manual定义了一个解析器，可用于手动将解析后的地址发送到ClientConn
除了balance中的方式，这里提供了一种更简单的注册方式

type Resolver

  1. type Resolver struct {
  2.     // ResolveNowCallback is called when the ResolveNow method is called on the
  3.     // resolver.  Must not be nil.  Must not be changed after the resolver may
  4.     // be built.
  5.     ResolveNowCallback func(resolver.ResolveNowOptions)
  7.     // Fields actually belong to the resolver.
  8.     CC  resolver.ClientConn
  9.     // contains filtered or unexported fields
  10. }

func NewBuilderWithScheme(scheme string) *Resolver

func (r *Resolver) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error)

  • Build为解析器返回自身，因为它既是一个构建器也是一个解析器
  • 这个函数其实啥有没做，只负责将InitialState的s做一个UpdateState

func (*Resolver) Close() Resolver的空实现

func (r *Resolver) InitialState(s resolver.State)

  • InitialState向解析器添加初始状态，这样就不需要在拨号后显式调用UpdateState
  • 源码比较简单，可以看出NewBuilderWithScheme后，再调用InitialState就可以实现手动解析了

func (r *Resolver) ResolveNow(o resolver.ResolveNowOptions) Resolver的空实现

func (r *Resolver) Scheme() string 返回scheme

func (r *Resolver) UpdateState(s resolver.State) UpdateState会调用CC.UpdateState

源码比较简单

  2. // NewBuilderWithScheme creates a new test resolver builder with the given scheme.
  3. func NewBuilderWithScheme(scheme string) *Resolver {
  4.     return &Resolver{
  5.         ResolveNowCallback: func(resolver.ResolveNowOptions) {},
  6.         scheme:             scheme,
  7.     }
  8. }
  10. // Resolver is also a resolver builder.
  11. // It's build() function always returns itself.
  12. type Resolver struct {
  13.     // ResolveNowCallback is called when the ResolveNow method is called on the
  14.     // resolver.  Must not be nil.  Must not be changed after the resolver may
  15.     // be built.
  16.     ResolveNowCallback func(resolver.ResolveNowOptions)
  17.     scheme             string
  19.     // Fields actually belong to the resolver.
  20.     CC             resolver.ClientConn
  21.     bootstrapState *resolver.State
  22. }
  24. // InitialState adds initial state to the resolver so that UpdateState doesn't
  25. // need to be explicitly called after Dial.
  26. func (r *Resolver) InitialState(s resolver.State) {
  27.     r.bootstrapState = &s
  28. }
  30. // Build returns itself for Resolver, because it's both a builder and a resolver.
  31. func (r *Resolver) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error) {
  32.     r.CC = cc
  33.     if r.bootstrapState != nil {
  34.         r.UpdateState(*r.bootstrapState)
  35.     }
  36.     return r, nil
  37. }
  39. // Scheme returns the test scheme.
  40. func (r *Resolver) Scheme() string {
  41.     return r.scheme
  42. }
  44. // ResolveNow is a noop for Resolver.
  45. func (r *Resolver) ResolveNow(o resolver.ResolveNowOptions) {
  46.     r.ResolveNowCallback(o)
  47. }
  49. // Close is a noop for Resolver.
  50. func (*Resolver) Close() {}
  52. // UpdateState calls CC.UpdateState.
  53. func (r *Resolver) UpdateState(s resolver.State) {
  54.     r.CC.UpdateState(s)
  55. }