SOCKS error: traceback instead of error message

[barsnick]

Checklist

• I'm reporting a broken site support issue
• I've verified that I'm running youtube-dl version 2020.02.16
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar bug reports including closed ones
• I've read bugs section in FAQ

Verbose log

[barsnick@goodtimes ~]$ ~/Downloads/youtube-dl --verbose --proxy socks5://213.101.151.4:1080/ -F https://www.svtplay.se/video/25685944/den-sista-sommaren/den-sista-sommaren-sasong-1-klara-ar-fo
rsvunnen
[debug] System config: [u'--prefer-free-formats']
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'--verbose', u'--proxy', u'socks5://213.101.151.4:1080/', u'-F', u'https://www.svtplay.se/video/25685944/den-sista-sommaren/den-sista-sommaren-sasong-1-klara-ar-for
svunnen']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.02.16
[debug] Python version 2.7.15 (CPython) - Linux-4.18.19-100.fc27.x86_64-x86_64-with-fedora-27-Twenty_Seven                                                                                      
[debug] exe versions: ffmpeg 4.1, ffprobe 4.1, rtmpdump 2.4
[debug] Proxy map: {u'http': u'socks5://213.101.151.4:1080/', u'https': u'socks5://213.101.151.4:1080/'}                                                                                        
[debug] Using fake IP 78.74.51.32 (SE) as X-Forwarded-For.
[SVTPlay] 25685944: Downloading webpage
Traceback (most recent call last):
  File "/usr/lib64/python2.7/runpy.py", line 174, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib64/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/home/barsnick/Downloads/youtube-dl/__main__.py", line 19, in <module>
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/__init__.py", line 474, in main
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/__init__.py", line 464, in _real_main
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/YoutubeDL.py", line 2018, in download
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/YoutubeDL.py", line 796, in extract_info
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/extractor/common.py", line 530, in extract
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/extractor/svt.py", line 204, in _real_extract
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/extractor/common.py", line 794, in _download_webpage
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/extractor/common.py", line 660, in _download_webpage_handle
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/extractor/common.py", line 627, in _request_webpage
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/YoutubeDL.py", line 2237, in urlopen
  File "/usr/lib64/python2.7/urllib2.py", line 429, in open
    response = self._open(req, data)
  File "/usr/lib64/python2.7/urllib2.py", line 447, in _open
    '_open', req)
  File "/usr/lib64/python2.7/urllib2.py", line 407, in _call_chain
    result = func(*args)
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/utils.py", line 2728, in https_open
  File "/usr/lib64/python2.7/urllib2.py", line 1197, in do_open
    h.request(req.get_method(), req.get_selector(), req.data, headers)
  File "/usr/lib64/python2.7/httplib.py", line 1042, in request
    self._send_request(method, url, body, headers)
  File "/usr/lib64/python2.7/httplib.py", line 1082, in _send_request
    self.endheaders(body)
  File "/usr/lib64/python2.7/httplib.py", line 1038, in endheaders
    self._send_output(message_body)
  File "/usr/lib64/python2.7/httplib.py", line 882, in _send_output
    self.send(msg)
  File "/usr/lib64/python2.7/httplib.py", line 844, in send
    self.connect()
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/utils.py", line 2694, in connect
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/socks.py", line 270, in connect
    """socksocket([family[, type[, proto]]]) -> socket object
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/socks.py", line 266, in _make_proxy
    _BaseSocket._savenames.append(name)
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/socks.py", line 221, in _setup_socks5
    sock.settimeout(timeout)
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/socks.py", line 192, in _socks5_auth
    before returning the socket object.
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/socks.py", line 131, in _recv_bytes
    SOCKS5_ERRORS = { 0x01: "General SOCKS server failure",
  File "/home/barsnick/Downloads/youtube-dl/youtube_dl/socks.py", line 126, in recvall
    SOCKS4_ERRORS = { 0x5B: "Request rejected or failed",
EOFError: 2 bytes missing

Description

When providing a SOCKS proxy (SOCKS4 or SOCKS5, same issue) which isn't operational, youtube-dl gives a large traceback. It detects the issue (and reason) though, and should be able to emit a more friendly and better readable error message instead.

A "simple"

General SOCKS server failure: Request rejected or failed.

would be much more obvious if not hidden in the traceback.