",

test/test-json.js

@@ -51,7 +51,8 @@ test('json option should not parse responses without a body', function (t) {
 test('json option wrap parsing errors', function (t) {
 	got(s.url + '/invalid', {json: true}, function (err) {
 		t.ok(err);
-		t.equal(err.message, 'Unexpected token /');
+		t.ok(/Unexpected token/.test(err.message), err.message);
+		t.ok(err.message.indexOf(err.hostname) !== -1, err.message);
 		t.equal(err.path, '/invalid');
 		t.end();
 	});
@@ -68,8 +69,8 @@ test('json option should parse non-200 responses', function (t) {
 test('json option should catch errors on invalid non-200 responses', function (t) {
 	got(s.url + '/non200-invalid', {json: true}, function (err, json) {
 		t.ok(err);
+		t.ok(/Unexpected token/.test(err.message), err.message);
 		t.deepEqual(json, 'Internal error');
-		t.equal(err.message, 'Unexpected token I');
 		t.equal(err.path, '/non200-invalid');
 		t.end();
 	});