Improve const use in zlib-using code

From 81f053c68109d85ae657f6d9f652d90f1d55fb2a Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 3 Aug 2023 08:47:02 +0200
Subject: [PATCH v2 1/2] Improve const use in zlib-using code

If we define ZLIB_CONST before including zlib.h, zlib augments some
interfaces with const decorations.  By doing that we can keep our own
interfaces cleaner and can remove some unconstify calls.

ZLIB_CONST was introduced in zlib 1.2.5.2 (17 Dec 2011).

XXX CentOS 6 has zlib-1.2.3-29.el6.x86_64
---
 contrib/pgcrypto/pgp-compress.c         | 2 +-
 src/bin/pg_basebackup/bbstreamer_gzip.c | 2 +-
 src/bin/pg_basebackup/walmethods.c      | 5 ++---
 src/include/c.h                         | 5 +++++
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/contrib/pgcrypto/pgp-compress.c b/contrib/pgcrypto/pgp-compress.c
index 086bec31ae..961cf21e74 100644
--- a/contrib/pgcrypto/pgp-compress.c
+++ b/contrib/pgcrypto/pgp-compress.c
@@ -113,7 +113,7 @@ compress_process(PushFilter *next, void *priv, const uint8 *data, int len)
 	/*
 	 * process data
 	 */
-	st->stream.next_in = unconstify(uint8 *, data);
+	st->stream.next_in = data;
 	st->stream.avail_in = len;
 	while (st->stream.avail_in > 0)
 	{
diff --git a/src/bin/pg_basebackup/bbstreamer_gzip.c b/src/bin/pg_basebackup/bbstreamer_gzip.c
index 3bdbfa0bc4..fb25fef150 100644
--- a/src/bin/pg_basebackup/bbstreamer_gzip.c
+++ b/src/bin/pg_basebackup/bbstreamer_gzip.c
@@ -269,7 +269,7 @@ bbstreamer_gzip_decompressor_content(bbstreamer *streamer,
 	mystreamer = (bbstreamer_gzip_decompressor *) streamer;
 
 	zs = &mystreamer->zstream;
-	zs->next_in = (uint8 *) data;
+	zs->next_in = (const uint8 *) data;
 	zs->avail_in = len;
 
 	/* Process the current chunk */
diff --git a/src/bin/pg_basebackup/walmethods.c b/src/bin/pg_basebackup/walmethods.c
index 376ddf72b7..965d49dec4 100644
--- a/src/bin/pg_basebackup/walmethods.c
+++ b/src/bin/pg_basebackup/walmethods.c
@@ -705,7 +705,7 @@ typedef struct TarMethodData
 
 #ifdef HAVE_LIBZ
 static bool
-tar_write_compressed_data(TarMethodData *tar_data, void *buf, size_t count,
+tar_write_compressed_data(TarMethodData *tar_data, const void *buf, size_t count,
 						  bool flush)
 {
 	tar_data->zp->next_in = buf;
@@ -782,8 +782,7 @@ tar_write(Walfile *f, const void *buf, size_t count)
 #ifdef HAVE_LIBZ
 	else if (f->wwmethod->compression_algorithm == PG_COMPRESSION_GZIP)
 	{
-		if (!tar_write_compressed_data(tar_data, unconstify(void *, buf),
-									   count, false))
+		if (!tar_write_compressed_data(tar_data, buf, count, false))
 			return -1;
 		f->currpos += count;
 		return count;
diff --git a/src/include/c.h b/src/include/c.h
index f69d739be5..82f8e9d4c7 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -75,6 +75,11 @@
 #include <libintl.h>
 #endif
 
+/* Define before including zlib.h to add const decorations to zlib API. */
+#ifdef HAVE_LIBZ
+#define ZLIB_CONST
+#endif
+
 
 /* ----------------------------------------------------------------
  *				Section 1: compiler characteristics
-- 
2.41.0

From 76fb004fa151746d584816befb3a070570697298 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 3 Aug 2023 08:52:30 +0200
Subject: [PATCH v2 2/2] Remove check for z_streamp

This is surely obsolete.  zlib version 1.0.4, which includes
z_streamp, was released 1996-07-24.  When this check was put in in
2001 (19c97b8579), it was already labeling that release ancient.
---
 configure    | 15 ---------------
 configure.ac |  9 ---------
 meson.build  |  8 --------
 3 files changed, 32 deletions(-)

diff --git a/configure b/configure
index 2e518c8007..963fbbcf1e 100755
--- a/configure
+++ b/configure
@@ -15162,21 +15162,6 @@ _ACEOF
 fi
 
 
-if test "$with_zlib" = yes; then
-  # Check that <zlib.h> defines z_streamp (versions before about 1.0.4
-  # did not).  While we could work around the lack of z_streamp, it
-  # seems unwise to encourage people to use such old zlib versions...
-  ac_fn_c_check_type "$LINENO" "z_streamp" "ac_cv_type_z_streamp" "#include <zlib.h>
-"
-if test "x$ac_cv_type_z_streamp" = xyes; then :
-
-else
-  as_fn_error $? "zlib version is too old
-Use --without-zlib to disable zlib support." "$LINENO" 5
-fi
-
-fi
-
 case $host_cpu in
   x86_64)
     # On x86_64, check if we can compile a popcntq instruction
diff --git a/configure.ac b/configure.ac
index 3ebe1a796d..5153b8b3fd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1678,15 +1678,6 @@ AC_CHECK_TYPES([struct option], [], [],
 #include <getopt.h>
 #endif])
 
-if test "$with_zlib" = yes; then
-  # Check that <zlib.h> defines z_streamp (versions before about 1.0.4
-  # did not).  While we could work around the lack of z_streamp, it
-  # seems unwise to encourage people to use such old zlib versions...
-  AC_CHECK_TYPE(z_streamp, [], [AC_MSG_ERROR([zlib version is too old
-Use --without-zlib to disable zlib support.])],
-                [#include <zlib.h>])
-fi
-
 case $host_cpu in
   x86_64)
     # On x86_64, check if we can compile a popcntq instruction
diff --git a/meson.build b/meson.build
index 04ea348852..0a11efc97a 100644
--- a/meson.build
+++ b/meson.build
@@ -1384,14 +1384,6 @@ if not zlibopt.disabled()
       args: test_c_args, include_directories: postgres_inc,
       dependencies: [zlib_t], required: zlibopt)
     warning('zlib header not found')
-  elif not cc.has_type('z_streamp',
-      dependencies: [zlib_t], prefix: '#include <zlib.h>',
-      args: test_c_args, include_directories: postgres_inc)
-    if zlibopt.enabled()
-      error('zlib version is too old')
-    else
-      warning('zlib version is too old')
-    endif
   else
     zlib = zlib_t
   endif
-- 
2.41.0