net::http::do: place buffer on stack

We can afford 4K of stack space

net/http/do.ha

@@ -9,18 +9,14 @@ use os;
 type context = struct {
 	conn: io::handle,
 	file: bufio::bufstream,
-	buf: []u8,
+	buf: [os::BUFSIZ]u8,
 };
 
 // Performs an HTTP [[request]] with the given [[client]]. The request is
 // performed synchronously; this function blocks until the server has returned
 // the response status and all HTTP headers associated with the response.
 export fn do(client: *client, req: *request) (response | error) = {
-	let ctx = context {
-		buf = alloc([0...], os::BUFSIZ),
-		...
-	};
-	defer free(ctx.buf);
+	let ctx = context { ... };
 
 	assert(req.target.scheme == "http"); // TODO: https
 	const conn = dial::dial_uri("tcp", req.target)?;