ssh: Introduce 'retry' helper

initialConnection retries multiple times to establish the TCP connection
which will be used for ssh communication.
This commit adds a generic helper to handle the retry which will be
useful in the next commits.

Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>

pkg/sshclient/ssh_forwarder.go

@@ -2,6 +2,7 @@ package sshclient
 
 import (
 	"context"
+	"fmt"
 	"io"
 	"net"
 	"net/url"
@@ -180,16 +181,19 @@ func setupProxy(ctx context.Context, socketURI *url.URL, dest *url.URL, identity
 	return &SSHForward{listener, &bastion, socketURI}, nil
 }
 
-func initialConnection(ctx context.Context, connectFunc ConnectCallback) (net.Conn, error) {
+const maxRetries = 60
+const initialBackoff = 100 * time.Millisecond
+
+func retry[T comparable](ctx context.Context, retryFunc func() (T, error), retryMsg string) (T, error) {
 	var (
-		conn net.Conn
+		returnVal T
-		err  error
+		err       error
 	)
 
-	backoff := 100 * time.Millisecond
+	backoff := initialBackoff
 
 loop:
-	for i := 0; i < 60; i++ {
+	for i := 0; i < maxRetries; i++ {
 		select {
 		case <-ctx.Done():
 			break loop
@@ -197,15 +201,22 @@ loop:
 			// proceed
 		}
 
-		conn, err = connectFunc(ctx, nil)
+		returnVal, err = retryFunc()
 		if err == nil {
-			break
+			return returnVal, nil
 		}
-		logrus.Debugf("Waiting for sshd: %s", backoff)
+		logrus.Debugf("%s (%s)", retryMsg, backoff)
 		sleep(ctx, backoff)
 		backoff = backOff(backoff)
 	}
-	return conn, err
+	return returnVal, fmt.Errorf("timeout: %w", err)
+}
+
+func initialConnection(ctx context.Context, connectFunc ConnectCallback) (net.Conn, error) {
+	retryFunc := func() (net.Conn, error) {
+		return connectFunc(ctx, nil)
+	}
+	return retry(ctx, retryFunc, "Waiting for sshd socket")
 }
 
 func acceptConnection(ctx context.Context, listener net.Listener, bastion *Bastion, socketURI *url.URL) error {