在C中以块的形式将内存写入套接字答案

【问题标题】：Writing memory to socket in chunks in C在C中以块的形式将内存写入套接字
【发布时间】：2009-10-27 03:15:25
【问题描述】：

我正在尝试将内存内容分块写入套接字。我可以写比我的缓冲区小的文件，但其他任何东西我都在深水里。

/* allocate memory for file contents */
char fileContents = malloc(sizeof(char)*filesize);

/* read a file into memory */
read(fileDescriptor, fileContents , filesize);

int chunksWritten;

/* Write the memory to socket? */
if (filesize > MAX_BLOCK_SIZE){

    while (chunksWritten < filesize){
        // what goes here?
    }

} else {
    chunksWritten = writen(sd, fileContents, filesize);     // this works for files < MAX_BLOCK_SIZE
}

writen here 写入我的套接字：

int writen(int fd, char *buf, int nbytes) {
    short data_size = nbytes;
    int n, nw;
    if (nbytes > MAX_BLOCK_SIZE)
        return (-3);

    data_size = htons(data_size);
    if (write(fd, (char *) & data_size, 1) != 1) return (-1);
    if (write(fd, (char *) (&data_size) + 1, 1) != 1) return (-1);
    /* send nbytes */
    for (n = 0; n < nbytes; n += nw) {
        if ((nw = write(fd, buf + n, nbytes - n)) <= 0)
            return (nw);
    }
    return (n);
}

这似乎应该很容易，但我正在努力寻找任何好的例子。

【问题讨论】：

标签： c sockets stream chunks

【解决方案1】：

/* outside the loop */
chunksWritten = 0;
int smaller;
int r;
int sizeRemaining = filesize;
//char *fileChunk = malloc(sizeof(char)*MAX_BLOCK_SIZE+1);
//memcpy(fileChunk, fileContents, sizeof(char)*MAX_BLOCK_SIZE);
//r = writen(sd, fileChunk, MAX_BLOCK_SIZE);
r = writen(sd, fileContents, MAX_BLOCK_SIZE);
if(r==-1) {
  /* deal with error in a manner that fits the rest of your program */
}
chunksWritten = chunksWritten + r;
sizeRemaining = sizeRemaining - MAX_BLOCK_SIZE;

while(sizeRemaining > 0){
  if(sizeRemaining > MAX_BLOCK_SIZE){
    smaller = MAX_BLOCK_SIZE;
  } else {
    smaller = sizeRemaining;
  }
  //memcpy(fileChunk, fileContents+sizeof(char)*chunksWritten, sizeof(char)*smaller);
  //r = writen(sd, fileChunk, MAX_BLOCK_SIZE);
  r = writen(sd, fileContents[filesize - sizeRemaining], smaller);
  if(r==-1) {
    /* deal with error in a manner that fits the rest of your program */
  }
  sizeRemaining = sizeRemaining - MAX_BLOCK_SIZE;
}

/*
Reminder: clean-up fileChunk & fileContents if you don't need them later on
*/

您当然可以重新设计循环以向上计数而不是向下计数。我认为倒计时更好。

编辑：基于 cmets 进行了一些更改。

【讨论】：

将 char fileChunk 更改为 char *fileChunk，效果很好。完美-非常感谢。
你真的不需要（昂贵的）memcopy！。 .... writen(ds, fileContents[filesize - sizeRemaining],smaller);
如果 writen() 返回
@Jason 和@asveikau 两者都很好。我已经更新了代码以反映它们。
我最终得到了这个工作。此处提供完整的实现：github.com/blairyeah/FTP-Client--Server

【解决方案2】：

不知道你为什么想要这个，但似乎你想要这样的东西：

#define MIN(x, y) ((x) < (y) ? (x) : (y))

while (chunksWritten < filesize) {
    int writtenThisPass = writen(fd,
                                 fileContents + chunksWritten,
                                 MIN(filesize - chunksWritten, MAX_BLOCK_SIZE));

    if (writtenThisPass <= 0)
    {
        // TODO: handle the error
    }
    else
    {
        chunksWritten += writtenThisPass;
    }
}

【讨论】：