Implement `--add-header` without modifying `std_headers`

Closes #2526, #1614

1 files changed, 6 insertions, 1 deletions

diff --git a/yt_dlp/utils.py b/yt_dlp/utils.py
index ef2c6bb24..be0c69d8f 100644
--- a/yt_dlp/utils.py
+++ b/yt_dlp/utils.py
@@ -1372,7 +1372,7 @@ class YoutubeDLHandler(compat_urllib_request.HTTPHandler):
         if url != url_escaped:
             req = update_Request(req, url=url_escaped)
 
-        for h, v in std_headers.items():
+        for h, v in self._params.get('http_headers', std_headers).items():
             # Capitalize is needed because of Python bug 2275: http://bugs.python.org/issue2275
             # The dict keys are capitalized because of this bug by urllib
             if h.capitalize() not in req.headers:
@@ -5436,3 +5436,8 @@ class WebSocketsWrapper():
 
 
 has_websockets = bool(compat_websockets)
+
+
+def merge_headers(*dicts):
+    """Merge dicts of network headers case insensitively, prioritizing the latter ones"""
+    return {k.capitalize(): v for k, v in itertools.chain.from_iterable(map(dict.items, dicts))}