Add getpeerid compat.

compat/getpeereid.c

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2022 Nicholas Marriott <nicholas.marriott@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#include <stdio.h>
+
+#include "compat.h"
+
+int
+getpeereid(int s, uid_t *uid, gid_t *gid)
+{
+#ifdef HAVE_SO_PEERCRED
+	struct ucred	uc;
+	int		len = sizeof uc;
+
+	if (getsockopt(s, SOL_SOCKET, SO_PEERCRED, &uc, &len) == -1)
+		return (-1);
+	*uid = uc.uid;
+	*gid = uc.gid;
+	return (0);
+#else
+	errno = EOPNOTSUPP;
+	return (-1);
+#endif
+}

configure.ac

@@ -160,6 +160,7 @@ AC_REPLACE_FUNCS([ \
 	freezero \
 	getdtablecount \
 	getdtablesize \
+	getpeereid \
 	getline \
 	getprogname \
 	memmem \
@@ -169,7 +170,7 @@ AC_REPLACE_FUNCS([ \
 	strlcat \
 	strlcpy \
 	strndup \
-	strsep \
+	strsep
 ])
 AC_FUNC_STRNLEN
 
@@ -684,6 +685,14 @@ AC_CHECK_DECL(
 	[#include <sys/prctl.h>]
 )
 
+# Look for setsockopt(SO_PEERCRED).
+AC_CHECK_DECL(
+	SO_PEERCRED,
+	AC_DEFINE(HAVE_SO_PEERCRED),
+	,
+	[#include <sys/socket.h>]
+)
+
 # Look for fcntl(F_CLOSEM).
 AC_CHECK_DECL(
 	F_CLOSEM,