From b6bb54c963e1748b9a24568dddd375cdb8f7e192 Mon Sep 17 00:00:00 2001
From: Dan Engelbrecht <dan.engelbrecht@epicgames.com>
Date: Fri, 12 May 2023 13:23:56 +0200
Subject: better logging/exception when reading file in IoBuffer::Materialize
 fails (#294)

* better logging/exception when reading file in IoBuffer::Materialize fails
* changelog
---
 CHANGELOG.md             |  1 +
 src/zencore/iobuffer.cpp | 45 +++++++++++++++++++++++++++++++++++++--------
 2 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 97b0c0502..b76e5905f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 - Bugfix: Return error code on exit as set by application
 - Bugfix: Fix crash at startup if dead process handles are detected in ZenServerState
 - Bugfix: Fixed assert/error when running block store GC and a block to GC does not exist
+- Improvement: Log details about file and read operation when it fails inside IoBuffer::Materialize()
 
 ## 0.2.10
 - Feature: zenserver now writes a state_marker file in the root of the data directory. Deleting this file will cause zenserver to exit. This is used to detect if user is deleting the data folder while zenserver is running
diff --git a/src/zencore/iobuffer.cpp b/src/zencore/iobuffer.cpp
index e28bf11b2..96653c670 100644
--- a/src/zencore/iobuffer.cpp
+++ b/src/zencore/iobuffer.cpp
@@ -283,6 +283,8 @@ IoBufferExtendedCore::Materialize() const
 	{
 		AllocateBuffer(m_DataBytes, sizeof(void*));
 		NewFlags |= kIsOwnedByThis;
+		int32_t Error	  = 0;
+		size_t	BytesRead = 0;
 
 #if ZEN_PLATFORM_WINDOWS
 		OVERLAPPED Ovl{};
@@ -291,16 +293,43 @@ IoBufferExtendedCore::Materialize() const
 		Ovl.OffsetHigh = DWORD(m_FileOffset >> 32);
 
 		DWORD dwNumberOfBytesRead = 0;
-		BOOL  Success			  = ::ReadFile(m_FileHandle, (void*)m_DataPtr, DWORD(m_DataBytes), &dwNumberOfBytesRead, &Ovl);
-
-		ZEN_ASSERT(Success);
-		ZEN_ASSERT(dwNumberOfBytesRead == m_DataBytes);
+		BOOL  Success			  = ::ReadFile(m_FileHandle, (void*)m_DataPtr, DWORD(m_DataBytes), &dwNumberOfBytesRead, &Ovl) == TRUE;
+		if (Success)
+		{
+			BytesRead = size_t(dwNumberOfBytesRead);
+		}
+		else
+		{
+			Error = zen::GetLastError();
+		}
 #else
 		static_assert(sizeof(off_t) >= sizeof(uint64_t), "sizeof(off_t) does not support large files");
-		int	 Fd		   = int(uintptr_t(m_FileHandle));
-		int	 BytesRead = pread(Fd, (void*)m_DataPtr, m_DataBytes, m_FileOffset);
-		bool Success   = (BytesRead > 0);
+		int Fd		   = int(uintptr_t(m_FileHandle));
+		int ReadResult = pread(Fd, (void*)m_DataPtr, m_DataBytes, m_FileOffset);
+		if (ReadResult != -1)
+		{
+			BytesRead = size_t(ReadResult);
+		}
+		else
+		{
+			Error = zen::GetLastError();
+		}
 #endif	// ZEN_PLATFORM_WINDOWS
+		if (Error || (BytesRead != m_DataBytes))
+		{
+			ZEN_ERROR("ReadFile/pread failed (offset {:#x}, size {:#x}) file: '{}' (size {:#x}), {}",
+					  m_FileOffset,
+					  m_DataBytes,
+					  zen::PathFromHandle(m_FileHandle),
+					  zen::FileSizeFromHandle(m_FileHandle),
+					  GetSystemErrorAsString(Error));
+			throw std::system_error(std::error_code(Error, std::system_category()),
+									fmt::format("ReadFile/pread failed (offset {:#x}, size {:#x}) file: '{}' (size {:#x})",
+												m_FileOffset,
+												m_DataBytes,
+												PathFromHandle(m_FileHandle),
+												FileSizeFromHandle(m_FileHandle)));
+		}
 
 		m_Flags.fetch_or(NewFlags, std::memory_order_release);
 		return;
@@ -357,7 +386,7 @@ IoBufferExtendedCore::Materialize() const
 		CloseHandle(NewMmapHandle);
 #endif	// ZEN_PLATFORM_WINDOWS
 
-		ZEN_ERROR("MapViewOfFile failed (offset {:#x}, size {:#x}) file: '{}' (size {:#x}), {}",
+		ZEN_ERROR("MapViewOfFile/mmap failed (offset {:#x}, size {:#x}) file: '{}' (size {:#x}), {}",
 				  MapOffset,
 				  MapSize,
 				  zen::PathFromHandle(m_FileHandle),
-- 
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