c - tcp 服务器阻塞读取 C

Question

我想实现一个带有阻塞读取的简单 TCP 服务器，它接收从客户端发送的消息，一个字符一个字符地接收消息，直到一个分隔符。一旦收到一条消息，它必须等到下一条消息出现。这是我的伪代码:

// Messages sent from the client
char *message1 = "mssg1\n"
char *message2 = "mssg2\n"

// On server side
char buffer;
char completeMessage[5]

while(1){

    while(buffer != '\n'){
        recv(sock, &buffer, 1, 0); // 1 is the read size

        if(buffer != '\n') {
            printf("buffer: %c\n", buffer);
            completeMessage[n] = buffer;
            count ++;  
        }
        else{
            printf("Complete message: %s\n", completeMessage);
            count = 0;
        }
    }
}

结果如下:

buffer: m
buffer: s
buffer: s
buffer: g
buffer: 1
Complete message: mssg1
buffer:
buffer:
buffer:
buffer:
buffer:
buffer:
// Error due to buffer overflow

我不知道为什么 recv 不是等待下一个消息字符(阻塞读取)，而是继续读取空格。我的问题如下:

• recv 真的是套接字阻塞读函数吗？
• 代码中是否有错误或缺失？
• 还有其他实现此建议的建议吗？

Answer 1

Is recv really a socket blocking read function?

是的，除非您将句柄设为非阻塞。

Is there something wrong or missing in the code?,

• 您没有检查 recv 返回的内容。 0表示EOF，-1表示错误。

• 您不检查缓冲区有多满，因此有缓冲区溢出的风险。

• 您没有按照 printf %s 的要求使用 NUL 终止 completeMessage 中的字符串。

Any other suggestions for implementing this?

你不应该一次读一个字符!

---

#define BUFFER_SIZE (64*1024)

char* extract_string(const char* start, const char* end) {
    size_t len = end - start;
    char* dst = malloc(len+1);
    if (dst == NULL)
        return NULL;

    memcpy(dst, src, len);
    dst[len] = '\0';
    return dst;
}

{
    char buf_start[BUFFER_SIZE];
    char* buf_end = buf_start + BUFFER_SIZE;
    char* window_start = buf_start;
    char* window_end = buf_start;
    while (1) {
        if (window_end == buf_end) { // No more space.
            fprintf(stderr, "Overly large message");
            return 0;
        }

        ssize_t rv = recv(sock, window_end, buf_end-window_end, 0);
        if (rv == -1) {  // Error.
            perror("recv");
            return 0;
        }

        if (rv == 0) {  // EOF.
            return 1;
        }

        while (rv--) {
            if (*(window_end++) == '\n') {
                char* msg = extract_string(window_start, window_end-1);  // Excl LF.
                if (msg == NULL) {
                    fprintf(stderr, "Out of memory");
                    return 0;
                }

                // Do something with msg
                printf("Complete message: %s\n", msg);
                free(msg);

                window_start = window_end;
            }
        }

        memmove(buf_start, window_start, window_end-window_start);
        window_end -= (window_start - buf_start);
        window_start = buf_start;
    }
}