A BUNCH OF STUFF

Metadata reading
Directory reading
Decompile cache
Actual SfsFile implementation
Finished Inode implementation
Actually build unsquashfs

build.zig

@@ -36,7 +36,7 @@ pub fn build(b: *std.Build) !void {
     const deps = try getDependencies(b, optimize, target, allow_lzo);
 
     const lib = b.addLibrary(.{
-        .name = "unsquashfs",
+        .name = "squashfs",
         .use_llvm = debug,
         .version = version,
         .root_module = b.createModule(.{
@@ -54,6 +54,23 @@ pub fn build(b: *std.Build) !void {
     for (deps) |d|
         lib.root_module.linkLibrary(d);
 
+    b.installArtifact(lib);
+
+    const exe = b.addExecutable(.{
+        .name = "unsquashfs",
+        .use_llvm = debug,
+        .version = version,
+        .root_module = b.createModule(.{
+            .optimize = optimize,
+            .target = target,
+            .root_source_file = b.path("src/bin/unsquashfs.zig"),
+            .valgrind = debug,
+        }),
+    });
+    exe.root_module.linkLibrary(lib);
+
+    b.installArtifact(exe);
+
     const lib_test = b.addTest(.{
         .name = "squashfs-test",
         .root_module = lib.root_module,
@@ -66,9 +83,14 @@ pub fn build(b: *std.Build) !void {
         .name = "squashfs-check",
         .root_module = lib.root_module,
     });
+    const exe_check = b.addLibrary(.{
+        .name = "unsquashfs-check",
+        .root_module = exe.root_module,
+    });
 
     const check = b.step("check", "Check if squashfs compiles");
     check.dependOn(&lib_check.step);
+    check.dependOn(&exe_check.step);
 }
 
 fn getDependencies(b: *Build, optimize: std.builtin.OptimizeMode, target: Build.ResolvedTarget, allow_lzo: bool) ![]*Build.Step.Compile {

src/archive.zig

@@ -4,28 +4,83 @@ const File = Io.File;
 const MemoryMap = File.MemoryMap;
 
 const Decomp = @import("decomp.zig");
+const DecompCache = @import("decomp_cache.zig");
 const ExtractionOptions = @import("options.zig");
 const Inode = @import("inode.zig");
 const SfsFile = @import("file.zig");
 
 const Archive = @This();
 
-map: MemoryMap,
+const CACHE_MEM_MAX = 1024 * 1024 * 1024;
 
-decomp: Decomp.Fn,
+super: Superblock,
 
-pub fn init(io: Io, fil: File) !Archive {
+cache: DecompCache,
-    return initAdvanced(io, fil, 0);
+
+pub fn init(alloc: std.mem.Allocator, io: Io, fil: File) !Archive {
+    return initAdvanced(alloc, io, fil, 0, 0);
+}
+pub fn initAdvanced(alloc: std.mem.Allocator, io: Io, fil: File, offset: u64, cache_memory_max: u64) !Archive {
+    var rdr = fil.reader(io, &[0]u8{});
+    try rdr.seekTo(offset);
+    var super: Superblock = undefined;
+    try rdr.interface.readSliceEndian(Superblock, @ptrCast(&super), .little);
+    try super.validate();
+
+    const map = try fil.createMemoryMap(io, .{
+        .offset = offset,
+        .len = super.size,
+        .protection = .{ .read = true },
+    });
+
+    return .{
+        .super = super,
+
+        .cache = .init(
+            alloc,
+            map,
+            super.compression,
+            if (cache_memory_max != 0)
+                cache_memory_max
+            else
+                @min(CACHE_MEM_MAX, (try std.process.totalSystemMemory()) / 2),
+        ),
+    };
 }
-pub fn initAdvanced(io: Io, fil: File, offset: u64) !Archive {}
 pub fn deinit(self: *Archive, io: Io) void {
-    self.map.destroy(io);
+    self.cache.deinit(io);
 }
 
-pub fn root(self: Archive, alloc: std.mem.Allocator) !SfsFile {}
+pub fn root(self: *Archive, alloc: std.mem.Allocator, io: Io) !SfsFile {
-pub fn open(self: Archive, alloc: std.mem.Allocator, filepath: []const u8) !SfsFile {}
+    const inode: Inode = try .initRef(
+        alloc,
+        io,
+        &self.cache,
+        self.super.inode_start,
+        self.super.block_size,
+        self.super.root_ref,
+    );
+    return .init(alloc, self, inode, "");
+}
+pub fn open(self: *Archive, alloc: std.mem.Allocator, io: Io, filepath: []const u8) !SfsFile {
+    const path = std.mem.trim(u8, filepath, "/");
 
