readIndirect

fn readIndirect(r: *Reader) Reader.Error!usize {
    const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
    const gpa = d.gpa;
    const input = d.input;

    var allocating = Writer.Allocating.initOwnedSlice(gpa, r.buffer);
    allocating.writer.end = r.end;
    defer {
        r.buffer = allocating.writer.buffer;
        r.end = allocating.writer.end;
    }

    if (d.err != null) return error.ReadFailed;
    if (d.block_count == std.math.maxInt(usize)) return error.EndOfStream;

    readBlock(input, &allocating) catch |err| switch (err) {
        error.WriteFailed => {
            d.err = error.OutOfMemory;
            return error.ReadFailed;
        },
        error.SuccessfulEndOfStream => {
            finish(d) catch |finish_err| {
                d.err = finish_err;
                return error.ReadFailed;
            };
            d.block_count = std.math.maxInt(usize);
            return error.EndOfStream;
        },
        else => |e| {
            d.err = e;
            return error.ReadFailed;
        },
    };
    switch (d.check) {
        .none => {},
        .crc32 => {
            const declared_checksum = try input.takeInt(u32, .little);
            // TODO
            //const hash_a = Crc32.hash(unpacked_bytes);
            //if (hash_a != hash_b) return error.WrongChecksum;
            _ = declared_checksum;
        },
        .crc64 => {
            const declared_checksum = try input.takeInt(u64, .little);
            // TODO
            //const hash_a = Crc64.hash(unpacked_bytes);
            //if (hash_a != hash_b) return error.WrongChecksum;
            _ = declared_checksum;
        },
        .sha256 => {
            const declared_hash = try input.take(Sha256.digest_length);
            // TODO
            //var hash_a: [Sha256.digest_length]u8 = undefined;
            //Sha256.hash(unpacked_bytes, &hash_a, .{});
            //if (!std.mem.eql(u8, &hash_a, &hash_b))
            //    return error.WrongChecksum;
            _ = declared_hash;
        },
        else => {
            d.err = error.Unsupported;
            return error.ReadFailed;
        },
    }
    d.block_count += 1;
    return 0;
}