Moved to File.MemoryMap instead of direct file I/O

src/util/offset_file.zig

@@ -3,22 +3,25 @@
 const std = @import("std");
 const Io = std.Io;
 const File = Io.File;
-const Reader = File.Reader;
+const Reader = Io.Reader;
 
 const OffsetFile = @This();
 
-fil: File,
-offset: u64,
+map: Io.File.MemoryMap,
 
-pub fn init(fil: File, init_offset: u64) OffsetFile {
-    return .{ .fil = fil, .offset = init_offset };
+pub fn init(io: Io, fil: File, archive_size: u64, init_offset: u64) !OffsetFile {
+    return .{
+        .map = try fil.createMemoryMap(io, .{
+            .protection = .{ .read = true, .write = false, .execute = false },
+            .len = archive_size,
+            .offset = init_offset,
+        }),
+    };
+}
+pub fn deinit(self: @This(), io: Io) void {
+    self.map.destroy(io);
 }
 
-pub fn readerAt(self: OffsetFile, io: Io, offset: u64, buffer: []u8) Reader.SeekError!Reader {
-    var rdr = self.fil.reader(io, buffer);
-    try rdr.seekTo(self.offset + offset);
-    return rdr;
-}
-pub fn readAt(self: OffsetFile, io: Io, offset: u64, buf: []u8) File.ReadPositionalError!void {
-    _ = try self.fil.readPositionalAll(io, buf, self.offset + offset);
+pub fn readerAt(self: OffsetFile, offset: u64) Reader {
+    return .fixed(self.map.memory[offset..]);
 }