socket: introduce `SOCK_EAGAIN()` and use it by vszakats · Pull Request #21992 · curl/curl

vszakats · 2026-06-12T14:45:30Z

To contain the logic of checking for both EWOULDBLOCK and/or EAGAIN
depending on platform/availability. Also to avoid checking for both if
they mapp to the same value, and to avoid PP guards around use.

This also ensures EAGAIN is consistently not checked on Windows, where
headers defined it, but SOCKERRNO never returns it, because curl maps
it to WSAGetLastError().

If they map to the same value, checking them both in an if expression
trips GCC warning -Wlogical-op (the same way it triggers duplicate
case value error in switch).

Also:

replace two switch() statements with the new macro.
tests/server/sws: make two outliers use the new macro that were only
checking for EWOULDBLOCK before this patch, in connect_to().
move variables to the left-side of expressions, where missing.
rustls: use a variant of this macro that uses raw EWOULDBLOCK.
Tried tracing it back to the origins, but I couldn't figure out if
this is working as expected on all supported Windows versions in
Rust. It seems to be using GetLastError(), according to
https://docs.rs/system_error/0.2.0/system_error/, which would be
probably incorrect.

Notes:

it's probably a good idea to assign SOCKERRNO to a variable before
passing it to this macro.

Cherry-picked from #21893

https://github.com/curl/curl/pull/21992/files?w=1

better name than SOCK_EWOULDBLOCK_EAGAIN() for the macro? I figure it's nice to include both names
it's covering, but don't feel strongly about it. → [trying SOCK_EAGAIN() for short]
cf-socket: maybe turn a 3-way switch into an if and use this macro? [DONE, also for another instance]
there was indication in code/history that some rare platforms may not
have EWOULDBLOCK but do have EAGAIN. This wasn't consistently
supported and this patch leaves it as-is. If this causes an issue, it
should be easy to support this case with the new macro.
Feature request : Improve portability libssh2/libssh2#171
Add an EWOULDBLOCK check for better portability libssh2/libssh2#172
libssh2/libssh2@92f7686
On a second read this seem overkill, and EWOULDBLOCK was added for VMS-only
then later extended to more platforms but keeping a check for EWOULDBLOCK.
POSIX should have this macro. Also curl never handled a build without it.

``` /Users/runner/work/curl/curl/lib/cf-socket.c: In function 'cf_socket_send': /Users/runner/work/curl/curl/lib/cf-socket.c:1498:36: error: logical 'or' of equal expressions [-Werror=logical-op] 1498 | (SOCKEWOULDBLOCK == sockerr) || | ^~ /Users/runner/work/curl/curl/lib/cf-socket.c: In function 'cf_socket_recv': /Users/runner/work/curl/curl/lib/cf-socket.c:1564:36: error: logical 'or' of equal expressions [-Werror=logical-op] 1564 | (SOCKEWOULDBLOCK == sockerr) || | ^~ In file included from /Users/runner/work/curl/curl/bld/lib/CMakeFiles/libcurl_shared.dir/Unity/unity_0_c.c:331: /Users/runner/work/curl/curl/lib/socketpair.c: In function 'Curl_wakeup_signal': /Users/runner/work/curl/curl/lib/socketpair.c:329:35: error: logical 'or' of equal expressions [-Werror=logical-op] 329 | if((err == SOCKEWOULDBLOCK) || (err == EAGAIN)) | ^~ ```

``` /Users/runner/work/curl/curl/lib/socketpair.c:329:15: error: equality comparison with extraneous parentheses [-Werror,-Wparentheses-equality] if((err == SOCKEWOULDBLOCK) ~~~~^~~~~~~~~~~~~~~~~~ /Users/runner/work/curl/curl/lib/socketpair.c:329:15: note: remove extraneous parentheses around the comparison to silence this warning if((err == SOCKEWOULDBLOCK) ~ ^ ~ /Users/runner/work/curl/curl/lib/socketpair.c:329:15: note: use '=' to turn this equality comparison into an assignment if((err == SOCKEWOULDBLOCK) ^~ = /Users/runner/work/curl/curl/lib/socketpair.c:359:21: error: equality comparison with extraneous parentheses [-Werror,-Wparentheses-equality] if((SOCKERRNO == SOCKEWOULDBLOCK) ~~~~~~~~~~^~~~~~~~~~~~~~~~~~ /Users/runner/work/curl/curl/lib/socketpair.c:359:21: note: remove extraneous parentheses around the comparison to silence this warning if((SOCKERRNO == SOCKEWOULDBLOCK) ~ ^ ~ /Users/runner/work/curl/curl/lib/socketpair.c:359:21: note: use '=' to turn this equality comparison into an assignment if((SOCKERRNO == SOCKEWOULDBLOCK) ^~ = 2 errors generated. ``` https://github.com/curl/curl/actions/runs/27107980068/job/80000462156?pr=21893

