New constraints management.

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>

pkg/provider/constraints/constraints.go

@@ -0,0 +1,100 @@
+package constraints
+
+import (
+	"errors"
+	"regexp"
+	"strings"
+
+	"github.com/vulcand/predicate"
+)
+
+// MarathonConstraintPrefix is the prefix for each label's key created from a Marathon application constraint.
+// It is used in order to create a specific and unique pattern for these labels.
+const MarathonConstraintPrefix = "Traefik-Marathon-505F9E15-BDC7-45E7-828D-C06C7BAB8091"
+
+type constraintFunc func(map[string]string) bool
+
+// Match reports whether the expression matches with the given labels.
+// The expression must match any logical boolean combination of:
+// - `Label(labelName, labelValue)`
+// - `LabelRegex(labelName, regexValue)`
+// - `MarathonConstraint(field:operator:value)`
+func Match(labels map[string]string, expr string) (bool, error) {
+	if expr == "" {
+		return true, nil
+	}
+
+	p, err := predicate.NewParser(predicate.Def{
+		Operators: predicate.Operators{
+			AND: andFunc,
+			NOT: notFunc,
+			OR:  orFunc,
+		},
+		Functions: map[string]interface{}{
+			"Label":              labelFn,
+			"LabelRegex":         labelRegexFn,
+			"MarathonConstraint": marathonFn,
+		},
+	})
+	if err != nil {
+		return false, err
+	}
+
+	parse, err := p.Parse(expr)
+	if err != nil {
+		return false, err
+	}
+
+	fn, ok := parse.(constraintFunc)
+	if !ok {
+		return false, errors.New("not a constraintFunc")
+	}
+	return fn(labels), nil
+}
+
+func labelFn(name, value string) constraintFunc {
+	return func(labels map[string]string) bool {
+		return labels[name] == value
+	}
+}
+
+func labelRegexFn(name, expr string) constraintFunc {
+	return func(labels map[string]string) bool {
+		matched, err := regexp.MatchString(expr, labels[name])
+		if err != nil {
+			return false
+		}
+		return matched
+	}
+}
+
+func marathonFn(value string) constraintFunc {
+	return func(labels map[string]string) bool {
+		for k, v := range labels {
+			if strings.HasPrefix(k, MarathonConstraintPrefix) {
+				if v == value {
+					return true
+				}
+			}
+		}
+		return false
+	}
+}
+
+func andFunc(a, b constraintFunc) constraintFunc {
+	return func(labels map[string]string) bool {
+		return a(labels) && b(labels)
+	}
+}
+
+func orFunc(a, b constraintFunc) constraintFunc {
+	return func(labels map[string]string) bool {
+		return a(labels) || b(labels)
+	}
+}
+
+func notFunc(a constraintFunc) constraintFunc {
+	return func(labels map[string]string) bool {
+		return !a(labels)
+	}
+}