readIndirect

    fn readIndirect(r: *Reader) Reader.Error!usize {
        const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
        const gpa = d.gpa;
        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.decode.state == math.maxInt(usize)) return error.EndOfStream;

        process_next: {
            if (d.unpacked_size) |unpacked_size| {
                if (d.buffer.len >= unpacked_size) break :process_next;
            } else if (d.range_decoder.isFinished()) {
                break :process_next;
            }
            var n_read: u64 = 0;
            switch (d.decode.process(d.input, &allocating, &d.buffer, &d.range_decoder, &n_read) catch |err| switch (err) {
                error.WriteFailed => {
                    d.err = error.OutOfMemory;
                    return error.ReadFailed;
                },
                error.EndOfStream => {
                    d.err = error.EndOfStream;
                    return error.ReadFailed;
                },
                else => |e| {
                    d.err = e;
                    return error.ReadFailed;
                },
            }) {
                .more => return 0,
                .finished => break :process_next,
            }
        }

        if (d.unpacked_size) |unpacked_size| {
            if (d.buffer.len != unpacked_size) {
                d.err = error.DecompressedSizeMismatch;
                return error.ReadFailed;
            }
        }

        d.buffer.finish(&allocating.writer) catch |err| switch (err) {
            error.WriteFailed => {
                d.err = error.OutOfMemory;
                return error.ReadFailed;
            },
        };
        d.decode.state = math.maxInt(usize);
        return 0;
    }