# ip65 technical reference

# File : ip65/telnet.s

    minimal telnet implementation (dumb terminal emulation only)
    to use:
    set the following variables - telnet_use_native_charset,telnet_port,telnet_ip
    then call telnet_connect
    you must also define (and export) these function
     telnet_menu - called whenever the F1 key is pressed.
     telnet_on_connection - called after succesful connection

## functions

function | description
--- | ---
telnet_connect |
    connect to a remote telnet server
    inputs:
    telnet_use_native_charset: set to 0 if remote server uses standard ASCII, 1 if remote server uses the 'native' charset (i.e. PETSCII)
    telnet_port: port number to connect to
    telnet_ip: ip address of remote server

## variables

variable | description | size (bytes)
--- | --- | ---
telnet_ip | ip address of remote server | 4
telnet_port | port number to connect to | 2
telnet_use_native_charset | 0 means all data is translated to/from NVT ASCII | 1

## implementation

    ;minimal telnet implementation (dumb terminal emulation only)
    ;to use:
    ;set the following variables - telnet_use_native_charset,telnet_port,telnet_ip
    ;then call telnet_connect
    ;you must also define (and export) these function
    ; telnet_menu - called whenever the F1 key is pressed.
    ; telnet_on_connection - called after succesful connection

    .include "../inc/common.i"

      .import tcp_connect
      .import tcp_callback
      .import tcp_connect_ip
      .import tcp_listen
      .importzp KEYCODE_F1
      .import tcp_inbound_data_ptr
      .import tcp_inbound_data_length
      .import tcp_send
      .import tcp_send_data_len
      .import tcp_close
      .import print_a
      .import print_cr
      .import vt100_init_terminal
      .import vt100_process_inbound_char
      .import vt100_transform_outbound_char
      .import tcp_send_keep_alive
      .import timer_read

      .import ip65_process
      .import get_key_if_available
      .import get_filtered_input
      .import check_for_abort_key
      .import ok_msg
      .import failed_msg
      .import print
      .import print_errorcode
      .import native_to_ascii
      .import ascii_to_native

    .export telnet_connect
    .export telnet_use_native_charset
    .export telnet_port
    .export telnet_ip

    .import telnet_menu
    .import telnet_on_connection

    .segment "IP65ZP" : zeropage

    ; pointer for moving through buffers
    buffer_ptr:  .res 2      ; source pointer

    .code

    ;connect to a remote telnet server
    ;inputs:
    ;telnet_use_native_charset: set to 0 if remote server uses standard ASCII, 1 if remote server uses the 'native' charset (i.e. PETSCII)
    ;telnet_port: port number to connect to
    ;telnet_ip: ip address of remote server
    telnet_connect:
      lda telnet_use_native_charset
      bne :+
      jsr vt100_init_terminal
    :
      ldax #telnet_callback
      stax tcp_callback
      ldx #3
    @copy_dest_ip:
      lda telnet_ip,x
      sta tcp_connect_ip,x
      dex
      bpl @copy_dest_ip

      ldax telnet_port
      jsr tcp_connect

      bcc @connect_ok
      jsr print_cr
      ldax #failed_msg
      jsr print
      jsr print_cr
      jsr print_errorcode
      rts
    @connect_ok:

      jsr telnet_on_connection

      ldax #ok_msg
      jsr print
      jsr print_cr
      lda #0
      sta connection_closed
      sta iac_response_buffer_length

    @main_polling_loop:

      jsr check_for_abort_key
      bcc  @no_abort
      jsr  tcp_close
      jmp   @disconnected

    @no_abort:
      jsr timer_read
      txa
      adc #$20  ;32 x 1/4 = ~ 8seconds
      sta telnet_timeout
    @wait_for_keypress:
      jsr timer_read
      cpx telnet_timeout
      bne @no_timeout
      jsr tcp_send_keep_alive
      jmp @main_polling_loop
    @no_timeout:
      jsr ip65_process
      lda connection_closed
      beq @not_disconnected
    @disconnected:
      ldax #disconnected
      jsr print
      rts
    @not_disconnected:
      lda iac_response_buffer_length
      beq @no_iac_response
      ldx #0
      stax tcp_send_data_len
      stx iac_response_buffer_length
      ldax  #iac_response_buffer
      jsr tcp_send
    @no_iac_response:

