deps: update and fix chardet import (#9351)

vendor/github.com/gogs/chardet/utf8.go

@@ -0,0 +1,71 @@
+package chardet
+
+import (
+	"bytes"
+)
+
+var utf8Bom = []byte{0xEF, 0xBB, 0xBF}
+
+type recognizerUtf8 struct {
+}
+
+func newRecognizer_utf8() *recognizerUtf8 {
+	return &recognizerUtf8{}
+}
+
+func (*recognizerUtf8) Match(input *recognizerInput) (output recognizerOutput) {
+	output = recognizerOutput{
+		Charset: "UTF-8",
+	}
+	hasBom := bytes.HasPrefix(input.raw, utf8Bom)
+	inputLen := len(input.raw)
+	var numValid, numInvalid uint32
+	var trailBytes uint8
+	for i := 0; i < inputLen; i++ {
+		c := input.raw[i]
+		if c&0x80 == 0 {
+			continue
+		}
+		if c&0xE0 == 0xC0 {
+			trailBytes = 1
+		} else if c&0xF0 == 0xE0 {
+			trailBytes = 2
+		} else if c&0xF8 == 0xF0 {
+			trailBytes = 3
+		} else {
+			numInvalid++
+			if numInvalid > 5 {
+				break
+			}
+			trailBytes = 0
+		}
+
+		for i++; i < inputLen; i++ {
+			c = input.raw[i]
+			if c&0xC0 != 0x80 {
+				numInvalid++
+				break
+			}
+			if trailBytes--; trailBytes == 0 {
+				numValid++
+				break
+			}
+		}
+	}
+
+	if hasBom && numInvalid == 0 {
+		output.Confidence = 100
+	} else if hasBom && numValid > numInvalid*10 {
+		output.Confidence = 80
+	} else if numValid > 3 && numInvalid == 0 {
+		output.Confidence = 100
+	} else if numValid > 0 && numInvalid == 0 {
+		output.Confidence = 80
+	} else if numValid == 0 && numInvalid == 0 {
+		// Plain ASCII
+		output.Confidence = 10
+	} else if numValid > numInvalid*10 {
+		output.Confidence = 25
+	}
+	return
+}