-pub fn extract(self: Archive, alloc: std.mem.Allocator, io: Io, ext_loc: []const u8, options: ExtractionOptions) !void {}
+    var root_file = try self.root(alloc, io);
+
+    if (path.len == 0 or path[0] == '.') return root_file;
+
+    defer root_file.deinit();
+    return root_file.open(alloc, io, filepath);
+}
+
+pub fn extract(self: *Archive, alloc: std.mem.Allocator, io: Io, ext_loc: []const u8, options: ExtractionOptions) !void {
+    _ = self;
+    _ = alloc;
+    _ = io;
+    _ = ext_loc;
+    _ = options;
+    return error.TODO;
+}
 
 // Superblock
 
@@ -37,7 +92,9 @@ pub const Superblock = extern struct {
     frag_count: u32,
     compression: Decomp.Enum,
     block_log: u16,
-    flags: packed struct(u16) {},
+    flags: packed struct(u16) {
+        TODO: u16,
+    },
     id_count: u16,
     ver_maj: u16,
     ver_min: u16,
@@ -49,6 +106,15 @@ pub const Superblock = extern struct {
     dir_start: u64,
     frag_start: u64,
     export_start: u64,
+
+    pub fn validate(self: Superblock) !void {
+        if (self.magic != std.mem.readInt(u32, "hsqs", .little))
+            return error.BadMagic;
+        if (self.ver_maj != 4 or self.ver_min != 0)
+            return error.InvalidVersion;
+        if (self.block_log != std.math.log2(self.block_size))
+            return error.BadBlockLog;
+    }
 };
 
 // Test
@@ -61,7 +127,7 @@ test "Basics" {
 
     var archive_file = try Io.Dir.cwd().openFile(io, TestArchive, .{});
     defer archive_file.close(io);
-    var arc: Archive = .init(io, archive_file);
+    var arc: Archive = try .init(io, archive_file);
     defer arc.deinit(io);
 
     var root_file = try arc.root(alloc);
@@ -77,7 +143,7 @@ test "SingleFileExtraction" {
 
     var archive_file = try Io.Dir.cwd().openFile(io, TestArchive, .{});
     defer archive_file.close(io);
-    var arc: Archive = .init(io, archive_file);
+    var arc: Archive = try .init(io, archive_file);
     defer arc.deinit(io);
 
     var ext_file = try arc.open(alloc, TestFile);
@@ -94,7 +160,7 @@ test "FullExtraction" {
 
     var archive_file = try Io.Dir.cwd().openFile(io, TestArchive, .{});
     defer archive_file.close(io);
-    var arc: Archive = .init(io, archive_file);
+    var arc: Archive = try .init(io, archive_file);
     defer arc.deinit(io);
 
     try arc.extract(alloc, io, TestFullExtractLocation, .default);

