python - 为什么我的缓冲区输出被切碎了？ C++套接字编程

Question

我正在尝试打开一个 TCP 套接字并将数据转储到一个文件中。我试图获得与我的 python3 版本相同的结果。逐行输出到控制台和文件，如下所示:

python3 logsvrd.py

Server started on port: 8901
Client (172.16.1.1, 4937) connected

b'<166>%ASA-6-414007: TCP syslog server connection restored.  New connections allowed.\n'
b'<166>%ASA-6-302016: Teardown UDP connection 778663 for OUTSIDE:172.31.252.15/514 to INSIDE:172.16.1.12/514 duration 0:02:10 bytes 258\n'
b'<166>%ASA-6-302020: Built inbound ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0\n'
b'<166>%ASA-6-302021: Teardown ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0\n'
b'<166>%ASA-6-305011: Built dynamic TCP translation from INSIDE:172.16.1.117/63215 to OUTSIDE:68.202.229.140/63215\n'
b'<166>%ASA-6-302013: Built outbound TCP connection 778712 for OUTSIDE:172.25.5.10/8443 (172.25.5.10/8443) to INSIDE:172.16.1.117/63215 (68.202.229.140/63215)\n'
b'<166>%ASA-6-302020: Built inbound ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0\n'
b'<166>%ASA-6-302021: Teardown ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0\n'
b'<166>%ASA-6-302020: Built inbound ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0\n'
b'<166>%ASA-6-302021: Teardown ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0\n'
b'<166>%ASA-6-302014: Teardown TCP connection 776408 for OUTSIDE:17.154.66.156/443 to INSIDE:172.16.1.112/58335 duration 1:06:50 bytes 3651 Connection timeout\n'
b'<166>%ASA-6-305012: Teardown dynamic TCP translation from INSIDE:172.16.1.112/58335 to OUTSIDE:68.202.229.140/13531 duration 1:06:50\n'
b'<166>%ASA-6-302014: Teardown TCP connection 778706 for OUTSIDE:172.25.5.10/8443 to INSIDE:172.16.1.117/63193 duration 0:00:30 bytes 0 SYN Timeout\n'
b'<166>%ASA-6-305012: Teardown dynamic TCP translation from INSIDE:172.16.1.117/63193 to OUTSIDE:68.202.229.140/63193 duration 0:00:30\n'
b'<166>%ASA-6-302020: Built inbound ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0\n'
b'<166>%ASA-6-302021: Teardown ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0\n'
b'<166>%ASA-6-305012: Teardown dynamic UDP translation from INSIDE:172.16.1.117/58331 to OUTSIDE:68.202.229.140/58331 duration 0:02:33\n'
b'<166>%ASA-6-302014: Teardown TCP connection 776406 for OUTSIDE:17.154.66.156/443 to INSIDE:172.16.1.112/58333 duration 1:06:55 bytes 11658 Connection timeout\n'
b'<166>%ASA-6-305012: Teardown dynamic TCP translation from INSIDE:172.16.1.112/58333 to OUTSIDE:68.202.229.140/58333 duration 1:06:55\n'

当我在 c++ 中执行此操作时，它会产生断断续续的结果:

