1 files changed, 132 insertions, 0 deletions
diff --git a/plugin/rewrite/condition.go b/plugin/rewrite/condition.go
new file mode 100644
index 000000000..2f20d71aa
--- /dev/null
+++ b/plugin/rewrite/condition.go
@@ -0,0 +1,132 @@
+package rewrite
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/coredns/coredns/plugin/pkg/replacer"
+
+	"github.com/miekg/dns"
+)
+
+// Operators
+const (
+	Is         = "is"
+	Not        = "not"
+	Has        = "has"
+	NotHas     = "not_has"
+	StartsWith = "starts_with"
+	EndsWith   = "ends_with"
+	Match      = "match"
+	NotMatch   = "not_match"
+)
+
+func operatorError(operator string) error {
+	return fmt.Errorf("invalid operator %v", operator)
+}
+
+func newReplacer(r *dns.Msg) replacer.Replacer {
+	return replacer.New(r, nil, "")
+}
+
+// condition is a rewrite condition.
+type condition func(string, string) bool
+
+var conditions = map[string]condition{
+	Is:         isFunc,
+	Not:        notFunc,
+	Has:        hasFunc,
+	NotHas:     notHasFunc,
+	StartsWith: startsWithFunc,
+	EndsWith:   endsWithFunc,
+	Match:      matchFunc,
+	NotMatch:   notMatchFunc,
+}
+
+// isFunc is condition for Is operator.
+// It checks for equality.
+func isFunc(a, b string) bool {
+	return a == b
+}
+
+// notFunc is condition for Not operator.
+// It checks for inequality.
+func notFunc(a, b string) bool {
+	return a != b
+}
+
+// hasFunc is condition for Has operator.
+// It checks if b is a substring of a.
+func hasFunc(a, b string) bool {
+	return strings.Contains(a, b)
+}
+
+// notHasFunc is condition for NotHas operator.
+// It checks if b is not a substring of a.
+func notHasFunc(a, b string) bool {
+	return !strings.Contains(a, b)
+}
+
+// startsWithFunc is condition for StartsWith operator.
+// It checks if b is a prefix of a.
+func startsWithFunc(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 {
+	// TODO(miek): IsSubDomain
+	return strings.HasSuffix(a, b)
+}
+
+// matchFunc is condition for Match operator.
+// It does regexp matching of a against pattern in b
+// and returns if they match.
+func matchFunc(a, b string) bool {
+	matched, _ := regexp.MatchString(b, a)
+	return matched
+}
+
+// notMatchFunc is condition for NotMatch operator.
+// It does regexp matching of a against pattern in b
+// and returns if they do not match.
+func notMatchFunc(a, b string) bool {
+	matched, _ := regexp.MatchString(b, a)
+	return !matched
+}
+
+// If is statement for a rewrite condition.
+type If struct {
+	A        string
+	Operator string
+	B        string
+}
+
+// True returns true if the condition is true and false otherwise.
+// If r is not nil, it replaces placeholders before comparison.
+func (i If) True(r *dns.Msg) bool {
+	if c, ok := conditions[i.Operator]; ok {
+		a, b := i.A, i.B
+		if r != nil {
+			replacer := newReplacer(r)
+			a = replacer.Replace(i.A)
+			b = replacer.Replace(i.B)
+		}
+		return c(a, b)
+	}
+	return false
+}
+
+// NewIf creates a new If condition.
+func NewIf(a, operator, b string) (If, error) {
+	if _, ok := conditions[operator]; !ok {
+		return If{}, operatorError(operator)
+	}
+	return If{
+		A:        a,
+		Operator: operator,
+		B:        b,
+	}, nil
+}