src/decomp_cache.zig

@@ -0,0 +1,116 @@
+const std = @import("std");
+const Io = std.Io;
+const File = Io.File;
+const MemoryMap = File.MemoryMap;
+const Atomic = std.atomic.Value;
+
+const Decomp = @import("decomp.zig");
+
+const DecompCache = @This();
+
+alloc: std.mem.Allocator,
+map: MemoryMap,
+decomp_fn: Decomp.Fn,
+
+cache: std.AutoHashMap(u64, Cache),
+mut: std.Io.RwLock = .init,
+cond: std.Io.Condition = .init,
+
+max_mem: u64,
+cur_mem: u64 = 0,
+
+pub fn init(alloc: std.mem.Allocator, map: MemoryMap, compression: Decomp.Enum, max_mem: u64) DecompCache {
+    return .{
+        .alloc = alloc,
+        .map = map,
+        .decomp_fn = try Decomp.DecompFn(compression),
+
+        .cache = .init(alloc),
+
+        .max_mem = max_mem,
+    };
+}
+pub fn deinit(self: *DecompCache, io: Io) void {
+    self.mut.lockUncancelable(io);
+
+    var iter = self.cache.valueIterator();
+    while (iter.next()) |v|
+        self.alloc.free(v.data);
+    self.cache.deinit();
+}
+
+pub fn get(self: *DecompCache, io: Io, offset: u64, compressed_size: u32, max_size: u32) ![]u8 {
+    {
+        try self.mut.lockShared(io);
+        defer self.mut.unlockShared(io);
+
+        const cache = self.cache.getPtr(offset);
+        if (cache != null) {
+            _ = cache.?.usage.fetchAdd(1, .acquire);
+            return cache.?.data;
+        }
+    }
+    try self.mut.lock(io);
+    defer self.mut.unlock(io);
+
+    const cache = try self.cache.getOrPut(offset);
+    if (cache.found_existing) {
+        _ = cache.?.usage.fetchAdd(1, .acquire);
+        return cache.?.data;
+    }
+    errdefer self.cache.removeByPtr(cache.key_ptr);
+
+    try self.ensureSpace(io, max_size);
+
+    var out = try self.alloc.alloc(u8, max_size);
+    errdefer self.alloc.free(out);
+
+    const decomp_size = try self.decomp_fn(self.alloc, self.map.memory[offset..][0..compressed_size], out);
+    if (decomp_size != max_size) {
+        if (!self.alloc.resize(out, decomp_size)) {
+            const new_out = try self.alloc.alloc(u8, decomp_size);
+            @memcpy(new_out, out[0..decomp_size]);
+            out = new_out;
+        } else {
+            out.len = decomp_size;
+        }
+    }
+    self.cur_mem += decomp_size;
+
+    cache.value_ptr.data = out;
+    _ = cache.value_ptr.usage.fetchAdd(1, .acquire);
+    return out;
+}
+pub fn finished(self: *DecompCache, io: Io, offset: u64) void {
+    const cache = self.cache.getPtr(offset);
+    if (cache == null) {
+        std.debug.print("Finished using cache, but cache does not exist: {}\n", .{offset});
+        return;
+    }
+    const use = cache.?.usage.fetchSub(1, .acquire);
+    if (use == 0)
+        self.cond.broadcast(io);
+}
+
+fn ensureSpace(self: *DecompCache, io: Io, size: u64) !void {
+    while (self.cur_mem + size > self.max_mem) {
+        var iter = self.cache.valueIterator();
+        while (iter.next()) |cache| {
+            if (cache.usage.load(.unordered) == 0) {
+                self.alloc.free(cache.data);
+                self.cur_mem -= cache.data.len;
+
+                if (self.cur_mem + size <= self.max_mem) return;
+            }
+        }
+        if (self.cur_mem + size <= self.max_mem) return;
+        try self.cond.wait(io, self.mut.mutex);
+    }
+}
+
+// Types
+
+const Cache = struct {
+    data: []u8,
+    usage: Atomic(u32),
+};

src/directory.zig

@@ -0,0 +1,81 @@
+const std = @import("std");
+const Io = std.Io;
+const Reader = Io.Reader;
+
+const Inode = @import("inode.zig");
+
+const Directory = @This();
+
+entries: []Entry,
+
+pub fn init(alloc: std.mem.Allocator, rdr: *Reader, size: u32) !Directory {
+    if (size <= 3) return .{ .entries = &[0]Entry{} };
+
+    var entries: std.ArrayList(Entry) = try .initCapacity(alloc, 50);
+    errdefer {
+        for (entries.items) |ent|
+            ent.deinit(alloc);
+        entries.deinit(alloc);
+    }
+
+    var read: u32 = 3;
+    while (read < size) {
+        var hdr: Header = undefined;
+        try rdr.readSliceEndian(Header, @ptrCast(&hdr), .little);
+        read += @sizeOf(Header);
+
+        try entries.ensureUnusedCapacity(alloc, hdr.count + 1);
+        for (0..hdr.count + 1) |_| {
+            var raw: RawEntry = undefined;
+            try rdr.readSliceEndian(RawEntry, @ptrCast(&raw), .little);
+
+            const name = try alloc.alloc(u8, raw.name_size + 1);
+            errdefer alloc.free(name);
+            try rdr.readSliceEndian(u8, name, .little);
+
+            entries.appendAssumeCapacity(.{
+                .inode_num = if (raw.inode_num_offset > 0)
+                    hdr.inode_num + @abs(raw.inode_num_offset)
+                else
+                    hdr.inode_num - @abs(raw.inode_num_offset),
+                .block_start = hdr.block_start,
+                .block_offset = raw.block_offset,
+                .type = raw.type,
+                .name = name,
+            });
+        }
+    }
+
+    return entries.toOwnedSlice(alloc);
+}
+pub fn deinit(self: Directory, alloc: std.mem.Allocator) void {
+    for (self.entries) |entry|
+        entry.deinit(alloc);
+    alloc.free(self.entries);
+}
+
+// Types
+
+pub const Entry = struct {
+    inode_num: u32,
+    block_start: u32,
+    block_offset: u16,
+    type: Inode.Enum,
+    name: []const u8,
+
+    pub fn deinit(self: Entry, alloc: std.mem.Allocator) void {
+        alloc.free(self.name);
+    }
+};
+
+const Header = extern struct {
+    count: u32,
+    block_start: u32,
+    inode_num: u32,
+};
+const RawEntry = extern struct {
+    block_offset: u16,
+    inode_num_offset: i16,
+    type: Inode.Enum,
+    name_size: u16,
+};

