When we send any videos or music in whatsapp how it is resuming when it is interrupted by any circumstances?

Question

When we send any media in whatsapp to our friends how it is resuming upload when we are interrupted by any call or some internet problem ? The retry button will resume the upload

Answer 1

It is likely to work something like this:

1. Whatsapp client will send the size of the upload to the server so the server knows how many bytes to expect.

2. When upload begins, the server will send an acknowledgement for a batch of bytes it has successfully uploaded.

3. The server will know the upload has complete when it has received all the bytes.

Point 2 means that the Whatsapp client will know exactly what bytes have been sent to the server, so that when connectivity resumes, it knows exactly where to resume sending bytes from.

The server will also have a mechanism to handle receiving the same bytes more than once just incase the acknowledgement didn't reach the client.