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connect: Fix happy eyeballs logic for IPv4-only builds

Browse Source 
Bug: https://github.com/bagder/curl/pull/168

(trynextip)
- Don't try the "other" protocol family unless IPv6 is available. In an
IPv4-only build the other family can only be IPv6 which is unavailable.

This change essentially stops IPv4-only builds from attempting the
"happy eyeballs" secondary parallel connection that is supposed to be
used by the "other" address family.

Prior to this change in IPv4-only builds that secondary parallel
connection attempt could be erroneously used by the same family (IPv4)
which caused a bug where every address after the first for a host could
be tried twice, often in parallel. This change fixes that bug. An
example of the bug is shown below.

Assume MTEST resolves to 3 addresses 127.0.0.2, 127.0.0.3 and 127.0.0.4:

* STATE: INIT => CONNECT handle 0x64f4b0; line 1046 (connection #-5000)
* Rebuilt URL to: http://MTEST/
* Added connection 0. The cache now contains 1 members
* STATE: CONNECT => WAITRESOLVE handle 0x64f4b0; line 1083
(connection #0)
*   Trying 127.0.0.2...
* STATE: WAITRESOLVE => WAITCONNECT handle 0x64f4b0; line 1163
(connection #0)
*   Trying 127.0.0.3...
* connect to 127.0.0.2 port 80 failed: Connection refused
*   Trying 127.0.0.3...
* connect to 127.0.0.3 port 80 failed: Connection refused
*   Trying 127.0.0.4...
* connect to 127.0.0.3 port 80 failed: Connection refused
*   Trying 127.0.0.4...
* connect to 127.0.0.4 port 80 failed: Connection refused
* connect to 127.0.0.4 port 80 failed: Connection refused
* Failed to connect to MTEST port 80: Connection refused
* Closing connection 0
* The cache now contains 0 members
* Expire cleared
curl: (7) Failed to connect to MTEST port 80: Connection refused

The bug was born in commit bagder/curl@2d435c7.
This commit is contained in:
Jay Satiro 2015-03-15 15:30:17 -04:00 committed by Daniel Stenberg
parent 918e040953
commit 059b3a5770
1 changed files with 2 additions and 4 deletions
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6
lib/connect.c
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@ -559,16 +559,14 @@ static CURLcode trynextip(struct connectdata *conn,
family = conn->tempaddr[tempindex]->ai_family;
ai = conn->tempaddr[tempindex]->ai_next;
}
#ifdef ENABLE_IPV6
else if(conn->tempaddr[0]) {
/* happy eyeballs - try the other protocol family */
int firstfamily = conn->tempaddr[0]->ai_family;
#ifdef ENABLE_IPV6
family = (firstfamily == AF_INET) ? AF_INET6 : AF_INET;
#else
family = firstfamily;
#endif
ai = conn->tempaddr[0]->ai_next;
}
#endif
while(ai) {
if(conn->tempaddr[other]) {