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CURLOPT_IPRESOLVE: preventing wrong IP version from being used

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In some situations, it was possible that a transfer was setup to
use an specific IP version, but due do DNS caching or connection
reuse, it ended up using a different IP version from requested.

This commit changes the effect of CURLOPT_IPRESOLVE from simply
restricting address resolution to preventing the wrong connection
type being used, when choosing a connection from the pool, and
to restricting what addresses could be used when establishing
a new connection.

It is important that all addresses versions are resolved, even if
not used in that transfer in particular, because the result is
cached, and could be useful for a different transfer with a
different CURLOPT_IPRESOLVE setting.

Closes #6853
This commit is contained in:
Lucas Clemente Vella 2021-04-24 20:04:53 +01:00 • committed by Daniel Stenberg
parent ac54b10933
commit 84d2839740
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GPG key ID: 5CC908FDB71E12C2
11 changed files with 69 additions and 100 deletions
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2
docs/libcurl/curl_easy_setopt.3
View file

@ -494,7 +494,7 @@ Timeout for the connection phase. See \fICURLOPT_CONNECTTIMEOUT(3)\fP
.IP CURLOPT_CONNECTTIMEOUT_MS
Millisecond timeout for the connection phase. See \fICURLOPT_CONNECTTIMEOUT_MS(3)\fP
.IP CURLOPT_IPRESOLVE
IP version to resolve to. See \fICURLOPT_IPRESOLVE(3)\fP
IP version to use. See \fICURLOPT_IPRESOLVE(3)\fP
.IP CURLOPT_CONNECT_ONLY
Only connect, nothing else. See \fICURLOPT_CONNECT_ONLY(3)\fP
.IP CURLOPT_USE_SSL

13
docs/libcurl/opts/CURLOPT_IPRESOLVE.3
View file

@ -29,14 +29,15 @@ CURLOPT_IPRESOLVE \- specify which IP protocol version to use
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_IPRESOLVE, long resolve);
.SH DESCRIPTION
Allows an application to select what kind of IP addresses to use when
resolving host names. This is only interesting when using host names that
resolve addresses using more than one version of IP. The allowed values are:
establishing a connection or choosing one from the connection pool. This is
interesting when using host names that resolve addresses using more than
one version of IP. The allowed values are:
.IP CURL_IPRESOLVE_WHATEVER
Default, resolves addresses to all IP versions that your system allows.
Default, can use addresses of all IP versions that your system allows.
.IP CURL_IPRESOLVE_V4
Resolve to IPv4 addresses.
Uses only IPv4 addresses.
.IP CURL_IPRESOLVE_V6
Resolve to IPv6 addresses.
Uses only IPv6 addresses.
.SH DEFAULT
CURL_IPRESOLVE_WHATEVER
.SH PROTOCOLS
@ -47,7 +48,7 @@ CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
/* resolve host name using IPv6-names only */
/* of all addresses example.com resolves to, only IPv6 ones are used */
curl_easy_setopt(curl, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V6);
ret = curl_easy_perform(curl);

4
docs/libcurl/opts/CURLOPT_RESOLVE.3
View file

@ -57,8 +57,8 @@ this entry will be removed and a new entry will be created. This is because
the old entry may have have different addresses or a different time-out
setting.
The provided ADDRESS set by this option will be used even if
\fICURLOPT_IPRESOLVE(3)\fP is set to make libcurl use another IP version.
An ADDRESS provided by this option will only be use if not restricted by
the setting of \fICURLOPT_IPRESOLVE(3)\fP to a different IP version.
Remove names from the DNS cache again, to stop providing these fake resolves,
by including a string in the linked list that uses the format