From b64f4bdb3aa0687f80bb3f10dd80cfd8d0fd5771 Mon Sep 17 00:00:00 2001
From: sfan5 <sfan5@live.de>
Date: Sat, 20 Jan 2024 17:16:16 +0100
Subject: [PATCH] Optimize fs::CopyFileContents on Linux and Windows

---
 src/filesys.cpp | 181 +++++++++++++++++++++++++++++++++---------------
 1 file changed, 127 insertions(+), 54 deletions(-)

diff --git a/src/filesys.cpp b/src/filesys.cpp
index d91199594..2239bac66 100644
--- a/src/filesys.cpp
+++ b/src/filesys.cpp
@@ -31,6 +31,13 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #ifndef SERVER
 #include "irr_ptr.h"
 #endif
+#ifdef __linux__
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#ifndef FICLONE
+#define FICLONE _IOW(0x94, 9, int)
+#endif
+#endif
 
 namespace fs
 {
@@ -214,6 +221,31 @@ std::string CreateTempFile()
 	return path;
 }
 
+bool CopyFileContents(const std::string &source, const std::string &target)
+{
+	BOOL ok = CopyFileEx(source.c_str(), target.c_str(), nullptr, nullptr,
+		nullptr, COPY_FILE_ALLOW_DECRYPTED_DESTINATION);
+	if (!ok) {
+		errorstream << "copying " << source << " to " << target
+			<< " failed: " << GetLastError() << std::endl;
+		return false;
+	}
+
+	// docs: "File attributes for the existing file are copied to the new file."
+	// This is not our intention so get rid of unwanted attributes:
+	DWORD attr = GetFileAttributes(target.c_str());
+	if (attr == INVALID_FILE_ATTRIBUTES) {
+		errorstream << target << ": file disappeared after copy" << std::endl;
+		return false;
+	}
+	attr &= ~(FILE_ATTRIBUTE_READONLY | FILE_ATTRIBUTE_HIDDEN);
+	SetFileAttributes(target.c_str(), attr);
+
+	tracestream << "copied " << source << " to " << target
+		<< " using CopyFileEx" << std::endl;
+	return true;
+}
+
 #else
 
 /*********
@@ -412,6 +444,101 @@ std::string CreateTempFile()
 	return path;
 }
 
+namespace {
+	struct FileDeleter {
+		void operator()(FILE *stream) {
+			fclose(stream);
+		}
+	};
+
+	typedef std::unique_ptr<FILE, FileDeleter> FileUniquePtr;
+}
+
+bool CopyFileContents(const std::string &source, const std::string &target)
+{
+	FileUniquePtr sourcefile, targetfile;
+
+#ifdef __linux__
+	// Try to clone using Copy-on-Write (CoW). This is instant but supported
+	// only by some filesystems.
+
+	int srcfd, tgtfd;
+	srcfd = open(source.c_str(), O_RDONLY);
+	if (srcfd == -1) {
+		errorstream << source << ": can't open for reading: "
+			<< strerror(errno) << std::endl;
+		return false;
+	}
+	tgtfd = open(target.c_str(), O_WRONLY | O_CREAT | O_TRUNC, 0644);
+	if (tgtfd == -1) {
+		errorstream << target << ": can't open for writing: "
+			<< strerror(errno) << std::endl;
+		close(srcfd);
+		return false;
+	}
+
+	if (ioctl(tgtfd, FICLONE, srcfd) == 0) {
+		tracestream << "copied " << source << " to " << target
+			<< " using FICLONE" << std::endl;
+		close(srcfd);
+		close(tgtfd);
+		return true;
+	}
+
+	// fallback to normal copy, but no need to reopen the files
+	sourcefile.reset(fdopen(srcfd, "rb"));
+	targetfile.reset(fdopen(tgtfd, "wb"));
+	goto fallback;
+
+#endif
+
+	sourcefile.reset(fopen(source.c_str(), "rb"));
+	targetfile.reset(fopen(target.c_str(), "wb"));
+
+fallback:
+
+	if (!sourcefile) {
+		errorstream << source << ": can't open for reading: "
+			<< strerror(errno) << std::endl;
+		return false;
+	}
+	if (!targetfile) {
+		errorstream << target << ": can't open for writing: "
+			<< strerror(errno) << std::endl;
+		return false;
+	}
+
+	size_t total = 0;
+	bool done = false;
+	char readbuffer[BUFSIZ];
+	while (!done) {
+		size_t readbytes = fread(readbuffer, 1,
+				sizeof(readbuffer), sourcefile.get());
+		total += readbytes;
+		if (ferror(sourcefile.get())) {
+			errorstream << source << ": IO error: "
+				<< strerror(errno) << std::endl;
+			return false;
+		}
+		if (readbytes > 0)
+			fwrite(readbuffer, 1, readbytes, targetfile.get());
+		if (feof(sourcefile.get())) {
+			// flush destination file to catch write errors (e.g. disk full)
+			fflush(targetfile.get());
+			done = true;
+		}
+		if (ferror(targetfile.get())) {
+			errorstream << target << ": IO error: "
+					<< strerror(errno) << std::endl;
+			return false;
+		}
+	}
+	tracestream << "copied " << total << " bytes from "
+		<< source << " to " << target << std::endl;
+
+	return true;
+}
+
 #endif
 
 /****************************
@@ -486,60 +613,6 @@ bool CreateAllDirs(const std::string &path)
 	return true;
 }
 
-bool CopyFileContents(const std::string &source, const std::string &target)
-{
-	FILE *sourcefile = fopen(source.c_str(), "rb");
-	if(sourcefile == NULL){
-		errorstream<<source<<": can't open for reading: "
-			<<strerror(errno)<<std::endl;
-		return false;
-	}
-
-	FILE *targetfile = fopen(target.c_str(), "wb");
-	if(targetfile == NULL){
-		errorstream<<target<<": can't open for writing: "
-			<<strerror(errno)<<std::endl;
-		fclose(sourcefile);
-		return false;
-	}
-
-	size_t total = 0;
-	bool retval = true;
-	bool done = false;
-	char readbuffer[BUFSIZ];
-	while(!done){
-		size_t readbytes = fread(readbuffer, 1,
-				sizeof(readbuffer), sourcefile);
-		total += readbytes;
-		if(ferror(sourcefile)){
-			errorstream<<source<<": IO error: "
-				<<strerror(errno)<<std::endl;
-			retval = false;
-			done = true;
-		}
-		if(readbytes > 0){
-			fwrite(readbuffer, 1, readbytes, targetfile);
-		}
-		if(feof(sourcefile) || ferror(sourcefile)){
-			// flush destination file to catch write errors
-			// (e.g. disk full)
-			fflush(targetfile);
-			done = true;
-		}
-		if(ferror(targetfile)){
-			errorstream<<target<<": IO error: "
-					<<strerror(errno)<<std::endl;
-			retval = false;
-			done = true;
-		}
-	}
-	infostream<<"copied "<<total<<" bytes from "
-		<<source<<" to "<<target<<std::endl;
-	fclose(sourcefile);
-	fclose(targetfile);
-	return retval;
-}
-
 bool CopyDir(const std::string &source, const std::string &target)
 {
 	if(PathExists(source)){