Only add Content-Type if not specified in headers. Fixes #20046 (#20234)

* Only add Content-Type if not specified in headers. Fixes #20046

* Update documentation to indicate body_format will not override Content-Type if specified in headers

lib/ansible/modules/network/basics/uri.py

@@ -65,6 +65,8 @@ options:
     description:
       - The serialization format of the body. When set to json, encodes the
         body argument, if needed, and automatically sets the Content-Type header accordingly.
+        As of C(2.3) it is possible to override the `Content-Type` header, when
+        set to json via the I(headers) option.
     required: false
     choices: [ "raw", "json" ]
     default: raw
@@ -134,7 +136,9 @@ options:
     default: null
   headers:
     description:
-        - Add custom HTTP headers to a request in the format of a YAML hash
+        - Add custom HTTP headers to a request in the format of a YAML hash. As
+          of C(2.3) supplying C(Content-Type) here will override the header
+          generated by supplying C(json) for I(body_format).
     required: false
     default: null
     version_added: '2.1'
@@ -399,6 +403,8 @@ def main():
         # Encode the body unless its a string, then assume it is pre-formatted JSON
         if not isinstance(body, basestring):
             body = json.dumps(body)
+        lower_header_keys = [key.lower() for key in dict_headers]
+        if 'content-type' not in lower_header_keys:
              dict_headers['Content-Type'] = 'application/json'
 
     # Grab all the http headers. Need this hack since passing multi-values is

test/integration/targets/uri/tasks/main.yml

@@ -280,3 +280,16 @@
     status_code: 202
     method: POST
     body: foo
+
+- name: Validate body_format json does not override content-type in 2.3 or newer
+  uri:
+    url: "https://{{ httpbin_host }}/post"
+    method: POST
+    body:
+      foo: bar
+    body_format: json
+    headers:
+      'Content-Type': 'text/json'
+    return_content: true
+  register: result
+  failed_when: result.json.headers['Content-Type'] != 'text/json'