1. // chainUnaryClientInterceptors chains all unary client interceptors into one.
  2. func chainUnaryClientInterceptors(cc *ClientConn) {
  3.     interceptors := cc.dopts.chainUnaryInts
  4.     // Prepend dopts.unaryInt to the chaining interceptors if it exists, since unaryInt will
  5.     // be executed before any other chained interceptors.
  6.     if cc.dopts.unaryInt != nil {
  7.         interceptors = append([]UnaryClientInterceptor{cc.dopts.unaryInt}, interceptors...)
  8.     }
  9.     var chainedInt UnaryClientInterceptor
  10.     if len(interceptors) == 0 {
  11.         chainedInt = nil
  12.     } else if len(interceptors) == 1 {
  13.         chainedInt = interceptors[0]
  14.     } else {
  15.         chainedInt = func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, invoker UnaryInvoker, opts ...CallOption) error {
  16.             return interceptors[0](ctx, method, req, reply, cc, getChainUnaryInvoker(interceptors, 0, invoker), opts...)
  17.         }
  18.     }
  19.     cc.dopts.unaryInt = chainedInt
  20. }
  22. func getChainUnaryInvoker(interceptors []UnaryClientInterceptor, curr int, finalInvoker UnaryInvoker) UnaryInvoker {
  23.     if curr == len(interceptors)-1 {
  24.         return finalInvoker
  25.     }
  26.     return func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, opts ...CallOption) error {
  27.         return interceptors[curr+1](ctx, method, req, reply, cc, getChainUnaryInvoker(interceptors, curr+1, finalInvoker), opts...)
  28.     }
  29. }

总结：

通过层层套娃形式，将拦截器数组变成一个链式拦截器，拦截器的next指向他的下一个拦截器。