import { matchAfterPrefix } from "https://dotland.deno.dev/x/abc@v1.3.3/vendor/https/deno.land/std/mime/multipart.ts";
Checks whether buf should be considered to match the boundary.
The prefix is "--boundary" or "\r\n--boundary" or "\n--boundary", and the
caller has verified already that hasPrefix(buf, prefix) is true.
matchAfterPrefix() returns 1 if the buffer does match the boundary,
meaning the prefix is followed by a dash, space, tab, cr, nl, or EOF.
It returns -1 if the buffer definitely does NOT match the boundary,
meaning the prefix is followed by some other character.
For example, "--foobar" does not match "--foo".
It returns 0 more input needs to be read to make the decision,
meaning that buf.length and prefix.length are the same.