Use POSIX fallbacks on non-OpenBSD instead of compat functions

Replace the compat strlcpy/closefrom/strtonum functions with
macros that use POSIX equivalents (snprintf, close loop,
strtol wrapper).  This avoids conflicts with system header
declarations that vary across glibc versions, musl, and
macOS.  On OpenBSD, the native BSD functions are used
directly.

Drop accept4(SOCK_NONBLOCK) which required _GNU_SOURCE on
glibc.  The fallback accept() + set_nonblock() works on
all platforms.

Author: renaudallard

thinproxy.c

@@ -24,9 +24,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef _GNU_SOURCE
-#define _GNU_SOURCE
-#endif
+#define _DEFAULT_SOURCE
 
 #include <sys/types.h>
 #include <sys/socket.h>
@@ -41,7 +39,6 @@
 #include <errno.h>
 #include <stdarg.h>
 #include <stdio.h>
-#include <limits.h>
 #include <stdlib.h>
 #include <string.h>
 #include <strings.h>
@@ -68,75 +65,26 @@
 /* ---- portability ---- */
 
 #ifndef __dead
-#if defined(__OpenBSD__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
-    defined(__DragonFly__)
-/* provided by <sys/cdefs.h> */
-#else
 #define __dead	__attribute__((__noreturn__))
 #endif
-#endif
 
-#ifndef HAVE_STRLCPY
-#if defined(__OpenBSD__) || defined(__FreeBSD__) || defined(__APPLE__) || \
-    defined(__NetBSD__) || defined(__DragonFly__) || \
-    (defined(__GLIBC__) && (__GLIBC__ > 2 || \
-    (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 38))) || \
-    (defined(__linux__) && !defined(__GLIBC__))	/* musl */
-#define HAVE_STRLCPY
-#endif
-#endif
-
-#ifndef HAVE_CLOSEFROM
-#if defined(__OpenBSD__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
-    defined(__APPLE__) || \
-    (defined(__GLIBC__) && (__GLIBC__ > 2 || \
-    (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 34)))
-#define HAVE_CLOSEFROM
-#endif
-#endif
-
-#ifndef HAVE_STRTONUM
-#if defined(__OpenBSD__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
-    defined(__DragonFly__) || \
-    (defined(__GLIBC__) && (__GLIBC__ > 2 || \
-    (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 39)))
-#define HAVE_STRTONUM
-#endif
-#endif
-
-#ifndef HAVE_STRLCPY
-static size_t
-strlcpy(char *dst, const char *src, size_t dstsize)
-{
-	size_t n;
-
-	for (n = 0; n + 1 < dstsize && src[n] != '\0'; n++)
-		dst[n] = src[n];
-	if (dstsize > 0)
-		dst[n] = '\0';
-	while (src[n] != '\0')
-		n++;
-	return n;
-}
-#endif
-
-#ifndef HAVE_CLOSEFROM
+/*
+ * On non-OpenBSD, provide inline wrappers that use POSIX
+ * equivalents instead of BSD functions, avoiding compat
+ * function conflicts with varying system headers.
+ */
+#ifndef __OpenBSD__
+#define strlcpy(d, s, n)	(size_t)snprintf((d), (n), "%s", (s))
 static void
-closefrom(int lowfd)
+closefrom_compat(int lowfd)
 {
-	int fd, maxfd;
-
-	maxfd = (int)sysconf(_SC_OPEN_MAX);
-	if (maxfd < 0)
-		maxfd = 256;
-	for (fd = lowfd; fd < maxfd; fd++)
+	int fd;
+	for (fd = lowfd; fd < MAX_FDS; fd++)
 		(void)close(fd);
 }
-#endif
-
-#ifndef HAVE_STRTONUM
+#define closefrom	closefrom_compat
 static long long
-strtonum(const char *numstr, long long minval, long long maxval,
+strtonum_compat(const char *numstr, long long minval, long long maxval,
     const char **errstrp)
 {
 	long long ll;
@@ -146,16 +94,17 @@ strtonum(const char *numstr, long long minval, long long maxval,
 	ll = strtoll(numstr, &ep, 10);
 	if (numstr == ep || *ep != '\0')
 		*errstrp = "invalid";
-	else if ((ll == LLONG_MIN && errno == ERANGE) || ll < minval)
+	else if (ll < minval)
 		*errstrp = "too small";
-	else if ((ll == LLONG_MAX && errno == ERANGE) || ll > maxval)
+	else if (ll > maxval)
 		*errstrp = "too large";
 	else {
 		*errstrp = NULL;
 		return ll;
 	}
 	return 0;
 }
+#define strtonum	strtonum_compat
 #endif
 
 #define ERR_400	"HTTP/1.1 400 Bad Request\r\nConnection: close\r\n\r\n"
@@ -1574,11 +1523,7 @@ accept_conn(int lfd)
 	struct conn *c;
 
 	sl = sizeof(ss);
-#ifdef SOCK_NONBLOCK
-	fd = accept4(lfd, (struct sockaddr *)&ss, &sl, SOCK_NONBLOCK);
-#else
 	fd = accept(lfd, (struct sockaddr *)&ss, &sl);
-#endif
 	if (fd == -1) {
 		if (errno == EMFILE || errno == ENFILE) {
 			logmsg(LOG_ERR, "accept: %s", strerror(errno));
@@ -1610,12 +1555,10 @@ accept_conn(int lfd)
 		return;
 	}
 
-#ifndef SOCK_NONBLOCK
 	if (set_nonblock(fd) == -1) {
 		close(fd);
 		return;
 	}
-#endif
 
 	on = 1;
 	(void)setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof(on));