…idy up)

comparing to raw EWOULDBLOCK may not be working as expected on Windows. Based on this: https://doc.rust-lang.org/std/io/struct.Error.html#method.last_os_error Rust doesn't seem to be returning the socket error on Windows, but a GetLastError() which does not return EWOULDBLOCK or SOCKEWOULDBLOCK.

There was an unprotected unconditional use in src. Also in vquic and socketpair, on conditions.

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Follow-up to 879a151 #21992 Closes #21893

vszakats added 28 commits June 12, 2026 16:34

silence 2

935c724

socketpair.c move variable to the left-side of equality expression (t…

b970538

…idy up)

apply to sws

fcb7a9f

rustls

deb40d1

vquic

921c610

sws shorten

7f931de

socketpair shorten

c7b4f96

cf-socket shorten

14cd3ff

maybe

3951d04

socketpair.c one more

7bb5a09

rely more on EWOULDBLOCK

fb0d07e

vquic.c guard off EAGAIN as in cf-socket.c

e23f4a1

move raw macros to rustls

796ac64

winsock

86bdd0a

rename macros

54ced28

there is EAGAIN on Windows nowadays, but never returned by SOCKERRNO

6e44399

vquic.c sync guard with cf-socket.c

78b3de6

rest of code sync guard with cf-socket.c

670e3fc

drop defined(EAGAIN) checks everywhere

8a192a5

There was an unprotected unconditional use in src. Also in vquic and socketpair, on conditions.

move variable to the left-side of equality expression

613056a

merge checks on Win/non-Win

d2687af

socketpair.c use interim err var in Curl_wakeup_consume

6ae0917

indent

14d5cab

socketpair.c use interim err var in Curl_wakeup_consume f

ac9dba0

inline two comments

ffb9991

github-actions Bot added cmdline tool tests labels Jun 12, 2026

sws.c also check for EAGAIN in connect_to()

7b1458c

vszakats force-pushed the eagain branch from 9e8a271 to 7b1458c Compare June 12, 2026 15:25

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vszakats added 3 commits June 12, 2026 17:37

vquic.c use new local var in err msgs

7556b07

comment nits

06c8744

comment nits 2

483c140

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comment cleanups

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shorten name

4da0f86

vszakats changed the title ~~socket: introduce SOCK_EWOULDBLOCK_EAGAIN(), use it~~ socket: introduce SOCK_EAGAIN(), use it Jun 12, 2026

vszakats added 5 commits June 12, 2026 22:11

sp

238a0dd

cleanup

0dae05b

dedupe comments

17a823b

drop therefore

9550e9c

name new vars sockerr

dba77a8

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Comment thread lib/curl_setup.h

Comment thread lib/vtls/rustls.c

vszakats changed the title ~~socket: introduce SOCK_EAGAIN(), use it~~ socket: introduce SOCK_EAGAIN() and use it Jun 12, 2026

vszakats closed this in 879a151 Jun 12, 2026

vszakats deleted the eagain branch June 12, 2026 21:28

vszakats added a commit that referenced this pull request Jun 12, 2026

build: enable -Wlogical-op picky warning for GCC 4.4+

c951368

Follow-up to 879a151 #21992 Closes #21893

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socket: introduce `SOCK_EAGAIN()` and use it#21992

socket: introduce `SOCK_EAGAIN()` and use it#21992
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vszakats commented Jun 12, 2026 •

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vszakats commented Jun 12, 2026 •

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