src/file.zig

@@ -1,7 +1,92 @@
+const SfsFile = @This();
+
+alloc: std.mem.Allocator,
+archive: *Archive,
+
+inode: Inode,
+name: []const u8,
+
+/// The given allocator must have been used to create the Inode and name.
+pub fn init(alloc: std.mem.Allocator, archive: *Archive, inode: Inode, name: []const u8) SfsFile {
+    return .{
+        .alloc = alloc,
+        .archive = archive,
+
+        .inode = inode,
+        .name = name,
+    };
+}
+pub fn initDirEntry(alloc: std.mem.Allocator, io: Io, archive: *Archive, entry: Directory.Entry) !SfsFile {
+    const new_name = try alloc.alloc(u8, entry.name.len);
+    defer alloc.free(new_name);
+    @memcpy(new_name, entry.name);
+
+    return .{
+        .alloc = alloc,
+        .archive = archive,
+
+        .inode = try .initDirEntry(
+            alloc,
+            io,
+            archive.cache,
+            archive.super.inode_start,
+            archive.super.block_size,
+            entry,
+        ),
+        .name = new_name,
+    };
+}
+/// Creates a new copy of the given SfsFile using the given allocator
+pub fn copy(self: SfsFile, alloc: std.mem.Allocator) !SfsFile {
+    const new_name = try alloc(u8, self.name.len);
+    errdefer alloc.free(new_name);
+
+    return .{
+        .alloc = alloc,
+        .archive = self.archive,
+
+        .inode = try self.inode.copy(alloc),
+        .name = new_name,
+    };
+}
+pub fn deinit(self: SfsFile) void {
+    self.inode.deinit(self.alloc);
+    self.alloc.free(self.name);
+}
+
+/// Attempts to open the filepath if the SfsFile is a directory.
+/// If the given path refers to itself (such as "" or "."), a copied SfsFile is returned.
+pub fn open(self: SfsFile, alloc: std.mem.Allocator, io: Io, filepath: []const u8) !SfsFile {
+    const path = std.mem.trim(u8, filepath, "/");
+
+    const first_element: []const u8 = std.mem.sliceTo(path, '/');
+
+    const dir: Directory = try self.inode.directory(alloc, io, self.archive.cache, self.archive.super.dir_start);
+    defer dir.deinit(alloc);
+
+    var cur_slice = dir.entries;
+    var idx: usize = undefined;
+    while (cur_slice.len > 0) {
+        idx = cur_slice.len / 2;
+        switch (std.mem.order(u8, first_element, cur_slice[idx].name)) {
+            .eq => break,
+            .lt => cur_slice = cur_slice[0..idx],
+            .gt => cur_slice = cur_slice[idx..],
+        }
+    } else {
+        return error.NotFound;
+    }
+    if (first_element.len == path) return .initDirEntry(alloc, io, self.archive, cur_slice[idx]);
+    if (cur_slice[idx].type != .dir) return error.NotFound;
+    const tmp_file: SfsFile = try .initDirEntry(alloc, io, self.archive, cur_slice[idx]);
+    defer tmp_file.deinit();
+
+    return tmp_file.open(alloc, io, path[first_element.len..]);
+}
+
 const std = @import("std");
 const Io = std.Io;
 
