Further work on making everything work

Directory table reading
Finished MetadataReader

src/utils/meta.zig

@@ -1,8 +1,109 @@
 const std = @import("std");
+const Io = std.Io;
+
+const util = @import("util.zig");
 
 const Decomp = @import("../decomp.zig");
 
 const MetadataReader = @This();
 
+alloc: std.mem.Allocator,
+
 data: []u8,
 decomp: Decomp.Fn,
+
+decomp_block: [8192]u8 = undefined,
+
+interface: Io.Reader = .{
+    .buffer = &[0]u8,
+    .end = 0,
+    .seek = 0,
+    .vtable = &.{
+        .stream = stream,
+        .discard = discard,
+        .readVec = readVec,
+    },
+},
+
+pub fn init(alloc: std.mem.Allocator, data: []u8, decomp: Decomp.Fn) MetadataReader {
+    return .{
+        .alloc = alloc,
+
+        .data = data,
+        .decomp = decomp,
+    };
+}
+
+fn advance(self: *MetadataReader) Io.Reader.Error!void {
+    self.interface.seek = 0;
+    errdefer self.interface.end = 0;
+
+    const hdr = util.readValue(Header, self.data[0..2]);
+
+    const block = self.data[2..][0..hdr.size];
+
+    self.data = self.data[hdr.size + 2 ..];
+
+    if (hdr.uncompressed) {
+        self.interface.end = hdr.size;
+        self.interface.buffer = block;
+        return;
+    }
+
+    self.interface.end = self.decomp(self.alloc, block, &self.decomp_block) catch return error.ReadFailed;
+    self.interface.buffer = self.decomp_block[0..self.interface.end];
+}
+
+fn stream(rdr: *Io.Reader, wrt: *Io.Writer, limit: Io.Limit) Io.Reader.StreamError!usize {
+    if (rdr.seek >= rdr.end) {
+        var meta: *MetadataReader = @fieldParentPtr("interface", rdr);
+        try meta.advance();
+    }
+    if (limit == .nothing) return 0;
+
+    const size = @min(@intFromEnum(limit), rdr.end - rdr.seek);
+
+    const wrote = try wrt.write(rdr.buffer[rdr.seek..][0..size]);
+    rdr.seek += wrote;
+
+    return wrote;
+}
+fn discard(rdr: *Io.Reader, limit: Io.Limit) Io.Reader.Error!usize {
+    if (rdr.seek >= rdr.end) {
+        var meta: *MetadataReader = @fieldParentPtr("interface", rdr);
+        try meta.advance();
+    }
+    if (limit == .nothing) return 0;
+
+    const size = @min(@intFromEnum(limit), rdr.end - rdr.seek);
+    rdr.seek += size;
+
+    return size;
+}
+fn readVec(rdr: *Io.Reader, vec: [][]u8) Io.Reader.Error!usize {
+    if (rdr.seek >= rdr.end) {
+        var meta: *MetadataReader = @fieldParentPtr("interface", rdr);
+        try meta.advance();
+    }
+
+    var wrote: usize = 0;
+    for (vec) |s| {
+        const size = @min(rdr.end - rdr.seek, s.len);
+
+        @memcpy(s[0..size], rdr.buffer[rdr.seek..][0..size]);
+
+        wrote += size;
+        rdr.seek += size;
+
+        if (rdr.seek >= rdr.end) break;
+    }
+
+    return wrote;
+}
+
+// Types
+
+const Header = packed struct(u16) {
+    size: u15,
+    uncompressed: bool,
+};