tree-wide: make format_ifname() or friends return negative errno on failure

Also,
- drop unnecessary +1 from buffer size, as IF_NAMESIZE or IFNAMSIZ
  includes the nul at the end.
- format_ifname() does not update buffer on failure,
- introduces format_ifname_alloc(), FORMAT_IFNAME(), and their friends.

src/basic/format-util.c

@@ -3,23 +3,43 @@
 #include "format-util.h"
 #include "memory-util.h"
 #include "stdio-util.h"
+#include "strxcpyx.h"
+
+assert_cc(STRLEN("%") + DECIMAL_STR_MAX(int) <= IF_NAMESIZE);
+int format_ifname_full(int ifindex, FormatIfnameFlag flag, char buf[static IF_NAMESIZE]) {
+        if (ifindex <= 0)
+                return -EINVAL;
 
-assert_cc(DECIMAL_STR_MAX(int) + 1 <= IF_NAMESIZE + 1);
-char *format_ifname_full(int ifindex, char buf[static IF_NAMESIZE + 1], FormatIfnameFlag flag) {
-        /* Buffer is always cleared */
-        memzero(buf, IF_NAMESIZE + 1);
         if (if_indextoname(ifindex, buf))
-                return buf;
+                return 0;
 
         if (!FLAGS_SET(flag, FORMAT_IFNAME_IFINDEX))
-                return NULL;
+                return -errno;
 
         if (FLAGS_SET(flag, FORMAT_IFNAME_IFINDEX_WITH_PERCENT))
-                assert(snprintf_ok(buf, IF_NAMESIZE + 1, "%%%d", ifindex));
+                assert(snprintf_ok(buf, IF_NAMESIZE, "%%%d", ifindex));
         else
-                assert(snprintf_ok(buf, IF_NAMESIZE + 1, "%d", ifindex));
+                assert(snprintf_ok(buf, IF_NAMESIZE, "%d", ifindex));
 
-        return buf;
+        return 0;
+}
+
+int format_ifname_full_alloc(int ifindex, FormatIfnameFlag flag, char **ret) {
+        char buf[IF_NAMESIZE], *copy;
+        int r;
+
+        assert(ret);
+
+        r = format_ifname_full(ifindex, flag, buf);
+        if (r < 0)
+                return r;
+
+        copy = strdup(buf);
+        if (!copy)
+                return -ENOMEM;
+
+        *ret = copy;
+        return 0;
 }
 
 char *format_bytes_full(char *buf, size_t l, uint64_t t, FormatBytesFlag flag) {

src/basic/format-util.h

@@ -61,10 +61,23 @@ typedef enum {
         FORMAT_IFNAME_IFINDEX_WITH_PERCENT = (1 << 1) | FORMAT_IFNAME_IFINDEX,
 } FormatIfnameFlag;
 
-char *format_ifname_full(int ifindex, char buf[static IF_NAMESIZE + 1], FormatIfnameFlag flag);
-static inline char *format_ifname(int ifindex, char buf[static IF_NAMESIZE + 1]) {
-        return format_ifname_full(ifindex, buf, 0);
+int format_ifname_full(int ifindex, FormatIfnameFlag flag, char buf[static IF_NAMESIZE]);
+int format_ifname_full_alloc(int ifindex, FormatIfnameFlag flag, char **ret);
+
+static inline int format_ifname(int ifindex, char buf[static IF_NAMESIZE]) {
+        return format_ifname_full(ifindex, 0, buf);
 }
+static inline int format_ifname_alloc(int ifindex, char **ret) {
+        return format_ifname_full_alloc(ifindex, 0, ret);
+}
+
+static inline char *_format_ifname_full(int ifindex, FormatIfnameFlag flag, char buf[static IF_NAMESIZE]) {
+        (void) format_ifname_full(ifindex, flag, buf);
+        return buf;
+}
+
+#define FORMAT_IFNAME_FULL(index, flag) _format_ifname_full(index, flag, (char[IF_NAMESIZE]){})
+#define FORMAT_IFNAME(index) _format_ifname_full(index, 0, (char[IF_NAMESIZE]){})
 
 typedef enum {
         FORMAT_BYTES_USE_IEC     = 1 << 0,

src/basic/socket-util.c

@@ -455,23 +455,23 @@ int sockaddr_pretty(
                         if (r < 0)
                                 return -ENOMEM;
                 } else {
-                        char a[INET6_ADDRSTRLEN], ifname[IF_NAMESIZE + 1];
+                        char a[INET6_ADDRSTRLEN];
 
                         inet_ntop(AF_INET6, &sa->in6.sin6_addr, a, sizeof(a));
-                        if (sa->in6.sin6_scope_id != 0)
-                                format_ifname_full(sa->in6.sin6_scope_id, ifname, FORMAT_IFNAME_IFINDEX);
 
                         if (include_port) {
-                                r = asprintf(&p,
+                                if (asprintf(&p,
                                              "[%s]:%u%s%s",
                                              a,
                                              be16toh(sa->in6.sin6_port),
                                              sa->in6.sin6_scope_id != 0 ? "%" : "",
-                                             sa->in6.sin6_scope_id != 0 ? ifname : "");
-                                if (r < 0)
+                                             FORMAT_IFNAME_FULL(sa->in6.sin6_scope_id, FORMAT_IFNAME_IFINDEX)) < 0)
                                         return -ENOMEM;
                         } else {
-                                p = sa->in6.sin6_scope_id != 0 ? strjoin(a, "%", ifname) : strdup(a);
+                                if (sa->in6.sin6_scope_id != 0)
+                                        p = strjoin(a, "%", FORMAT_IFNAME_FULL(sa->in6.sin6_scope_id, FORMAT_IFNAME_IFINDEX));
+                                else
+                                        p = strdup(a);
                                 if (!p)
                                         return -ENOMEM;
                         }
@@ -1233,7 +1233,7 @@ int socket_bind_to_ifname(int fd, const char *ifname) {
 }
 
 int socket_bind_to_ifindex(int fd, int ifindex) {
-        char ifname[IF_NAMESIZE + 1];
+        char ifname[IF_NAMESIZE];
         int r;
 
         assert(fd >= 0);
@@ -1251,8 +1251,9 @@ int socket_bind_to_ifindex(int fd, int ifindex) {
                 return r;
 
         /* Fall back to SO_BINDTODEVICE on kernels < 5.0 which didn't have SO_BINDTOIFINDEX */
-        if (!format_ifname(ifindex, ifname))
-                return -errno;
+        r = format_ifname(ifindex, ifname);
+        if (r < 0)
+                return r;
 
         return socket_bind_to_ifname(fd, ifname);
 }