+const Archive = @import("archive.zig");
+const Directory = @import("directory.zig");
 const Inode = @import("inode.zig");
-
-name: []const u8,
-inode: Inode,

src/inode.zig

@@ -1,10 +1,109 @@
 const std = @import("std");
+const Io = std.Io;
+const Reader = Io.Reader;
+
+const DecompCache = @import("decomp_cache.zig");
+const Directory = @import("directory.zig");
+const MetadataReader = @import("meta_rdr.zig");
 
 const Inode = @This();
 
 hdr: Header,
 data: Data,
 
+/// Read an inode given an inode Ref.
+pub fn initRef(alloc: std.mem.Allocator, io: Io, cache: *DecompCache, inode_start: u64, block_size: u32, ref: Ref) !Inode {
+    var meta: MetadataReader = .init(io, cache, inode_start + ref.block_start);
+    defer meta.deinit(io);
+    try meta.interface.discardAll(ref.block_offset);
+
+    return .init(alloc, &meta.interface, block_size);
+}
+pub fn initDirEntry(alloc: std.mem.Allocator, io: Io, cache: *DecompCache, inode_start: u64, block_size: u32, entry: Directory.Entry) !Inode {
+    var meta: MetadataReader = .init(io, cache, inode_start + entry.block_start);
+    defer meta.deinit(io);
+    try meta.interface.discardAll(entry.block_offset);
+
+    return .init(alloc, &meta.interface, block_size);
+}
+/// Read the inode from the given Reader.
+pub fn init(alloc: std.mem.Allocator, rdr: *Reader, block_size: u32) !Inode {
+    var hdr: Header = undefined;
+    try rdr.readSliceEndian(Header, @ptrCast(&hdr), .little);
+    const data: Data = switch (hdr.type) {
+        .dir => .{ .dir = try .init(rdr) },
+        .file => .{ .file = try .init(alloc, rdr, block_size) },
+        .symlink => .{ .symlink = try .init(alloc, rdr) },
+        .block_dev => .{ .block_dev = try .init(rdr) },
+        .char_dev => .{ .char_dev = try .init(rdr) },
+        .fifo => .{ .fifo = try .init(rdr) },
+        .socket => .{ .socket = try .init(rdr) },
+        .ext_dir => .{ .ext_dir = try .init(rdr) },
+        .ext_file => .{ .ext_file = try .init(alloc, rdr, block_size) },
+        .ext_symlink => .{ .ext_symlink = try .init(alloc, rdr) },
+        .ext_block_dev => .{ .ext_block_dev = try .init(rdr) },
+        .ext_char_dev => .{ .ext_char_dev = try .init(rdr) },
+        .ext_fifo => .{ .ext_fifo = try .init(rdr) },
+        .ext_socket => .{ .ext_socket = try .init(rdr) },
+    };
+    return .{
+        .hdr = hdr,
+        .data = data,
+    };
+}
+pub fn copy(self: Inode, alloc: std.mem.Allocator) !Inode {
+    var new_inode = self;
+    switch (new_inode.data) {
+        .file => |*f| {
+            if (f.blocks.len > 0) {
+                f.blocks = try alloc.alloc(DataBlock, f.blocks.len);
+                @memcpy(f.blocks, self.data.file.blocks);
+            }
+        },
+        .ext_file => |*f| {
+            if (f.blocks.len > 0) {
+                f.blocks = try alloc.alloc(DataBlock, f.blocks.len);
+                @memcpy(f.blocks, self.data.ext_file.blocks);
+            }
+        },
+        .symlink => |*s| {
+            s.target = try alloc.alloc(u8, s.target.len);
+            @memcpy(s.target, self.data.symlink.target);
+        },
+        .ext_symlink => |*s| {
+            s.target = try alloc.alloc(u8, s.target.len);
+            @memcpy(s.target, self.data.ext_symlink.target);
+        },
+    }
+    return new_inode;
+}
+pub fn deinit(self: Inode, alloc: std.mem.Allocator) void {
+    switch (self.data) {
+        .file => |f| f.deinit(alloc),
+        .ext_file => |f| f.deinit(alloc),
+        .symlink => |s| s.deinit(alloc),
+        .ext_symlink => |s| s.deinit(alloc),
+        else => {},
+    }
+}
+
+// Utility functions
+
+pub fn directory(self: Inode, alloc: std.mem.Allocator, io: Io, cache: *DecompCache, dir_start: u64) !Directory {
+    return switch (self.data) {
+        .dir => |d| readDirectory(alloc, io, cache, dir_start, d),
+        .ext_dir => |d| readDirectory(alloc, io, cache, dir_start, d),
+        else => error.NotDirectory,
+    };
+}
+fn readDirectory(alloc: std.mem.Allocator, io: Io, cache: *DecompCache, dir_start: u64, d: anytype) !Directory {
+    var meta: MetadataReader = .init(io, cache, dir_start + d.block_start);
+    defer meta.deinit(io);
+    try meta.interface.discardAll(d.block_offset);
+
+    return .init(alloc, &meta.interface, d.size);
+}
+
 // Types
 
