coder · scsmithr · Jul 2, 2020 · Jul 1, 2020 · Jul 1, 2020 · Jul 2, 2020
diff --git a/cmd/coder/sync.go b/cmd/coder/sync.go
@@ -1,7 +1,11 @@
 package main
 
 import (
+	"bytes"
+	"fmt"
+	"log"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"strings"
 
@@ -29,6 +33,23 @@ func (cmd *syncCmd) RegisterFlags(fl *pflag.FlagSet) {
 	fl.BoolVarP(&cmd.init, "init", "i", false, "do initial transfer and exit")
 }
 
+// version returns local rsync protocol version as a string.
+func (_ *syncCmd) version() string {
+	cmd := exec.Command("rsync", "--version")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	firstLine, err := bytes.NewBuffer(out).ReadString('\n')
+	if err != nil {
+		log.Fatal(err)
+	}
+	versionString := strings.Split(firstLine, "protocol version ")
+
+	return versionString[1]
+}
+
 func (cmd *syncCmd) Run(fl *pflag.FlagSet) {
 	var (
 		local  = fl.Arg(0)
@@ -71,6 +92,16 @@ func (cmd *syncCmd) Run(fl *pflag.FlagSet) {
 		LocalDir:  absLocal,
 		Client:    entClient,
 	}
+
+	localVersion := cmd.version()
+	remoteVersion, rsyncErr := s.Version()
+
+	if rsyncErr != nil {
+		flog.Info("Unable to determine remote rsync version.  Proceeding cautiously.")
+	} else if localVersion != remoteVersion {
+		flog.Fatal(fmt.Sprintf("rsync protocol mismatch. %s.", localVersion, rsyncErr))
+	}
+
 	for err == nil || err == sync.ErrRestartSync {
 		err = s.Run()
 	}

diff --git a/internal/sync/sync.go b/internal/sync/sync.go
@@ -1,6 +1,7 @@
 package sync
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -10,6 +11,7 @@ import (
 	"os/exec"
 	"path"
 	"path/filepath"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -261,6 +263,44 @@ const (
 	maxAcceptableDispatch = time.Millisecond * 50
 )
 
+// Version returns remote protocol version as a string.
+// Or, an error if one exists.
+func (s Sync) Version() (string, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
+	defer cancel()
+
+	conn, err := s.Client.DialWsep(ctx, s.Env)
+	if err != nil {
+		return "", err
+	}
+	defer conn.Close(websocket.CloseNormalClosure, "")
+
+	execer := wsep.RemoteExecer(conn)
+	process, err := execer.Start(ctx, wsep.Command{
+		Command: "rsync",
+		Args:    []string{"--version"},
+	})
+	if err != nil {
+		return "", err
+	}
+	buf := &bytes.Buffer{}
+	io.Copy(buf, process.Stdout())
+
+	err = process.Wait()
+	if err != nil {
+		return "", err
+	}
+
+	firstLine, err := buf.ReadString('\n')
+	if err != nil {
+		return "", err
+	}
+
+	versionString := strings.Split(firstLine, "protocol version ")
+
+	return versionString[1], nil
+}
+
 // Run starts the sync synchronously.
 // Use this command to debug what wasn't sync'd correctly:
 // rsync -e "coder sh" -nicr ~/Projects/cdr/coder-cli/. ammar:/home/coder/coder-cli/