Add CEL library with custom healthchecks to runtime

Signed-off-by: Matheus Pimenta <matheuscscp@gmail.com>

runtime/cel/doc.go

@@ -0,0 +1,18 @@
+/*
+Copyright 2025 The Flux 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
+
+    http://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.
+*/
+
+// cel provides utilities for evaluating Common Expression Language (CEL) expressions.
+package cel

runtime/cel/expression.go

@@ -0,0 +1,121 @@
+/*
+Copyright 2025 The Flux 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
+
+    http://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 cel
+
+import (
+	"fmt"
+
+	"github.com/google/cel-go/cel"
+	"github.com/google/cel-go/common/types"
+	"github.com/google/cel-go/ext"
+)
+
+// Expression represents a parsed CEL expression.
+type Expression struct {
+	expr string
+	prog cel.Program
+}
+
+// Option is a function that configures the CEL expression.
+type Option func(*options)
+
+type options struct {
+	compile bool
+	envOpts []cel.EnvOption
+}
+
+// WithCompile specifies that the expression should be compiled,
+// which provides stricter checks at parse time, before evaluation.
+func WithCompile() Option {
+	return func(o *options) {
+		o.compile = true
+	}
+}
+
+// WithStructVariables declares variables of type google.protobuf.Struct.
+func WithStructVariables(vars ...string) Option {
+	return func(o *options) {
+		for _, v := range vars {
+			d := cel.Variable(v, cel.ObjectType("google.protobuf.Struct"))
+			o.envOpts = append(o.envOpts, d)
+		}
+	}
+}
+
+// NewExpression parses the given CEL expression and returns a new Expression.
+func NewExpression(expr string, opts ...Option) (*Expression, error) {
+	var o options
+	for _, opt := range opts {
+		opt(&o)
+	}
+
+	envOpts := append([]cel.EnvOption{
+		cel.HomogeneousAggregateLiterals(),
+		cel.EagerlyValidateDeclarations(true),
+		cel.DefaultUTCTimeZone(true),
+		cel.CrossTypeNumericComparisons(true),
+		cel.OptionalTypes(),
+		ext.Strings(),
+		ext.Sets(),
+		ext.Encoders(),
+	}, o.envOpts...)
+
+	env, err := cel.NewEnv(envOpts...)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create CEL environment: %w", err)
+	}
+
+	parse := env.Parse
+	if o.compile {
+		parse = env.Compile
+	}
+	e, issues := parse(expr)
+	if issues != nil {
+		return nil, fmt.Errorf("failed to parse the CEL expression '%s': %s", expr, issues.String())
+	}
+
+	progOpts := []cel.ProgramOption{
+		cel.EvalOptions(cel.OptOptimize),
+
+		// 100 is the kubernetes default:
+		// https://github.com/kubernetes/kubernetes/blob/3f26d005571dc5903e7cebae33ada67986bc40f3/staging/src/k8s.io/apiserver/pkg/apis/cel/config.go#L33-L35
+		cel.InterruptCheckFrequency(100),
+	}
+
+	prog, err := env.Program(e, progOpts...)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create CEL program: %w", err)
+	}
+
+	return &Expression{
+		expr: expr,
+		prog: prog,
+	}, nil
+}
+
+// EvaluateBoolean evaluates the expression with the given data and returns the result as a boolean.
+func (e *Expression) EvaluateBoolean(data map[string]any) (bool, error) {
+	val, _, err := e.prog.Eval(data)
+	if err != nil {
+		return false, fmt.Errorf("failed to evaluate the CEL expression '%s': %w", e.expr, err)
+	}
+	result, ok := val.(types.Bool)
+	if !ok {
+		return false, fmt.Errorf("failed to evaluate CEL expression as boolean: '%s'", e.expr)
+	}
+	return bool(result), nil
+}

