chore: import upstream snapshot with attribution

detect/codec/hex.go

@@ -0,0 +1,60 @@
+package codec
+
+// hexMap is a precalculated map of hex nibbles
+const hexMap = "" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\xff\xff\xff\xff\xff\xff" +
+	"\xff\x0a\x0b\x0c\x0d\x0e\x0f\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\x0a\x0b\x0c\x0d\x0e\x0f\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
+
+// likelyHexChars is a set of characters that you would expect to find at
+// least one of in hex encoded data. This risks missing some hex data that
+// doesn't contain these characters, but gives you the performance gain of not
+// trying to decode a lot of long symbols in code.
+var likelyHexChars = make([]bool, 256)
+
+func init() {
+	for _, c := range `0123456789` {
+		likelyHexChars[c] = true
+	}
+}
+
+// decodeHex decodes hex data
+func decodeHex(encodedValue string) string {
+	size := len(encodedValue)
+	// hex should have two characters per byte
+	if size%2 != 0 {
+		return ""
+	}
+	if !hasByte(encodedValue, likelyHexChars) {
+		return ""
+	}
+
+	decodedValue := make([]byte, size/2)
+	for i := 0; i < size; i += 2 {
+		n1 := hexMap[encodedValue[i]]
+		n2 := hexMap[encodedValue[i+1]]
+		if n1|n2 == '\xff' {
+			return ""
+		}
+		b := n1<<4 | n2
+		if !printableASCII[b] {
+			return ""
+		}
+		decodedValue[i/2] = b
+	}
+
+	return string(decodedValue)
+}