; The MIT License (MIT)
;
; Copyright (c) 2026 pacman64
;
; Permission is hereby granted, free of charge, to any person obtaining a copy
; of this software and associated documentation files (the "Software"), to deal
; in the Software without restriction, including without limitation the rights
; to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
; copies of the Software, and to permit persons to whom the Software is
; furnished to do so, subject to the following conditions:
;
; The above copyright notice and this permission notice shall be included in
; all copies or substantial portions of the Software.
;
; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
; SOFTWARE.


; To compile this app for linux/amd64, use the commands
;
; nasm -f elf64 -o nil-linux-amd64.o nil-linux-amd64.asm
; ld -n -s nil-linux-amd64.o -o nil


; nil
;
; Emit nothing, while also discarding all bytes from the standard input, if
; data are being piped into it.


stdin equ 0
statbuf_size equ 32
chunk_max_size equ 32 * 1024
sys_read equ 0
sys_fstat equ 5
sys_exit equ 60

section .text

global _start

_start:

sub rsp, statbuf_size

; fstat(stdin, stat = rsp)
    mov rax, sys_fstat
    mov rdi, stdin
    mov rsi, rsp
    syscall

cmp rax, 0
jne fail

mov al, [rsp+8]
cmp al, 3
jne piped

add rsp, statbuf_size

quit:

; exit(0)
    mov rax, sys_exit
    mov rdi, 0
    syscall

fail:

; exit(1)
    mov rax, sys_exit
    mov rdi, 1
    syscall

piped:

add rsp, statbuf_size
sub rsp, chunk_max_size
mov rbx, rsp

discard_stdin:
    push rbx

    ; read(stdin, buf = rbx, size = chunk_max_size)
        mov rax, sys_read
        mov rdi, stdin
        mov rsi, rbx
        mov rdx, chunk_max_size
        syscall

    pop rbx

    cmp rax, -1
    je fail
    cmp rax, 0
    je quit

    jmp discard_stdin