go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/grpc/discovery/discovery.go (about)

     1  // Copyright 2016 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 discovery implements RPC service introspection.
    16  package discovery
    17  
    18  import (
    19  	"context"
    20  	"crypto/sha256"
    21  	"fmt"
    22  	"reflect"
    23  	"sync"
    24  
    25  	"google.golang.org/grpc/codes"
    26  	"google.golang.org/grpc/status"
    27  	"google.golang.org/protobuf/proto"
    28  	"google.golang.org/protobuf/types/descriptorpb"
    29  
    30  	"go.chromium.org/luci/grpc/prpc"
    31  )
    32  
    33  // New creates a discovery server for all given services.
    34  //
    35  // Service names have form "<pkg>.<service>", where "<pkg>" is name of the proto
    36  // package and "<service>" is name of the service in the proto.
    37  //
    38  // The service descriptions must be registered already using
    39  // RegisterDescriptorSetCompressed which is called by init() function
    40  // generated by go.chromium.org/luci/grpc/cmd/cproto.
    41  func New(serviceNames ...string) DiscoveryServer {
    42  	return &service{exposed: func() []string { return serviceNames }}
    43  }
    44  
    45  // Enable registers a discovery service in the server.
    46  //
    47  // It makes all services registered in the server (now or later), including the
    48  // discovery service itself, discoverable.
    49  func Enable(server *prpc.Server) {
    50  	RegisterDiscoveryServer(server, &service{exposed: server.ServiceNames})
    51  }
    52  
    53  type service struct {
    54  	exposed func() []string // a dynamic list of services to expose
    55  
    56  	m           sync.Mutex
    57  	services    []string                        // services exposed in last Describe
    58  	description *descriptorpb.FileDescriptorSet // their combined descriptor set
    59  }
    60  
    61  func (s *service) Describe(ctx context.Context, _ *Void) (*DescribeResponse, error) {
    62  	services := s.exposed()
    63  
    64  	s.m.Lock()
    65  	defer s.m.Unlock()
    66  
    67  	if !reflect.DeepEqual(services, s.services) {
    68  		desc, err := combineDescriptors(services)
    69  		if err != nil {
    70  			return nil, status.Error(codes.Internal, err.Error())
    71  		}
    72  		s.description = desc
    73  		s.services = append([]string(nil), services...)
    74  	}
    75  
    76  	return &DescribeResponse{
    77  		Description: s.description,
    78  		Services:    s.services,
    79  	}, nil
    80  }
    81  
    82  // combineDescriptors creates one FileDescriptorSet that covers all services
    83  // and their dependencies.
    84  func combineDescriptors(serviceNames []string) (*descriptorpb.FileDescriptorSet, error) {
    85  	result := &descriptorpb.FileDescriptorSet{}
    86  	// seenFiles is a set of descriptor files keyed by SHA256 of their contents.
    87  	seenFiles := map[[sha256.Size]byte]bool{}
    88  
    89  	for _, s := range serviceNames {
    90  		desc, err := GetDescriptorSet(s)
    91  		if err != nil {
    92  			return nil, fmt.Errorf("service %s: %s", s, err)
    93  		}
    94  		if desc == nil {
    95  			return nil, fmt.Errorf(
    96  				"descriptor for service %q is not found. "+
    97  					"Did you compile it with go.chromium.org/luci/grpc/cmd/cproto?",
    98  				s)
    99  		}
   100  		for _, f := range desc.GetFile() {
   101  			binary, err := proto.Marshal(f)
   102  			if err != nil {
   103  				return nil, fmt.Errorf("could not marshal description of %s", f.GetName())
   104  			}
   105  			if hash := sha256.Sum256(binary); !seenFiles[hash] {
   106  				result.File = append(result.File, f)
   107  				seenFiles[hash] = true
   108  			}
   109  		}
   110  	}
   111  	return result, nil
   112  }