libproxyprotocol: add test and options to link the library if present

Makefile.in

@@ -37,7 +37,7 @@ AR ?= ar
 CFLAGS +=-Wall -O2 -DLIBPCRE -g $(CFLAGS_COV) $(CFLAGS_SAN)
 
 
-LIBS=-lm -lpcre2-8
+LIBS=-lm -lpcre2-8 @LIBS@
 OBJS=sslh-conf.o common.o log.o sslh-main.o probe.o tls.o argtable3.o collection.o gap.o tcp-probe.o landlock.o
 OBJS_A=libsslh.a
 FORK_OBJS=sslh-fork.o $(OBJS_A)

config.h.in

@@ -6,4 +6,7 @@
 /* Landlock sandboxing Linux LSM */
 #undef HAVE_LANDLOCK
 
+/* Support for Proxy-protocol using libproxyprotocol */
+#undef HAVE_PROXYPROTOCOL
+
 #endif

configure

@@ -2163,6 +2163,7 @@ ac_config_headers="$ac_config_headers config.h"
 ac_config_files="$ac_config_files Makefile"
 
 
+have_proxyprotocol=0
 
 
 
@@ -3199,6 +3200,27 @@ then :
 fi
 
 done
+       for ac_header in proxy_protocol.h
+do :
+  ac_fn_c_check_header_compile "$LINENO" "proxy_protocol.h" "ac_cv_header_proxy_protocol_h" "$ac_includes_default"
+if test "x$ac_cv_header_proxy_protocol_h" = xyes
+then :
+  printf "%s\n" "#define HAVE_PROXY_PROTOCOL_H 1" >>confdefs.h
+ printf "%s\n" "#define HAVE_PROXYPROTOCOL 1" >>confdefs.h
+
+else $as_nop
+  have_proxyprotocol=1
+fi
+
+done
+if test $have_proxyprotocol == 0
+then
+    LIBS="$LIBS -lproxyprotocol"
+fi
+
+LIBS="$LIBS"
+
+
 cat >confcache <<\_ACEOF
 # This file is a shell script that caches the results of configure
 # tests run on this system so they can be shared between configure

configure.ac

@@ -1,9 +1,21 @@
 
 dnl Use autoconf to generate the `configure` script from this and Makefile.in
+dnl This is awkardly adapted from https://github.com/edrosten/autoconf_tutorial
+dnl (all mistakes mine)
 
 AC_INIT
 AC_CONFIG_HEADERS(config.h)
 AC_CONFIG_FILES([Makefile])
 
+have_proxyprotocol=0
 AC_CHECK_HEADERS(linux/landlock.h, AC_DEFINE(HAVE_LANDLOCK), [])
+AC_CHECK_HEADERS(proxy_protocol.h, AC_DEFINE(HAVE_PROXYPROTOCOL), [have_proxyprotocol=1])
+if test $have_proxyprotocol == 0
+then
+    LIBS="$LIBS -lproxyprotocol"
+fi
+
+LIBS="$LIBS"
+AC_SUBST([LIBS])
+
 AC_OUTPUT

doc/INSTALL.md

@@ -42,6 +42,15 @@ Dependencies
 * libev-dev, in package `libev-dev`.
   If you build a binary specifically and do not build `sslh-ev`, you don't need this.
 
+* [libproxyprotocol](https://github.com/kosmas-valianos/libproxyprotocol.git)
+  to support HAProxy's [ProxyProtocol](https://www.haproxy.org/download/2.3/doc/proxy-protocol.txt).
+  As this is not part of the distribution packages, set
+  C_INCLUDE_PATH and LD_LIBRARY_PATH to the appropriate
+  values:
+  ```
+    export C_INCLUDE_PATH=/home/user/src/libproxyprotocol/src 
+    export LD_LIBRARY_PATH=/home/user/src/libproxyprotocol/src
+  ```
 
 For OpenSUSE, these are contained in packages libconfig9 and
 libconfig-dev in repository