go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/common/flag/protomsgsliceflag.go (about)

     1  // Copyright 2020 The LUCI Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package flag
    16  
    17  import (
    18  	"flag"
    19  	"fmt"
    20  	"reflect"
    21  	"strings"
    22  
    23  	"google.golang.org/protobuf/encoding/protojson"
    24  	"google.golang.org/protobuf/proto"
    25  )
    26  
    27  var protoMsgBaseType = reflect.TypeOf((*proto.Message)(nil)).Elem()
    28  
    29  type messageSliceFlag struct {
    30  	// msgSliceVal is a slice of pointers to concrete proto message structs.
    31  	msgSliceVal reflect.Value
    32  	// refMsg is a zero value concrete message struct instance that is used as
    33  	// reference to create new instance for deserialization purposes.
    34  	refMsg proto.Message
    35  }
    36  
    37  // MessageSliceFlag returns a new flag for a slice of pointer to concrete proto
    38  // message struct which implements the proto.Message interface. Expect input to
    39  // be of type *[]*B where B is concrete struct of proto message like pb.Build.
    40  // A flag value must be a JSON string of the provided concrete proto message.
    41  func MessageSliceFlag(msgSlicePtr any) flag.Getter {
    42  	slicePtrVal := reflect.ValueOf(msgSlicePtr)
    43  	assertKind(slicePtrVal.Type(), reflect.Ptr)
    44  
    45  	sliceType := slicePtrVal.Elem().Type()
    46  	assertKind(sliceType, reflect.Slice)
    47  
    48  	sliceElemType := sliceType.Elem()
    49  	if !sliceElemType.Implements(protoMsgBaseType) {
    50  		panic(fmt.Sprintf("Expect elements of the slice to implement interface: %s, however, got type: %s", protoMsgBaseType, sliceElemType))
    51  	}
    52  	// type that implement proto.message should be of pointer.
    53  	assertKind(sliceElemType, reflect.Ptr)
    54  
    55  	protoMsgStructType := sliceElemType.Elem()
    56  	assertKind(protoMsgStructType, reflect.Struct)
    57  
    58  	// reflect new return ptr to the message struct which implements the
    59  	// proto.Message interface
    60  	refMsg := reflect.New(protoMsgStructType).Interface().(proto.Message)
    61  
    62  	return &messageSliceFlag{
    63  		msgSliceVal: slicePtrVal.Elem(),
    64  		refMsg:      refMsg,
    65  	}
    66  }
    67  
    68  // String returns all messages serailzed in JSON and separated by a new line.
    69  // Empty string will be returned if flag is a zero value.
    70  func (m messageSliceFlag) String() string {
    71  	if !m.msgSliceVal.IsValid() {
    72  		return ""
    73  	}
    74  	var sb strings.Builder
    75  	for i := 0; i < m.msgSliceVal.Len(); i++ {
    76  		msg := m.msgSliceVal.Index(i).Interface().(proto.Message)
    77  
    78  		if buf, err := protojson.Marshal(msg); err != nil {
    79  			panic(fmt.Errorf("failed to marshal a message: %s", err))
    80  		} else {
    81  			sb.Write(buf)
    82  		}
    83  		sb.WriteString("\n")
    84  	}
    85  	return sb.String()
    86  }
    87  
    88  // Set deserializes the JSON datagram of proto message and appends it
    89  // to the slice.
    90  func (m *messageSliceFlag) Set(val string) error {
    91  	newMsg := proto.Clone(m.refMsg)
    92  	if err := protojson.Unmarshal([]byte(val), newMsg); err != nil {
    93  		return err
    94  	}
    95  	m.msgSliceVal.Set(reflect.Append(m.msgSliceVal, reflect.ValueOf(newMsg)))
    96  	return nil
    97  }
    98  
    99  // Get retrieves the raw flag value.
   100  func (m *messageSliceFlag) Get() any {
   101  	return m.msgSliceVal.Interface()
   102  }
   103  
   104  // assertKind panics when the given actual type does not match the expected
   105  // kind.
   106  func assertKind(actual reflect.Type, expected reflect.Kind) {
   107  	if actual.Kind() != expected {
   108  		panic(fmt.Sprintf("Expect kind: %s, however, got type: %s of kind %s",
   109  			expected, actual, actual.Kind()))
   110  	}
   111  }