Bug #15773
closed
Net::HTTP doesn't try next IP address in case of timeout
Description
This example requires to have a working IPv6 address. Since IPv6 is used in first priority, I am using it to demonstrate the problem, but it exists with plain IPv4, which will be more round-robin-style, so less deterministic to show a reproduction case. I have made two URLs that have both IPv4 and IPv6 addresses: http://ipv6.grumpycoder.net/ and http://bad-ipv6.grumpycoder.net/ - both URLs should work in an IPv6-enabled web browser, as well as curl or wget for instance. The difference is that the bad-ipv6 subdomain doesn't have an IPv6 that will actually connect. Therefore, browsers, curl and wget will fallback to using the IPv4 when the initial IPv6 connection attempt failed:
$ wget -T1 http://bad-ipv6.grumpycoder.net -O - # demonstrating using wget because its output is more clear than curl's verbose
--2019-04-16 15:56:52-- http://bad-ipv6.grumpycoder.net/
Resolving bad-ipv6.grumpycoder.net (bad-ipv6.grumpycoder.net)... 2001:bc8:3690:200::2, 62.210.214.144
Connecting to bad-ipv6.grumpycoder.net (bad-ipv6.grumpycoder.net)|2001:bc8:3690:200::2|:80... failed: Connection timed out.
Connecting to bad-ipv6.grumpycoder.net (bad-ipv6.grumpycoder.net)|62.210.214.144|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 45 [text/html]
Saving to: ‘STDOUT’
- 0%[ ] 0 --.-KB/s <html><body><h1>It works!</h1></body></html>
- 100%[=====================================================================>] 45 --.-KB/s in 0s
2019-04-16 15:56:53 (6.55 MB/s) - written to stdout [45/45]
However, in Ruby, using Net::HTTP (or OpenURI), that's not going to be the case:
$ ruby bad-ipv6.rb
http://ipv6.grumpycoder.net
<html><body><h1>It works!</h1></body></html>
http://bad-ipv6.grumpycoder.net
Net::OpenTimeout: execution expired
Contents of my test file:
require 'open-uri'
['ipv6', 'bad-ipv6'].each do |s|
url = 'http://%s.grumpycoder.net' %[s]
puts url
begin
puts open(url).read
rescue StandardError => e
puts "#{e.class}: #{e.message}"
next
end
end
The proper behavior should be to retry the next IP address and exhaust all of the IPs in the DNS resolution results before throwing out an error.
Updated by naruse (Yui NARUSE) over 5 years ago
- Status changed from Open to Rejected
In general resolving DNS is done by libc (getaddrinfo) and Ruby just uses their result.
Therefore it is not a bug and won't be a small feature.
Updated by nicolasnoble (Nicolas Noble) over 5 years ago
I thought long and hard about how to reply to this.
Let's put it this way: the fact that you are using glibc isn't the problem at all. The fact that you are badly using its results is.
Any other big piece of code out there that is doing any sort of abstraction is going to be establishing an internet connection will retry on all the entries returned by the DNS, in a round robin fashion. Ruby is the only one that I know of that doesn't do that. In fact, if you run my reproduction case on jruby, it will work correctly. If anything, the bug should be that jruby and ruby are acting differently.
It is important to realize that when one is attempting to write any abstraction layer, there's an expectation of correctness. In this one case, the current chosen model of abstraction means that the http downloader system will catastrophically fail to work in certain conditions without any sort of recourse by the user of the abstraction.
Updated by guss77 (Oded Arbel) over 4 years ago
I've encountered this issue as well. My workaround - in case someone else has the same problem:
require 'net/http'
require 'resolv'
# ...
url = URI.parse(url) unless url.is_a?(URI)
addrs = Resolv::DNS.new.getaddresses(url.host).sort { |a,b| b.class.to_s <=> a.class.to_s }.collect { |ip| ip.to_s }
begin
response = Net::HTTP.start(url.host, url.port, use_ssl: url.scheme == 'https', open_timeout: 3, ipaddr: addrs.shift) do |http|
http.request(Net::HTTP::Get.new(url.request_uri))
end
rescue Timeout::Error => e
retry unless addrs.empty?
raise e
end
Updated by benlangfeld (Ben Langfeld) over 4 years ago
naruse (Yui NARUSE) wrote in #note-1:
In general resolving DNS is done by libc (getaddrinfo) and Ruby just uses their result.
Therefore it is not a bug and won't be a small feature.
RFC3484 (https://www.ietf.org/rfc/rfc3484.txt) very clearly states:
Well-behaved applications SHOULD iterate through the list of
addresses returned from getaddrinfo() until they find a working
address.
That Ruby does not do this should be considered a bug, and I would ask that you please re-open this ticket on that basis. Ruby is in contravention of the RFC and the documentation of getaddrinfo(3). This is not a missing feature; Ruby is broken. Note that I am not asking that anyone fix this; I will prepare a fix. All I ask is that this ticket be acknowledged as valid and not rejected based on misunderstanding it.
Updated by phluid61 (Matthew Kerwin) over 4 years ago
benlangfeld (Ben Langfeld) wrote in #note-4:
RFC3484 (https://www.ietf.org/rfc/rfc3484.txt) very clearly states:
Minor point, I don't think it affects much, but RFC 3484 is obsolete and is replaced by RFC 6724 https://tools.ietf.org/html/rfc6724
Cheers
Updated by benlangfeld (Ben Langfeld) over 4 years ago
phluid61 (Matthew Kerwin) wrote in #note-5:
benlangfeld (Ben Langfeld) wrote in #note-4:
RFC3484 (https://www.ietf.org/rfc/rfc3484.txt) very clearly states:
Minor point, I don't think it affects much, but RFC 3484 is obsolete and is replaced by RFC 6724 https://tools.ietf.org/html/rfc6724
Cheers
Thank you for pointing that out. RFC 6724 is even more explicit:
Well-behaved applications SHOULD NOT simply use the first address
returned from an API such as getaddrinfo() and then give up if it
fails. For many applications, it is appropriate to iterate through
the list of addresses returned from getaddrinfo() until a working
address is found. For other applications, it might be appropriate to
try multiple addresses in parallel (e.g., with some small delay in
between) and use the first one to succeed.