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const std = @import("std");
const os = std.os;
const math = std.math;
const CopyFileError = error{SystemResources} || os.CopyFileRangeError || os.SendFileError;
// Transfer all the data between two file descriptors in the most efficient way.
// The copy starts at offset 0, the initial offsets are preserved.
// No metadata is transferred over.
pub fn copy(fd_in: os.fd_t, fd_out: os.fd_t) CopyFileError!void {
if (comptime std.Target.current.isDarwin()) {
const rc = os.system.fcopyfile(fd_in, fd_out, null, os.system.COPYFILE_DATA);
switch (os.errno(rc)) {
.SUCCESS => return,
.INVAL => unreachable,
.NOMEM => return error.SystemResources,
// The source file is not a directory, symbolic link, or regular file.
// Try with the fallback path before giving up.
.OPNOTSUPP => {},
else => |err| return os.unexpectedErrno(err),
}
}
if (comptime std.Target.current.os.tag == .linux) {
// Try copy_file_range first as that works at the FS level and is the
// most efficient method (if available).
var offset: u64 = 0;
cfr_loop: while (true) {
// The kernel checks the u64 value `offset+count` for overflow, use
// a 32 bit value so that the syscall won't return EINVAL except for
// impossibly large files (> 2^64-1 - 2^32-1).
const amt = try os.copy_file_range(fd_in, offset, fd_out, offset, math.maxInt(u32), 0);
// Terminate when no data was copied
if (amt == 0) break :cfr_loop;
offset += amt;
}
return;
}
// Sendfile is a zero-copy mechanism iff the OS supports it, otherwise the
// fallback code will copy the contents chunk by chunk.
const empty_iovec = [0]os.iovec_const{};
var offset: u64 = 0;
sendfile_loop: while (true) {
const amt = try os.sendfile(fd_out, fd_in, offset, 0, &empty_iovec, &empty_iovec, 0);
// Terminate when no data was copied
if (amt == 0) break :sendfile_loop;
offset += amt;
}
}
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