Fix issue with reading zero bytes in Gzip_read.

pg_dump expects a read request of zero bytes to be a no-op; see for
example ReadStr().  Gzip_read got this wrong and falsely supposed
that the resulting gzret == 0 indicated an error.  We could complicate
that error-checking logic some more, but it seems best to just fall
out immediately when passed size == 0.

This bug breaks the nominally-supported case of manually gzip'ing
the toc.dat file within a directory-style dump, so back-patch to v16
where this code came in.  (Prior branches already have a short-circuit
for size == 0 before their only gzread call.)

Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/3515357.1760128017@sss.pgh.pa.us
Backpatch-through: 16

diff --git a/src/bin/pg_dump/compress_gzip.c b/src/bin/pg_dump/compress_gzip.c
index 0a457463e0535b57dfd73c3816dad4fedde7a3f3..85b5da3790f1d71e7c8767e1bfef2e29c2184225 100644 (file)
--- a/src/bin/pg_dump/compress_gzip.c
+++ b/src/bin/pg_dump/compress_gzip.c
@@ -257,6 +257,10 @@ Gzip_read(void *ptr, size_t size, CompressFileHandle *CFH)
    gzFile      gzfp = (gzFile) CFH->private_data;
    int         gzret;
 
+   /* Reading zero bytes must be a no-op */
+   if (size == 0)
+       return 0;
+
    gzret = gzread(gzfp, ptr, size);
 
    /*