Rework output processing

Currently the output processing is done via first casting the byte
slice to a string and then processing each rune in that.
This causes issues where we need to process the byte stream in a raw
format.
This commit alters the processing of the output stream, only casting to
a rune when appropriate.
This is a nessesarry prerequisite for transparent printing features.
This commit also adds the state to the terminal struct, this allows for
no side effects when dealing with multiple threads altering the state.

output.go

@@ -2,6 +2,7 @@ package terminal
 
 import (
 	"time"
+	"unicode/utf8"
 
 	"fyne.io/fyne/v2/widget"
 )
@@ -79,8 +80,6 @@ var decSpecialGraphics = map[rune]rune{
 	'~': '·', // centered dot
 }
 
-var previous *parseState
-
 type parseState struct {
 	code  string
 	esc   int
@@ -92,67 +91,44 @@ func (t *Terminal) handleOutput(buf []byte) {
 	if t.hasSelectedText() {
 		t.clearSelectedText()
 	}
-	state := &parseState{}
-	if previous != nil {
-		state = previous
-		previous = nil
-	} else {
-		state.esc = noEscape
+	if t.state == nil {
+		t.state = &parseState{
+			esc: noEscape,
+		}
 	}
+	var (
+		size int
+		r    rune
+		i    = -1
+	)
+	for {
+		i++
+		buf = buf[size:]
+		r, size = utf8.DecodeRune(buf)
+		if size == 0 {
+			break
+		}
 
-	for i, r := range []rune(string(buf)) {
 		if r == asciiEscape {
-			state.esc = i
+			t.state.esc = i
 			continue
 		}
-		if state.esc == i-1 {
-			if r == '[' {
+		if t.state.esc == i-1 {
+			if cont := t.parseEscState(r); cont {
 				continue
 			}
-			switch r {
-			case '\\':
-				t.handleOSC(state.code)
-				state.code = ""
-				state.osc = false
-			case ']':
-				state.osc = true
-			case '(', ')':
-				state.vt100 = r
-			case '7':
-				t.savedRow = t.cursorRow
-				t.savedCol = t.cursorCol
-			case '8':
-				t.cursorRow = t.savedRow
-				t.cursorCol = t.savedCol
-			case 'D':
-				t.scrollDown()
-			case 'M':
-				t.scrollUp()
-			case '=', '>':
-			}
-			state.esc = noEscape
+			t.state.esc = noEscape
 			continue
 		}
-		if state.osc {
-			if r == asciiBell || r == 0 {
-				t.handleOSC(state.code)
-				state.code = ""
-				state.osc = false
-			} else {
-				state.code += string(r)
-			}
+		if t.state.osc {
+			t.parseOSC(r)
 			continue
-		} else if state.vt100 != 0 {
-			t.handleVT100(string([]rune{state.vt100, r}))
-			state.vt100 = 0
+		} else if t.state.vt100 != 0 {
+			t.handleVT100(string([]rune{t.state.vt100, r}))
+			t.state.vt100 = 0
 			continue
-		} else if state.esc != noEscape {
-			state.code += string(r)
-			if (r < '0' || r > '9') && r != ';' && r != '=' && r != '?' && r != '>' {
-				t.handleEscape(state.code)
-				state.code = ""
-				state.esc = noEscape
-			}
+		} else if t.state.esc != noEscape {
+			t.parseEscape(r)
 			continue
 		}
 
@@ -173,9 +149,56 @@ func (t *Terminal) handleOutput(buf []byte) {
 	}
 
 	// record progress for next chunk of buffer
-	if state.esc != noEscape {
-		state.esc = -1 - (len(state.code))
-		previous = state
+	if t.state.esc != noEscape {
+		t.state.esc = -1
+	}
+}
+
+func (t *Terminal) parseEscState(r rune) (shouldContinue bool) {
+	switch r {
+	case '[':
+		return true
+	case '\\':
+		if t.state.osc {
+			t.handleOSC(t.state.code)
+		}
+		t.state.code = ""
+		t.state.osc = false
+	case ']':
+		t.state.osc = true
+	case '(', ')':
+		t.state.vt100 = r
+	case '7':
+		t.savedRow = t.cursorRow
+		t.savedCol = t.cursorCol
+	case '8':
+		t.cursorRow = t.savedRow
+		t.cursorCol = t.savedCol
+	case 'D':
+		t.scrollDown()
+	case 'M':
+		t.scrollUp()
+	case '=', '>':
+	}
+	return false
+}
+
+func (t *Terminal) parseEscape(r rune) {
+	t.state.code += string(r)
+	if (r < '0' || r > '9') && r != ';' && r != '=' && r != '?' && r != '>' {
+		t.handleEscape(t.state.code)
+		t.state.code = ""
+		t.state.esc = noEscape
+	}
+}
+
+func (t *Terminal) parseOSC(r rune) {
+	if r == asciiBell || r == 0 {
+		t.handleOSC(t.state.code)
+		t.state.code = ""
+		t.state.osc = false
+	} else {
+		t.state.code += string(r)
 	}
 }
 

term.go

@@ -74,6 +74,7 @@ type Terminal struct {
 	}
 	newLineMode        bool // new line mode or line feed mode
 	bracketedPasteMode bool
+	state              *parseState
 }
 
 // Cursor is used for displaying a specific cursor.