<166>%ASA-6-302020: Built inbound ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0
E:172.16.1.117/62572 (68.202.229.140/62572)
<166>%ASA-6-302021: Teardown ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0
.1/0
E:172.16.1.117/62572 (68.202.229.140/62572)
<166>%ASA-6-302020: Built inbound ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0
E:172.16.1.117/62572 (68.202.229.140/62572)
<166>%ASA-6-302021: Teardown ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0
.1/0
E:172.16.1.117/62572 (68.202.229.140/62572)
<166>%ASA-6-302014: Teardown TCP connection 778219 for OUTSIDE:172.25.5.10/8443 to INSIDE:172.16.1.117/62550 duration 0:00:30 bytes 0 SYN Timeout
140/62572)
<166>%ASA-6-305012: Teardown dynamic TCP translation from INSIDE:172.16.1.117/62550 to OUTSIDE:68.202.229.140/62550 duration 0:00:30
 SYN Timeout
140/62572)
<166>%ASA-6-302016: Teardown UDP connection 778171 for INSIDE:172.16.1.117/68 to identity:172.16.1.1/67 duration 0:02:02 bytes 620
0
 SYN Timeout
140/62572)
<166>%ASA-6-302016: Teardown UDP connection 778172 for OUTSIDE:172.31.253.8/53 to INSIDE:172.16.1.117/58307 duration 0:02:02 bytes 163
YN Timeout
140/62572)
<166>%ASA-6-302016: Teardown UDP connection 778173 for OUTSIDE:172.31.253.8/53 to INSIDE:172.16.1.117/56906 duration 0:02:01 bytes 147
YN Timeout
140/62572)
<166>%ASA-6-604103: DHCP daemon interface INSIDE:  address granted 0110.4a7d.af14.fa (172.16.1.122)
7/56906 duration 0:02:01 bytes 147
YN Timeout
140/62572)
<166>%ASA-6-302020: Built inbound ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0
ion 0:02:01 bytes 147
YN Timeout
140/62572)
<166>%ASA-6-302021: Teardown ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0
.1/0
ion 0:02:01 bytes 147
YN Timeout
140/62572)
<166>%ASA-6-305011: Built dynamic TCP translation from INSIDE:172.16.1.122/61908 to OUTSIDE:68.202.229.140/61908
<166>%ASA-6-302013: Built outbound TCP connection 778266 for OUTSIDE:172.16.82.10/389 (172.16.82.10/389) to INSIDE:172.16.1.122/61908 (68.202.229.140/61908)
<166>%ASA-6-302014: Teardown TCP connection 778221 for OUTSIDE:10.201.218.61/443 to INSIDE:172.16.1.122/61901 duration 0:00:30 bytes 0 SYN Timeout
 TCP connection 778266 for OUTSIDE:172.16.82.10/389 (172.16.82.10/389) to INSIDE:172.16.1.122/61908 (68.202.229.140/61908)
<166>%ASA-6-305012: Teardown dynamic TCP translation from INSIDE:172.16.1.122/61901 to OUTSIDE:68.202.229.140/61901 duration 0:00:30
0 SYN Timeout
 TCP connection 778266 for OUTSIDE:172.16.82.10/389 (172.16.82.10/389) to INSIDE:172.16.1.122/61908 (68.202.229.140/61908)
<166>%ASA-6-302015: Built outbound UDP connection 778267 for OUTSIDE:172.31.253.8/53 (172.31.253.8/53) to INSIDE:172.16.1.122/49834 (172.16.1.122/49834)
onnection 778266 for OUTSIDE:172.16.82.10/389 (172.16.82.10/389) to INSIDE:172.16.1.122/61908 (68.202.229.140/61908)
<166>%ASA-6-302015: Built outbound UDP connection 778268 for OUTSIDE:172.31.253.8/53 (172.31.253.8/53) to INSIDE:172.16.1.117/22843 (172.16.1.117/22843)
onnection 778266 for OUTSIDE:172.16.82.10/389 (172.16.82.10/389) to INSIDE:172.16.1.122/61908 (68.202.229.140/61908)
<166>%ASA-6-305011: Built dynamic UDP translation from INSIDE:172.16.1.117/49549 to OUTSIDE:68.202.229.140/49549
<166>%ASA-6-302015: Built outbound UDP connection 778269 for OUTSIDE:216.58.216.78/443 (216.58.216.78/443) to INSIDE:172.16.1.117/49549 (68.202.229.140/49549)
<166>%ASA-6-305011: Built dynamic TCP translation from INSIDE:172.16.1.117/62591 to OUTSIDE:68.202.229.140/62591
<166>%ASA-6-302013: Built outbound TCP connection 778270 for OUTSIDE:216.58.216.78/443 (216.58.216.78/443) to INSIDE:172.16.1.117/62591 (68.202.229.140/62591)
<166>%ASA-6-302015: Built outbound UDP connection 778271 for OUTSIDE:172.31.253.8/53 (172.31.253.8/53) to INSIDE:172.16.1.117/63224 (172.16.1.117/63224)
<166>%ASA-6-305011: Built dynamic UDP translation from INSIDE:172.16.1.117/57906 to OUTSIDE:68.202.229.140/57906
<166>%ASA-6-302015: Built outbound UDP connection 778272 for OUTSIDE:192.168.10.2/53 (192.168.10.2/53) to INSIDE:172.16.1.117/57906 (68.202.229.140/57906)
91)
<166>%ASA-6-302015: Built outbound UDP connection 778271 for OUTSIDE:172.31.253.8/53 (172.31.253.8/53) to INSIDE:172.16.1.117/63224 (172.16.1.117/63224)
<166>%ASA-6-302020: Built inbound ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0
<166>%ASA-6-302015: Built outbound UDP connection 778272 for OUTSIDE:192.168.10.2/53 (192.168.10.2/53) to INSIDE:172.16.1.117/57906 (68.202.229.140/57906)
91)
<166>%ASA-6-302015: Built outbound UDP connection 778271 for OUTSIDE:172.31.253.8/53 (172.31.253.8/53) to INSIDE:172.16.1.117/63224 (172.16.1.117/63224)
<166>%ASA-6-302021: Teardown ICMP connection for faddr 172.16.1.123/0 gaddr 172.16.1.1/0 laddr 172.16.1.1/0
.1/0
<166>%ASA-6-302015: Built outbound UDP connection 778272 for OUTSIDE:192.168.10.2/53 (192.168.10.2/53) to INSIDE:172.16.1.117/57906 (68.202.229.140/57906)
91)
<166>%ASA-6-302015: Built outbound UDP connection 778271 for OUTSIDE:172.31.253.8/53 (172.31.253.8/53) to INSIDE:172.16.1.117/63224 (172.16.1.117/63224)
<166>%ASA-6-305011: Built dynamic TCP translation from INSIDE:172.16.1.117/62594 to OUTSIDE:68.202.229.140/62594
<166>%ASA-6-302015: Built outbound UDP connection 778272 for OUTSIDE:192.168.10.2/53 (192.168.10.2/53) to INSIDE:172.16.1.117/57906 (68.202.229.140/57906)
91)
<166>%ASA-6-302015: Built outbound UDP connection 778271 for OUTSIDE:172.31.253.8/53 (172.31.253.8/53) to INSIDE:172.16.1.117/63224 (172.16.1.117/63224)
<166>%ASA-6-302013: Built outbound TCP connection 778274 for OUTSIDE:172.25.5.10/8443 (172.25.5.10/8443) to INSIDE:172.16.1.117/62594 (68.202.229.140/62594)
ction 778272 for OUTSIDE:192.168.10.2/53 (192.168.10.2/53) to INSIDE:172.16.1.117/57906 (68.202.229.140/57906)
91)
<166>%ASA-6-302015: Built outbound UDP connection 778271 for OUTSIDE:172.31.253.8/53 (172.31.253.8/53) to INSIDE:172.16.1.117/63224 (172.16.1.117/63224)

