Use of string functions with manually set NUL-terminator-CodePudding

This might sound like a silly question, but I learned that sometimes, especially in C, there are things that seem obvious but aren't really safe or correct.

I have a char buffer that gets filled with text (no binary data is expected) via HTTP.

Now I want to process the request body and I think strstr() is exactly what I want.

However, strstr() needs both strings to be nul terminated.

Since I have no control over what the user will actually send, I decided to just terminate the "string" (buffer) at the end like this:

char buffer[1024];

// receive request
readHTTPRequest(buffer, sizeof(buffer));

// buffer contents is undetermined
buffer[sizeof(buffer) - 1] = 0; // always terminate buffer

const char *request_body = strstr(buffer, "\r\n\r\n");

if (request_body) {
    size_t request_body_size = strlen(request_body);
}

Is this approach safe? Am I missing something?

CodePudding user response：

This will only work if the buffer was completely filled. If not, you'll have uninitialized bytes in between what was actually read and the last byte.

A simple way to handle this is to initialize the buffer with all zeros:

char buffer[1024] = {0};

Or, if readHTTPRequest returns the number of bytes read, use that value instead as the index to write the 0 byte to.