Stats Monitoring Handler

This example demonstrates the use of the stats package for reporting various
network and RPC stats.
Note that all fields are READ-ONLY and the APIs of the stats package are
experimental.

Try it

go run server/main.go

go run client/main.go

Explanation

gRPC provides a mechanism to hook on to various events (phases) of the
request-response network cycle through the stats.Handler interface. To access
these events, a concrete type that implements stats.Handler should be passed to
grpc.WithStatsHandler() on the client side and grpc.StatsHandler() on the
server side.

The HandleRPC(context.Context, RPCStats) method on stats.Handler is called
multiple times during a request-response cycle, and various event stats are
passed to its RPCStats parameter (an interface). The concrete types that
implement this interface are: *stats.Begin, *stats.InHeader, *stats.InPayload,
*stats.InTrailer, *stats.OutHeader, *stats.OutPayload, *stats.OutTrailer, and
*stats.End. The order of these events differs on client and server.

Similarly, the HandleConn(context.Context, ConnStats) method on stats.Handler
is called twice, once at the beginning of the connection with *stats.ConnBegin
and once at the end with *stats.ConnEnd.

The stats.Handler interface also provides
TagRPC(context.Context, *RPCTagInfo) context.Context and
TagConn(context.Context, *ConnTagInfo) context.Context methods. These methods
are mainly used to attach network related information to the given context.

The TagRPC(context.Context, *RPCTagInfo) context.Context method returns a
context from which the context used for the rest lifetime of the RPC will be
derived. This behavior is consistent between the gRPC client and server.

The context returned from
TagConn(context.Context, *ConnTagInfo) context.Context has varied lifespan:

• In the gRPC client:
  The context used for the rest lifetime of the RPC will NOT be derived from
  this context. Hence the information attached to this context can only be
  consumed by HandleConn(context.Context, ConnStats) method.
• In the gRPC server:
  The context used for the rest lifetime of the RPC will be derived from
  this context.

NOTE: The stats package should only be used for network monitoring purposes,
and not as an alternative to interceptors.