dubbo.apache.org/dubbo-go/v3@v3.1.1/xds/balancer/clusterresolver/resource_resolver_dns.go (about)

     1  /*
     2   * Licensed to the Apache Software Foundation (ASF) under one or more
     3   * contributor license agreements.  See the NOTICE file distributed with
     4   * this work for additional information regarding copyright ownership.
     5   * The ASF licenses this file to You under the Apache License, Version 2.0
     6   * (the "License"); you may not use this file except in compliance with
     7   * the License.  You may obtain a copy of the License at
     8   *
     9   *     http://www.apache.org/licenses/LICENSE-2.0
    10   *
    11   * Unless required by applicable law or agreed to in writing, software
    12   * distributed under the License is distributed on an "AS IS" BASIS,
    13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    14   * See the License for the specific language governing permissions and
    15   * limitations under the License.
    16   */
    17  
    18  /*
    19   *
    20   * Copyright 2021 gRPC authors.
    21   *
    22   */
    23  
    24  package clusterresolver
    25  
    26  import (
    27  	"fmt"
    28  )
    29  
    30  import (
    31  	"google.golang.org/grpc/resolver"
    32  
    33  	"google.golang.org/grpc/serviceconfig"
    34  )
    35  
    36  var (
    37  	newDNS = func(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error) {
    38  		// The dns resolver is registered by the grpc package. So, this call to
    39  		// resolver.Get() is never expected to return nil.
    40  		return resolver.Get("dns").Build(target, cc, opts)
    41  	}
    42  )
    43  
    44  // dnsDiscoveryMechanism watches updates for the given DNS hostname.
    45  //
    46  // It implements resolver.ClientConn interface to work with the DNS resolver.
    47  type dnsDiscoveryMechanism struct {
    48  	target           string
    49  	topLevelResolver *resourceResolver
    50  	r                resolver.Resolver
    51  
    52  	addrs          []string
    53  	updateReceived bool
    54  }
    55  
    56  func newDNSResolver(target string, topLevelResolver *resourceResolver) *dnsDiscoveryMechanism {
    57  	ret := &dnsDiscoveryMechanism{
    58  		target:           target,
    59  		topLevelResolver: topLevelResolver,
    60  	}
    61  	r, err := newDNS(resolver.Target{Scheme: "dns", Endpoint: target}, ret, resolver.BuildOptions{})
    62  	if err != nil {
    63  		select {
    64  		case <-topLevelResolver.updateChannel:
    65  		default:
    66  		}
    67  		topLevelResolver.updateChannel <- &resourceUpdate{err: err}
    68  	}
    69  	ret.r = r
    70  	return ret
    71  }
    72  
    73  func (dr *dnsDiscoveryMechanism) lastUpdate() (interface{}, bool) {
    74  	if !dr.updateReceived {
    75  		return nil, false
    76  	}
    77  	return dr.addrs, true
    78  }
    79  
    80  func (dr *dnsDiscoveryMechanism) resolveNow() {
    81  	dr.r.ResolveNow(resolver.ResolveNowOptions{})
    82  }
    83  
    84  func (dr *dnsDiscoveryMechanism) stop() {
    85  	dr.r.Close()
    86  }
    87  
    88  // dnsDiscoveryMechanism needs to implement resolver.ClientConn interface to receive
    89  // updates from the real DNS resolver.
    90  
    91  func (dr *dnsDiscoveryMechanism) UpdateState(state resolver.State) error {
    92  	dr.topLevelResolver.mu.Lock()
    93  	defer dr.topLevelResolver.mu.Unlock()
    94  	addrs := make([]string, len(state.Addresses))
    95  	for i, a := range state.Addresses {
    96  		addrs[i] = a.Addr
    97  	}
    98  	dr.addrs = addrs
    99  	dr.updateReceived = true
   100  	dr.topLevelResolver.generate()
   101  	return nil
   102  }
   103  
   104  func (dr *dnsDiscoveryMechanism) ReportError(err error) {
   105  	select {
   106  	case <-dr.topLevelResolver.updateChannel:
   107  	default:
   108  	}
   109  	dr.topLevelResolver.updateChannel <- &resourceUpdate{err: err}
   110  }
   111  
   112  func (dr *dnsDiscoveryMechanism) NewAddress(addresses []resolver.Address) {
   113  	dr.UpdateState(resolver.State{Addresses: addresses})
   114  }
   115  
   116  func (dr *dnsDiscoveryMechanism) NewServiceConfig(string) {
   117  	// This method is deprecated, and service config isn't supported.
   118  }
   119  
   120  func (dr *dnsDiscoveryMechanism) ParseServiceConfig(string) *serviceconfig.ParseResult {
   121  	return &serviceconfig.ParseResult{Err: fmt.Errorf("service config not supported")}
   122  }