; minimal dns implementation - requires a DNS server that supports recursion MAX_DNS_MESSAGES_SENT = 8 ; timeout after sending 8 messages will be about 7 seconds (1+2+3+4+5+6+7+8)/4 .include "zeropage.inc" .include "../inc/common.inc" .include "../inc/error.inc" .export dns_set_hostname .export dns_resolve .export dns_ip .export dns_hostname_is_dotted_quad .import ip65_error .import cfg_dns .import parse_dotted_quad .import dotted_quad_value .import ip65_process .import udp_add_listener .import udp_remove_listener .import udp_callback .import udp_send .import udp_inp .import output_buffer .importzp udp_data .import udp_send_dest .import udp_send_src_port .import udp_send_dest_port .import udp_send_len .import check_for_abort_key .import timer_read dns_hostname = ptr1 .bss ; dns packet offsets dns_inp = udp_inp + udp_data dns_id = 0 dns_flags = 2 dns_qdcount = 4 dns_ancount = 6 dns_nscount = 8 dns_arcount = 10 dns_qname = 12 dns_server_port = 53 dns_client_port_high_byte: .res 1 dns_ip: .res 4 ; will be contain ip address of hostname after succesful exection of dns_resolve dns_msg_id: .res 2 dns_current_label_length: .res 1 dns_current_label_offset: .res 1 dns_message_sent_count: .res 1 dns_packed_hostname: .res 128 ; dns state machine dns_initializing = 1 ; initial state dns_query_sent = 2 ; sent a query, waiting for a response dns_complete = 3 ; got a good response dns_failed = 4 ; got either a 'no such name' or 'recursion declined' response dns_state: .res 1 ; flag indicating the current stage in the dns resolution process dns_timer: .res 1 dns_loop_count: .res 1 dns_break_polling_loop: .res 1 hostname_copied: .res 1 questions_in_response: .res 1 dns_hostname_is_dotted_quad: .res 1 .code ; sets up for resolution of a hostname to an ip address ; inputs: ; AX = pointer to null terminated string that contains either a dns hostname ; (e.g. "host.example.com",0) or an address in "dotted quad" format, ; (e.g. "192.168.1.0",0) ; outputs: ; carry flag is set on error (i.e. hostname too long), clear otherwise ; dns_hostname_is_dotted_quad: 1 if the hostname is an address in "dotted quad" format, 0 otherwise ; dns_ip: set to the ip address of the hostname (if dns_hostname_is_dotted_quad is 1) dns_set_hostname: stax dns_hostname ; copy the hostname into a buffer suitable to copy directly into the qname field ; we need to split on dots jsr parse_dotted_quad ; if we are passed an IP address instead of a hostname, don't bother looking it up in dns bcs @wasnt_dotted_quad ; if the string was a dotted quad, then copy the parsed 4 bytes in to dns_ip lda #1 sta dns_hostname_is_dotted_quad ldx #3 ; set destination address : lda dotted_quad_value,x sta dns_ip,x dex bpl :- rts ; done! @wasnt_dotted_quad: ldy #0 ; input pointer ldx #1 ; output pointer (start at 1, to skip first length offset, which will be filled in later) sty dns_hostname_is_dotted_quad sty dns_current_label_length sty dns_current_label_offset sty hostname_copied @next_hostname_byte: lda (dns_hostname),y ; get next char in hostname beq @end_of_hostname cmp #'/' ; allow hostnames to be terminated by "/" or ":" to help with URL parsing beq @end_of_hostname cmp #':' bne :+ @end_of_hostname: inc hostname_copied bne @set_length_of_last_label : cmp #'.' ; do we need to split the labels? bne @not_a_dot @set_length_of_last_label: txa pha lda dns_current_label_length ldx dns_current_label_offset sta dns_packed_hostname,x lda #0 sta dns_current_label_length pla tax stx