Allow diagnostics endpoints command to receive more than one message (#13285)

The `linkerd diagnostics endpoints` command initiates a `Get` lookup to the destination controller to get the set of endpoints for a destination.  This is a streaming response API and the command takes only the first response message and displays it.  However, the full current state of endpoints may be split across multiple messages, resulting in an incomplete list of endpoints displayed.

We instead read continuously from the response stream for a short amount of time (5 seconds) before displaying the full set of endpoints received.

Signed-off-by: Alex Leong <[email protected]>

Author: adleong

cli/cmd/endpoints.go

@@ -6,11 +6,12 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"os"
 	"sort"
 	"strings"
-	"sync"
 	"text/tabwriter"
+	"time"
 
 	destinationPb "github.com/linkerd/linkerd2-proxy-api/go/destination"
 	netPb "github.com/linkerd/linkerd2-proxy-api/go/net"
@@ -142,15 +143,11 @@ destination.`,
 
 func requestEndpointsFromAPI(client destinationPb.DestinationClient, token string, authorities []string) (endpointsInfo, error) {
 	info := make(endpointsInfo)
-	// buffered channels to avoid blocking
-	events := make(chan *destinationPb.Update, len(authorities))
-	errs := make(chan error, len(authorities))
-	var wg sync.WaitGroup
+	events := make(chan *destinationPb.Update, 1000)
+	errs := make(chan error, 1000)
 
 	for _, authority := range authorities {
-		wg.Add(1)
 		go func(authority string) {
-			defer wg.Done()
 			if len(errs) == 0 {
 				dest := &destinationPb.GetDestination{
 					Scheme:       "http:",
@@ -164,22 +161,31 @@ func requestEndpointsFromAPI(client destinationPb.DestinationClient, token strin
 					return
 				}
 
-				event, err := rsp.Recv()
-				if err != nil {
-					if grpcError, ok := status.FromError(err); ok {
-						err = errors.New(grpcError.Message())
+				// Endpoint state may be sent in multiple messages so it's not
+				// sufficient to read only the first message. Instead, we
+				// continuously read from the stream. This goroutine will never
+				// terminate if there are no errors, but this is okay for a
+				// short lived CLI command.
+				for {
+					event, err := rsp.Recv()
+					if errors.Is(err, io.EOF) {
+						return
+					} else if err != nil {
+						if grpcError, ok := status.FromError(err); ok {
+							err = errors.New(grpcError.Message())
+						}
+						errs <- err
+						return
 					}
-					errs <- err
-					return
+					events <- event
 				}
-				events <- event
 			}
 		}(authority)
 	}
-	// Block till all goroutines above are done
-	wg.Wait()
+	// Wait an amount of time for some endpoint responses to be received.
+	timeout := time.NewTimer(5 * time.Second)
 
-	for i := 0; i < len(authorities); i++ {
+	for {
 		select {
 		case err := <-errs:
 			// we only care about the first error
@@ -210,10 +216,10 @@ func requestEndpointsFromAPI(client destinationPb.DestinationClient, token strin
 					http2:   addr.GetHttp2(),
 				})
 			}
+		case <-timeout.C:
+			return info, nil
 		}
 	}
-
-	return info, nil
 }
 
 func getIP(tcpAddr *netPb.TcpAddress) string {