[cezaraugusto]

a one-byte file comes back with Content-Length: 0, and the byte is still written after the headers. on a keep-alive socket that breaks the next response

the cause is this line in createReadStreamOrReadFileSync

byteLength = end === 0 ? 0 : end - start + 1;

it was written for the empty file, but calcStartAndEnd clamps a one-byte file to end = 0 as well, so both look the same here. a bytes=0-0 range on any file hits it too

the caller already knows the byte count, the file size or the range length, so the stream is now sized from that. a stat with no size falls back to the old arithmetic

two tests, both red on main: a one-byte file answers Content-Length: 1 with its byte, and bytes=0-0 answers 206 with bytes 0-0/1

fixes #69

[chenjiahan]

LGTM, thank you!