enable curl cookie engine

Enabling Curl cookie engine brings advantage:
* handle cookies during a redirection: when a srv redirects including
  cookies, curl sends back the cookies correctly during the next request

Author: krichprollsch

src/http/Client.zig

@@ -602,6 +602,18 @@ pub const Transfer = struct {
 
         const header = buffer[0 .. buf_len - 2];
 
+        {
+            const SET_COOKIE_LEN = "set-cookie:".len;
+            if (header.len > SET_COOKIE_LEN) {
+                if (std.ascii.eqlIgnoreCase(header[0..SET_COOKIE_LEN], "set-cookie:")) {
+                    const value = std.mem.trimLeft(u8, header[SET_COOKIE_LEN..], " ");
+                    transfer.req.cookie_jar.populateFromResponse(&transfer.uri, value) catch |err| {
+                        log.err(.http, "set cookie", .{ .err = err, .req = transfer });
+                    };
+                }
+            }
+        }
+
         if (transfer.response_header == null) {
             if (buf_len < 13 or std.mem.startsWith(u8, header, "HTTP/") == false) {
                 if (transfer._redirecting) {
@@ -655,18 +667,6 @@ pub const Transfer = struct {
             }
         }
 
-        {
-            const SET_COOKIE_LEN = "set-cookie:".len;
-            if (header.len > SET_COOKIE_LEN) {
-                if (std.ascii.eqlIgnoreCase(header[0..SET_COOKIE_LEN], "set-cookie:")) {
-                    const value = std.mem.trimLeft(u8, header[SET_COOKIE_LEN..], " ");
-                    transfer.req.cookie_jar.populateFromResponse(&transfer.uri, value) catch |err| {
-                        log.err(.http, "set cookie", .{ .err = err, .req = transfer });
-                    };
-                }
-            }
-        }
-
         if (buf_len == 2) {
             if (getResponseHeader(easy, "content-type")) |value| {
                 const len = @min(value.len, hdr._content_type.len);

src/http/Http.zig

@@ -110,6 +110,9 @@ pub const Connection = struct {
         try errorCheck(c.curl_easy_setopt(easy, c.CURLOPT_FOLLOWLOCATION, @as(c_long, 2)));
         try errorCheck(c.curl_easy_setopt(easy, c.CURLOPT_REDIR_PROTOCOLS_STR, "HTTP,HTTPS")); // remove FTP and FTPS from the default
 
+        // enable cookie engine for redirections handled directly by Curl.
+        try errorCheck(c.curl_easy_setopt(easy, c.CURLOPT_COOKIEFILE, ""));
+
         // proxy
         if (opts.http_proxy) |proxy| {
             try errorCheck(c.curl_easy_setopt(easy, c.CURLOPT_PROXY, proxy.ptr));