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>

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/libalpm/dload.c b/lib/libalpm/dload.c
index 5b0a691f..aec0b5ca 100644
--- a/lib/libalpm/dload.c
+++ b/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;