Only remove user agent if it matches.

In some cases we may want to provide a custom user agent

README.md

@@ -289,7 +289,11 @@ While all the other dependencies are optional, `ffmpeg` and `ffprobe` are highly
 * [**brotli**](https://github.com/google/brotli)\* or [**brotlicffi**](https://github.com/python-hyper/brotlicffi) - [Brotli](https://en.wikipedia.org/wiki/Brotli) content encoding support. Both licensed under MIT <sup>[1](https://github.com/google/brotli/blob/master/LICENSE) [2](https://github.com/python-hyper/brotlicffi/blob/master/LICENSE) </sup>
 * [**websockets**](https://github.com/aaugustin/websockets)\* - For downloading over websocket. Licensed under [BSD-3-Clause](https://github.com/aaugustin/websockets/blob/main/LICENSE)
 * [**requests**](https://github.com/psf/requests)\* - HTTP library. For HTTPS proxy and persistent connections support. Licensed under [Apache-2.0](https://github.com/psf/requests/blob/main/LICENSE)
-* [**curl_cffi**](https://github.com/yifeikong/curl_cffi)\* - Python binding for [curl-impersonate](https://github.com/lwthiker/curl-impersonate). Provides impersonation support for chrome, edge and safari. Licensed under [MIT](https://github.com/yifeikong/curl_cffi/blob/main/LICENSE)
+
+#### Impersonation
+
+The following provide support for impersonating browser requests. This may be required for some sites that employ TLS fingerprinting and other checks. 
+* [**curl_cffi**](https://github.com/yifeikong/curl_cffi)\* (recommended) - Python binding for [curl-impersonate](https://github.com/lwthiker/curl-impersonate). Provides impersonation targets for Chrome, Edge and Safari. Licensed under [MIT](https://github.com/yifeikong/curl_cffi/blob/main/LICENSE)
 
 
 ### Metadata

yt_dlp/YoutubeDL.py

@@ -157,6 +157,7 @@ from .utils import (
     windows_enable_vt_mode,
     write_json_file,
     write_string,
+    YoutubeDLError,
 )
 from .utils._utils import _YDLLogger
 from .utils.networking import (
@@ -714,9 +715,10 @@ class YoutubeDL:
         impersonate_target = self.params.get('impersonate')
         if impersonate_target is not None:
             if not self.impersonate_target_available(impersonate_target):
-                raise ValueError(
+                raise YoutubeDLError(
                     f'Impersonate target "{self.params.get("impersonate")}" is not available. '
-                    f'Use --list-impersonate-targets to see available targets.')
+                    f'Use --list-impersonate-targets to see available targets. '
+                    f'You may be missing dependencies required to support this target - check the manual for what dependencies you may need to install.')
 
         if 'list-formats' in self.params['compat_opts']:
             self.params['listformats_table'] = False
@@ -4133,8 +4135,9 @@ class YoutubeDL:
                 elif re.match(r'unsupported (?:extensions: impersonate|impersonate target)', ue.msg.lower()):
                     raise RequestError(
                         f'Impersonate target "{req.extensions["impersonate"]}" is not available.'
+                        f' See --list-impersonate-targets for available targets.'
                         f' This request requires browser impersonation, however you may be missing dependencies'
-                        f' required to support this target. See the documentation for more information.')
+                        f' required to support this target. Check the manual for what dependencies you may need to install.')
             raise
         except SSLError as e:
             if 'UNSAFE_LEGACY_RENEGOTIATION_DISABLED' in str(e):

yt_dlp/__init__.py

@@ -997,10 +997,6 @@ def _real_main(argv=None):
             ydl.to_stdout(
                 render_table(['Client', 'Version', 'OS', 'OS Version', 'Source'], rows)
             )
-            if not available_targets:
-                ydl.to_stdout('You are missing dependencies for impersonation. See the README for more info.')
-            ydl.to_stdout(
-                'If the above table is missing targets, you may be missing dependencies for impersonation.')
             return
 
         if not actual_use:

yt_dlp/networking/impersonate.py

@@ -131,7 +131,6 @@ class ImpersonateRequestHandler(RequestHandler, ABC):
         headers = self._merge_headers(request.headers)
         if self._get_request_target(request) is not None:
             # remove all headers present in std_headers
-            headers.pop('User-Agent', None)
             for header in std_headers:
                 if header in headers and std_headers[header] == headers[header]:
                     headers.pop(header, None)