remote-curl: include curl_errorstr on SSL setup failures

For curl error 35 (CURLE_SSL_CONNECT_ERROR) users need the
additional text stored in CURLOPT_ERRORBUFFER to debug why
the connection did not start. This is curl_errorstr inside
of http.c, so include that in the message if it is non-empty.

Sometimes HTTP response codes aren't yet available, such as
when the SSL setup fails. Don't include HTTP 0 in the message.

Signed-off-by: Shawn Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

remote-curl.c

@@ -439,8 +439,20 @@ static int run_slot(struct active_request_slot *slot,
 	err = run_one_slot(slot, results);
 
 	if (err != HTTP_OK && err != HTTP_REAUTH) {
-		error("RPC failed; result=%d, HTTP code = %ld",
-		      results->curl_result, results->http_code);
+		struct strbuf msg = STRBUF_INIT;
+		if (results->http_code && results->http_code != 200)
+			strbuf_addf(&msg, "HTTP %ld", results->http_code);
+		if (results->curl_result != CURLE_OK) {
+			if (msg.len)
+				strbuf_addch(&msg, ' ');
+			strbuf_addf(&msg, "curl %d", results->curl_result);
+			if (curl_errorstr[0]) {
+				strbuf_addch(&msg, ' ');
+				strbuf_addstr(&msg, curl_errorstr);
+			}
+		}
+		error("RPC failed; %s", msg.buf);
+		strbuf_release(&msg);
 	}
 
 	return err;