Minor refactor to support strings with embedded zeros.

    // The cost of sending two strings outweighs the cost of formatting.

    // "adb sync" performance is affected by this.

    return WriteFdFmt(fd, "%04x%.*s", length, length, s.c_str());

    auto str = android::base::StringPrintf("%04x", length).append(s);

    return WriteFdExactly(fd, str);

}

bool ReadProtocolString(int fd, std::string* s, std::string* error) {