`fgets()` returns prematurely in non-canonical input mode

[Galfurian]

fgets() returns prematurely in non-canonical input mode

Description:

When fgets() is used with STDIN_FILENO and the process has ICANON disabled in its termios configuration, the function may return immediately without blocking for a full line, even if no input is available. This violates the expected behavior of fgets(), which should block until a full line is available (ending with \n) or EOF is reached.

Steps to Reproduce:

1. Disable ICANON and ECHO in a user process.
2. Call fgets(buf, size, STDIN_FILENO).
3. Observe that the call returns immediately with a possibly empty or partial string.

Expected Behavior:
fgets() should block until a full line is available, even in non-canonical mode, or otherwise simulate canonical behavior.

Suggested Fix:
Either:

• Force fgets() to block and accumulate until \n is read, regardless of terminal mode, or
• Document that fgets() must be used in canonical mode only.