Further progress in parsing format

src/directory.zig

@@ -0,0 +1,70 @@
+const std = @import("std");
+
+const InodeType = @import("inode.zig").Type;
+const Compression = @import("superblock.zig").Compression;
+
+const Header = extern struct { //use extern instead of packed, due to bit alignment
+    count: u32,
+    block: u32,
+    num: u32,
+};
+
+const RawEntry = struct {
+    offset: u16,
+    num_offset: i16,
+    type: InodeType,
+    size: u16,
+    name: []const u8,
+
+    pub fn init(alloc: std.mem.Allocator, rdr: anytype) !RawEntry {
+        const fixed: [8]u8 = undefined;
+        _ = try rdr.read(&fixed);
+        const size = std.mem.readInt(u16, fixed[6..8], .little);
+        const name = try alloc.alloc(u8, size + 1);
+        _ = try rdr.read(name);
+        return .{
+            .offset = std.mem.readInt(u16, fixed[0..2], .little),
+            .num_offset = std.mem.readInt(i16, fixed[2..4], .little),
+            .type = std.mem.readInt(u16, fixed[4..6], .little),
+            .size = size,
+            .name = name,
+        };
+    }
+};
+
+pub const Entry = struct {
+    block: u32,
+    offset: u16,
+    num: u32,
+    type: InodeType,
+    name: []const u8,
+
+    pub fn deinit(self: Entry, alloc: std.mem.Allocator) void {
+        alloc.free(self.name);
+    }
+};
+
+pub fn readDirectory(alloc: std.mem.Allocator, rdr: anytype, size: u32) []Entry {
+    const entries: std.ArrayList(Entry) = .init(alloc);
+    errdefer entries.deinit();
+    var cur_red: u32 = 3; // dir size includes "." & "..", so its actual size is off by 3.
+    var hdr: Header = undefined;
+    while (cur_red < size) {
+        _ = try rdr.read(std.mem.asBytes(&hdr));
+        cur_red += 12;
+        try entries.ensureUnusedCapacity(hdr.count + 1);
+        for (0..hdr.count + 1) |_| {
+            const raw_ent: RawEntry = try .init(alloc, rdr);
+            cur_red += 9 + raw_ent.size;
+            errdefer alloc.free(raw_ent.name);
+            entries.appendAssumeCapacity(.{
+                .block = hdr.block,
+                .offset = raw_ent.offset,
+                .num = hdr.num + raw_ent.num_offset,
+                .type = raw_ent.type,
+                .name = raw_ent.name,
+            });
+        }
+    }
+    return entries.toOwnedSlice();
+}