可以使用strncpy复制tcp流导致故障吗？

Question

I am making a simple proxy server. And I have a very hard time with parsing response.

// Case 1
do {
    memset(buffer, 0, BUFSIZE);
    con = read(sockfd, buffer, BUFSIZE);
    write(client, buffer, con);
} while(con);

// Case 2
do {
    memset(buffer, 0, BUFSIZE);
    con = read(sockfd, buffer, BUFSIZE);
    size += con;
    cachebuf = (char*)realloc(cachebuf, size);
    strncpy(cachebuf+(size-con), buffer, con);
} while(con);
write(client, cachebuf, size);

These two samples receive a TCP stream from the end server, and forward it to browser. The only difference is that first one forwards the stream as soon as it receives it, and second one saves the stream in the cachebuf pointer and sends as a whole(which it the case I want to use)

It seems same, and both works fine when it receives a HTML file. However, the second one can not send images. Why does this happen?

Answer 1

You can't use strncpy (and friends) to copy binary data. This function copies bytes until it encounters nul-terminator ( '\\0' ). Binary data, in particularly, images, have a lot of those characters in them, and string functions will not copy it completely.

To copy binary data, you can use memcpy or std::copy .

On a side note, your memset before read is completely unnecessary and just contributes to global warming without doing anything useful.