 pub const Ref = packed struct(u64) {
@@ -40,18 +139,260 @@ pub const Header = extern struct {
 };
 
 pub const Data = union(Enum) {
-    dir: ,
+    dir: Dir,
-    file: ,
+    file: File,
-    symlink: ,
+    symlink: Symlink,
-    block_dev: ,
+    block_dev: Device,
-    char_dev: ,
+    char_dev: Device,
-    fifo: ,
+    fifo: IPC,
-    socket: ,
+    socket: IPC,
-    ext_dir: ,
+    ext_dir: ExtDir,
-    ext_file: ,
+    ext_file: ExtFile,
-    ext_symlink: ,
+    ext_symlink: ExtSymlink,
-    ext_block_dev: ,
+    ext_block_dev: ExtDevice,
-    ext_char_dev: ,
+    ext_char_dev: ExtDevice,
-    ext_fifo: ,
+    ext_fifo: ExtIPC,
-    ext_socket: ,
+    ext_socket: ExtIPC,
+};
+
+pub const DataBlock = packed struct(u32) {
+    size: u24,
+    uncompressed: bool,
+    _: u7,
+};
+
+const Dir = extern struct {
+    block_start: u32,
+    hard_links: u32,
+    size: u16,
+    block_offset: u16,
+    parent: u32,
+
+    const Self = @This();
+
+    fn init(rdr: *Reader) !Self {
+        var dir: Self = undefined;
+        try rdr.readSliceEndian(Self, @ptrCast(&dir), .little);
+        return dir;
+    }
+};
+const ExtDir = extern struct {
+    hard_links: u32,
+    size: u32,
+    block_start: u32,
+    parent: u32,
+    idx_count: u16,
+    block_offset: u16,
+    xattr_idx: u32,
+    // []DirIndex
+
+    const Self = @This();
+
+    fn init(rdr: *Reader) !Self {
+        var dir: Self = undefined;
+        try rdr.readSliceEndian(Self, @ptrCast(&dir), .little);
+        return dir;
+    }
+};
+
+const File = struct {
+    data_start: u32,
+    frag_idx: u32,
+    frag_offset: u32,
+    size: u32,
+    blocks: []DataBlock,
+
+    const Raw = extern struct {
+        data_start: u32,
+        frag_idx: u32,
+        frag_offset: u32,
+        size: u32,
+    };
+
+    const Self = @This();
+
+    pub fn init(alloc: std.mem.Allocator, rdr: *Reader, block_size: u32) !Self {
+        var raw: Raw = undefined;
+        try rdr.readSliceEndian(Raw, @ptrCast(&raw), .little);
+
+        var blocks_num = raw.size / block_size;
+        if (raw.frag_idx == 0xFFFFFFFF and raw.size % block_size > 0)
+            blocks_num += 1;
+
+        const blocks: []DataBlock = try alloc.alloc(DataBlock, blocks_num);
+        errdefer alloc.free(blocks);
+
+        try rdr.readSliceEndian(DataBlock, blocks, .little);
+        return .{
+            .data_start = raw.data_start,
+            .frag_idx = raw.frag_idx,
+            .frag_offset = raw.frag_offset,
+            .size = raw.size,
+            .blocks = blocks,
+        };
+    }
+    pub fn deinit(self: File, alloc: std.mem.Allocator) void {
+        alloc.free(self.blocks);
+    }
+};
+const ExtFile = struct {
+    data_start: u64,
+    size: u64,
+    sparse: u64,
+    hard_links: u32,
+    frag_idx: u32,
+    frag_offset: u32,
+    xattr_idx: u32,
+    blocks: []DataBlock,
+
+    const Raw = extern struct {
+        data_start: u64,
+        size: u64,
+        sparse: u64,
+        hard_links: u32,
+        frag_idx: u32,
+        frag_offset: u32,
+        xattr_idx: u32,
+    };
+
+    const Self = @This();
+
+    pub fn init(alloc: std.mem.Allocator, rdr: *Reader, block_size: u32) !Self {
+        var raw: Raw = undefined;
+        try rdr.readSliceEndian(Raw, @ptrCast(&raw), .little);
+
+        var blocks_num = raw.size / block_size;
+        if (raw.frag_idx == 0xFFFFFFFF and raw.size % block_size > 0)
