fix(term): ansi: allow ESC in DCS string state

Allow ESC character during DCS string collection state. We use ECMA-48
string parameters format to build DCS sequences. However, some
applications and multiplexers like screen and tmux, don't implement this
format and only pass data through DCS sequences. This data can include
ESC characters so we need to make a special case to accept that as part
of the data string.

exp/term/ansi/parser.go

@@ -68,6 +68,12 @@ func NewParser(paramsSize, dataSize int) *Parser {
 
 // Reset resets the parser to its initial state.
 func (p *Parser) Reset() {
+	p.clear()
+	p.State = parser.GroundState
+}
+
+// clear clears the parser parameters and command.
+func (p *Parser) clear() {
 	if len(p.Params) > 0 {
 		p.Params[0] = parser.MissingParam
 	}
@@ -147,6 +153,13 @@ func (p *Parser) advance(d ParserDispatcher, b byte, more bool) parser.Action {
 		case parser.EscapeState:
 			p.performAction(d, parser.ClearAction, b)
 		}
+		if action == parser.PutAction &&
+			p.State == parser.DcsEntryState && state == parser.DcsStringState {
+			// XXX: This is a special case where we need to start collecting
+			// non-string parameterized data i.e. doesn't follow the ECMA-48 §
+			// 5.4.1 string parameters format.
+			p.performAction(d, parser.StartAction, 0)
+		}
 	}
 
 	// Handle special cases
@@ -194,7 +207,7 @@ func (p *Parser) performAction(dispatcher ParserDispatcher, action parser.Action
 		break
 
 	case parser.ClearAction:
-		p.Reset()
+		p.clear()
 
 	case parser.PrintAction:
 		if utf8ByteLen(b) > 1 {

exp/term/ansi/parser/transition_table.go

@@ -165,7 +165,8 @@ func GenerateTransitionTable() TransitionTable {
 	}
 
 	// Dcs_entry
-	table.AddRange(0x00, 0x17, DcsEntryState, IgnoreAction, DcsEntryState)
+	table.AddRange(0x00, 0x07, DcsEntryState, IgnoreAction, DcsEntryState)
+	table.AddRange(0x0E, 0x17, DcsEntryState, IgnoreAction, DcsEntryState)
 	table.AddOne(0x19, DcsEntryState, IgnoreAction, DcsEntryState)
 	table.AddRange(0x1C, 0x1F, DcsEntryState, IgnoreAction, DcsEntryState)
 	table.AddOne(0x7F, DcsEntryState, IgnoreAction, DcsEntryState)
@@ -175,6 +176,10 @@ func GenerateTransitionTable() TransitionTable {
 	table.AddRange(0x30, 0x3B, DcsEntryState, ParamAction, DcsParamState)
 	table.AddRange(0x3C, 0x3F, DcsEntryState, MarkerAction, DcsParamState)
 	// Dcs_entry -> Dcs_passthrough
+	table.AddRange(0x08, 0x0D, DcsEntryState, PutAction, DcsStringState) // Follows ECMA-48 § 8.3.27
+	// XXX: allows passing ESC (not a ECMA-48 standard) this to allow for
+	// passthrough of ANSI sequences like in Screen or Tmux passthrough mode.
+	table.AddOne(0x1B, DcsEntryState, PutAction, DcsStringState)
 	table.AddRange(0x40, 0x7E, DcsEntryState, StartAction, DcsStringState)
 
 	// Dcs_intermediate