zipites, A better approach might be to simply append four bytes to the gzip file, and ignore the "decompression OK, trailing garbage ignored" warning when decompressing (it can be suppressed with -q). Eventually new versions of gzip that don't issue that warning in that case would replace the old ones. We could stick in a small extra field that simply indicates that those extra four bytes are there. (We'd have to always accept that hit in the streaming case, since you wouldn't know until too late that you needed the longer length. The total hit would be eight bytes -- four for the extra field and four for the extended length at the end.)
Concatenated gzip streams with older gzips unaware of the extra field would still be supported by preventing the two-byte magic header (1f 8b) in the appended length extension. Simply shift the 32-bit value up one bit, forcing the low bit to be zero. Then it can't match 8b1f on the bottom. That limits the total length to 63 bits, but that's not really a loss since the off_t type is signed anyway. Mark
