go3270/screen.go

// This file is part of https://github.com/racingmars/go3270/
// Copyright 2020 by Matthew R. Wilson, licensed under the MIT license. See
// LICENSE in the project root for license information.

package go3270

import (
	"bytes"
	"net"
)

// Field is a field on the 3270 screen.
type Field struct {
	// Row is the row, 0-based, that the field attribute character should
	// begin at. This library currently only supports 24 rows, so Row must
	// be 0-23.
	Row int

	// Col is the column, 0-based, that the field attribute character should
	// begin at. This library currently only supposed 80 columns, so Column
	// must be 0-79.
	Col int

	// Text is the content of the field to display.
	Content string

	// Write allows the user to edit the value of the field.
	Write bool

	// Intense indicates this field should be displayed with high intensity.
	Intense bool

	// Name is the name of this field, which is used to get the user-entered
	// data. All writeable fields on a screen must have a unique name.
	Name string
}

// Screen is an array of Fields which compose a complete 3270 screen.
// No checking is performed for lack of overlapping fields, unique field
// names,
type Screen []Field

// fieldmap is a map of field buffer addresses and the corresponding field
// name.
type fieldmap map[int]string

// ShowScreen writes the 3270 datastream for the screen to a connection.
// Fields that aren't valid (e.g. outside of the 24x80 screen) are silently
// ignored. If a named field has an entry in the values map, the content of
// the field from the values map is used INSTEAD OF the Field struct's Content
// field. The values map may be nil if no overrides are needed. After writing
// the fields, the cursor is set to crow, ccol, which are 0-based positions:
// row 0-23 and col 0-79. Errors from conn.Write() are returned if
// encountered.
func ShowScreen(screen Screen, values map[string]string, crow, ccol int,
	conn net.Conn) (Response, error) {

	var b bytes.Buffer
	var fm = make(fieldmap) // field buffer positions -> name

	b.WriteByte(0xf5) // Erase/Write to terminal
	b.WriteByte(0xc3) // WCC = Reset, Unlock Keyboard, Reset MDT

	// Build the commands for each field on the screen
	for _, fld := range screen {
		if fld.Row < 0 || fld.Row > 23 || fld.Col < 0 || fld.Col > 79 {
			// Invalid field position
			continue
		}

		b.Write(sba(fld.Row, fld.Col))
		b.Write(sf(fld.Write, fld.Intense))

		// Use fld.Content, unless the field is named and appears in the
		// value map.
		content := fld.Content
		if fld.Name != "" {
			if val, ok := values[fld.Name]; ok {
				content = val
			}
		}
		if content != "" {
			b.Write(a2e([]byte(content)))
		}

		// If a writable field, add it to the field map. We add 1 to bufaddr
		// to make the value match the reported position (I'm guessing it's
		// because we get the position of the field's first input position,
		// not the position of the field attribute byte).
		if fld.Write {
			bufaddr := fld.Row*80 + fld.Col
			fm[bufaddr+1] = fld.Name
		}
	}

	// Set cursor position. Correct out-of-bounds values to 0.
	if crow < 0 || crow > 23 {
		crow = 0
	}
	if ccol < 0 || ccol > 79 {
		ccol = 0
	}
	b.Write(ic(crow, ccol))

	b.Write([]byte{0xff, 0xef}) // Telnet IAC EOR

	// Now write the datastream to the writer, returning any potential error.
	debugf("sending datastream: %x\n", b.Bytes())
	if _, err := conn.Write(b.Bytes()); err != nil {
		return Response{}, err
	}

	return readResponse(conn, fm)
}

// sba is the "set buffer address" 3270 command.
func sba(row, col int) []byte {
	result := make([]byte, 1, 3)
	result[0] = 0x11 // SBA
	result = append(result, getpos(row, col)...)
	return result
}

// sf is the "start field" 3270 command
func sf(write, intense bool) []byte {
	result := make([]byte, 2)
	result[0] = 0x1d // SF
	if !write {
		result[1] |= 1 << 5 // set "bit 2"
	} else {
		// The MDT bit -- we always want writable field values returned,
		// even if unchanged
		result[1] |= 1 // set "bit 7"

	}
	if intense {
		result[1] |= 1 << 3 // set "bit 4"
	}
	// Fill in top 2 bits with appropriate values
	result[1] = codes[result[1]]
	return result
}

// ic is the "insert cursor" 3270 command. This function will include the
// appropriate SBA command.
func ic(row, col int) []byte {
	result := make([]byte, 0, 3)
	result = append(result, sba(row, col)...)
	result = append(result, 0x13) // IC
	return result
}

// getpos translates row and col to buffer address control characters.
func getpos(row, col int) []byte {
	result := make([]byte, 2)
	address := row*80 + col
	hi := (address & 0xfc0) >> 6
	lo := address & 0x3f
	result[0] = codes[hi]
	result[1] = codes[lo]
	return result
}

type readerState int

const (
	stateNone readerState = iota
	stateGotAID
	stateGotFirstAddr
	stateGotSecondAddr
	stateInField
	stateGotFirstFieldAddr
	stateGotSecondFieldAddr
	stateGot
)