On alpine/musl, LIBS=-lbrotlicommon is needed with -lbrotlidec

[cpboyd]

I did this

LDFLAGS="-static" LIBS="-lbrotlicommon" PKG_CONFIG="pkg-config --static" ./configure --prefix=$INSTALL_PATH --disable-shared --enable-static --disable-ldap --enable-ipv6 --enable-unix-sockets --with-ssl --with-libssh2 --disable-docs --disable-manual --with-libpsl

I expected the following

This should work without specifying LIBS="-lbrotlicommon", but this check fails since it only adds LIBS="-lbrotlidec $LIBS":

  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for BrotliDecoderDecompress in -lbrotlidec" >&5
printf %s "checking for BrotliDecoderDecompress in -lbrotlidec... " >&6; }
if test ${ac_cv_lib_brotlidec_BrotliDecoderDecompress+y}
then :
  printf %s "(cached) " >&6
else $as_nop
  ac_check_lib_save_LIBS=$LIBS
LIBS="-lbrotlidec  $LIBS"
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h.  */


#ifdef __cplusplus
extern "C"
#endif
char BrotliDecoderDecompress ();
int main(void)
{
return BrotliDecoderDecompress ();
  return 0;
}
_ACEOF
if ac_fn_c_try_link "$LINENO"

This should add LIBS="-lbrotlidec -lbrotlicommon $LIBS"

curl/libcurl version

curl 8.14.1

operating system

alpine:latest

[bagder]

Because you build statically (which is a pain and will never be certain to work 100%). Does the brotli pkg-config bring the correct libs?

[vszakats]

It is picked up by pkg-config but only when passing --static. autotools and cmake don't pass this option, and it's kind of difficult to make them do it. For cmake the solution was to detect brotlicommon and always link it. This may work for autotools too. (It may result in "overlinking" in theory, but in practice it seems to work fine, and haven't dug into it further.)

[cpboyd]

@bagder For the libs, I'm using all the available dev and static packages in alpine:

apk add build-base clang openssl-dev nghttp2-dev nghttp2-static libssh2-dev libssh2-static perl \
    libpsl-dev libpsl-static libunistring-dev libunistring-static libidn2-dev libidn2-static \
    brotli-dev brotli-static zstd-dev zstd-static openssl-libs-static zlib-static 

@vszakats Ah, yeah. I figured it might be a limitation of autotools.
I was wondering if there might be a way to simply add a check for -lbrotlicommon that happens before the -lbrotlidec (if -with-brotli) since it seems that the LIBS value keeps getting appended to.

[bagder]

Calling it a "limitation of autotools" seems incorrect (but it probably does not matter). The check is done for the library it needs, and its dependencies are presumed to work with either shared library loading or pkg-config data.

[vszakats]

It isn't an autotools property indeed. This detection is done via custom configure code.
The issue rather lays in the design of static/shared selection/discovery in C toolchains
and package management.

These curl dependencies require multiple pkg-config modules:
brotli, LDAP, mbedTLS, ngtcp2

(and OpenSSL, but it also provides an umbrella pkg-config module,
so not affected.)

Of these, LDAP and mbedTLS don't have pkg-config detection
in ./configure, but ngtcp2 does, and may possibly be used as
a template to extend/fix brotli detection to also check for brotlicommon.

With a note that the order of libs is significant and the correct order
is: brotlidec, then brotlicommon.

The lack of brotlicommon detection is the reason for this workaround
to pass GHA/configure-vs-cmake: 69cda1b.
Part of patch f2adb3b #15431.

[vszakats]

@cpboyd Does this patch fix the build for you on Alpine?: #17723