veb: reduce veb_max_write_bytes from 16KB to 2KB (fix sending large dynamic responses from veb on macos/freebsd) (fix #24523) (#24522)

vlib/net/tcp.c.v

@@ -239,6 +239,9 @@ pub fn (mut c TcpConn) write_ptr(b &u8, len int) !int {
 			}
 			if sent < 0 {
 				code := error_code()
+				$if trace_tcp_send_failures ? {
+					eprintln('>>> TcpConn.write_ptr | send_failure, data.len: ${len:6}, total_sent: ${total_sent:6}, remaining: ${remaining:6}, ptr: ${voidptr(ptr):x}, c.write_timeout: ${c.write_timeout:3} => sent: ${sent:6}, error code: ${code:3}')
+				}
 				if code in [int(error_ewouldblock), int(error_eagain), C.EINTR] {
 					c.wait_for_write()!
 					continue

vlib/veb/consts.v

@@ -4,7 +4,7 @@ import net.http
 
 // max read and write limits in bytes
 const max_read = int($d('veb_max_read_bytes', 8192))
-const max_write = int($d('veb_max_write_bytes', 16384))
+const max_write = int($d('veb_max_write_bytes', 2048))
 
 pub const max_http_post_size = $d('veb_max_http_post_size_bytes', 1048576)
 pub const default_port = int($d('veb_default_port', 8080))

vlib/veb/tests/veb_test.v

@@ -376,3 +376,10 @@ fn test_empty_querypath() {
 	x = http.get('http://${localserver}///') or { panic(err) }
 	assert x.body == 'Welcome to veb'
 }
+
+fn test_large_response() {
+	received := simple_tcp_client(path: '/large_response') or { panic(err) }
+	assert_common_headers(received)
+	assert received.ends_with('}]')
+	assert received.len == 830778
+}

vlib/veb/tests/veb_test_server.v

@@ -152,3 +152,22 @@ fn (mut app ServerApp) exit_gracefully() {
 	time.sleep(100 * time.millisecond)
 	exit(0)
 }
+
+pub fn (mut app ServerApp) large_response(mut ctx ServerContext) veb.Result {
+	struct Tick {
+		date_time string
+		timestamp i64
+		value     f64
+	}
+
+	mut arr := []Tick{}
+	for i in 0 .. 16000 {
+		arr << Tick{
+			date_time: i.str()
+			timestamp: i
+			value:     i
+		}
+	}
+
+	return ctx.json(arr)
+}