Commit 483546ce4f ("libctf: make ctf_serialize() actually serialize")
accidentally broke dict compression. There were two bugs:
- ctf_arc_write_one_ctf was still making its own decision about
whether to compress the dict via direct ctf_size comparison, which is
unfortunate because now that it no longer calls ctf_serialize itself,
ctf_size is always zero when it does this: it should let the writing
functions decide on the threshold, which they contain code to do which is
simply not used for lack of one trivial wrapper to write to an fd and
also provide a compression threshold
- ctf_write_mem, the function underlying all writing as of the commit
above, was calling zlib's compressBound and avoiding compression if this
returned a value larger than the input. Unfortunately compressBound does
not do a trial compression and determine whether the result is
compressible: it just adds zlib header sizes to the value passed in, so
our test would *always* have concluded that the value was incompressible!
Avoid by simply always compressing if the raw size is larger than the
threshold: zlib is quite clever enough to avoid actually compressing
if the data is incompressible.
Add a testcase for this.
libctf/
* ctf-impl.h (ctf_write_thresholded): New...
* ctf-serialize.c (ctf_write_thresholded): ... defined here,
a wrapper around...
(ctf_write_mem): ... this. Don't check compressibility.
(ctf_compress_write): Reimplement as a ctf_write_thresholded
wrapper.
(ctf_write): Likewise.
* ctf-archive.c (arc_write_one_ctf): Just call
ctf_write_thresholded rather than trying to work out whether
to compress.
* testsuite/libctf-writable/ctf-compressed.*: New test.
36c771b179