How to get real data size before "Client sends ACK" scenario

[antoniocarnavelli]

Hi,

I am trying to write a divert socket application via gopacket with url filtering.
If url is not permitted according to our policy, the packet is not injected into kernel.
For example(real scenario): I request to get 2MB jpg data, image not injected to kernel, the tcp payload length is just 600bytes as it's supposed to be.
At this point how can i get requested real data size ?

Note: Client sends SYN to server, Server sends SYN+ACK, i want to get real data size before "Client sends ACK" scenario

packetSource := gopacket.NewPacketSource(pc, layers.LayerTypeTCP)	
for packet := range packetSource.Packets() {
	// Http Request
	readerClient := bufio.NewReader(bytes.NewReader(tcp.Payload))
	httpReq, _ := http.ReadRequest(readerClient)
	if(httpReq!=nil){
		reqHost:=fmt.Sprintf("%v",httpReq.Host)
		reqURL:=fmt.Sprintf("%v",httpReq.URL)
		webURL=reqHost+reqURL

		boolVar:=CheckWebUrl(webURL)
		if(boolVar){
			pc.WritePacketData(packet.Data())	
		}
	}
}