support in ~/ and SSH_DIR/ in filenames instead of %s/

Get rid of snprintf to fixed sized buffers in setting options.
Instead make locations starting with ~/ relative to the
users initial working directory (as libssh does not look into
the home directory but only at the initial home directory).
and starting with SSH_DIR/ relative to the configured ssh directory.

libssh/options.c

@@ -236,6 +236,41 @@ static int ssh_options_set_algo(ssh_options opt, int algo, const char *list) {
   return 0;
 }
 
+static char *dir_expand_dup(ssh_options opt, const char *value, int allowsshdir) {
+  char *n;
+
+  if (value[0] == '~' && value[1] == '/') {
+    const char *homedir = ssh_get_user_home_dir();
+    size_t lv = strlen(value + 1), lh = strlen(homedir);
+
+    n = malloc(lv + lh + 1);
+    if (n == NULL)
+      return NULL;
+    memcpy(n, homedir, lh);
+    memcpy(n + lh + 1, value + 1, lv + 1);
+    return n;
+  }
+  if (allowsshdir && strncmp(value, "SSH_DIR/", 8) == 0) {
+    size_t lv, ls;
+    if (opt->ssh_dir == NULL) {
+      if (ssh_options_set(opt, SSH_OPTIONS_SSH_DIR, NULL) < 0)
+	return NULL;
+    }
+
+    value += 7;
+    lv = strlen(value);
+    ls = strlen(opt->ssh_dir);
+
+    n = malloc(lv + ls + 1);
+    if (n == NULL)
+      return NULL;
+    memcpy(n, opt->ssh_dir, ls);
+    memcpy(n + ls + 1, value, lv + 1);
+    return n;
+  }
+  return strdup(value);
+}
+
 /**
  * @brief This function can set all possible ssh options.
  *
@@ -390,7 +425,6 @@ static int ssh_options_set_algo(ssh_options opt, int algo, const char *list) {
  */
 int ssh_options_set(ssh_options opt, enum ssh_options_e type,
     const void *value) {
-  char buf[1024] = {0};
   char *p, *q;
   int i;
 
@@ -484,16 +518,16 @@ int ssh_options_set(ssh_options opt, enum ssh_options_e type,
       break;
     case SSH_OPTIONS_SSH_DIR:
       if (value == NULL) {
-        snprintf(buf, sizeof(buf), "%s/.ssh/", ssh_get_user_home_dir());
-        opt->ssh_dir = strdup(buf);
+        SAFE_FREE(opt->ssh_dir);
+	/* TODO: why ~/.ssh/ instead of ~/.ssh ? */
+
+        opt->ssh_dir = dir_expand_dup(opt, "~/.ssh/", 0);
         if (opt->ssh_dir == NULL) {
           return -1;
         }
       } else {
-        /* do we really want it this way? */
-        snprintf(buf, sizeof(buf), value, ssh_get_user_home_dir());
         SAFE_FREE(opt->ssh_dir);
-        opt->ssh_dir = strdup(buf);
+        opt->ssh_dir = dir_expand_dup(opt, value, 0);
         if (opt->ssh_dir == NULL) {
           return -1;
         }
@@ -504,28 +538,23 @@ int ssh_options_set(ssh_options opt, enum ssh_options_e type,
       if (value == NULL) {
         return -1;
       }
-      snprintf(buf, sizeof(buf), value, ssh_get_user_home_dir());
       SAFE_FREE(opt->identity);
-      opt->identity = strdup(buf);
+      opt->identity = dir_expand_dup(opt, value, 1);
       if (opt->identity == NULL) {
         return -1;
       }
       break;
     case SSH_OPTIONS_KNOWNHOSTS:
       if (value == NULL) {
-        if (ssh_options_set(opt, SSH_OPTIONS_SSH_DIR, NULL) < 0) {
-          return -1;
-        }
-
-        snprintf(buf, sizeof(buf), "%s/known_hosts", opt->ssh_dir);
-        opt->known_hosts_file = strdup(buf);
+        SAFE_FREE(opt->known_hosts_file);
+        opt->known_hosts_file = dir_expand_dup(opt,
+			"SSH_DIR/known_hosts", 1);
         if (opt->known_hosts_file == NULL) {
           return -1;
         }
       } else {
-        snprintf(buf, sizeof(buf), value, ssh_get_user_home_dir());
         SAFE_FREE(opt->known_hosts_file);
-        opt->known_hosts_file = strdup(buf);
+        opt->known_hosts_file = dir_expand_dup(opt, value, 1);
         if (opt->known_hosts_file == NULL) {
           return -1;
         }
@@ -1287,25 +1316,25 @@ int ssh_options_set_auth_callback(ssh_options opt, ssh_auth_callback cb,
  * @see ssh_options_set_host()
  */
 int ssh_options_parse_config(ssh_options opt, const char *filename) {
-  char buffer[1024] = {0};
+  char *expanded_filename;
+  int r;
 
   if (opt == NULL || opt->host == NULL) {
     return -1;
   }
 
-  if (opt->ssh_dir == NULL) {
-    if (ssh_options_default_ssh_dir(opt) < 0) {
-      return -1;
-    }
-  }
-
   /* set default filename */
   if (filename == NULL) {
-    snprintf(buffer, 1024, "%s/config", opt->ssh_dir);
-    filename = buffer;
+    expanded_filename = dir_expand_dup(opt, "SSH_DIR/config", 1);
+  } else {
+    expanded_filename = dir_expand_dup(opt, filename, 1);
   }
+  if (expanded_filename == NULL)
+    return -1;
 
-  return ssh_config_parse_file(opt, filename);
+  r = ssh_config_parse_file(opt, filename);
+  free(expanded_filename);
+  return r;
 }
 
 /** @} */