deflate.zig: check for distances past beginning of output stream #9860
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InflateStream
doesn't check if the distance in a backward reference extends past the beginning of the decompressed "output stream". For example, if the first block starts by encoding the literals 'A', 'B', and 'C' followed a (length, distance) pair of (4, 4), we will reach one byte past the beginning of the output stream. This will output "ABCxABC" where x is a garbage byte (in this case, whatever happened to be in the last slot of the window buffer). This should not be allowed according to the RFC, and the reference implementation in Mark Adler'spuff.c
checks for this as well. The fix is simply to havewindow
keep track of the total number of bytes written out, independent of the number of unread elements inel
.