v3-0004-Fix-issues-with-reading-zero-bytes-in-Gzip_read-a.patch

From 6e65ac1ff26071024cfcf24d15819aa6b72af137 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 11 Oct 2025 21:16:12 -0400
Subject: [PATCH v3 4/4] Fix issues with reading zero bytes in Gzip_read and
 Zstd_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.  Zstd_read got the right result, but only after
doing a lot more work than necessary, because it checked at
the bottom of the loop not the top.

The Gzip_read fix perhaps should be back-patched, because
it breaks the nominally-supported case of manually gzip'ing
the toc.dat file within a directory-style dump.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/3515357.1760128017@sss.pgh.pa.us
---
 src/bin/pg_dump/compress_gzip.c | 4 ++++
 src/bin/pg_dump/compress_zstd.c | 5 +----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/bin/pg_dump/compress_gzip.c b/src/bin/pg_dump/compress_gzip.c
index 4a067e1402c..ad3b6486027 100644
--- 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);
 
 	/*
diff --git a/src/bin/pg_dump/compress_zstd.c b/src/bin/pg_dump/compress_zstd.c
index 5fe2279faae..36c1fd264ee 100644
--- a/src/bin/pg_dump/compress_zstd.c
+++ b/src/bin/pg_dump/compress_zstd.c
@@ -287,7 +287,7 @@ Zstd_read_internal(void *ptr, size_t size, CompressFileHandle *CFH, bool exit_on
 	output->dst = ptr;
 	output->pos = 0;
 
-	for (;;)
+	while (output->pos < output->size)
 	{
 		Assert(input->pos <= input->size);
 		Assert(input->size <= input_allocated_size);
@@ -341,9 +341,6 @@ Zstd_read_internal(void *ptr, size_t size, CompressFileHandle *CFH, bool exit_on
 			if (res == 0)
 				break;			/* End of frame */
 		}
-
-		if (output->pos == output->size)
-			break;				/* We read all the data that fits */
 	}
 
 	return output->pos;
-- 
2.43.7