hostname-util: add relax parameter to hostname_is_valid

Tests are modified to check behaviour with relax and without relax.
New tests are added for hostname_cleanup().
Tests are moved a new file (test-hostname-util) because there's
now a bunch of them.

New parameter is not used anywhere, except in tests, so there should
be no observable change.

src/basic/hostname-util.c

@@ -61,14 +61,22 @@ static bool hostname_valid_char(char c) {
                 c == '.';
 }
 
-bool hostname_is_valid(const char *s) {
+/**
+ * Check if s looks like a valid host name 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
+ * relax is true and at least two components are present in the name.
+ */
+bool hostname_is_valid(const char *s, bool relax) {
         const char *p;
         bool dot;
+        unsigned dots = 0;
 
         if (isempty(s))
                 return false;
 
-        /* Doesn't accept empty hostnames, hostnames with trailing or
+        /* 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. */
@@ -79,6 +87,7 @@ bool hostname_is_valid(const char *s) {
                                 return false;
 
                         dot = true;
+                        dots ++;
                 } else {
                         if (!hostname_valid_char(*p))
                                 return false;
@@ -87,7 +96,7 @@ bool hostname_is_valid(const char *s) {
                 }
         }
 
-        if (dot)
+        if (dot && (dots < 2 || !relax))
                 return false;
 
         if (p-s > HOST_NAME_MAX)

src/basic/hostname-util.h

@@ -29,7 +29,7 @@ bool hostname_is_set(void);
 
 char* gethostname_malloc(void);
 
-bool hostname_is_valid(const char *s) _pure_;
+bool hostname_is_valid(const char *s, bool relax) _pure_;
 char* hostname_cleanup(char *s, bool lowercase);
 
 bool is_localhost(const char *hostname);

src/basic/util.c

@@ -2997,7 +2997,7 @@ char* strshorten(char *s, size_t l) {
 
 bool machine_name_is_valid(const char *s) {
 
-        if (!hostname_is_valid(s))
+        if (!hostname_is_valid(s, false))
                 return false;
 
         /* Machine names should be useful hostnames, but also be

src/basic/util.h

@@ -858,6 +858,11 @@ int unquote_first_word(const char **p, char **ret, UnquoteFlags flags);
 int unquote_first_word_and_warn(const char **p, char **ret, UnquoteFlags flags, const char *unit, const char *filename, unsigned line, const char *rvalue);
 int unquote_many_words(const char **p, UnquoteFlags flags, ...) _sentinel_;
 
+static inline void free_and_replace(char **s, char *v) {
+        free(*s);
+        *s = v;
+}
+
 int free_and_strdup(char **p, const char *s);
 
 #define INOTIFY_EVENT_MAX (sizeof(struct inotify_event) + NAME_MAX + 1)