From 9807d1ec4025893c0e0374fd8406cbf9b667dfe3 Mon Sep 17 00:00:00 2001
From: Guillaume FORTAINE <guillaume+github@fortaine.com>
Date: Sun, 5 Sep 2021 19:24:51 +0200
Subject: [PATCH] fix json transform when data is pre-stringified

---
 lib/defaults.js             | 17 ++++++++++++++++-
 test/specs/defaults.spec.js | 13 +++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/lib/defaults.js b/lib/defaults.js
index fb96bdbd13..55e69d9ae5 100644
--- a/lib/defaults.js
+++ b/lib/defaults.js
@@ -26,6 +26,21 @@ function getDefaultAdapter() {
   return adapter;
 }
 
+function stringifySafely(rawValue, parser, encoder) {
+  if (utils.isString(rawValue)) {
+    try {
+      (parser || JSON.parse)(rawValue);
+      return utils.trim(rawValue);
+    } catch (e) {
+      if (e.name !== 'SyntaxError') {
+        throw e;
+      }
+    }
+  }
+
+  return (encoder || JSON.stringify)(rawValue);
+}
+
 var defaults = {
 
   transitional: {
@@ -58,7 +73,7 @@ var defaults = {
     }
     if (utils.isObject(data) || (headers && headers['Content-Type'] === 'application/json')) {
       setContentTypeIfUnset(headers, 'application/json');
-      return JSON.stringify(data);
+      return stringifySafely(data);
     }
     return data;
   }],
diff --git a/test/specs/defaults.spec.js b/test/specs/defaults.spec.js
index d71cd66a4e..ff0f15febe 100644
--- a/test/specs/defaults.spec.js
+++ b/test/specs/defaults.spec.js
@@ -20,6 +20,19 @@ describe('defaults', function () {
     expect(defaults.transformRequest[0]({foo: 'bar'})).toEqual('{"foo":"bar"}');
   });
 
+  it("should also transform request json when 'Content-Type' is 'application/json'", function () {
+    var headers = {
+      'Content-Type': 'application/json',
+    };
+    expect(defaults.transformRequest[0](JSON.stringify({ foo: 'bar' }), headers)).toEqual('{"foo":"bar"}');
+    expect(defaults.transformRequest[0]([42, 43], headers)).toEqual('[42,43]');
+    expect(defaults.transformRequest[0]('foo', headers)).toEqual('"foo"');
+    expect(defaults.transformRequest[0](42, headers)).toEqual('42');
+    expect(defaults.transformRequest[0](true, headers)).toEqual('true');
+    expect(defaults.transformRequest[0](false, headers)).toEqual('false');
+    expect(defaults.transformRequest[0](null, headers)).toEqual('null');
+  });  
+
   it('should do nothing to request string', function () {
     expect(defaults.transformRequest[0]('foo=bar')).toEqual('foo=bar');
   });