[PATCH] http: check curl_multi_remove_handle error code

[Eric Wong <e@80x24.org>]

This should help detect bugs in future changes.  While we're at
it, fix a (probably innocuous) bug in our http_cleanup function
for users of older curl.

curl_multi_remove_handle was not idempotent until curl 7.33.0
with commit 84f3b3dd448399f9548468676e1bd1475dba8de5
("curl_multi_remove_handle: allow multiple removes"),
so we track the "curlm" membership of the curl easy handle
ourselves with a new "in_multi" flag.

Tested with curl 7.26.0 and 7.38.0 on Debian 7.x (wheezy) and
Debian 8.x (jessie) respectively.

Signed-off-by: Eric Wong <e@80x24.org>
---
 http.c | 12 ++++++++++--
 http.h |  1 +
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/http.c b/http.c
index 82ed542..9f97749 100644
--- a/http.c
+++ b/http.c
@@ -204,7 +204,12 @@ static void finish_active_slot(struct active_request_slot *slot)
 static void xmulti_remove_handle(struct active_request_slot *slot)
 {
 #ifdef USE_CURL_MULTI
-	curl_multi_remove_handle(curlm, slot->curl);
+	CURLMcode code = curl_multi_remove_handle(curlm, slot->curl);
+
+	if (code != CURLM_OK)
+		die("curl_multi_remove_handle failed (%p): %s",
+			slot->curl, curl_multi_strerror(code));
+	slot->in_multi = 0;
 #endif
 }
 
@@ -888,7 +893,8 @@ void http_cleanup(void)
 	while (slot != NULL) {
 		struct active_request_slot *next = slot->next;
 		if (slot->curl != NULL) {
-			xmulti_remove_handle(slot);
+			if (slot->in_multi)
+				xmulti_remove_handle(slot);
 			curl_easy_cleanup(slot->curl);
 		}
 		free(slot);
@@ -965,6 +971,7 @@ struct active_request_slot *get_active_slot(void)
 		newslot = xmalloc(sizeof(*newslot));
 		newslot->curl = NULL;
 		newslot->in_use = 0;
+		newslot->in_multi = 0;
 		newslot->next = NULL;
 
 		slot = active_queue_head;
@@ -1033,6 +1040,7 @@ int start_active_slot(struct active_request_slot *slot)
 		slot->in_use = 0;
 		return 0;
 	}
+	slot->in_multi = 1;
 
 	/*
 	 * We know there must be something to do, since we just added
diff --git a/http.h b/http.h
index 5ab9d9c..3339d70 100644
--- a/http.h
+++ b/http.h
@@ -60,6 +60,7 @@ struct slot_results {
 struct active_request_slot {
 	CURL *curl;
 	int in_use;
+	int in_multi;
 	CURLcode curl_result;
 	long http_code;
 	int *finished;
-- 
EW