From 47b58450a59ee01054b5e33df08d5b521e10137c Mon Sep 17 00:00:00 2001
From: hpa <hpa>
Date: Mon, 27 Dec 2004 00:26:43 +0000
Subject: [PATCH] Beginnings of a DNS resolver

---
 dnsresolv.inc | 115 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 dnsresolv.inc

diff --git a/dnsresolv.inc b/dnsresolv.inc
new file mode 100644
index 0000000..a8a5192
--- /dev/null
+++ b/dnsresolv.inc
@@ -0,0 +1,115 @@
+; -*- fundamental -*-
+; -----------------------------------------------------------------------
+;   
+;   Copyright 2004 H. Peter Anvin - All Rights Reserved
+;
+;   This program is free software; you can redistribute it and/or modify
+;   it under the terms of the GNU General Public License as published by
+;   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
+;   Bostom MA 02111-1307, USA; either version 2 of the License, or
+;   (at your option) any later version; incorporated herein by reference.
+;
+; -----------------------------------------------------------------------
+
+;
+; dnsresolv.inc
+;
+; Very simple DNS resolver (assumes recursion-enabled DNS server;
+; this should be the normal thing for client-serving DNS servers.)
+;
+
+		section .text
+
+;
+; Turn a string in DS:SI into a DNS "label set" in ES:DI.
+; On return, DI points to the first byte after the label set.
+;
+mangle_dnsname:
+		push ax
+		push cx
+		xor cx,cx
+.getbyte:
+		jcxz .nostart	
+.gotstart:
+		lodsb
+		and al,al
+		jz .endstring
+		cmp al,'.'
+		je .isdot
+		inc byte [es:cx]
+		stosb
+		jmp .getbyte
+.nostart:
+		xor al,al
+		mov cx,di
+		stosb
+		jmp .gotstart
+.isdot:
+		xor cx,cx
+		jmp .getbyte
+.endstring:
+		mov al,[es:cx]
+		and al,al
+		jz .done
+		xor al,al
+		stosb
+.done:
+		pop cx
+		pop ax
+		ret
+
+;
+; Compare two sets of DNS labels, in DS:SI and DS:DI; the one in SI
+; is allowed pointers relative to a packet address in BX.
+;
+; Assumes DS == ES.  ZF = 1 if same; no registers changed.
+;
+dns_compare:
+		pusha
+
+.label:
+		lodsb
+		cmp al,0C0h
+		jb .noptr
+		and al,03Fh
+		mov ah,al
+		lodsb
+		mov si,bx
+		add si,ax
+		jmp .label
+.noptr:
+		cmp al,[di]
+		jne .done			; Mismatch
+		inc di
+		movzx cx,al			; End label?
+		and cx,cx			; ZF = 1 if match
+		jz .done
+		
+		; We have a string of bytes that need to match now
+		repe cmpsb
+		jz .label
+
+.done:
+		popa
+		ret
+
+;
+; Skip past a DNS label set in DS:SI.
+;
+dns_skiplabel:
+		push ax
+		xor ax,ax			; AH == 0
+.loop:
+		lodsb
+		cmp al,0C0h
+		jae .ptr
+		and al,al
+		jz .done
+		add si,ax
+		jmp .loop
+.ptr:
+		inc si
+.done:
+		pop ax
+		ret
+
-- 
2.7.4