Describe the bug

Trying to compress from a pipe using --patch-from fails.

To Reproduce

cat foo | zstd --patch-from=bar -o patch.zstd

Outputs:

zstd: fileio.c:774: FIO_adjustMemLimitForPatchFromMode: Assertion `maxSize != UTIL_FILESIZE_UNKNOWN' failed.

Similarly adding --long and or --memory produces the same result:

cat foo | zstd --long --patch-from=bar -o patch.zstd

zstd: fileio.c:774: FIO_adjustMemLimitForPatchFromMode: Assertion `maxSize != UTIL_FILESIZE_UNKNOWN' failed.

Expected behavior

Using --patch-from in this manner should produce a working patch.

If patching from stdin is not possible, it'd be preferable to print an error message explaining the situation.

Desktop (please complete the following information):

• OS: fedora
• Version: 32
• Compiler: gcc
• Build system: meson