Caleb J. Gardner
113 lines
2.6 KiB
Zig
113 lines
2.6 KiB
Zig
const std = @import("std");
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const Io = std.Io;
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const Reader = Io.Reader;
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const Writer = Io.Writer;
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const Limit = Io.Limit;
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const Decomp = @import("decomp.zig");
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const MetadataReader = @This();
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alloc: std.mem.Allocator,
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data: []u8,
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decomp: Decomp.Fn,
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cur_offset: u64,
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block: [8192]u8 = undefined,
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interface: Reader = .{
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.buffer = &[0]u8{},
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.end = 0,
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.seek = 0,
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.vtable = &.{
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.stream = stream,
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.discard = discard,
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.readVec = readVec,
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},
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},
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pub fn init(alloc: std.mem.Allocator, data: []u8, decomp: Decomp.Fn, offset: u64) MetadataReader {
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return .{
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.alloc = alloc,
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.data = data,
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.decomp = decomp,
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.cur_offset = offset,
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};
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}
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fn advance(self: *MetadataReader) Reader.Error!void {
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self.interface.seek = 0;
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errdefer self.interface.end = 0;
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const hdr: Header = @intCast(std.mem.readInt(u16, self.data[self.cur_offset..][0..2], .little));
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defer self.cur_offset += hdr.size;
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const block = self.data[self.cur_offset + 2 ..][0..hdr.size];
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if (hdr.uncompressed) {
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self.interface.end = hdr.size;
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self.interface.buffer = block;
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return;
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}
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const decomp_size = self.decomp(self.alloc, block, &self.block) catch return Reader.Error.ReadFailed;
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self.interface.buffer = self.block[0..decomp_size];
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self.interface.end = decomp_size;
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}
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fn stream(r: *Reader, w: *Writer, limit: Limit) Reader.StreamError!usize {
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if (r.seek >= r.end) {
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const self: *MetadataReader = @fieldParentPtr("interface", r);
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try self.advance();
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}
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if (limit == .nothing) return 0;
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const to_write = @min(@intFromEnum(limit), r.end - r.seek);
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const wrote = try w.write(r.buffer[r.seek..][0..to_write]);
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r.seek += wrote;
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return wrote;
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}
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fn discard(r: *Reader, limit: Limit) Reader.Error!usize {
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if (r.seek >= r.end) {
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const self: *MetadataReader = @fieldParentPtr("interface", r);
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try self.advance();
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}
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if (limit == .nothing) return 0;
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const to_discard = @min(@intFromEnum(limit), r.end - r.seek);
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r.seek += to_discard;
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return to_discard;
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}
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fn readVec(r: *Reader, vec: [][]u8) Reader.Error!usize {
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if (r.seek >= r.end) {
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const self: *MetadataReader = @fieldParentPtr("interface", r);
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try self.advance();
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}
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var wrote: usize = 0;
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for (vec) |v| {
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const to_cpy = @min(v.len, r.end - r.seek);
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@memcpy(v[0..to_cpy], r.buffer[r.seek..][0..to_cpy]);
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wrote += to_cpy;
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if (r.seek >= r.end) break;
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}
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return wrote;
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}
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// Types
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const Header = packed struct(u16) {
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size: u15,
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uncompressed: bool,
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};
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