Update dependencies and go1.18

vendor/github.com/gomarkdown/markdown/internal/valid/valid.go

@@ -1,5 +1,9 @@
 package valid
 
+import (
+	"bytes"
+)
+
 var URIs = [][]byte{
 	[]byte("http://"),
 	[]byte("https://"),
@@ -12,3 +16,44 @@ var Paths = [][]byte{
 	[]byte("./"),
 	[]byte("../"),
 }
+
+// TODO: documentation
+func IsSafeURL(url []byte) bool {
+	nLink := len(url)
+	for _, path := range Paths {
+		nPath := len(path)
+		linkPrefix := url[:nPath]
+		if nLink >= nPath && bytes.Equal(linkPrefix, path) {
+			if nLink == nPath {
+				return true
+			} else if isAlnum(url[nPath]) {
+				return true
+			}
+		}
+	}
+
+	for _, prefix := range URIs {
+		// TODO: handle unicode here
+		// case-insensitive prefix test
+		nPrefix := len(prefix)
+		if nLink > nPrefix {
+			linkPrefix := bytes.ToLower(url[:nPrefix])
+			if bytes.Equal(linkPrefix, prefix) && isAlnum(url[nPrefix]) {
+				return true
+			}
+		}
+	}
+
+	return false
+}
+
+// isAlnum returns true if c is a digit or letter
+// TODO: check when this is looking for ASCII alnum and when it should use unicode
+func isAlnum(c byte) bool {
+	return (c >= '0' && c <= '9') || isLetter(c)
+}
+
+// isLetter returns true if c is ascii letter
+func isLetter(c byte) bool {
+	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
+}