Make sure session and default headers play nice

Before: headers = default + args + session
Now:    headers = default + session + args

Fixes #180

httpie/client.py

@@ -18,26 +18,27 @@ DEFAULT_UA = 'HTTPie/%s' % __version__
 def get_response(args, config_dir):
     """Send the request and return a `request.Response`."""
 
-    requests_kwargs = get_requests_kwargs(args)
-
-    if args.debug:
-        sys.stderr.write('\n>>> requests.request(%s)\n\n'
-                         % pformat(requests_kwargs))
-
     if not args.session and not args.session_read_only:
+        requests_kwargs = get_requests_kwargs(args)
+        if args.debug:
+            dump_request(requests_kwargs)
         response = requests.request(**requests_kwargs)
     else:
         response = sessions.get_response(
             args=args,
             config_dir=config_dir,
             session_name=args.session or args.session_read_only,
-            requests_kwargs=requests_kwargs,
             read_only=bool(args.session_read_only),
         )
 
     return response
 
 
+def dump_request(kwargs):
+    sys.stderr.write('\n>>> requests.request(%s)\n\n'
+                     % pformat(kwargs))
+
+
 def encode_headers(headers):
     # This allows for unicode headers which is non-standard but practical.
     # See: https://github.com/jakubroztocil/httpie/issues/212
@@ -47,36 +48,47 @@ def encode_headers(headers):
     )
 
 
-def get_requests_kwargs(args):
-    """Translate our `args` into `requests.request` keyword arguments."""
-
-    implicit_headers = {
+def get_default_headers(args):
+    default_headers = {
         'User-Agent': DEFAULT_UA
     }
 
     auto_json = args.data and not args.form
     # FIXME: Accept is set to JSON with `http url @./file.txt`.
     if args.json or auto_json:
-        implicit_headers['Accept'] = 'application/json'
+        default_headers['Accept'] = 'application/json'
         if args.json or (auto_json and args.data):
-            implicit_headers['Content-Type'] = JSON
-
-        if isinstance(args.data, dict):
-            if args.data:
-                args.data = json.dumps(args.data)
-            else:
-                # We need to set data to an empty string to prevent requests
-                # from assigning an empty list to `response.request.data`.
-                args.data = ''
+            default_headers['Content-Type'] = JSON
 
     elif args.form and not args.files:
         # If sending files, `requests` will set
         # the `Content-Type` for us.
-        implicit_headers['Content-Type'] = FORM
+        default_headers['Content-Type'] = FORM
+    return default_headers
 
-    for name, value in implicit_headers.items():
-        if name not in args.headers:
-            args.headers[name] = value
+
+def get_requests_kwargs(args, base_headers=None):
+    """
+    Translate our `args` into `requests.request` keyword arguments.
+
+    """
+    # Serialize JSON data, if needed.
+    data = args.data
+    auto_json = data and not args.form
+    if args.json or auto_json and isinstance(data, dict):
+        if data:
+            data = json.dumps(data)
+        else:
+            # We need to set data to an empty string to prevent requests
+            # from assigning an empty list to `response.request.data`.
+            data = ''
+
+    # Finalize headers.
+    headers = get_default_headers(args)
+    if base_headers:
+        headers.update(base_headers)
+    headers.update(args.headers)
+    headers = encode_headers(headers)
 
     credentials = None
     if args.auth:
@@ -87,14 +99,14 @@ def get_requests_kwargs(args):
     if args.cert:
         cert = args.cert
         if args.certkey:
-            cert = (cert, args.certkey)
+            cert = cert, args.certkey
 
     kwargs = {
         'stream': True,
         'method': args.method.lower(),
         'url': args.url,
-        'headers': encode_headers(args.headers),
-        'data': args.data,
+        'headers': headers,
+        'data': data,
         'verify': {
             'yes': True,
             'no': False