Introduces a new interface for resolving bindings.

The previous BindingsResolver did not provide an interface for resolving multiple bindings of a given type. Some paketo use-cases such as dependency-mappings and ca-certficates should be able to support an arbitrary number of bindigns. This changes intoduces a new bindings package that exports both Resolve and ResolveOne. In addition it provides functionality that allows the consumer to filter on provider in addition to type.

Signed-off-by: Emily Casey <[email protected]>

bindings/init_test.go

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2018-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package bindings_test
+
+import (
+	"testing"
+
+	"github.com/sclevine/spec"
+	"github.com/sclevine/spec/report"
+)
+
+func TestUnit(t *testing.T) {
+	suite := spec.New("bindings", spec.Report(report.Terminal{}))
+	suite("Resolve", testResolve)
+	suite.Run(t)
+}

bindings/resolve.go

@@ -0,0 +1,89 @@
+/*
+ * Copyright 2018-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package bindings
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/buildpacks/libcnb"
+)
+
+// Predicate should return true if it matches a given binding.
+type Predicate func(bind libcnb.Binding) bool
+
+// OfType returns a Predicate that returns true if a given binding has Type that matches t. The comparison is
+// case-insensitive.
+func OfType(t string) Predicate {
+	return func(bind libcnb.Binding) bool {
+		return strings.ToLower(bind.Type) == strings.ToLower(t)
+	}
+}
+
+// OfType returns a Predicate that returns true if a given binding has Provider that matches p. The comparison is
+// case-insensitive.
+func OfProvider(p string) Predicate {
+	return func(bind libcnb.Binding) bool {
+		return strings.ToLower(bind.Provider) == strings.ToLower(p)
+	}
+}
+
+// Resolve returns all bindings from binds that match every Predicate in predicates.
+func Resolve(binds libcnb.Bindings, predicates ...Predicate) libcnb.Bindings {
+	var result libcnb.Bindings
+	// deep copy
+	for _, bind := range binds {
+		result = append(result, bind)
+	}
+	// filter on predicates
+	for _, p := range predicates {
+		result = filter(result, p)
+	}
+	return result
+}
+
+// ResolveOne returns a single binding from bindings that match every Predicate if present. If exactly one match is found
+// ResolveOne returns the binding and true. If zero matches are found, ResolveOne returns an empty binding and false.
+// An error is returned if multiple matches are found.
+func ResolveOne(binds libcnb.Bindings, predicates ...Predicate) (libcnb.Binding, bool, error) {
+	resolved := Resolve(binds, predicates...)
+	if len(resolved) == 0 {
+		return libcnb.Binding{}, false, nil
+	}
+	if len(resolved) > 1 {
+		return libcnb.Binding{}, false, errTooManyBindings(resolved)
+	}
+	return resolved[0], true, nil
+}
+
+func errTooManyBindings(binds libcnb.Bindings) error {
+	var names []string
+	for _, bind := range binds {
+		names = append(names, bind.Name)
+	}
+	return fmt.Errorf("multiple bindings matched the given predicates %+v", names)
+}
+
+func filter(binds libcnb.Bindings, p Predicate) libcnb.Bindings {
+	var result []libcnb.Binding
+	for _, bind := range binds {
+		if p(bind) {
+			result = append(result, bind)
+		}
+	}
+	return result
+}