+            blocks_num += 1;
+
+        const blocks: []DataBlock = try alloc.alloc(DataBlock, blocks_num);
+        errdefer alloc.free(blocks);
+
+        try rdr.readSliceEndian(DataBlock, blocks, .little);
+        return .{
+            .data_start = raw.data_start,
+            .size = raw.size,
+            .sparse = raw.sparse,
+            .hard_links = raw.hard_links,
+            .frag_idx = raw.frag_idx,
+            .frag_offset = raw.frag_offset,
+            .xattr_idx = raw.xattr_idx,
+            .blocks = blocks,
+        };
+    }
+    pub fn deinit(self: File, alloc: std.mem.Allocator) void {
+        alloc.free(self.blocks);
+    }
+};
+
+const Symlink = struct {
+    hard_links: u32,
+    target: []const u8,
+
+    const Raw = extern struct {
+        hard_links: u32,
+        target_size: u32,
+    };
+
+    const Self = @This();
+
+    pub fn init(alloc: std.mem.Allocator, rdr: *Reader) !Self {
+        var raw: Raw = undefined;
+        try rdr.readSliceEndian(Raw, @ptrCast(&raw), .little);
+
+        const target = try alloc.alloc(u8, raw.target_size);
+        try rdr.readSliceEndian(u8, target, .little);
+
+        return .{
+            .hard_links = raw.hard_links,
+            .target = target,
+        };
+    }
+    pub fn deinit(self: Symlink, alloc: std.mem.Allocator) void {
+        alloc.free(self.target);
+    }
+};
+const ExtSymlink = struct {
+    hard_links: u32,
+    xattr_idx: u32,
+    target: []const u8,
+
+    const Raw = extern struct {
+        hard_links: u32,
+        target_size: u32,
+    };
+
+    const Self = @This();
+
+    pub fn init(alloc: std.mem.Allocator, rdr: *Reader) !Self {
+        var raw: Raw = undefined;
+        try rdr.readSliceEndian(Raw, @ptrCast(&raw), .little);
+
+        const target = try alloc.alloc(u8, raw.target_size);
+        errdefer alloc.free(target);
+        try rdr.readSliceEndian(u8, target, .little);
+
+        var xattr_idx: u32 = undefined;
+        try rdr.readSliceEndian(u32, @ptrCast(&xattr_idx), .little);
+
+        return .{
+            .hard_links = raw.hard_links,
+            .target = target,
+            .xattr_idx = xattr_idx,
+        };
+    }
+
+    pub fn deinit(self: Symlink, alloc: std.mem.Allocator) void {
+        alloc.free(self.target);
+    }
+};
+
+const Device = extern struct {
+    hard_links: u32,
+    device: u32,
+
+    const Self = @This();
+
+    fn init(rdr: *Reader) !Self {
+        var dir: Self = undefined;
+        try rdr.readSliceEndian(Self, @ptrCast(&dir), .little);
+        return dir;
+    }
+};
+const ExtDevice = extern struct {
+    hard_links: u32,
+    device: u32,
+    xattr_idx: u32,
+
+    const Self = @This();
+
+    fn init(rdr: *Reader) !Self {
+        var dir: Self = undefined;
+        try rdr.readSliceEndian(Self, @ptrCast(&dir), .little);
+        return dir;
+    }
+};
+
+const IPC = extern struct {
+    hard_links: u32,
+
+    const Self = @This();
+
+    fn init(rdr: *Reader) !Self {
+        var dir: Self = undefined;
+        try rdr.readSliceEndian(Self, @ptrCast(&dir), .little);
+        return dir;
+    }
+};
+const ExtIPC = extern struct {
+    hard_links: u32,
+    xattr_idx: u32,
+
+    const Self = @This();
+
+    fn init(rdr: *Reader) !Self {
+        var dir: Self = undefined;
+        try rdr.readSliceEndian(Self, @ptrCast(&dir), .little);
+        return dir;
+    }
 };

