imap-send: URI encode server folder

When trying to send a patch using 'imap-send' with 'curl' and the
following configuration:

[imap]
	folder = "[Gmail]/Drafts"
	host = imaps://imap.gmail.com
	port = 993
	sslverify = false

results in the following error,

    curl_easy_perform() failed: URL using bad/illegal format or missing URL

This is a consequence of not URI-encoding the folder portion of
the URL which contains characters such as '[' which are not
allowed in a URI. According to RFC3986, these characters should be
URI-encoded.

So, URI-encode the folder before adding it to the URI to ensure it doesn't
contain characters that aren't allowed in a URI.

Reported-by: Doron Behar <doron.behar@gmail.com>
Signed-off-by: Nicolas Morey-Chaisemartin <NMoreyChaisemartin@suse.com>
Signed-off-by: Kaartic Sivaraam <kaartic.sivaraam@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

imap-send.c

@@ -1412,6 +1412,7 @@ static CURL *setup_curl(struct imap_server_conf *srvc, struct credential *cred)
 {
 	CURL *curl;
 	struct strbuf path = STRBUF_INIT;
+	char *uri_encoded_folder;
 
 	if (curl_global_init(CURL_GLOBAL_ALL) != CURLE_OK)
 		die("curl_global_init failed");
@@ -1429,7 +1430,12 @@ static CURL *setup_curl(struct imap_server_conf *srvc, struct credential *cred)
 	strbuf_addstr(&path, server.host);
 	if (!path.len || path.buf[path.len - 1] != '/')
 		strbuf_addch(&path, '/');
-	strbuf_addstr(&path, server.folder);
+
+	uri_encoded_folder = curl_easy_escape(curl, server.folder, 0);
+	if (!uri_encoded_folder)
+		die("failed to encode server folder");
+	strbuf_addstr(&path, uri_encoded_folder);
+	curl_free(uri_encoded_folder);
 
 	curl_easy_setopt(curl, CURLOPT_URL, path.buf);
 	strbuf_release(&path);