From 7de3d4218ee5969af6147f9ab20bda538a136d9a Mon Sep 17 00:00:00 2001
From: Dan Engelbrecht <dan.engelbrecht@epicgames.com>
Date: Mon, 10 Mar 2025 18:33:24 +0100
Subject: pick up existing cache (#299)

- Improvement: Scavenge .zen temp folders for existing data (downloaded, decompressed or written) from previous failed run
- Improvement: Faster abort during stream compression
- Improvement: Try to move downloaded blobs with rename if possible avoiding an extra disk write
- Improvement: Only clean temp folders on successful or cancelled build - keep it if download fails
---
 src/zencore/basicfile.cpp | 37 ++++++++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 13 deletions(-)

(limited to 'src/zencore/basicfile.cpp')

diff --git a/src/zencore/basicfile.cpp b/src/zencore/basicfile.cpp
index 6e879ca0d..95876cff4 100644
--- a/src/zencore/basicfile.cpp
+++ b/src/zencore/basicfile.cpp
@@ -858,7 +858,7 @@ BasicFileWriter::Flush()
 }
 
 IoBuffer
-WriteToTempFile(const CompositeBuffer& Buffer, const std::filesystem::path& Path)
+WriteToTempFile(CompositeBuffer&& Buffer, const std::filesystem::path& Path)
 {
 	TemporaryFile	Temp;
 	std::error_code Ec;
@@ -868,6 +868,7 @@ WriteToTempFile(const CompositeBuffer& Buffer, const std::filesystem::path& Path
 		throw std::system_error(Ec, fmt::format("Failed to create temp file for blob at '{}'", Path));
 	}
 
+	uint64_t BufferSize = Buffer.GetSize();
 	{
 		uint64_t			  Offset		= 0;
 		static const uint64_t BufferingSize = 256u * 1024u;
@@ -899,21 +900,31 @@ WriteToTempFile(const CompositeBuffer& Buffer, const std::filesystem::path& Path
 	Temp.MoveTemporaryIntoPlace(Path, Ec);
 	if (Ec)
 	{
-		IoBuffer TmpBuffer = IoBufferBuilder::MakeFromFile(Path);
-		if (TmpBuffer)
+		Ec.clear();
+		BasicFile OpenTemp(Path, BasicFile::Mode::kDelete, Ec);
+		if (Ec)
 		{
-			IoHash		 ExistingHash = IoHash::HashBuffer(TmpBuffer);
-			const IoHash ExpectedHash = IoHash::HashBuffer(Buffer);
-			if (ExistingHash == ExpectedHash)
-			{
-				TmpBuffer.SetDeleteOnClose(true);
-				return TmpBuffer;
-			}
+			throw std::system_error(Ec, fmt::format("Failed to move temp file to '{}'", Path));
 		}
-		throw std::system_error(Ec, fmt::format("Failed to move temp file to '{}'", Path));
-	}
+		if (OpenTemp.FileSize() != BufferSize)
+		{
+			throw std::runtime_error(fmt::format("Failed to move temp file to '{}' - mismatching file size already exists", Path));
+		}
+		IoBuffer TmpBuffer(IoBuffer::File, OpenTemp.Detach(), 0, BufferSize, true);
 
-	IoBuffer TmpBuffer = IoBufferBuilder::MakeFromFile(Path);
+		IoHash		 ExistingHash = IoHash::HashBuffer(TmpBuffer);
+		const IoHash ExpectedHash = IoHash::HashBuffer(Buffer);
+		if (ExistingHash != ExpectedHash)
+		{
+			throw std::runtime_error(fmt::format("Failed to move temp file to '{}' - mismatching file hash already exists", Path));
+		}
+		Buffer = CompositeBuffer{};
+		TmpBuffer.SetDeleteOnClose(true);
+		return TmpBuffer;
+	}
+	Buffer = CompositeBuffer{};
+	BasicFile OpenTemp(Path, BasicFile::Mode::kDelete);
+	IoBuffer  TmpBuffer(IoBuffer::File, OpenTemp.Detach(), 0, BufferSize, true);
 	TmpBuffer.SetDeleteOnClose(true);
 	return TmpBuffer;
 }
-- 
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