static off_t arithmetic_command(char* buf,
                                size_t bufsz,
                                uint8_t cmd,
                                const void* key,
                                size_t keylen,
                                uint64_t delta,
                                uint64_t initial,
                                uint32_t exp) {
    protocol_binary_request_incr *request = (void*)buf;
    assert(bufsz > sizeof(*request) + keylen);

    memset(request, 0, sizeof(*request));
    request->message.header.request.magic = PROTOCOL_BINARY_REQ;
    request->message.header.request.opcode = cmd;
    request->message.header.request.keylen = htons(keylen);
    request->message.header.request.extlen = 20;
    request->message.header.request.bodylen = htonl(keylen + 20);
    request->message.header.request.opaque = 0xdeadbeef;
    request->message.body.delta = htonll(delta);
    request->message.body.initial = htonll(initial);
    request->message.body.expiration = htonl(exp);

    off_t key_offset = sizeof(protocol_binary_request_no_extras) + 20;

    memcpy(buf + key_offset, key, keylen);
    return key_offset + keylen;
}
static off_t arithmetic_command(char* buf,
                                size_t bufsz,
                                uint8_t cmd,
                                const void* key,
                                size_t keylen,
                                uint64_t delta,
                                uint64_t initial,
                                uint32_t exp) {
    protocol_binary_request_incr *request = (void*)buf;
    assert(bufsz > sizeof(*request) + keylen);

    memset(request, 0, sizeof(*request));
    request->message.header.request.magic = PROTOCOL_BINARY_REQ;
    request->message.header.request.opcode = cmd;
    request->message.header.request.keylen = htons(keylen);
    request->message.header.request.extlen = 20;
    request->message.header.request.bodylen = htonl(keylen + 20);
    request->message.header.request.opaque = 0xdeadbeef;
    request->message.body.delta = htonll(delta);
    request->message.body.initial = htonll(initial);
    request->message.body.expiration = htonl(exp);

    off_t key_offset = sizeof(protocol_binary_request_no_extras) + 20;

    memcpy(buf + key_offset, key, keylen);
    return key_offset + keylen;
}