      jsr get_key_if_available
      beq @wait_for_keypress

      cmp #KEYCODE_F1
      bne @not_telnet_menu
      jsr telnet_menu
      jmp @main_polling_loop
    @not_telnet_menu:

      ldx #0
      stx tcp_send_data_len
      stx tcp_send_data_len+1

      ldx telnet_use_native_charset
      bne @no_conversion_required

      jsr vt100_transform_outbound_char

      sta temp_a
      tya
      bne :+
      jmp @main_polling_loop  ;Y=0 means nothing to send
    :

      cmp #2
      beq :+
      lda temp_a
      jmp @no_conversion_required
    :

      lda temp_a
      stax buffer_ptr
      ldy #0
    :
      lda (buffer_ptr),y
      beq @send_char
      sta scratch_buffer,y
      inc tcp_send_data_len
      iny
      bne :-
      jmp @send_char

    @no_conversion_required:
      ldy tcp_send_data_len
      sta scratch_buffer,y
      inc tcp_send_data_len

    @send_char:

      ldax  #scratch_buffer
      jsr tcp_send
      bcs @error_on_send
      jmp @main_polling_loop

    @error_on_send:
      ldax #transmission_error
      jsr print
      jmp print_errorcode

    ;tcp callback - will be executed whenever data arrives on the TCP connection
    telnet_callback:

      lda tcp_inbound_data_length+1
      cmp #$ff
      bne @not_eof
      lda #1
      sta connection_closed
      rts
    @not_eof:

      ldax tcp_inbound_data_ptr
      stax buffer_ptr
      lda tcp_inbound_data_length
      sta buffer_length
      lda tcp_inbound_data_length+1
      sta buffer_length+1

    @next_byte:
      ldy #0
      lda (buffer_ptr),y
      tax
      lda telnet_use_native_charset
      beq :+
      jmp  @no_conversion_req
    :

    ;if we get here, we are in ASCII 'char at a time' mode,  so look for (and process) Telnet style IAC bytes
      lda telnet_state
      cmp #telnet_state_got_command
      bne :+
      jmp @waiting_for_option
    :
      cmp #telnet_state_got_iac
      beq @waiting_for_command
      cmp #telnet_state_got_suboption
      beq @waiting_for_suboption_end
    ; we must be in 'normal' mode
      txa
      cmp #255
      beq :+
      jmp @not_iac
    :
      lda #telnet_state_got_iac
      sta telnet_state
      jmp @byte_processed

    @waiting_for_suboption_end:
      txa

      ldx iac_suboption_buffer_length
      sta iac_suboption_buffer,x
      inc iac_suboption_buffer_length
      cmp #$f0  ;SE - suboption end
      bne @exit_suboption

      lda #telnet_state_normal
      sta telnet_state
      lda iac_suboption_buffer
      cmp #$18
      bne @not_terminal_type

      ldx #0
    :
      lda terminal_type_response,x
      ldy iac_response_buffer_length
      inc iac_response_buffer_length
      sta iac_response_buffer,y
      inx
      txa
      cmp #terminal_type_response_length
      bne :-

    @not_terminal_type:

    @exit_suboption:
      jmp @byte_processed
    @waiting_for_command:
      txa
      sta telnet_command
      cmp #$fa ; SB - suboption begin
      beq @suboption
      cmp #$fb ;WILL
      beq @option
      cmp #$fc ;WONT
      beq @option
      cmp #$fd ; DO
      beq @option
      cmp #$fe ;DONT
      beq @option
    ;we got a command we don't understand - just ignore it
      lda #telnet_state_normal
      sta telnet_state
      jmp @byte_processed
    @suboption:

      lda #telnet_state_got_suboption
      sta telnet_state
      lda #0
      sta iac_suboption_buffer_length
      jmp @byte_processed

    @option:
      lda #telnet_state_got_command
      sta telnet_state
      jmp @byte_processed

