How do I know tcp data transfer progress

With socket transmit data, the receiving and sending hair How do I know the current progress ah? There resuming function which is how to achieve it?
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Custom transport protocol packet contains the information you want.
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quote 1 floor hslinux reply:

custom transport protocol packet contains the information you want.

Can be added to determine the size of your packets
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Resume is to set a value that represents the size of each download saved. Breakpoints can also calculate the size of the file, and then from that place to start the download. Examples are: set value of 50, the size of the file under 400k, if broken down to 325k, it will save 300k, 300k beginning next from the next.