url/ParseScheme: Minor performance improvements

README.md

@@ -438,6 +438,8 @@ ggman comes with the following builtin aliases:
 
 ### 1.23.0 (Upcoming)
 
+- minor performance improvements
+
 ### 1.22.0 (Released [Sep 22 2024](https://github.com/tkw1536/ggman/releases/tag/v1.22.0))
 
 - update to `go 1.23`

internal/url/url.go

@@ -70,28 +70,50 @@ func IsValidURLScheme(s string) bool {
 	//   regexp.MustCompile(`^[a-zA-Z][a-zA-Z0-9+\-\.]*$`).MatchString(s)
 	// However such an implementation would be a lot slower when called repeatedly.
 	// Instead we directly build code that implements this regex.
-	//
-	// For this we first check that the string is non-empty.
-	// Then we check that the first character is not a '+', '-' or '.'
-	// Then we check that each character is either alphanumeric or a '+', '-' or '.'
 
-	if len(s) == 0 {
+	// Iterate over the bytes in this string.
+	// We can do this safely, because any valid scheme must be ascii.
+	bytes := []byte(s)
+	if len(bytes) == 0 {
 		return false
 	}
 
-	// if the first rune is invalid, no need to check everything else
-	if s[0] == '+' || s[0] == '-' || s[0] == '.' {
-		return false
+	var (
+		idx = 0        // current index
+		c   = bytes[0] // current character
+	)
+
+	// scheme must start with a letter
+	// so omit the loop preamble
+	goto start
+
+nextLetter:
+	// go to the next letter
+	// or be done
+	idx++
+	if idx >= len(bytes) {
+		return true
 	}
 
-	for _, r := range s {
-		if !(('a' <= r && r <= 'z') || ('A' <= r && r <= 'Z')) && // more efficient version of [email protected](r) for ascii
-			r != '+' &&
-			r != '-' &&
-			r != '.' {
-			return false
-		}
+	// get the current letter
+	c = bytes[idx]
+
+	if '0' <= c && c <= '9' {
+		goto nextLetter
+	}
+
+	if c == '+' || c == '-' || c == '.' {
+		goto nextLetter
+	}
+
+start:
+	if 'a' <= c && c <= 'z' {
+		goto nextLetter
+	}
+
+	if 'A' <= c && c <= 'Z' {
+		goto nextLetter
 	}
 
-	return true
+	return false
 }

internal/url/url_test.go

@@ -91,6 +91,7 @@ func Test_IsValidURLScheme(t *testing.T) {
 		{"https scheme is valid", args{"https"}, true},
 		{"git scheme is valid", args{"git"}, true},
 		{"ssh scheme is valid", args{"ssh"}, true},
+		{"ssh2 scheme is valid", args{"ssh2"}, true},
 		{"file scheme is valid", args{"file"}, true},
 		{"combined with + scheme is valid", args{"ssh+git"}, true},
 		{"combined with - scheme is valid", args{"ssh-git"}, true},