Msf

const Msf = struct {
    directory: MsfStream,
    streams: []MsfStream,

    fn init(gpa: Allocator, file_reader: *File.Reader) !Msf {
        const superblock = try file_reader.interface.takeStruct(pdb.SuperBlock, .little);

        if (!std.mem.eql(u8, &superblock.file_magic, pdb.SuperBlock.expect_magic))
            return error.InvalidDebugInfo;
        if (superblock.free_block_map_block != 1 and superblock.free_block_map_block != 2)
            return error.InvalidDebugInfo;
        if (superblock.num_blocks * superblock.block_size != try file_reader.getSize())
            return error.InvalidDebugInfo;
        switch (superblock.block_size) {
            // llvm only supports 4096 but we can handle any of these values
            512, 1024, 2048, 4096 => {},
            else => return error.InvalidDebugInfo,
        }

        const dir_block_count = blockCountFromSize(superblock.num_directory_bytes, superblock.block_size);
        if (dir_block_count > superblock.block_size / @sizeOf(u32))
            return error.UnhandledBigDirectoryStream; // cf. BlockMapAddr comment.

        try file_reader.seekTo(superblock.block_size * superblock.block_map_addr);
        const dir_blocks = try gpa.alloc(u32, dir_block_count);
        errdefer gpa.free(dir_blocks);
        for (dir_blocks) |*b| {
            b.* = try file_reader.interface.takeInt(u32, .little);
        }
        var directory_buffer: [64]u8 = undefined;
        var directory = MsfStream.init(superblock.block_size, file_reader, dir_blocks, &directory_buffer);

        const begin = directory.logicalPos();
        const stream_count = try directory.interface.takeInt(u32, .little);
        const stream_sizes = try gpa.alloc(u32, stream_count);
        defer gpa.free(stream_sizes);

        // Microsoft's implementation uses @as(u32, -1) for inexistent streams.
        // These streams are not used, but still participate in the file
        // and must be taken into account when resolving stream indices.
        const nil_size = 0xFFFFFFFF;
        for (stream_sizes) |*s| {
            const size = try directory.interface.takeInt(u32, .little);
            s.* = if (size == nil_size) 0 else blockCountFromSize(size, superblock.block_size);
        }

        const streams = try gpa.alloc(MsfStream, stream_count);
        errdefer gpa.free(streams);

        for (streams, stream_sizes) |*stream, size| {
            if (size == 0) {
                stream.* = .empty;
                continue;
            }
            const blocks = try gpa.alloc(u32, size);
            errdefer gpa.free(blocks);
            for (blocks) |*block| {
                const block_id = try directory.interface.takeInt(u32, .little);
                // Index 0 is reserved for the superblock.
                // In theory, every page which is `n * block_size + 1` or `n * block_size + 2`
                // is also reserved, for one of the FPMs. However, LLVM has been observed to map
                // these into actual streams, so allow it for compatibility.
                if (block_id == 0 or block_id >= superblock.num_blocks) return error.InvalidBlockIndex;
                block.* = block_id;
            }
            const buffer = try gpa.alloc(u8, 64);
            errdefer gpa.free(buffer);
            stream.* = .init(superblock.block_size, file_reader, blocks, buffer);
        }

        const end = directory.logicalPos();
        if (end - begin != superblock.num_directory_bytes)
            return error.InvalidStreamDirectory;

        return .{
            .directory = directory,
            .streams = streams,
        };
    }

    fn deinit(self: *Msf, gpa: Allocator) void {
        gpa.free(self.directory.blocks);
        for (self.streams) |*stream| {
            gpa.free(stream.interface.buffer);
            gpa.free(stream.blocks);
        }
        gpa.free(self.streams);
    }
}