exception on basicfile read error (#642)

* Change BasicFile::Read to throw exception like IoBuffer
- Don't ASSERT on dwNumberOfBytesRead == NumberOfBytesToRead - throw exception with details instead
- Use proper return type for pread()

3 files changed, 33 insertions, 10 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3b336ffd1..bc1d7a2a8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,7 @@
 ##
+- Improvement: Add details when reading from BasicFile fails (number of bytes read is not expected size)
+
+## 0.2.39
 - Feature: add `--ignore-missing-attachments` to `oplog-import` command
 - Feature: add `--ignore-missing-attachments` to `oplog-export` command
 - Improvement: Removed use of <random> in stats, for better performance (runtime as well as build)
diff --git a/src/zencore/iobuffer.cpp b/src/zencore/iobuffer.cpp
index 80d0f4ee4..54f2aaee8 100644
--- a/src/zencore/iobuffer.cpp
+++ b/src/zencore/iobuffer.cpp
@@ -327,8 +327,8 @@ IoBufferExtendedCore::Materialize() const
 		}
 #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 ReadResult = pread(Fd, (void*)m_DataPtr, m_DataBytes, m_FileOffset);
+		int		Fd		   = int(uintptr_t(m_FileHandle));
+		ssize_t ReadResult = pread(Fd, (void*)m_DataPtr, m_DataBytes, m_FileOffset);
 		if (ReadResult != -1)
 		{
 			BytesRead = size_t(ReadResult);
diff --git a/src/zenutil/basicfile.cpp b/src/zenutil/basicfile.cpp
index dbae76717..ad98bf652 100644
--- a/src/zenutil/basicfile.cpp
+++ b/src/zenutil/basicfile.cpp
@@ -171,6 +171,8 @@ BasicFile::Read(void* Data, uint64_t BytesToRead, uint64_t FileOffset)
 	while (BytesToRead)
 	{
 		const uint64_t NumberOfBytesToRead = Min(BytesToRead, MaxChunkSize);
+		int32_t		   Error			   = 0;
+		size_t		   BytesRead		   = 0;
 
 #if ZEN_PLATFORM_WINDOWS
 		OVERLAPPED Ovl{};
@@ -180,19 +182,37 @@ BasicFile::Read(void* Data, uint64_t BytesToRead, uint64_t FileOffset)
 
 		DWORD dwNumberOfBytesRead = 0;
 		BOOL  Success			  = ::ReadFile(m_FileHandle, Data, DWORD(NumberOfBytesToRead), &dwNumberOfBytesRead, &Ovl);
-
-		ZEN_ASSERT(dwNumberOfBytesRead == NumberOfBytesToRead);
+		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, Data, NumberOfBytesToRead, FileOffset);
-		bool Success   = (BytesRead > 0);
+		int		Fd		   = int(uintptr_t(m_FileHandle));
+		ssize_t ReadResult = pread(Fd, Data, NumberOfBytesToRead, FileOffset);
+		if (ReadResult != -1)
+		{
+			BytesRead = size_t(ReadResult);
+		}
+		else
+		{
+			Error = zen::GetLastError();
+		}
 #endif
 
-		if (!Success)
+		if (Error || (BytesRead != NumberOfBytesToRead))
 		{
-			std::error_code Dummy;
-			ThrowLastError(fmt::format("Failed to read from file '{}'", zen::PathFromHandle(m_FileHandle, Dummy)));
+			std::error_code DummyEc;
+			throw std::system_error(std::error_code(Error, std::system_category()),
+									fmt::format("ReadFile/pread failed (offset {:#x}, size {:#x}) file: '{}' (size {:#x})",
+												FileOffset,
+												NumberOfBytesToRead,
+												PathFromHandle(m_FileHandle, DummyEc),
+												FileSizeFromHandle(m_FileHandle)));
 		}
 
 		BytesToRead -= NumberOfBytesToRead;