+/* Get the first line of a small file, without any trailing newline
+ * character.
+ */
+static char *
+first_line_of_file (guestfs_h *g, const char *filename)
+{
+ char **lines;
+ int64_t size;
+ char *ret;
+
+ /* Don't trust guestfs_head_n not to break with very large files.
+ * Check the file size is something reasonable first.
+ */
+ size = guestfs_filesize (g, filename);
+ if (size == -1)
+ /* guestfs_filesize failed and has already set error in handle */
+ return NULL;
+ if (size > 1000000) {
+ error (g, _("size of %s is unreasonably large (%" PRIi64 " bytes)"),
+ filename, size);
+ return NULL;
+ }
+
+ lines = guestfs_head_n (g, 1, filename);
+ if (lines == NULL)
+ return NULL;
+ if (lines[0] == NULL) {
+ error (g, _("%s: file is empty"), filename);
+ guestfs___free_string_list (lines);
+ return NULL;
+ }
+ /* lines[1] should be NULL because of '1' argument above ... */
+
+ ret = lines[0]; /* caller frees */
+ free (lines); /* free the array */
+
+ return ret;
+}
+