note an assumed invariant that may not be obvious

[jepler]

an assumption recently added in #8655

[dhalbert]

How do you know the length of the decompressed string? Suppose the buffer is too short, what happens? Is it OK if the buffer is larger than necessary?

[jepler]

This is just a note about the internal API (the function I'm commenting is a new static function added in #8655). The message length comes from decompress_length(message) and implementation wise it's stored as the first bits of the message itself. this was more efficient than storing a huffman-encoded NUL byte at the end of the str.