Metadata

Example: metadata

Clients and servers can communicate with extra data.

Metadata is a key-vaue pair and key/value must be string.

Client

If you want to send metadata, you must set share.ReqMetaDataKey in context. If you want to receive metadata, you must set share.ResMetaDataKey in context.

```go client.go reply := &example.Reply{} ctx := context.WithValue(context.Background(), share.ReqMetaDataKey, map[string]string{"aaa": "from client"}) ctx = context.WithValue(ctx, share.ResMetaDataKey, make(map[string]string)) err := xclient.Call(ctx, "Mul", args, reply)

## Server

Server can get `share.ReqMetaDataKey` and `share.ResMetaDataKey` from context:

```go server.go
    reqMeta := ctx.Value(share.ReqMetaDataKey).(map[string]string)
    resMeta := ctx.Value(share.ResMetaDataKey).(map[string]string)