From b856d200e52ccb3d841ba05df149173cb7cd8772 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 10 Oct 2025 15:01:57 +0900
Subject: [PATCH v1 1/5] Introduce API able to retrieve contents of PG_VERSION

This will be used by a set of follow-up patches, to be consumed in
various frontend tools.
---
 src/include/fe_utils/version.h | 23 ++++++++++
 src/fe_utils/Makefile          |  3 +-
 src/fe_utils/meson.build       |  1 +
 src/fe_utils/version.c         | 81 ++++++++++++++++++++++++++++++++++
 4 files changed, 107 insertions(+), 1 deletion(-)
 create mode 100644 src/include/fe_utils/version.h
 create mode 100644 src/fe_utils/version.c

diff --git a/src/include/fe_utils/version.h b/src/include/fe_utils/version.h
new file mode 100644
index 000000000000..3b8c1884de5f
--- /dev/null
+++ b/src/include/fe_utils/version.h
@@ -0,0 +1,23 @@
+/*-------------------------------------------------------------------------
+ *
+ * Routines to retrieve information of PG_VERSION
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/fe_utils/version.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef VERSION_H
+#define VERSION_H
+
+/*
+ * Retrieve the version major number, useful for major version checks
+ * based on PG_MAJORVERSION_NUM.
+ */
+#define GET_PG_MAJORVERSION_NUM(v)	((v) / 10000)
+
+extern uint32 get_pg_version(const char *datadir, char **version_str);
+
+#endif							/* VERSION_H */
diff --git a/src/fe_utils/Makefile b/src/fe_utils/Makefile
index 28196ce0f6ae..b9fd566ff873 100644
--- a/src/fe_utils/Makefile
+++ b/src/fe_utils/Makefile
@@ -37,7 +37,8 @@ OBJS = \
 	query_utils.o \
 	recovery_gen.o \
 	simple_list.o \
-	string_utils.o
+	string_utils.o \
+	version.o
 
 ifeq ($(PORTNAME), win32)
 override CPPFLAGS += -DFD_SETSIZE=1024
diff --git a/src/fe_utils/meson.build b/src/fe_utils/meson.build
index 5a9ddb73463e..ddac3c3a6584 100644
--- a/src/fe_utils/meson.build
+++ b/src/fe_utils/meson.build
@@ -18,6 +18,7 @@ fe_utils_sources = files(
   'recovery_gen.c',
   'simple_list.c',
   'string_utils.c',
+  'version.c',
 )
 
 psqlscan = custom_target('psqlscan',
diff --git a/src/fe_utils/version.c b/src/fe_utils/version.c
new file mode 100644
index 000000000000..8c06bb84b4d6
--- /dev/null
+++ b/src/fe_utils/version.c
@@ -0,0 +1,81 @@
+/*-------------------------------------------------------------------------
+ *
+ * version.c
+ *		Routine to retrieve information of PG_VERSION
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres_fe.h"
+
+#include <sys/stat.h>
+
+#include "common/logging.h"
+#include "fe_utils/version.h"
+
+/*
+ * Assumed maximum size of PG_VERSION.  This should be more than enough for
+ * any version numbers that need to be handled.
+ */
+#define PG_VERSION_MAX_SIZE	64
+
+/*
+ * get_major_version
+ *
+ * Retrieve the major version number of the given data folder, from
+ * PG_VERSION.  The result returned is a version number, that can be used
+ * for comparisons based on PG_VERSION_NUM.  For example, if PG_VERSION
+ * contains "18\n", this function returns 180000.
+ *
+ * This supports both the pre-v10 and the post-v10 version numbering.
+ * Optionally. "version_str" can be specified to store the contents
+ * retrieved from PG_VERSION.  It is allocated by this routine; the
+ * caller is responsible for pg_free()-ing it.
+ */
+uint32
+get_pg_version(const char *datadir, char **version_str)
+{
+	FILE	   *version_fd;
+	char		ver_filename[MAXPGPATH];
+	char		buf[PG_VERSION_MAX_SIZE];
+	int			v1 = 0,
+				v2 = 0;
+	struct stat st;
+
+	snprintf(ver_filename, sizeof(ver_filename), "%s/PG_VERSION",
+			 datadir);
+
+	if ((version_fd = fopen(ver_filename, "r")) == NULL)
+		pg_fatal("could not open version file \"%s\": %m", ver_filename);
+
+	if (fstat(fileno(version_fd), &st) != 0)
+		pg_fatal("could not stat file \"%s\": %m", ver_filename);
+	if (st.st_size > PG_VERSION_MAX_SIZE)
+		pg_fatal("file \"%s\" is too large", ver_filename);
+
+	if (fscanf(version_fd, "%63s", buf) == 0 ||
+		sscanf(buf, "%d.%d", &v1, &v2) < 1)
+		pg_fatal("could not parse version file \"%s\"", ver_filename);
+
+	fclose(version_fd);
+
+	if (version_str)
+	{
+		*version_str = pg_malloc(PG_VERSION_MAX_SIZE);
+		memcpy(*version_str, buf, st.st_size);
+	}
+
+	if (v1 < 10)
+	{
+		/* pre-v10 style, e.g. 9.6.1 */
+		return v1 * 10000 + v2 * 100;
+	}
+	else
+	{
+		/* post-v10 style, e.g. 10.1 */
+		return v1 * 10000;
+	}
+}
-- 
2.51.0