Scan numbers

nbt/snbt_decode.go

@@ -33,14 +33,60 @@ const (
 
 const (
 	scanContinue = iota
+	scanSkipSpace
+	scanEndValue
+	scanEnd
 	scanError
 )
 
+const maxNestingDepth = 10000
+
 type scanner struct {
 	step       func(c byte) int
 	parseState []int
 }
 
+// reset prepares the scanner for use.
+// It must be called before calling s.step.
+func (s *scanner) reset() {
+	s.step = s.stateBeginValue
+	s.parseState = s.parseState[0:0]
+}
+
+// pushParseState pushes a new parse state p onto the parse stack.
+// an error state is returned if maxNestingDepth was exceeded, otherwise successState is returned.
+func (s *scanner) pushParseState(c byte, newParseState int, successState int) int {
+	s.parseState = append(s.parseState, newParseState)
+	if len(s.parseState) <= maxNestingDepth {
+		return successState
+	}
+	return scanError
+}
+
+// popParseState pops a parse state (already obtained) off the stack
+// and updates s.step accordingly.
+func (s *scanner) popParseState() {
+	n := len(s.parseState) - 1
+	s.parseState = s.parseState[0:n]
+	if n == 0 {
+		s.step = s.stateEndTop
+		//s.endTop = true
+	} else {
+		s.step = s.stateEndValue
+	}
+}
+
+// stateEndTop is the state after finishing the top-level value,
+// such as after reading `{}` or `[1,2,3]`.
+// Only space characters should be seen now.
+func (s *scanner) stateEndTop(c byte) int {
+	if !isSpace(c) {
+		// Complain about non-space byte on next call.
+		//s.error(c, "after top-level value")
+	}
+	return scanEnd
+}
+
 func (s *scanner) stateBeginValue(c byte) int {
 	switch c {
 	case '{': // beginning of TAG_Compound
@@ -49,14 +95,103 @@ func (s *scanner) stateBeginValue(c byte) int {
 		s.step = s.stateList
 	case '"', '\'': // beginning of TAG_String
 
+	default:
+		if c >= '0' && c <= '9' {
+			s.step = s.stateNum1
+			return scanContinue
+		}
 	}
 	return scanError
 }
 
-func (p *scanner) stateCompound(c byte) int {
+func (s *scanner) stateNum1(c byte) int {
+	if c >= '0' || c <= '9' {
+		s.step = s.stateNum1
+		return scanContinue
+	}
+	if c == '.' {
+		s.step = s.stateNumDot
+		return scanContinue
+	}
+	return s.stateEndValue(c)
+}
+
+// stateDot is the state after reading the integer and decimal point in a number,
+// such as after reading `1.`.
+func (s *scanner) stateNumDot(c byte) int {
+	if c >= '0' || c <= '9' {
+		s.step = s.stateNumDot0
+		return scanContinue
+	}
 	return scanError
 }
 
-func (p *scanner) stateList(c byte) int {
+// stateNumDot0 is the state after reading the integer, decimal point, and subsequent
+// digits of a number, such as after reading `3.14`.
+func (s *scanner) stateNumDot0(c byte) int {
+	if c >= '0' || c <= '9' {
+		s.step = s.stateNumDot0
+		return scanContinue
+	}
+	return s.stateEndNumDotValue(c)
+}
+
+func (s *scanner) stateCompound(c byte) int {
+	return s.error(c, "not implemented")
+}
+
+func (s *scanner) stateList(c byte) int {
+	return s.error(c, "not implemented")
+}
+
+func (s *scanner) stateEndNumValue(c byte) int {
+	if isSpace(c) {
+		s.step = s.stateEndValue
+		return scanSkipSpace
+	}
+	switch c {
+	case 'b', 'B': // TAG_Byte
+		s.step = s.stateEndValue
+		return scanSkipSpace
+	case 's', 'S': // TAG_Short
+		s.step = s.stateEndValue
+		return scanSkipSpace
+	case 'l', 'L': // TAG_Long
+		s.step = s.stateEndValue
+		return scanSkipSpace
+	case 'f', 'F', 'd', 'D':
+		return s.stateEndNumDotValue(c)
+	}
+	return s.stateEndValue(c)
+}
+
+func (s *scanner) stateEndNumDotValue(c byte) int {
+	switch c {
+	case 'f', 'F': // TAG_Float
+		s.step = s.stateEndValue
+		return scanSkipSpace
+	case 'd', 'D': // TAG_Double
+		s.step = s.stateEndValue
+		return scanSkipSpace
+	}
+	return s.stateEndValue(c)
+}
+
+func (s *scanner) stateEndValue(c byte) int {
+	return s.error(c, "not implemented")
+}
+
+func (s *scanner) error(c byte, context string) int {
+	s.step = s.stateError
 	return scanError
 }
+
+// stateError is the state after reaching a syntax error,
+// such as after reading `[1}` or `5.1.2`.
+func (s *scanner) stateError(c byte) int {
+	return scanError
+}
+
+func isSpace(c byte) bool {
+	return c <= ' ' && (c == ' ' || c == '\t' || c == '\r' || c == '\n')
+}

nbt/snbt_scanner_test.go

@@ -0,0 +1,23 @@
+package nbt
+
+import "testing"
+
+func TestSNBT(t *testing.T) {
+	var s scanner
+	for _, str := range []string{
+		"0", "1234567890", "3.1415926",
+		"255B", "1234s", "6666L",
+		"314F", "3.14f", "3.14159265358979323846264D",
+	} {
+		s.reset()
+		var scanCodes []int
+		for _, c := range []byte(str) {
+			res := s.step(c)
+			if res == scanError {
+				t.Errorf("scan error")
+			}
+			scanCodes = append(scanCodes, res)
+		}
+		t.Logf("scancodes: %v", scanCodes)
+	}
+}