Give sensible feedback when a repo has no configured servers

This fixes FS#14899. When running an -Sp operation without servers
configured for a repository, we would segfault, so add an assert to the
backend method returning the first server preventing a null pointer
dereference.

In addition, add a new error code to libalpm that indicates we have no
servers configured for a repository. This makes -Sy and -S <package>
operations fail gracefully and helpfully when a repo is set up with no
servers, as the default mirrorlist in Arch is provided this way.

Signed-off-by: Dan McGee <dan@archlinux.org>

lib/libalpm/alpm.h

@@ -480,6 +480,7 @@ enum _pmerrno_t {
 	PM_ERR_DB_REMOVE,
 	/* Servers */
 	PM_ERR_SERVER_BAD_URL,
+	PM_ERR_SERVER_NONE,
 	/* Transactions */
 	PM_ERR_TRANS_NOT_NULL,
 	PM_ERR_TRANS_NULL,

lib/libalpm/db.c

@@ -232,6 +232,7 @@ const char SYMEXPORT *alpm_db_get_url(const pmdb_t *db)
 	/* Sanity checks */
 	ASSERT(handle != NULL, return(NULL));
 	ASSERT(db != NULL, return(NULL));
+	ASSERT(db->servers != NULL, return(NULL));
 
 	url = (char*)db->servers->data;
 

lib/libalpm/dload.c

@@ -388,6 +388,8 @@ int _alpm_download_single_file(const char *filename,
 	alpm_list_t *i;
 	int ret = -1;
 
+	ASSERT(servers != NULL, RET_ERR(PM_ERR_SERVER_NONE, -1));
+
 	for(i = servers; i; i = i->next) {
 		const char *server = i->data;
 		char *fileurl = NULL;

lib/libalpm/error.c

@@ -84,6 +84,8 @@ const char SYMEXPORT *alpm_strerror(int err)
 		/* Servers */
 		case PM_ERR_SERVER_BAD_URL:
 			return _("invalid url for server");
+		case PM_ERR_SERVER_NONE:
+			return _("no servers configured for repository");
 		/* Transactions */
 		case PM_ERR_TRANS_NOT_NULL:
 			return _("transaction already initialized");

lib/libalpm/sync.c

@@ -769,7 +769,9 @@ int _alpm_sync_commit(pmtrans_t *trans, pmdb_t *db_local, alpm_list_t **data)
 			if(_alpm_download_files(files, current->servers, cachedir)) {
 				_alpm_log(PM_LOG_WARNING, _("failed to retrieve some files from %s\n"),
 						current->treename);
-				pm_errno = PM_ERR_RETRIEVE;
+				if(pm_errno == 0) {
+					pm_errno = PM_ERR_RETRIEVE;
+				}
 				goto error;
 			}
 			FREELIST(files);

src/pacman/sync.c

@@ -675,7 +675,15 @@ static int sync_trans(alpm_list_t *targets)
 		for(i = packages; i; i = alpm_list_next(i)) {
 			pmpkg_t *pkg = alpm_list_getdata(i);
 			pmdb_t *db = alpm_pkg_get_db(pkg);
-			printf("%s/%s\n", alpm_db_get_url(db), alpm_pkg_get_filename(pkg));
+			const char *dburl = alpm_db_get_url(db);
+			if(dburl) {
+				printf("%s/%s\n", dburl, alpm_pkg_get_filename(pkg));
+			} else {
+				/* can't use WARNING here, we don't show warnings in -Sp... */
+				pm_fprintf(stderr, PM_LOG_ERROR, _("no database for package: %s\n"),
+						alpm_pkg_get_name(pkg));
+			}
+
 		}
 		/* we are done */
 		goto cleanup;