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// Copyright 2015 Matthew Holt and The Caddy 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 caddyhttp
import (
"encoding/json"
"fmt"
"net/http"
"reflect"
"regexp"
"strings"
"github.com/caddyserver/caddy/v2"
"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
"github.com/gogo/protobuf/proto"
"github.com/google/cel-go/cel"
"github.com/google/cel-go/checker/decls"
"github.com/google/cel-go/common/types"
"github.com/google/cel-go/common/types/ref"
"github.com/google/cel-go/common/types/traits"
"github.com/google/cel-go/ext"
"github.com/google/cel-go/interpreter/functions"
exprpb "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
)
func init() {
caddy.RegisterModule(MatchExpression{})
}
// MatchExpression matches requests by evaluating a
// [CEL](https://github.com/google/cel-spec) expression.
// This enables complex logic to be expressed using a comfortable,
// familiar syntax.
//
// COMPATIBILITY NOTE: This module is still experimental and is not
// subject to Caddy's compatibility guarantee.
type MatchExpression struct {
// The CEL expression to evaluate. Any Caddy placeholders
// will be expanded and situated into proper CEL function
// calls before evaluating.
Expr string
expandedExpr string
prg cel.Program
ta ref.TypeAdapter
}
// CaddyModule returns the Caddy module information.
func (MatchExpression) CaddyModule() caddy.ModuleInfo {
return caddy.ModuleInfo{
ID: "http.matchers.expression",
New: func() caddy.Module { return new(MatchExpression) },
}
}
// MarshalJSON marshals m's expression.
func (m MatchExpression) MarshalJSON() ([]byte, error) {
return json.Marshal(m.Expr)
}
// UnmarshalJSON unmarshals m's expression.
func (m *MatchExpression) UnmarshalJSON(data []byte) error {
return json.Unmarshal(data, &m.Expr)
}
// Provision sets ups m.
func (m *MatchExpression) Provision(_ caddy.Context) error {
// replace placeholders with a function call - this is just some
// light (and possibly naïve) syntactic sugar
m.expandedExpr = placeholderRegexp.ReplaceAllString(m.Expr, placeholderExpansion)
// our type adapter expands CEL's standard type support
m.ta = celTypeAdapter{}
// create the CEL environment
env, err := cel.NewEnv(
cel.Declarations(
decls.NewIdent("request", httpRequestObjectType, nil),
decls.NewFunction(placeholderFuncName,
decls.NewOverload(placeholderFuncName+"_httpRequest_string",
[]*exprpb.Type{httpRequestObjectType, decls.String},
decls.Any)),
),
cel.CustomTypeAdapter(m.ta),
ext.Strings(),
)
if err != nil {
return fmt.Errorf("setting up CEL environment: %v", err)
}
// parse and type-check the expression
checked, issues := env.Compile(m.expandedExpr)
if issues != nil && issues.Err() != nil {
return fmt.Errorf("compiling CEL program: %s", issues.Err())
}
// request matching is a boolean operation, so we don't really know
// what to do if the expression returns a non-boolean type
if !proto.Equal(checked.ResultType(), decls.Bool) {
return fmt.Errorf("CEL request matcher expects return type of bool, not %s", checked.ResultType())
}
// compile the "program"
m.prg, err = env.Program(checked,
cel.Functions(
&functions.Overload{
Operator: placeholderFuncName,
Binary: m.caddyPlaceholderFunc,
},
),
)
if err != nil {
return fmt.Errorf("compiling CEL program: %s", err)
}
return nil
}
// Match returns true if r matches m.
func (m MatchExpression) Match(r *http.Request) bool {
out, _, _ := m.prg.Eval(map[string]interface{}{
"request": celHTTPRequest{r},
})
if outBool, ok := out.Value().(bool); ok {
return outBool
}
return false
}
// UnmarshalCaddyfile implements caddyfile.Unmarshaler.
func (m *MatchExpression) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
for d.Next() {
m.Expr = strings.Join(d.RemainingArgs(), " ")
}
return nil
}
// caddyPlaceholderFunc implements the custom CEL function that accesses the
// Replacer on a request and gets values from it.
func (m MatchExpression) caddyPlaceholderFunc(lhs, rhs ref.Val) ref.Val {
celReq, ok := lhs.(celHTTPRequest)
if !ok {
return types.NewErr(
"invalid request of type '%v' to "+placeholderFuncName+"(request, placeholderVarName)",
lhs.Type())
}
phStr, ok := rhs.(types.String)
if !ok {
return types.NewErr(
"invalid placeholder variable name of type '%v' to "+placeholderFuncName+"(request, placeholderVarName)",
rhs.Type())
}
repl := celReq.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer)
val, _ := repl.Get(string(phStr))
return m.ta.NativeToValue(val)
}
// httpRequestCELType is the type representation of a native HTTP request.
var httpRequestCELType = types.NewTypeValue("http.Request", traits.ReceiverType)
// cellHTTPRequest wraps an http.Request with
// methods to satisfy the ref.Val interface.
type celHTTPRequest struct{ *http.Request }
func (cr celHTTPRequest) ConvertToNative(typeDesc reflect.Type) (interface{}, error) {
return cr.Request, nil
}
func (celHTTPRequest) ConvertToType(typeVal ref.Type) ref.Val {
panic("not implemented")
}
func (cr celHTTPRequest) Equal(other ref.Val) ref.Val {
if o, ok := other.Value().(celHTTPRequest); ok {
return types.Bool(o.Request == cr.Request)
}
return types.ValOrErr(other, "%v is not comparable type", other)
}
func (celHTTPRequest) Type() ref.Type { return httpRequestCELType }
func (cr celHTTPRequest) Value() interface{} { return cr }
// celTypeAdapter can adapt our custom types to a CEL value.
type celTypeAdapter struct{}
func (celTypeAdapter) NativeToValue(value interface{}) ref.Val {
switch v := value.(type) {
case celHTTPRequest:
return v
case error:
types.NewErr(v.Error())
}
return types.DefaultTypeAdapter.NativeToValue(value)
}
// Variables used for replacing Caddy placeholders in CEL
// expressions with a proper CEL function call; this is
// just for syntactic sugar.
var (
placeholderRegexp = regexp.MustCompile(`{([\w.-]+)}`)
placeholderExpansion = `caddyPlaceholder(request, "${1}")`
)
var httpRequestObjectType = decls.NewObjectType("http.Request")
// The name of the CEL function which accesses Replacer values.
const placeholderFuncName = "caddyPlaceholder"
// Interface guards
var (
_ caddy.Provisioner = (*MatchExpression)(nil)
_ RequestMatcher = (*MatchExpression)(nil)
_ caddyfile.Unmarshaler = (*MatchExpression)(nil)
_ json.Marshaler = (*MatchExpression)(nil)
_ json.Unmarshaler = (*MatchExpression)(nil)
)
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