Partially unify hostname_is_valid() and dns_name_is_valid()

This makes hostname_is_valid() apply the ldh checks too, rejecting more
hostnames.

src/basic/hostname-util.c

@@ -69,12 +69,12 @@ int gethostname_strict(char **ret) {
         return 0;
 }
 
-static bool hostname_valid_char(char c) {
+bool valid_ldh_char(char c) {
         return
                 (c >= 'a' && c <= 'z') ||
                 (c >= 'A' && c <= 'Z') ||
                 (c >= '0' && c <= '9') ||
-                IN_SET(c, '-', '_', '.');
+                c == '-';
 }
 
 /**
@@ -90,7 +90,7 @@ static bool hostname_valid_char(char c) {
 bool hostname_is_valid(const char *s, bool allow_trailing_dot) {
         unsigned n_dots = 0;
         const char *p;
-        bool dot;
+        bool dot, hyphen;
 
         if (isempty(s))
                 return false;
@@ -100,23 +100,34 @@ bool hostname_is_valid(const char *s, bool allow_trailing_dot) {
          * sequence. Also ensures that the length stays below
          * HOST_NAME_MAX. */
 
-        for (p = s, dot = true; *p; p++) {
+        for (p = s, dot = hyphen = true; *p; p++)
                 if (*p == '.') {
-                        if (dot)
+                        if (dot || hyphen)
                                 return false;
 
                         dot = true;
+                        hyphen = false;
                         n_dots++;
-                } else {
-                        if (!hostname_valid_char(*p))
+
+                } else if (*p == '-') {
+                        if (dot)
                                 return false;
 
                         dot = false;
+                        hyphen = true;
+
+                } else {
+                        if (!valid_ldh_char(*p))
+                                return false;
+
+                        dot = false;
+                        hyphen = false;
                 }
-        }
 
         if (dot && (n_dots < 2 || !allow_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
@@ -128,29 +139,40 @@ bool hostname_is_valid(const char *s, bool allow_trailing_dot) {
 
 char* hostname_cleanup(char *s) {
         char *p, *d;
-        bool dot;
+        bool dot, hyphen;
 
         assert(s);
 
         strshorten(s, HOST_NAME_MAX);
 
-        for (p = s, d = s, dot = true; *p; p++) {
+        for (p = s, d = s, dot = hyphen = true; *p; p++)
                 if (*p == '.') {
-                        if (dot)
+                        if (dot || hyphen)
                                 continue;
 
                         *(d++) = '.';
                         dot = true;
-                } else if (hostname_valid_char(*p)) {
+                        hyphen = false;
+
+                } else if (*p == '-') {
+                        if (dot)
+                                continue;
+
+                        *(d++) = '-';
+                        dot = false;
+                        hyphen = true;
+
+                } else if (valid_ldh_char(*p)) {
                         *(d++) = *p;
                         dot = false;
+                        hyphen = false;
                 }
-        }
 
-        if (dot && d > s)
-                d[-1] = 0;
-        else
-                *d = 0;
+        if (d > s && IN_SET(d[-1], '-', '.'))
+                /* The dot can occur at most once, but we might have multiple
+                 * hyphens, hence the loop */
+                d--;
+        *d = 0;
 
         return s;
 }

src/basic/hostname-util.h

@@ -11,6 +11,7 @@ bool hostname_is_set(void);
 char* gethostname_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);
 

src/shared/dns-domain.c

@@ -17,6 +17,7 @@
 #include "dns-domain.h"
 #include "hashmap.h"
 #include "hexdecoct.h"
+#include "hostname-util.h"
 #include "in-addr-util.h"
 #include "macro.h"
 #include "parse-util.h"
@@ -24,14 +25,6 @@
 #include "strv.h"
 #include "utf8.h"
 
-static bool valid_ldh_char(char c) {
-        return
-                (c >= 'a' && c <= 'z') ||
-                (c >= 'A' && c <= 'Z') ||
-                (c >= '0' && c <= '9') ||
-                c == '-';
-}
-
 int dns_label_unescape(const char **name, char *dest, size_t sz, DNSLabelFlags flags) {
         const char *n;
         char *d, last_char = 0;

src/test/test-hostname-util.c

@@ -53,6 +53,12 @@ static void test_hostname_cleanup(void) {
         assert_se(streq(hostname_cleanup(s), "foobar.com"));
         s = strdupa("foobar.com.");
         assert_se(streq(hostname_cleanup(s), "foobar.com"));
+        s = strdupa("foo-bar.-com-.");
+        assert_se(streq(hostname_cleanup(s), "foo-bar.com"));
+        s = strdupa("foo-bar-.-com-.");
+        assert_se(streq(hostname_cleanup(s), "foo-bar--com"));
+        s = strdupa("--foo-bar.-com");
+        assert_se(streq(hostname_cleanup(s), "foo-bar.com"));
         s = strdupa("fooBAR");
         assert_se(streq(hostname_cleanup(s), "fooBAR"));
         s = strdupa("fooBAR.com");