1/* 2 * 3 * Copyright 2017 gRPC authors. 4 * 5 * Licensed under the Apache License, Version 2.0 (the "License"); 6 * you may not use this file except in compliance with the License. 7 * 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// Package resolver defines APIs for name resolution in gRPC. 20// All APIs in this package are experimental. 21package resolver 22 23var ( 24 // m is a map from scheme to resolver builder. 25 m = make(map[string]Builder) 26 // defaultScheme is the default scheme to use. 27 defaultScheme = "passthrough" 28) 29 30// TODO(bar) install dns resolver in init(){}. 31 32// Register registers the resolver builder to the resolver map. b.Scheme will be 33// used as the scheme registered with this builder. 34// 35// NOTE: this function must only be called during initialization time (i.e. in 36// an init() function), and is not thread-safe. If multiple Resolvers are 37// registered with the same name, the one registered last will take effect. 38func Register(b Builder) { 39 m[b.Scheme()] = b 40} 41 42// Get returns the resolver builder registered with the given scheme. 43// 44// If no builder is register with the scheme, nil will be returned. 45func Get(scheme string) Builder { 46 if b, ok := m[scheme]; ok { 47 return b 48 } 49 return nil 50} 51 52// SetDefaultScheme sets the default scheme that will be used. 53// The default default scheme is "passthrough". 54func SetDefaultScheme(scheme string) { 55 defaultScheme = scheme 56} 57 58// GetDefaultScheme gets the default scheme that will be used. 59func GetDefaultScheme() string { 60 return defaultScheme 61} 62 63// AddressType indicates the address type returned by name resolution. 64type AddressType uint8 65 66const ( 67 // Backend indicates the address is for a backend server. 68 Backend AddressType = iota 69 // GRPCLB indicates the address is for a grpclb load balancer. 70 GRPCLB 71) 72 73// Address represents a server the client connects to. 74// This is the EXPERIMENTAL API and may be changed or extended in the future. 75type Address struct { 76 // Addr is the server address on which a connection will be established. 77 Addr string 78 // Type is the type of this address. 79 Type AddressType 80 // ServerName is the name of this address. 81 // 82 // e.g. if Type is GRPCLB, ServerName should be the name of the remote load 83 // balancer, not the name of the backend. 84 ServerName string 85 // Metadata is the information associated with Addr, which may be used 86 // to make load balancing decision. 87 Metadata interface{} 88} 89 90// BuildOption includes additional information for the builder to create 91// the resolver. 92type BuildOption struct { 93 // DisableServiceConfig indicates whether resolver should fetch service config data. 94 DisableServiceConfig bool 95} 96 97// ClientConn contains the callbacks for resolver to notify any updates 98// to the gRPC ClientConn. 99// 100// This interface is to be implemented by gRPC. Users should not need a 101// brand new implementation of this interface. For the situations like 102// testing, the new implementation should embed this interface. This allows 103// gRPC to add new methods to this interface. 104type ClientConn interface { 105 // NewAddress is called by resolver to notify ClientConn a new list 106 // of resolved addresses. 107 // The address list should be the complete list of resolved addresses. 108 NewAddress(addresses []Address) 109 // NewServiceConfig is called by resolver to notify ClientConn a new 110 // service config. The service config should be provided as a json string. 111 NewServiceConfig(serviceConfig string) 112} 113 114// Target represents a target for gRPC, as specified in: 115// https://github.com/grpc/grpc/blob/master/doc/naming.md. 116type Target struct { 117 Scheme string 118 Authority string 119 Endpoint string 120} 121 122// Builder creates a resolver that will be used to watch name resolution updates. 123type Builder interface { 124 // Build creates a new resolver for the given target. 125 // 126 // gRPC dial calls Build synchronously, and fails if the returned error is 127 // not nil. 128 Build(target Target, cc ClientConn, opts BuildOption) (Resolver, error) 129 // Scheme returns the scheme supported by this resolver. 130 // Scheme is defined at https://github.com/grpc/grpc/blob/master/doc/naming.md. 131 Scheme() string 132} 133 134// ResolveNowOption includes additional information for ResolveNow. 135type ResolveNowOption struct{} 136 137// Resolver watches for the updates on the specified target. 138// Updates include address updates and service config updates. 139type Resolver interface { 140 // ResolveNow will be called by gRPC to try to resolve the target name 141 // again. It's just a hint, resolver can ignore this if it's not necessary. 142 // 143 // It could be called multiple times concurrently. 144 ResolveNow(ResolveNowOption) 145 // Close closes the resolver. 146 Close() 147} 148 149// UnregisterForTesting removes the resolver builder with the given scheme from the 150// resolver map. 151// This function is for testing only. 152func UnregisterForTesting(scheme string) { 153 delete(m, scheme) 154} 155