dns_current_label_offset lda hostname_copied beq @update_counters jmp @hostname_done @not_a_dot: sta dns_packed_hostname,x inc dns_current_label_length @update_counters: iny inx bmi @hostname_too_long ; don't allow a hostname of more than 128 bytes jmp @next_hostname_byte @hostname_done: lda dns_packed_hostname-1,x ; get the last byte we wrote out beq :+ ; was it a zero? lda #0 sta dns_packed_hostname,x ; write a trailing zero (i.e. a zero length label) inx : clc ; no error rts @hostname_too_long: lda #IP65_ERROR_NAME_TOO_LONG sta ip65_error sec rts ; resolve a string containing a hostname (or a dotted quad) to an ip address ; inputs: ; cfg_dns must point to a DNS server that supports recursion ; dns_set_hostname must have been called to load the string to be resolved ; outputs: ; carry flag is set if there was an error, clear otherwise ; dns_ip: set to the ip address of the hostname (if no error) dns_resolve: lda dns_hostname_is_dotted_quad beq @hostname_not_dotted_quad clc rts ; we already set dns_ip when copying the hostname @hostname_not_dotted_quad: ldax #dns_in stax udp_callback ldx #53 inc dns_client_port_high_byte ; each call to resolve uses a different client address lda dns_client_port_high_byte ; so we don't get confused by late replies to a previous call jsr udp_add_listener bcc :+ rts : lda #dns_initializing sta dns_state lda #0 ; reset the "message sent" counter sta dns_message_sent_count jsr send_dns_query @dns_polling_loop: lda dns_message_sent_count adc #1 sta dns_loop_count ; we wait a bit longer between each resend @outer_delay_loop: lda #0 sta dns_break_polling_loop jsr timer_read stx dns_timer ; we only care about the high byte @inner_delay_loop: jsr ip65_process jsr check_for_abort_key bcc @no_abort lda #IP65_ERROR_ABORTED_BY_USER sta ip65_error rts @no_abort: lda dns_state cmp #dns_complete beq @complete cmp #dns_failed beq @failed lda #0 cmp dns_break_polling_loop bne @break_polling_loop jsr timer_read cpx dns_timer ; this will tick over after about 1/4 of a second beq @inner_delay_loop dec dns_loop_count bne @outer_delay_loop @break_polling_loop: jsr send_dns_query inc dns_message_sent_count lda dns_message_sent_count cmp #MAX_DNS_MESSAGES_SENT-1 bpl @too_many_messages_sent jmp @dns_polling_loop @too_many_messages_sent: lda #IP65_ERROR_TIMEOUT_ON_RECEIVE bne @error ; always @failed: lda #IP65_ERROR_DNS_LOOKUP_FAILED @error: sta ip65_error sec ; signal an error bcs @done ; always @complete: clc ; signal success @done: php ldx #53 lda dns_client_port_high_byte jsr udp_remove_listener plp rts send_dns_query: ldax dns_msg_id inx adc #0 stax dns_msg_id stax output_buffer+dns_id ldax #$0001 ; QR =0 (query), opcode = 0 (query), AA = 0, TC = 0,RD = 1,RA = 0,Z = 0,RCODE = 0 stax output_buffer+dns_flags ldax #$0100 ; we ask 1 question stax output_buffer+dns_qdcount ldax #$0000 stax output_buffer+dns_ancount ; we send no answers stax output_buffer+dns_nscount ; we send no name servers stax output_buffer+dns_arcount ; we send no authorative records ldx #0 : lda dns_packed_hostname,x sta output_buffer+dns_qname,x inx bpl @hostname_still_ok lda #IP65_ERROR_NAME_TOO_LONG sta ip65_error jmp @error_on_send ; if we got past 128 bytes, there's a problem @hostname_still_ok: cmp #0 bne :- ; keep looping until we have a zero byte. lda #0 sta output_buffer+dns_qname,x ; high byte of QTYPE = 1 (A) sta output_buffer+dns_qname+2,x ; high byte of QLASS = 1 (IN) lda #1 sta output_buffer+dns_qname+1,x ; low byte of QTYPE = 1 (A) sta output_buffer+dns_qname+3,x ; low byte of QLASS = 1 (IN) txa clc adc #(dns_qname+4) ldx #0 stax udp_send_len ldx #53 lda dns_client_port_high_byte stax udp_send_src_port ldx #3 ; set destination address : lda cfg_dns,x sta udp_send_dest,x dex bpl :- ldax #dns_server_port ; set destination port stax udp_send_dest_port ldax #output_buffer jsr udp_send bcs @error_on_send lda #dns_query_sent sta dns_state rts @error_on_send: sec rts dns_in: lda dns_inp+dns_flags+1 and #$0f ; get the RCODE cmp #0 beq @not_an_error_response lda #dns_failed sta dns_state rts @not_an_error_response: lda dns_inp+dns_qdcount+1 sta questions_in_response cmp #1 ; should be exactly 1 Q in the response (i.e. the one we sent) beq :+ jmp @error_in_response : lda dns_inp+dns_ancount+1 bne :+ jmp @error_in_response ; should be at least 1 answer in response : ; we need to skip over the question (we will assume it's the question we just asked) ldx #dns_qname : lda dns_inp,x ; get next length byte in question beq :+ ; we're done if length == 0 clc txa adc dns_inp,x ; add length of next label to ptr adc #1 ; +1 for the length byte itself tax bcs @error_in_response ; if we overflowed x, then message is too big bcc :- : inx ; skip past the nul byte lda dns_inp+1,x cmp #1 ; QTYPE should 1 lda dns_inp+3,x cmp #1 ; QCLASS should 1 bne @error_in_response inx ; skip past the QTYPE/QCLASS inx inx inx ; x now points to the start of the answers lda dns_inp,x bpl @error_in_response ; we are expecting the high bit to be set (we assume the server will send us back the answer to the question we just asked) inx ; skip past the compression inx ; we are now pointing at the TYPE field lda dns_inp+1,x cmp #5 ; is this a CNAME? bne @not_a_cname txa clc adc #10 ; skip 2 bytes TYPE, 2 bytes CLASS, 4 bytes TTL, 2 bytes RDLENGTH tax ; we're now pointing at the CNAME record ldy #0 ; start of CNAME hostname : lda dns_inp,x beq @last_byte_of_cname bmi @found_compression_marker sta dns_packed_hostname,y inx iny bmi @error_in_response ; if we go past 128 bytes, something is wrong bpl :- ; go get next byte @last_byte_of_cname: sta dns_packed_hostname,y lda #1 sta dns_break_polling_loop rts ; finished processing - the main dns polling loop should now resend a query, this time for the hostname from the CNAME record @found_compression_marker: lda dns_inp+1,x tax jmp :- @not_a_cname: cmp #1 ; should be 1 (A record) bne @error_in_response txa clc adc #10 ; skip 2 bytes TYPE, 2 bytes CLASS, 4 bytes TTL, 2 bytes RDLENGTH tax ; we're now pointing at the answer! lda dns_inp,x sta dns_ip lda dns_inp+1,x sta dns_ip+1 lda dns_inp+2,x sta dns_ip+2 lda dns_inp+3,x sta dns_ip+3 lda #dns_complete sta dns_state lda #1 sta dns_break_polling_loop @error_in_response: rts ; -- LICENSE FOR dns.s -- ; The contents of this file are subject to the Mozilla Public License ; Version 1.1 (the "License"); you may not use this file except in ; compliance with the License. You may obtain a copy of the License at ; http://www.mozilla.org/MPL/ ; ; Software distributed under the License is distributed on an "AS IS" ; basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the ; License for the specific language governing rights and limitations ; under the License. ; ; The Original Code is ip65. ; ; The Initial Developer of the Original Code is Jonno Downes, ; jonno@jamtronix.com. ; Portions created by the Initial Developer are Copyright (C) 2009 ; Jonno Downes. All Rights Reserved. ; -- LICENSE END --