httpserver: Add not_starts_with condition. (#1687)

* Add not_starts_with condition.

This adds the opposite of the starts_with condition, to check if a
given string does not start with another string.

* Correct white space problems

caddyhttp/httpserver/condition.go

@@ -50,6 +50,7 @@ const (
 	hasOp           = "has"
 	notHasOp        = "not_has"
 	startsWithOp    = "starts_with"
+	notStartsWithOp = "not_starts_with"
 	endsWithOp      = "ends_with"
 	matchOp         = "match"
 	notMatchOp      = "not_match"
@@ -68,6 +69,7 @@ var ifConditions = map[string]ifCondition{
 	hasOp:           hasFunc,
 	notHasOp:        notHasFunc,
 	startsWithOp:    startsWithFunc,
+	notStartsWithOp: notStartsWithFunc,
 	endsWithOp:      endsWithFunc,
 	matchOp:         matchFunc,
 	notMatchOp:      notMatchFunc,
@@ -103,6 +105,12 @@ func startsWithFunc(a, b string) bool {
 	return strings.HasPrefix(a, b)
 }
 
+// notStartsWithFunc is condition for NotStartsWith operator.
+// It checks if b is not a prefix of a.
+func notStartsWithFunc(a, b string) bool {
+	return !strings.HasPrefix(a, b)
+}
+
 // endsWithFunc is condition for EndsWith operator.
 // It checks if b is a suffix of a.
 func endsWithFunc(a, b string) bool {

caddyhttp/httpserver/condition_test.go

@@ -32,6 +32,9 @@ func TestConditions(t *testing.T) {
 		{"bab starts_with bb", false},
 		{"bab starts_with ba", true},
 		{"bab starts_with bab", true},
+		{"bab not_starts_with bb", true},
+		{"bab not_starts_with ba", false},
+		{"bab not_starts_with bab", false},
 		{"bab ends_with bb", false},
 		{"bab ends_with bab", true},
 		{"bab ends_with ab", true},