[nft PATCH v3 2/3] nftutils: add wrappers for getprotoby{name,number}_r(), getservbyport_r()

[Thomas Haller <thaller@redhat.com>]

We should aim to use the thread-safe variants of getprotoby{name,number}
and getservbyport(). However, they may not be available with other libc,
so it requires a configure check. As that is cumbersome, add wrappers
that do that at one place.

Signed-off-by: Thomas Haller <thaller@redhat.com>
---
 configure.ac   |  4 +++
 src/nftutils.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++
 src/nftutils.h | 16 +++++++++
 3 files changed, 117 insertions(+)

diff --git a/configure.ac b/configure.ac
index b0201ac3528e..42f0dc4cf392 100644
--- a/configure.ac
+++ b/configure.ac
@@ -108,6 +108,10 @@ AC_DEFINE([HAVE_LIBJANSSON], [1], [Define if you have libjansson])
 ])
 AM_CONDITIONAL([BUILD_JSON], [test "x$with_json" != xno])
 
+AC_CHECK_DECLS([getprotobyname_r, getprotobynumber_r, getservbyport_r], [], [], [[
+#include <netdb.h>
+]])
+
 AC_CONFIG_FILES([					\
 		Makefile				\
 		libnftables.pc				\
diff --git a/src/nftutils.c b/src/nftutils.c
index 758283d1b650..13f879ddc5c7 100644
--- a/src/nftutils.c
+++ b/src/nftutils.c
@@ -3,3 +3,100 @@
 #include <config.h>
 
 #include "nftutils.h"
+
+#include <netdb.h>
+#include <string.h>
+#include <stdint.h>
+
+/* Buffer size used for getprotobynumber_r() and similar. The manual comments
+ * that a buffer of 1024 should be sufficient "for most applications"(??), so
+ * let's double it.  It still fits reasonably on the stack, so no need to
+ * choose a smaller one. */
+#define NETDB_BUFSIZE 2048
+
+bool nft_getprotobynumber(int proto, char *out_name, size_t name_len)
+{
+	const struct protoent *result;
+
+#if HAVE_DECL_GETPROTOBYNUMBER_R
+	struct protoent result_buf;
+	char buf[NETDB_BUFSIZE];
+	int r;
+
+	r = getprotobynumber_r(proto,
+	                       &result_buf,
+	                       buf,
+	                       sizeof(buf),
+	                       (struct protoent **) &result);
+	if (r != 0 || result != &result_buf)
+		result = NULL;
+#else
+	result = getprotobynumber(proto);
+#endif
+
+	if (!result)
+		return false;
+
+	if (strlen(result->p_name) >= name_len)
+		return false;
+	strcpy(out_name, result->p_name);
+	return true;
+}
+
+int nft_getprotobyname(const char *name)
+{
+	const struct protoent *result;
+
+#if HAVE_DECL_GETPROTOBYNAME_R
+	struct protoent result_buf;
+	char buf[NETDB_BUFSIZE];
+	int r;
+
+	r = getprotobyname_r(name,
+	                     &result_buf,
+	                     buf,
+	                     sizeof(buf),
+	                     (struct protoent **) &result);
+	if (r != 0 || result != &result_buf)
+		result = NULL;
+#else
+	result = getprotobyname(name);
+#endif
+
+	if (!result)
+		return -1;
+
+	if (result->p_proto < 0 || result->p_proto > UINT8_MAX)
+		return -1;
+	return (uint8_t) result->p_proto;
+}
+
+bool nft_getservbyport(int port, const char *proto, char *out_name, size_t name_len)
+{
+	const struct servent *result;
+
+#if HAVE_DECL_GETSERVBYPORT_R
+	struct servent result_buf;
+	char buf[NETDB_BUFSIZE];
+	int r;
+
+	r = getservbyport_r(port,
+	                    proto,
+	                    &result_buf,
+	                    buf,
+	                    sizeof(buf),
+	                    (struct servent**) &result);
+	if (r != 0 || result != &result_buf)
+		result = NULL;
+#else
+	result = getservbyport(port, proto);
+#endif
+
+	if (!result)
+		return false;
+
+	if (strlen(result->s_name) >= name_len)
+		return false;
+	strcpy(out_name, result->s_name);
+	return true;
+}
diff --git a/src/nftutils.h b/src/nftutils.h
index 9ad68d55ce47..cb584b9ca32b 100644
--- a/src/nftutils.h
+++ b/src/nftutils.h
@@ -2,4 +2,20 @@
 #ifndef NFTUTILS_H
 #define NFTUTILS_H
 
+#include <stdbool.h>
+#include <stddef.h>
+
+/* The maximum buffer size for (struct protoent).p_name. It is excessively large,
+ * while still reasonably fitting on the stack. Arbitrarily chosen. */
+#define NFT_PROTONAME_MAXSIZE 1024
+
+bool nft_getprotobynumber(int number, char *out_name, size_t name_len);
+int nft_getprotobyname(const char *name);
+
+/* The maximum buffer size for (struct servent).s_name. It is excessively large,
+ * while still reasonably fitting on the stack. Arbitrarily chosen. */
+#define NFT_SERVNAME_MAXSIZE 1024
+
+bool nft_getservbyport(int port, const char *proto, char *out_name, size_t name_len);
+
 #endif /* NFTUTILS_H */
-- 
2.41.0