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►3 Network Virtual Terminal
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3.1 NVT Encoder
encode-nvt-buffer
3.2 NVT Options
nvt-code-names
set-nvt-option
set-nvt-option!
format-nvt-options
nvt-option-bytes
nvt-base-action
nvt-action-state
make-nvt-action/  option-key
split-nvt-action/  option-key
make-nvt-options
3.3 NVT Output Port
make-nvt-output-port
nvt-output-port?
write-nvt-raw-bytes
send-nvt-option
3.4 NVT Input Port
make-nvt-input-port
nvt-input-port?
nvt-input-port-options
3.5 NVT TCP Acceptor
nvt-tcp-accept-ports
3.6 NVT Term
nvt-tcp-accept-term
8.16.0.4
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3 Network Virtual Terminal🔗ℹ

Dominik Pantůček <dominik.pantucek@trustica.cz>

These modules handle the low-level NVT connections over a pair of input/output ports. In real-world deployments the nvt-tcp-accept-ports is to be used, however it is possible to transparently create a pair of NVT ports over any bi-directional connection. For example make-pipe is often used for testing many features provided by these modules.

3.1 NVT Encoder🔗ℹ

 (require tui/term/nvt-encoder) package: tui-term

Helper module for transparently escaping IAC bytes in the output. For bypassing this escaping feature of the nvt-output-port? the procedure write-nvt-raw-bytes must be used.

procedure

(encode-nvt-buffer buf) → (listof byteslice?)

  buf : bytes?
Encodes a buffer buf of bytes into a list of byteslices ensuring any occurences of IAC are doubled in output when write-byteslices is used on such list.

3.2 NVT Options🔗ℹ

 (require tui/term/nvt-options) package: tui-term

Handling of NVT options on both sides of the connection. It keeps track of either received or sent options. It is possible to interpret the currently negotiated NVT state based on the options on both its input and output ports.

value

nvt-code-names : hash?

The following NVT codes are provided:

IAC

#xff

DONT

#xfe

DO

#xfd

WONT

#xfc

WILL

#xfb

SB

#xfa

GA

#xf9

EL

#xf8

EC

#xf7

AYT

#xf6

AO

#xf5

IP

#xf4

BRK

#xf3

DM

#xf2

NOP

#xf1

SE

#xf0

LINEMODE

#x22

NAWS

#x1f

TTYPE

#x18

SGA

#x3

ECHO

#x1

BINARY

#x0

procedure

(set-nvt-option options action option) → hash?

  options : hash?
  action : byte?
  option : byte?
Maps given option to symbolic name and in options it sets given key to #t or #f based on action interpretation.

procedure

(set-nvt-option! options action option) → void?

  options : hash?
  action : byte?
  option : byte?
Like set-nvt-option but modifies options in place.

procedure

(format-nvt-options options) → string?

  options : hash?
Returns human-readable version of NVT options stored in options hash. It performs the binary to text mapping using nvt-code-names lookup table.

procedure

(nvt-option-bytes action option) → bytes?

  action : byte?
  option : byte?
Returns a 3-byte sequence that can be sent directly to the remote NVT.

procedure

(nvt-base-action action) → byte?

  action : byte?
For DO and DONT actions it returns DO and for WILL and WONT it returns WILL. Returns IAC for any other value.

procedure

(nvt-action-state action) → boolean?

  action : byte?
For DO and WILL it returns #t and for DONT and WONT #f is returned. An exception exn:fail? is raised for any other value.

procedure

(make-nvt-action/option-key action option)

 → (integer-in 0 65535)
  action : byte?
  option : byte?
Combines action and option into a single 16-bit number.

procedure

(split-nvt-action/option-key action/option) → 
byte? byte?
  action/option : (integer-in 0 65535)
Reverse operation to make-nvt-action/option-key which splits a single 16-bit representation into separate actoin and option bytes.

procedure

(make-nvt-options) → hash?

A convenience alias for make-hash to prevent API breakage should a future implementation change require different representation.

3.3 NVT Output Port🔗ℹ

 (require tui/term/nvt-output-port) package: tui-term

NVT output port ensures escaping of any IAC bytes (255) as doubles. For regular output everything is transparent for the port user. NVT protocol implementation must use write-nvt-raw-bytes for any negotiations and subnegotiations.

procedure

(make-nvt-output-port [out]) → nvt-output-port?

  out : output-port? = (current-output-port)
Creates new NVT output port on top of given port out.

procedure

(nvt-output-port? v) → boolean?

  v : any/c
A predicate returning #t if given value v is a NVT output port.

procedure

(write-nvt-raw-bytes bs [out]) → exact-nonnegative-integer?

  bs : bytes?
  out : nvt-output-port? = (current-output-port)
Writes bytes directly to the underlying raw port.

procedure

(send-nvt-option action option [out]) → void?

  action : fixnum?
  option : fixnum?
  out : nvt-output-port? = (current-output-port)
Sends given NVT option to the other party and updates the local information about options sent.

3.4 NVT Input Port🔗ℹ

 (require tui/term/nvt-input-port) package: tui-term

NVT input port de-escapes any escaped IAC bytes (255). It also provides machinery for handling incoming NVT options and allows for specific subnegotiations callbacks.

procedure

(make-nvt-input-port [#:resize-handler resize-handler 
  #:termtype-handler termtype-handler 
  #:max-sb-length max-sb-length 
  in]) 
 → nvt-input-port?
  resize-handler : procedure? = void
  termtype-handler : procedure? = void
  max-sb-length : exact-positive-integer? = 128
  in : input-port? = (current-input-port)
Creates new NVT input port on top of given in input port. The subnegotiation handlers are as follows:

The resize-handler must accept two arguments - the terminal width and height respectively.

The termtype-handler must accept one argument - a string representing the terminal type.

All subnegotiations must be shorter than max-sb-length to avoid infinite loops when corrupted input is received. When the subnegotiation length is exceeded, normal operation is resumed starting at the very next byte.

procedure

(nvt-input-port? v) → boolean?

  v : any/c
A predicate returning #t if given value v is a NVT input port.

procedure

(nvt-input-port-options nvti) → hash?

  nvti : nvt-input-port?
Returns the hash of current NVT options as received from the other party.

3.5 NVT TCP Acceptor🔗ℹ

 (require tui/term/nvt-ports) package: tui-term

This module is a glue between TCP stack and low-level NVT implementation.

procedure

(nvt-tcp-accept-ports tcp-listen-socket 
  [#:resize-handler resize-handler 
  #:termtype-handler termtype-handler]) 
 → 
nvt-input-port? nvt-output-port?
  tcp-listen-socket : tcp-listener?
  resize-handler : procedure? = void
  termtype-handler : procedure? = void
Accepts TCP connection and creates input and output NVT port on accepted TCP ports. Requests window size reporting, enables raw mode and notifies the other side that this side will perform character output - effectively disabling local terminal echo on the client side.

This is setup similar to a local TTY in "raw" mode.

3.6 NVT Term🔗ℹ

 (require tui/term/nvt) package: tui-term

This module wraps all the NVT layers into a tterm package.

procedure

(nvt-tcp-accept-term tcp-listen-socket) → tterm?

  tcp-listen-socket : tcp-listener?
Uses nvt-tcp-accept-ports on given tcp-listen-socket and creates a tterm wrapping the results. The ttype and size fields of the tterm struct are updated when appropriate message is received on the input port.

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