src/meta_rdr.zig

@@ -0,0 +1,109 @@
+const std = @import("std");
+const Io = std.Io;
+const Reader = Io.Reader;
+const Writer = Io.Writer;
+const Limit = Io.Limit;
+
+const DecompCache = @import("decomp_cache.zig");
+
+const MetadataReader = @This();
+
+io: Io,
+cache: *DecompCache,
+
+cur_offset: u64 = 0,
+next_offset: u64,
+
+interface: Reader = .{
+    .buffer = &[0]u8{},
+    .end = 0,
+    .seek = 0,
+    .vtable = &.{
+        .stream = stream,
+        .discard = discard,
+        .readVec = readVec,
+    },
+},
+
+pub fn init(io: Io, cache: *DecompCache, start: u64) MetadataReader {
+    return .{
+        .io = io,
+        .cache = cache,
+
+        .next_offset = start,
+    };
+}
+pub fn deinit(self: *MetadataReader, io: Io) void {
+    self.cache.finished(io, self.cur_offset);
+}
+
+fn advance(self: *MetadataReader) !void {
+    self.cache.finished(self.io, self.cur_offset);
+
+    self.interface.seek = 0;
+    errdefer self.interface.end = 0;
+
+    const hdr: Header = @bitCast(std.mem.readInt(u16, self.cache.map.memory[self.next_offset..][0..2], .little));
+    self.cur_offset = self.next_offset + 2;
+    self.next_offset = self.cur_offset + hdr.size;
+
+    if (hdr.uncompressed) {
+        self.interface.buffer = self.cache.map.memory[self.cur_offset..][0..hdr.size];
+        self.interface.end = hdr.size;
+        return;
+    }
+    self.interface.buffer = try self.cache.get(self.io, self.cur_offset, hdr.size, 8192);
+    self.interface.end = self.interface.buffer.len;
+}
+
+fn stream(r: *Reader, w: *Writer, limit: Limit) Reader.StreamError!usize {
+    if (r.seek >= r.end) {
+        const self: *MetadataReader = @fieldParentPtr("interface", r);
+        self.advance() catch |err| {
+            std.debug.print("error advancing metadata reader: {}\n", .{err});
+            return Reader.Error.ReadFailed;
+        };
+    }
+    const to_write = @min(r.end - r.seek, @intFromEnum(limit));
+    const wrote = try w.write(r.buffer[r.seek..][0..to_write]);
+    r.seek += wrote;
+    return wrote;
+}
+fn discard(r: *Reader, limit: Limit) Reader.Error!usize {
+    if (r.seek >= r.end) {
+        const self: *MetadataReader = @fieldParentPtr("interface", r);
+        self.advance() catch |err| {
+            std.debug.print("error advancing metadata reader: {}\n", .{err});
+            return Reader.Error.ReadFailed;
+        };
+    }
+    const to_discard = @min(r.end - r.seek, @intFromEnum(limit));
+    r.seek += to_discard;
+    return to_discard;
+}
+fn readVec(r: *Reader, vec: [][]u8) Reader.Error!usize {
+    if (r.seek >= r.end) {
+        const self: *MetadataReader = @fieldParentPtr("interface", r);
+        self.advance() catch |err| {
+            std.debug.print("error advancing metadata reader: {}\n", .{err});
+            return Reader.Error.ReadFailed;
+        };
+    }
+    var total: usize = 0;
+    for (vec) |v| {
+        const to_copy = @min(r.end - r.seek, v.len);
+        @memcpy(v[0..to_copy], r.buffer[r.seek..][0..to_copy]);
+        r.seek += to_copy;
+        total += to_copy;
+        if (r.seek >= r.end)
+            break;
+    }
+    return total;
+}
+
+// Types
+
+const Header = packed struct(u16) {
+    size: u15,
+    uncompressed: bool,
+};