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I send to opened by my client by web browser - socket, packets with encrypted (html page - payload ) by my vpn.
Client receives packets, and before Windows can process them, catches this packets ( using Pydivert) and decrypts payload, and sends it back to Windows network stack. But web browser is not  loading the page.
So, I tried to send some more data after the real page data, and page was loaded, but with this new added data, that was sent after real page.
I'm assuming that web browser gets the page, but waits for more data.
So, what I'm asking is - How to tell client, that I will send exact amount of bytes?
The answer were in the header of http packet, as i was sending 1500 bytes , but in CONTENT-LENGTH was said that i will send 1505 bytes.
How to tell web browser opened - socket, how much bytes i will send to it