From c5ce68512a54b7f586b458374f689df406f39ad6 Mon Sep 17 00:00:00 2001
From: Amul Sul <sulamul@gmail.com>
Date: Thu, 26 Jun 2025 11:42:53 +0530
Subject: [PATCH v8 2/8] Refactor: pg_waldump: Separate logic used to calculate
 the required read size.

This refactoring prepares the codebase for an upcoming patch that will
support reading WAL from tar files. The logic for calculating the
required read size has been updated to handle both normal WAL files
and WAL files located inside a tar archive.
---
 src/bin/pg_waldump/pg_waldump.c | 39 ++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 5846ee24f46..0dc28ea360c 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -326,6 +326,29 @@ identify_target_directory(char *directory, char *fname)
 	return NULL;				/* not reached */
 }
 
+/* Returns the size in bytes of the data to be read. */
+static inline int
+required_read_len(XLogDumpPrivate *private, XLogRecPtr targetPagePtr,
+				  int reqLen)
+{
+	int			count = XLOG_BLCKSZ;
+
+	if (XLogRecPtrIsValid(private->endptr))
+	{
+		if (targetPagePtr + XLOG_BLCKSZ <= private->endptr)
+			count = XLOG_BLCKSZ;
+		else if (targetPagePtr + reqLen <= private->endptr)
+			count = private->endptr - targetPagePtr;
+		else
+		{
+			private->endptr_reached = true;
+			return -1;
+		}
+	}
+
+	return count;
+}
+
 /* pg_waldump's XLogReaderRoutine->segment_open callback */
 static void
 WALDumpOpenSegment(XLogReaderState *state, XLogSegNo nextSegNo,
@@ -383,21 +406,11 @@ WALDumpReadPage(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen,
 				XLogRecPtr targetPtr, char *readBuff)
 {
 	XLogDumpPrivate *private = state->private_data;
-	int			count = XLOG_BLCKSZ;
+	int			count = required_read_len(private, targetPagePtr, reqLen);
 	WALReadError errinfo;
 
-	if (XLogRecPtrIsValid(private->endptr))
-	{
-		if (targetPagePtr + XLOG_BLCKSZ <= private->endptr)
-			count = XLOG_BLCKSZ;
-		else if (targetPagePtr + reqLen <= private->endptr)
-			count = private->endptr - targetPagePtr;
-		else
-		{
-			private->endptr_reached = true;
-			return -1;
-		}
-	}
+	if (private->endptr_reached)
+		return -1;
 
 	if (!WALRead(state, readBuff, targetPagePtr, count, private->timeline,
 				 &errinfo))
-- 
2.47.1