How to escape Multipart HTTP boundary

Question

Let's say I'm sending a multipart request (or response). I need to choose a multipart boundary which does not appear in any of my payloads. However, my payloads are large binary files and I am streaming them to the destination. I want to avoid streaming them twice - once to scan for the boundary and one to stream out.

So my question is: is it possible to escape the boundary if it appears in the payload? If so, how?

Answer 1

No, it's not possible; you need to either scan, or live with potential failures.

Answer 2

Don't Panic. Your boundary can be up to 70 characters long. If you go with that maximum and randomly generate it out of characters and numbers you'll have 62⁷⁰ possible combinations for each position in a file. Chance of having the same sequence of bytes in your binary files is so infinitesimal that it shouldn't bother your sleep at all

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