Fix crash when using external downloader

Commit 9d96bed9 attempts to use the same effective URL for the db and its
signature download.  However, this information is not available when we use
an external downloader, resulting in a crash.

Fall back to the old method when the effective URL is unavailable.

Signed-off-by: Allan McRae <allan@archlinux.org>

1 files changed, 17 insertions, 4 deletions

diff --git a/lib/libalpm/be_sync.c b/lib/libalpm/be_sync.c
index 62fd0f04..52459483 100644
--- a/lib/libalpm/be_sync.c
+++ b/lib/libalpm/be_sync.c
@@ -241,12 +241,25 @@ int SYMEXPORT alpm_db_update(int force, alpm_db_t *db)
 			unlink(sigpath);
 			free(sigpath);
 
-			/* if we downloaded a DB, we want the .sig from the same server */
-			/* print final_db_url into a buffer (leave space for .sig) */
-			len = strlen(final_db_url) + 5;
+			/* if we downloaded a DB, we want the .sig from the same server -
+			   this information is only available from the internal downloader */
+			if(handle->fetchcb == NULL) {
+				/* print final_db_url into a buffer (leave space for .sig) */
+				len = strlen(final_db_url) + 5;
+			} else {
+				/* print server + filename into a buffer (leave space for .sig) */
+				len = strlen(server) + strlen(db->treename) + 9;
+			}
+
 			/* TODO fix leak syncpath and umask unset */
 			MALLOC(payload.fileurl, len, RET_ERR(handle, ALPM_ERR_MEMORY, -1));
-			snprintf(payload.fileurl, len, "%s.sig", final_db_url);
+
+			if(handle->fetchcb == NULL) {
+				snprintf(payload.fileurl, len, "%s.sig", final_db_url);
+			} else {
+				snprintf(payload.fileurl, len, "%s/%s.db.sig", server, db->treename);
+			}
+
 			payload.handle = handle;
 			payload.force = 1;
 			payload.errors_ok = (level & ALPM_SIG_DATABASE_OPTIONAL);