c - 输入相关错误 : sendto() error code 22 (Invalid argument) depending on input size

Question

我在实现 C UDP 套接字程序时遇到问题。下面的代码适用于任何短于 56 个字符的输入，但如果我输入 56 个或更多字符，sendto 会提示我给它的参数无效(错误代码 22)。例如，这将正确发送:

 ./talkerDemo localhost qqqqqwwwwweeeeeqqqqqwwwwweeeeeqqqqqwwwwweeeeeqqqqqwwwww

但这不会:

 ./talkerDemo localhost qqqqqwwwwweeeeeqqqqqwwwwweeeeeqqqqqwwwwweeeeeqqqqqwwwwwH

什么给了？

/*
** talker.c
** Adapted from http://beej.us/guide/bgnet/html/single/bgnet.html#datagram
*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#define SERVERPORT "4242"    // the port users will be connecting to

int main(int argc, char *argv[])
{
    int sockfd;
    struct addrinfo hints, *servinfo, *p;
    int rv;
    int numbytes;

    if (argc != 3) {
        fprintf(stderr,"usage: talker hostname message\n");
        exit(1);
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_DGRAM;

    if ((rv = getaddrinfo(argv[1], SERVERPORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // loop through all the results and make a socket
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("talker: socket");
            continue;
        }

        break;
    }

    if (p == NULL) {
        fprintf(stderr, "talker: failed to create socket\n");
        return 2;
    }



//============================================================
// !!!!!!! Eror occurs here:   
    if ((numbytes = sendto(sockfd, argv[2], strlen(argv[2]), 0,
             p->ai_addr, p->ai_addrlen)) == -1) {
        perror("talker: sendto");
        exit(1);
    }
//============================================================

    freeaddrinfo(servinfo);

    printf("talker: sent %d bytes to %s\n", numbytes, argv[1]);
    close(sockfd);

    return 0;
}

编辑

这是我实际运行的代码版本。在发布问题之前，我已经回到原来的(上图)以查看该实现是否也出现了问题 - 我似乎是这样。但事实证明我太笨了，使用了错误的二进制文件……derp

/*
** UDPTalker.hpp -- a datagram sockets "server"
** Adapted from http://beej.us/guide/bgnet/html/single/bgnet.html#datagram
*/

#ifndef UDPTALKER_H
#define UDPTALKER_H

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#include <iostream>
#include <string>


#define UDPT_DEFAULT_PORT "4243"
#define UDPT_DEFAULT_HOST "localhost"

#define UDPT_MAXBUFLEN 2048


class UDPTalker {
    int sockfd;
    struct addrinfo hints, *servinfo, *p;
    int rv;
    int numbytes;

    std::string host;
    std::string port;

    public:
        //! Takes target hostname/ip and port as arguments. Defaults: ("localhost", "4243")
        UDPTalker(std::string host = UDPT_DEFAULT_HOST, std::string port = UDPT_DEFAULT_PORT);

        ~UDPTalker();

        void send(std::string msg);
};

#endif // UDPTALKER_H

这是相应的.cpp:

// File UDPTalker.cpp

#include "UDPTalker.hpp"

UDPTalker::UDPTalker(std::string h, std::string port) : host(h), port(port) {
    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_DGRAM;

    if ((rv = getaddrinfo(host.c_str(), port.c_str(), &hints, &servinfo)) != 0) {
        throw std::runtime_error(std::string("getaddrinfo: ").append(gai_strerror(rv)));
    }

    // loop through all the results and make a socket
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("talker: socket");
            continue;
        }

        break;
    }

    freeaddrinfo(servinfo);

    if (p == NULL) {
        throw std::runtime_error("talker: failed to create socket\n");
    }
}

UDPTalker::~UDPTalker() {
    close(sockfd);
}

void UDPTalker::send(std::string msg) {

    if ((numbytes = sendto(sockfd, msg.c_str(), msg.size(), 0,
             p->ai_addr, p->ai_addrlen)) == -1) {
        perror("talker: sendto! ");
    }

    // printf("talker: sent %d bytes to %s\n", numbytes, host.c_str());
}

Answer 1

freeaddrinfo(servinfo); 释放 servinfo 使用的内存。这意味着指针 p 现在指向空内存，因此当它传递给 sendto 时它可能包含无效内容。我的猜测是，由于某种原因，当类的 send 方法被调用时，输入字符串中的额外字节正在“滚动”该内存位置。修复是将 freeaddrinfo(servinfo); 从构造函数移动到析构函数:

UDPTalker::UDPTalker(std::string h, std::string port) : host(h), port(port) {
    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_DGRAM;

    if ((rv = getaddrinfo(host.c_str(), port.c_str(), &hints, &servinfo)) != 0) {
        throw std::runtime_error(std::string("getaddrinfo: ").append(gai_strerror(rv)));
    }

    // loop through all the results and make a socket
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("talker: socket");
            continue;
        }

        break;
    }

    if (p == NULL) {
        throw std::runtime_error("talker: failed to create socket\n");
    }
}

UDPTalker::~UDPTalker() {
    freeaddrinfo(servinfo);
    close(sockfd);
}