* lib/protocol: Require at least 3.125% savings from compression
The new lz4 library doesn't need its output buffer to be the maximum
size, unlike the old one (which would allocate if it weren't). It can
take a buffer that is of a smaller size and will report if compressed
data can fit inside the buffer (with a small chance of reporting a false
negative). Use that property to our advantage by requiring compressed
data to be at most n-n/32 = .96875*n bytes long for n input bytes.
* lib/protocol: Remove unused receivers
To make DeepSource happy.
* lib/protocol: Micro-optimize lz4Compress
Only write the length if compression was successful. This is a memory
write, so the compiler can't reorder it.
Only check the return value of lz4.CompressBlock. Length-zero inputs
are always expanded by LZ4 compression (the library documents this),
so the check on len(src) isn't needed.
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