when youtube-dl sends too many dns request to find video quality, dns server blocks the host running youtube-dl temporarily

[ghost]

The issue at hand is that when youtube-dl is trying more than one quality paramter on its own, it keeps making DNS-requests, because those requests became too many in a short span of time, the host running youtube-dl gets any DNS requests from it blocked.
please look into it.

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• Bug report (encountered problems with youtube-dl)
• Site support request (request for adding support for a new site)
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If the purpose of this issue is a bug report, site support request or you are not completely sure provide the full verbose output as follows:

Add -v flag to your command line you run youtube-dl with, copy the whole output and insert it here. It should look similar to one below (replace it with your log inserted between triple ```):

$ youtube-dl -v <your command line>
[debug] System config: []
[debug] User config: []
[debug] Command-line args: [u'-v', u'http://www.youtube.com/watch?v=BaW_jenozKcj']
[debug] Encodings: locale cp1251, fs mbcs, out cp866, pref cp1251
[debug] youtube-dl version 2017.07.23
[debug] Python version 2.7.11 - Windows-2003Server-5.2.3790-SP2
[debug] exe versions: ffmpeg N-75573-g1d0487f, ffprobe N-75573-g1d0487f, rtmpdump 2.4
[debug] Proxy map: {}
...
<end of log>

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If the purpose of this issue is a site support request please provide all kinds of example URLs support for which should be included (replace following example URLs by yours):

• Single video: https://www.youtube.com/watch?v=BaW_jenozKc
• Single video: https://youtu.be/BaW_jenozKc
• Playlist: https://www.youtube.com/playlist?list=PL4lCao7KL_QFVb7Iudeipvc2BCavECqzc

Note that youtube-dl does not support sites dedicated to copyright infringement. In order for site support request to be accepted all provided example URLs should not violate any copyrights.

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Description of your issue, suggested solution and other information

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[yan12125]

Which URL are you trying to download? Please paste a verbose log.

[ghost]

its not the URL i'm trying to download that is blocking me, it is my DNS server that blocks me when there are too many DNS requests happening when youtube-dl is running and trying to guess a quality for the video its downloading.

[dstftw]

Fix your DNS server obviously. youtube-dl is not any different from any other software in making DNS requests.

[ghost]

is it possible to make youtube-dl retain the answers for the DNS queries it makes for a short period of time 4 to 10 seconds?
I have no permission/control over my DNS server

[yan12125]

retain the answers for the DNS queries it makes for a short period

That's a system-level work, where upper applications like youtube-dl or even Python can't do much.

By the way, you may want to check out my proof-of-concept patch yan12125/youtube-dl@0cdc798 that adds an option --dns-servers. You can then choose a caching DNS server like dnsmasq or an external normal DNS server.

[remitamine]

a better solution would be to add support for HTTP persistent connection(HTTP keep-alive), it would help to improve performance in general and mostly for http/https fragment downloading.

[yan12125]

Persistent HTTP sounds better, but seems it's not going to be implemented in CPython in near future (http://bugs.python.org/issue9740)

[remitamine]

but seems it's not going to be implemented in CPython in near future (http://bugs.python.org/issue9740)

requests does supports HTTP persistent connection using the urllib3 Connection pooling, so it's possible to add support without depending on CPython implementation.

[yan12125]

That's a great suggestion. However, the culture in youtube-dl is reducing external dependencies unless there's a BIG problem. I vote for changing it if there's going to be a discussion.

[remitamine]

However, the culture in youtube-dl is reducing external dependencies unless there's a BIG problem. I vote for changing it if there's going to be a discussion.

it doesn't have to be a hard dependency, it can be used as an optional dependecy by creating a wrapper that will use urllib3 if it's available and fallback to urllib/urllib2(like what's been done with pycrypto).

[yan12125]

I'm afraid that co-existing of two backends would make codes extremely complicated and unreadable. If it turns out that switching between urllib/urllib2 and urllib3 is easy (ex: without numerous function wrappers), that would be a good choice.

[remitamine]

there is actually an old approche compatible with urllib/urllib2 by using a diffrent handler, but as the code is old, so it might require to be updated, it was used by urlgrabber before switching to pycurl(https://stackoverflow.com/questions/1037406/python-urllib2-with-keep-alive).
no sure about the compatibilty between public domain and LGPL.

[yan12125]

IMO it's better to use mature libraries like requests/urllib3 instead of importing rarely tested codes from random places. Also, using only urllib3 is better than supporting two backends. I hope the culture here can change one day.

About the license issue:

1. IIRC LGPL codes can't be used in public domain projects
2. Depending on libraries with incompatible licenses is never a problem. The whole code base remains public domain. In released binaries, only youtube-dl.exe bundles external dependencies, and it's already not pure public domain as it contains Python runtime. Adding LGPL files does not make things worse.