runtime/cel/expression_test.go

@@ -0,0 +1,190 @@
+/*
+Copyright 2025 The Flux 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
+
+    http://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 cel_test
+
+import (
+	"testing"
+
+	. "github.com/onsi/gomega"
+
+	"github.com/fluxcd/pkg/runtime/cel"
+)
+
+func TestNewExpression(t *testing.T) {
+	for _, tt := range []struct {
+		name string
+		expr string
+		opts []cel.Option
+		err  string
+	}{
+		{
+			name: "valid expression",
+			expr: "foo",
+		},
+		{
+			name: "invalid expression",
+			expr: "foo.",
+			err:  "failed to parse the CEL expression 'foo.': ERROR: <input>:1:5: Syntax error: no viable alternative at input '.'",
+		},
+		{
+			name: "compilation detects undeclared references",
+			expr: "foo",
+			opts: []cel.Option{cel.WithCompile()},
+			err:  "failed to parse the CEL expression 'foo': ERROR: <input>:1:1: undeclared reference to 'foo'",
+		},
+		{
+			name: "compilation detects type errors",
+			expr: "foo == 'bar'",
+			opts: []cel.Option{cel.WithCompile(), cel.WithStructVariables("foo")},
+			err:  "failed to parse the CEL expression 'foo == 'bar'': ERROR: <input>:1:5: found no matching overload for '_==_' applied to '(map(string, dyn), string)'",
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			g := NewWithT(t)
+
+			e, err := cel.NewExpression(tt.expr, tt.opts...)
+
+			if tt.err != "" {
+				g.Expect(err).To(HaveOccurred())
+				g.Expect(err.Error()).To(ContainSubstring(tt.err))
+				g.Expect(e).To(BeNil())
+			} else {
+				g.Expect(err).NotTo(HaveOccurred())
+				g.Expect(e).NotTo(BeNil())
+			}
+		})
+	}
+}
+
+func TestExpression_EvaluateBoolean(t *testing.T) {
+	for _, tt := range []struct {
+		name   string
+		expr   string
+		opts   []cel.Option
+		data   map[string]any
+		result bool
+		err    string
+	}{
+		{
+			name: "inexistent field",
+			expr: "foo",
+			data: map[string]any{},
+			err:  "failed to evaluate the CEL expression 'foo': no such attribute(s): foo",
+		},
+		{
+			name:   "boolean field true",
+			expr:   "foo",
+			data:   map[string]any{"foo": true},
+			result: true,
+		},
+		{
+			name:   "boolean field false",
+			expr:   "foo",
+			data:   map[string]any{"foo": false},
+			result: false,
+		},
+		{
+			name:   "nested boolean field true",
+			expr:   "foo.bar",
+			data:   map[string]any{"foo": map[string]any{"bar": true}},
+			result: true,
+		},
+		{
+			name:   "nested boolean field false",
+			expr:   "foo.bar",
+			data:   map[string]any{"foo": map[string]any{"bar": false}},
+			result: false,
+		},
+		{
+			name:   "boolean literal true",
+			expr:   "true",
+			data:   map[string]any{},
+			result: true,
+		},
+		{
+			name:   "boolean literal false",
+			expr:   "false",
+			data:   map[string]any{},
+			result: false,
+		},
+		{
+			name: "non-boolean literal",
+			expr: "'some-value'",
+			data: map[string]any{},
+			err:  "failed to evaluate CEL expression as boolean: ''some-value''",
+		},
+		{
+			name: "non-boolean field",
+			expr: "foo",
+			data: map[string]any{"foo": "some-value"},
+			err:  "failed to evaluate CEL expression as boolean: 'foo'",
+		},
+		{
+			name: "nested non-boolean field",
+			expr: "foo.bar",
+			data: map[string]any{"foo": map[string]any{"bar": "some-value"}},
+			err:  "failed to evaluate CEL expression as boolean: 'foo.bar'",
+		},
+		{
+			name:   "complex expression evaluating true",
+			expr:   "foo && bar",
+			data:   map[string]any{"foo": true, "bar": true},
+			result: true,
+		},
+		{
+			name:   "complex expression evaluating false",
+			expr:   "foo && bar",
+			data:   map[string]any{"foo": true, "bar": false},
+			result: false,
+		},
+		{
+			name:   "compiled expression returning true",
+			expr:   "foo.bar",
+			opts:   []cel.Option{cel.WithCompile(), cel.WithStructVariables("foo")},
+			data:   map[string]any{"foo": map[string]any{"bar": true}},
+			result: true,
+		},
+		{
+			name:   "compiled expression returning false",
+			expr:   "foo.bar",
+			opts:   []cel.Option{cel.WithCompile(), cel.WithStructVariables("foo")},
+			data:   map[string]any{"foo": map[string]any{"bar": false}},
+			result: false,
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			g := NewWithT(t)
+
+			e, err := cel.NewExpression(tt.expr, tt.opts...)
+			g.Expect(err).NotTo(HaveOccurred())
+
+			result, err := e.EvaluateBoolean(tt.data)
+
+			if tt.err != "" {
+				g.Expect(err).To(HaveOccurred())
+				g.Expect(err.Error()).To(ContainSubstring(tt.err))
+			} else {
+				g.Expect(err).NotTo(HaveOccurred())
+				g.Expect(result).To(Equal(tt.result))
+			}
+		})
+	}
+}