Add grpc plugin (#2758)

* Add grpc plugin

* remove stale readmes

server/grpc/util.go

@@ -0,0 +1,49 @@
+package grpc
+
+import (
+	"context"
+	"io"
+	"os"
+	"sync"
+
+	"google.golang.org/grpc/codes"
+)
+
+// convertCode converts a standard Go error into its canonical code. Note that
+// this is only used to translate the error returned by the server applications.
+func convertCode(err error) codes.Code {
+	switch err {
+	case nil:
+		return codes.OK
+	case io.EOF:
+		return codes.OutOfRange
+	case io.ErrClosedPipe, io.ErrNoProgress, io.ErrShortBuffer, io.ErrShortWrite, io.ErrUnexpectedEOF:
+		return codes.FailedPrecondition
+	case os.ErrInvalid:
+		return codes.InvalidArgument
+	case context.Canceled:
+		return codes.Canceled
+	case context.DeadlineExceeded:
+		return codes.DeadlineExceeded
+	}
+	switch {
+	case os.IsExist(err):
+		return codes.AlreadyExists
+	case os.IsNotExist(err):
+		return codes.NotFound
+	case os.IsPermission(err):
+		return codes.PermissionDenied
+	}
+	return codes.Unknown
+}
+
+func wait(ctx context.Context) *sync.WaitGroup {
+	if ctx == nil {
+		return nil
+	}
+	wg, ok := ctx.Value("wait").(*sync.WaitGroup)
+	if !ok {
+		return nil
+	}
+	return wg
+}