代码如下:

// Handle errors with messages
void error(const char *msg){
  perror(msg);
  exit(1);
}

// Handle TCP client
void HandleClient(int clntSession, std::string logmsg_path){
  char buffer[BUFSIZE];

  // build the bin file time stamp
  std::time_t epoch = std::time(nullptr);
  std::string ts = std::to_string(epoch);
  std::string logmsg = logmsg_path + "log_msg.bin." + ts;
  std::ofstream bin_outfile(logmsg, std::ios::out | std::ios::binary | std::ios::app);

  // receive syslog message
  ssize_t numBytesRcved = recv(clntSession, buffer, BUFSIZE, 0);
  if (numBytesRcved <0) {
    error("revived failed");
  }

  // Send received string and receive again until end of stream
  while(numBytesRcved > 0){

    // Echo message back to client
    ssize_t numBytesSent = send(clntSession, buffer, numBytesRcved, 0);
    if (numBytesSent < 0) {
      error("send failed");
    }
    else if (numBytesSent != numBytesRcved) {
      error("unexpected number of bytes sent");
      numBytesRcved = recv(clntSession, buffer, BUFSIZE, 0);
    }

    // See if there is more data to receive
    numBytesRcved = recv(clntSession, buffer, BUFSIZE, 0 );
    if (numBytesRcved < 0) {
      error("recive faild");
    }

    // write buffer to binary file and std::cout
    //bin_outfile << buffer;
    std::cout << buffer;
  }
  close(clntSession); // close the session when done
}

Answer 1

您应该做但没有做的一件事是确保您使用适当的函数来输出完整数据。

您当前的代码使用的函数将在遇到 NULL 字节时停止处理返回的缓冲区。 printf等函数使用 %s格式说明符，和 std::cout当给出一个字符指针作为 operator << 的参数时将停止在 NULL 上。如果您的数据包含嵌入的 NULL，您将无法处理(或查看)完整数据，从而得到截断的结果。

numBytesRcved您声明的变量应该以某种方式用于通知后续代码确切如何处理返回的缓冲区。因此，例如，如果您想将缓冲区输出到 std::cout ，而不是这个:

std::cout << buffer;

应该是这样的:

std::cout.write(buffer, numBytesRcvd);

对于 strcpy 等函数也可以这样说, strlen等，在 NULL 字节上停止——不要使用它们来处理或操作可能嵌入 NULL 的缓冲区。

---

补充一下(因为我在使用 std::string 存储缓冲区时多次看到这个错误):

对于诸如 std::string 之类的事情.而不是这样的:

std::string s = buffer;

应该是这样的:

std::string s = std::string(buffer, numBytesRcvd);

或者如果附加到现有数据:

std::string s;
//... assume s has data already, now append
s.append(buffer, numBytesRcvd);