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// Copyright 2019 Google LLC
//
// 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 (
"context"
"fmt"
"log"
"github.com/google/cel-go/cel"
"github.com/google/cel-go/common/types"
"github.com/google/cel-go/common/types/ref"
)
func Example() {
// Create the CEL environment with declarations for the input attributes and the extension functions.
// In many cases the desired functionality will be present in a built-in function.
e, err := cel.NewEnv(
// Variable identifiers used within this expression.
cel.Variable("i", cel.StringType),
cel.Variable("you", cel.StringType),
// Function to generate a greeting from one person to another: i.greet(you)
cel.Function("greet",
cel.MemberOverload("string_greet_string", []*cel.Type{cel.StringType, cel.StringType}, cel.StringType,
cel.BinaryBinding(func(lhs, rhs ref.Val) ref.Val {
return types.String(fmt.Sprintf("Hello %s! Nice to meet you, I'm %s.\n", rhs, lhs))
}),
),
),
)
if err != nil {
log.Fatalf("environment creation error: %s\n", err)
}
// Compile the expression.
ast, iss := e.Compile("i.greet(you)")
if iss.Err() != nil {
log.Fatalln(iss.Err())
}
// Create the program.
prg, err := e.Program(ast)
if err != nil {
log.Fatalf("program creation error: %s\n", err)
}
// Evaluate the program against some inputs. Note: the details return is not used.
out, _, err := prg.Eval(map[string]any{
// Native values are converted to CEL values under the covers.
"i": "CEL",
// Values may also be lazily supplied.
"you": func() ref.Val { return types.String("world") },
})
if err != nil {
log.Fatalf("runtime error: %s\n", err)
}
fmt.Println(out)
// Output:Hello world! Nice to meet you, I'm CEL.
}
func Example_globalOverload() {
// The GlobalOverload example demonstrates how to define global overload function.
// Create the CEL environment with declarations for the input attributes and
// the desired extension functions. In many cases the desired functionality will
// be present in a built-in function.
e, err := cel.NewEnv(
// Identifiers used within this expression.
cel.Variable("i", cel.StringType),
cel.Variable("you", cel.StringType),
// Function to generate shake_hands between two people.
// shake_hands(i,you)
cel.Function("shake_hands",
cel.Overload("shake_hands_string_string", []*cel.Type{cel.StringType, cel.StringType}, cel.StringType,
cel.BinaryBinding(func(arg1, arg2 ref.Val) ref.Val {
return types.String(fmt.Sprintf("%v and %v are shaking hands.\n", arg1, arg2))
}),
),
),
)
if err != nil {
log.Fatalf("environment creation error: %s\n", err)
}
// Compile the expression.
ast, iss := e.Compile(`shake_hands(i,you)`)
if iss.Err() != nil {
log.Fatalln(iss.Err())
}
// Create the program.
prg, err := e.Program(ast)
if err != nil {
log.Fatalf("program creation error: %s\n", err)
}
// Evaluate the program against some inputs. Note: the details return is not used.
out, _, err := prg.Eval(map[string]any{
"i": "CEL",
"you": func() ref.Val { return types.String("world") },
})
if err != nil {
log.Fatalf("runtime error: %s\n", err)
}
fmt.Println(out)
// Output:CEL and world are shaking hands.
}
func Example_statefulOverload() {
// makeFetch produces a consistent function signature with a different function
// implementation depending on the provided context.
makeFetch := func(ctx any) cel.EnvOption {
fn := func(arg ref.Val) ref.Val {
return types.NewErr("stateful context not bound")
}
if ctx != nil {
fn = func(resource ref.Val) ref.Val {
return types.DefaultTypeAdapter.NativeToValue(
ctx.(context.Context).Value(contextString(string(resource.(types.String)))),
)
}
}
return cel.Function("fetch",
cel.Overload("fetch_string",
[]*cel.Type{cel.StringType}, cel.StringType,
cel.UnaryBinding(fn),
),
)
}
// The base environment declares the fetch function with a dummy binding that errors
// if it is invoked without being replaced by a subsequent call to `baseEnv.Extend`
baseEnv, err := cel.NewEnv(
// Identifiers used within this expression.
cel.Variable("resource", cel.StringType),
// Function to fetch a resource.
// fetch(resource)
makeFetch(nil),
)
if err != nil {
log.Fatalf("environment creation error: %s\n", err)
}
ast, iss := baseEnv.Compile("fetch('my-resource') == 'my-value'")
if iss.Err() != nil {
log.Fatalf("Compile() failed: %v", iss.Err())
}
// The runtime environment extends the base environment with a contextual binding for
// the 'fetch' function.
ctx := context.WithValue(context.TODO(), contextString("my-resource"), "my-value")
runtimeEnv, err := baseEnv.Extend(makeFetch(ctx))
if err != nil {
log.Fatalf("baseEnv.Extend() failed with error: %s\n", err)
}
prg, err := runtimeEnv.Program(ast)
if err != nil {
log.Fatalf("runtimeEnv.Program() error: %s\n", err)
}
out, _, err := prg.Eval(cel.NoVars())
if err != nil {
log.Fatalf("runtime error: %s\n", err)
}
fmt.Println(out)
// Output:true
}
type contextString string
|
