[Bug] simplex-talk server: addr_len passed to accept() is uninitialized (Undefined Behavior) #100

Description
In the simplex-talk server code (Chapter 1.4, Software), the variable addr_len is passed to accept() without being initialized. Reading this uninitialized variable is Undefined Behavior (UB) in C.

Location

· Release Version 6.1 PDF Page 36-37

Code Snippet

int buf_len, addr_len;
// ...
while(1) {
    if ((new_s = accept(s, (struct sockaddr *)&sin, &addr_len)) < 0) {
        perror("simplex-talk: accept");
        exit(1);
    }
    // ...
}

Issue
accept()'s third argument (addrlen) is a value-result parameter. As an input, it must be initialized to the size of the sockaddr buffer (sizeof(sin)). Passing an uninitialized int means the OS receives an indeterminate value as the buffer length. This is a latent bug that can cause accept() to fail (e.g., EINVAL) or lead to memory corruption depending on the stack state.

Suggested Fix
Initialize addr_len at declaration (or reset it before each accept() call if sin is reused):

int buf_len;
socklen_t addr_len = sizeof(sin); // Initialize here
// ...
while(1) {
    // Optional but recommended: addr_len = sizeof(sin);
    if ((new_s = accept(s, (struct sockaddr *)&sin, &addr_len)) < 0) {
    // ...
}