gpg: Detect already compressed data also when using a pipe.
* common/iobuf.c (file_filter_ctx_t): Add fields for the peek feature. (file_filter): Implement peeking. (iobuf_ioctl): Add new IOBUF_IOCTL_PEEK. * common/iobuf.h (IOBUF_IOCTL_PEEK, IOBUFCTRL_PEEK): New. * common/miscellaneous.c (is_file_compressed): Rewrite. Detect PDF. * g10/encrypt.c (encrypt_simple): Peek before detecting compression. (encrypt_crypt): Ditto. * g10/sign.c (sign_file): Also detect already compressed data. * g10/options.h (opt): Add explicit_compress_option. * g10/gpg.c (main): Set opt.explicit_compress_option for -z.
Note that this patch also introduces a compression check for signing
which was never done in the past.
Note that sign.c (sign_file) has been re-indented to ease future
- GnuPG-bug-id: T6332