hostname-util: flagsify hostname_is_valid(), drop machine_name_is_valid()

Let's clean up hostname_is_valid() a bit: let's turn the second boolean
argument into a more explanatory flags field, and add a flag that
accepts the special name ".host" as valid. This is useful for the
container logic, where the special hostname ".host" refers to the "root
container", i.e. the host system itself, and can be specified at various
places.

let's also get rid of machine_name_is_valid(). It was just an alias,
which is confusing and even more so now that we have the flags param.

src/basic/hostname-util.c

@@ -98,28 +98,24 @@ bool valid_ldh_char(char c) {
                 c == '-';
 }
 
-/**
- * Check if s looks like a valid hostname or FQDN. This does not do
- * full DNS validation, but only checks if the name is composed of
- * allowed characters and the length is not above the maximum allowed
- * by Linux (c.f. dns_name_is_valid()). Trailing dot is allowed if
- * allow_trailing_dot is true and at least two components are present
- * in the name. Note that due to the restricted charset and length
- * this call is substantially more conservative than
- * dns_name_is_valid().
- */
-bool hostname_is_valid(const char *s, bool allow_trailing_dot) {
+bool hostname_is_valid(const char *s, ValidHostnameFlags flags) {
         unsigned n_dots = 0;
         const char *p;
         bool dot, hyphen;
 
+        /* Check if s looks like a valid hostname or FQDN. This does not do full DNS validation, but only
+         * checks if the name is composed of allowed characters and the length is not above the maximum
+         * allowed by Linux (c.f. dns_name_is_valid()). A trailing dot is allowed if
+         * VALID_HOSTNAME_TRAILING_DOT flag is set and at least two components are present in the name. Note
+         * that due to the restricted charset and length this call is substantially more conservative than
+         * dns_name_is_valid(). Doesn't accept empty hostnames, hostnames with leading dots, and hostnames
+         * with multiple dots in a sequence. Doesn't allow hyphens at the beginning or end of label. */
+
         if (isempty(s))
                 return false;
 
-        /* Doesn't accept empty hostnames, hostnames with
-         * leading dots, and hostnames with multiple dots in a
-         * sequence. Also ensures that the length stays below
-         * HOST_NAME_MAX. */
+        if (streq(s, ".host")) /* Used by the container logic to denote the "root container" */
+                return FLAGS_SET(flags, VALID_HOSTNAME_DOT_HOST);
 
         for (p = s, dot = hyphen = true; *p; p++)
                 if (*p == '.') {
@@ -145,14 +141,13 @@ bool hostname_is_valid(const char *s, bool allow_trailing_dot) {
                         hyphen = false;
                 }
 
-        if (dot && (n_dots < 2 || !allow_trailing_dot))
+        if (dot && (n_dots < 2 || !FLAGS_SET(flags, VALID_HOSTNAME_TRAILING_DOT)))
                 return false;
         if (hyphen)
                 return false;
 
-        if (p-s > HOST_NAME_MAX) /* Note that HOST_NAME_MAX is 64 on
-                                  * Linux, but DNS allows domain names
-                                  * up to 255 characters */
+        if (p-s > HOST_NAME_MAX) /* Note that HOST_NAME_MAX is 64 on Linux, but DNS allows domain names up to
+                                  * 255 characters */
                 return false;
 
         return true;
@@ -243,7 +238,7 @@ int shorten_overlong(const char *s, char **ret) {
         if (!h)
                 return -ENOMEM;
 
-        if (hostname_is_valid(h, false)) {
+        if (hostname_is_valid(h, 0)) {
                 *ret = h;
                 return 0;
         }
@@ -254,7 +249,7 @@ int shorten_overlong(const char *s, char **ret) {
 
         strshorten(h, HOST_NAME_MAX);
 
-        if (!hostname_is_valid(h, false)) {
+        if (!hostname_is_valid(h, 0)) {
                 free(h);
                 return -EDOM;
         }
@@ -287,7 +282,7 @@ int read_etc_hostname_stream(FILE *f, char **ret) {
 
                         hostname_cleanup(p); /* normalize the hostname */
 
-                        if (!hostname_is_valid(p, true)) /* check that the hostname we return is valid */
+                        if (!hostname_is_valid(p, VALID_HOSTNAME_TRAILING_DOT)) /* check that the hostname we return is valid */
                                 return -EBADMSG;
 
                         copy = strdup(p);

src/basic/hostname-util.h

@@ -14,10 +14,14 @@ char* gethostname_short_malloc(void);
 int gethostname_strict(char **ret);
 
 bool valid_ldh_char(char c) _const_;
-bool hostname_is_valid(const char *s, bool allow_trailing_dot) _pure_;
-char* hostname_cleanup(char *s);
 
-#define machine_name_is_valid(s) hostname_is_valid(s, false)
+typedef enum ValidHostnameFlags {
+        VALID_HOSTNAME_TRAILING_DOT = 1 << 0,   /* Accept trailing dot on multi-label names */
+        VALID_HOSTNAME_DOT_HOST     = 1 << 1,   /* Accept ".host" as valid hostname */
+} ValidHostnameFlags;
+
+bool hostname_is_valid(const char *s, ValidHostnameFlags flags) _pure_;
+char* hostname_cleanup(char *s);
 
 bool is_localhost(const char *hostname);
 

src/basic/util.c

@@ -165,7 +165,7 @@ int container_get_leader(const char *machine, pid_t *pid) {
                 return 0;
         }
 
-        if (!machine_name_is_valid(machine))
+        if (!hostname_is_valid(machine, 0))
                 return -EINVAL;
 
         p = strjoina("/run/systemd/machines/", machine);