    @waiting_for_option:
    ;we have now got IAC, ,
      txa
      sta telnet_option
      lda telnet_command

      cmp #$fb
      beq @iac_will

      cmp #$fc
      beq @iac_wont

      cmp #$fe
      beq @iac_dont

      ;if we get here, then it's a "do"

      lda telnet_option

      cmp #$18  ;terminal type
      beq @do_terminaltype

      cmp #$1f
      beq @do_naws

      ;if we get here, then it's a "do" command we don't honour

    @iac_dont:
      lda #$fc ;wont
    @add_iac_response:
      ldx iac_response_buffer_length
      sta iac_response_buffer+1,x
      lda #255
      sta iac_response_buffer,x
      lda telnet_option
      sta iac_response_buffer+2,x

      inc iac_response_buffer_length
      inc iac_response_buffer_length
      inc iac_response_buffer_length
    @after_set_iac_response:
      lda #telnet_state_normal
      sta telnet_state
      jmp @byte_processed
    @iac_will:
      lda telnet_option
      cmp #$01 ;ECHO
      beq @will_echo
      cmp #$03 ;DO SUPPRESS GA
      beq @will_suppress_ga

    @iac_wont:
      lda #$fe ;dont
      jmp @add_iac_response

    @will_echo:
      lda #$fd ;DO
      jmp @add_iac_response

    @will_suppress_ga:
      lda #$fd ;DO
      jmp @add_iac_response

    @do_naws:
      ldx #0
    :
      lda naws_response,x
      ldy iac_response_buffer_length
      inc iac_response_buffer_length
      sta iac_response_buffer,y
      inx
      txa
      cmp #naws_response_length
      bne :-

      jmp @after_set_iac_response

    @do_terminaltype:
      lda #$fb ;WILL
      jmp @add_iac_response

    @not_iac:
    @convert_to_native:
      txa
      jsr vt100_process_inbound_char
      jmp @byte_processed
    @no_conversion_req:
      txa
      jsr print_a
    @byte_processed:
      inc buffer_ptr
      bne :+
      inc buffer_ptr+1
    :
      lda buffer_length+1
      beq @last_page
      lda buffer_length
      bne @not_end_of_page
      dec buffer_length+1
    @not_end_of_page:
      dec buffer_length
      jmp @next_byte
    @last_page:
      dec buffer_length
      beq @finished

      jmp @next_byte

    @finished:

      rts

    ;constants
    closing_connection: .byte "CLOSING CONNECTION",13,0
    disconnected: .byte 13,"CONNECTION CLOSED",13,0
    transmission_error: .byte "ERROR WHILE SENDING ",0

    ;initial_telnet_options:
    ;  .byte $ff,$fb,$1F   ;IAC WILL NAWS
    ;  .byte $ff,$fb,$18   ;IAC WILL TERMINAL TYPE

    ;initial_telnet_options_length=*-initial_telnet_options

    terminal_type_response:
      .byte $ff ; IAC
      .byte $fa; SB
      .byte  $18 ; TERMINAL TYPE
      .byte $0 ; IS
      .byte "vt100" ;what we pretend to be
      .byte $ff ; IAC
      .byte $f0 ; SE
    terminal_type_response_length=*-terminal_type_response

    naws_response:
      .byte $ff,$fb,$1F   ;IAC WILL NAWS
      .byte $ff ; IAC
      .byte $fa; SB
      .byte  $1F ; NAWS
      .byte $00 ;  width (high byte)
      .byte 40 ;  width (low byte)
      .byte $00 ;  height (high byte)
      .byte 25 ;  height (low byte)

      .byte $ff ; IAC
      .byte $f0 ; SE

    naws_response_length=*-naws_response

    ;variables
    .segment "APP_SCRATCH"
    telnet_ip:  .res 4  ;ip address of remote server
    telnet_port: .res 2 ;port number to connect to
    telnet_timeout: .res 1
    connection_closed: .res 1
    telnet_use_native_charset: .res 1 ; 0 means all data is translated to/from NVT ASCII
    buffer_offset: .res 1
    telnet_command: .res 1
    telnet_option: .res 1

    telnet_state_normal = 0
    telnet_state_got_iac = 1
    telnet_state_got_command = 2
    telnet_state_got_suboption=3

    buffer_length: .res 2

    telnet_state: .res 1
    temp_a: .res 1
    iac_response_buffer: .res 64
    iac_response_buffer_length: .res 1
    scratch_buffer : .res 40
    iac_suboption_buffer: .res 64
    iac_suboption_buffer_length: .res 1

    ;-- LICENSE FOR telnet.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 --