From eeb9cd8075886722df84e91ab64f9513f41cd0fa Mon Sep 17 00:00:00 2001
From: Andy Street <andrews@fb.com>
Date: Thu, 7 Jul 2016 11:03:09 -0700
Subject: [PATCH] Better error message when trying to parse a empty body in
 fetch

Summary: Previously, trying to parse an empty network body would throw "Unexpected EOF" from JSON.parse. Now we explicitly call out the error and provide steps for possible mitigation.

Reviewed By: frantic

Differential Revision: D3528297

fbshipit-source-id: 3b52c9491c1504c282eb9bc12ed46069cb6cbd60
---
 Libraries/Fetch/fetch.js | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/Libraries/Fetch/fetch.js b/Libraries/Fetch/fetch.js
index 7cb122a07..171030496 100644
--- a/Libraries/Fetch/fetch.js
+++ b/Libraries/Fetch/fetch.js
@@ -11,6 +11,8 @@
  *
  * @providesModule fetch
  * @nolint
+ *
+ * NOTE: This file has local changes for RN and is not a straight copy!
  */
 /* eslint-disable */
 'use strict';
@@ -240,7 +242,26 @@ var self = {};
     }
 
     this.json = function() {
-      return this.text().then(JSON.parse)
+      var status = this.status;
+      return this.text().then(function(text) {
+        if (!text) {
+          var errorText =
+            'Trying to parse the body of a network response as JSON, but the ' +
+            'body is null or empty.';
+          if (status !== 200) {
+            errorText +=
+              '\n\nThis can be the result of not properly checking for a 200 OK ' +
+              'status code before trying to parse the body (the status code for ' +
+              'this response was ' + status + ').';
+          } else {
+            errorText +=
+              '\n\nThe status code for this response was 200 OK, so nothing ' +
+              'went obviously wrong. Is your server configured properly?';
+          }
+          throw new Error(errorText);
+        }
+        return JSON.parse(text);
+      });
     }
 
     return this