Allow install root to be set as flag

This change allows the destination / root to be set as the
first positional argument OR as a command line flag. This
allows for the GPU Operator to transition to a case where
on the flag / envvar is used.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

tools/container/nvidia-toolkit/run.go

@@ -35,7 +35,6 @@ type options struct {
 	noDaemon    bool
 	runtime     string
 	runtimeArgs string
-
 	root        string
 }
 
@@ -43,14 +42,18 @@ type options struct {
 var Version = "development"
 
 func main() {
+	remainingArgs, root, err := ParseArgs(os.Args)
+	if err != nil {
+		log.Errorf("Error: unable to parse arguments: %v", err)
+		os.Exit(1)
+	}
 
 	options := options{}
-
 	// Create the top-level CLI
 	c := cli.NewApp()
 	c.Name = "nvidia-toolkit"
 	c.Usage = "Install the nvidia-container-toolkit for use by a given runtime"
-	c.UsageText = "DESTINATION [-n | --no-daemon] [-r | --runtime] [-u | --runtime-args]"
+	c.UsageText = "[DESTINATION] [-n | --no-daemon] [-r | --runtime] [-u | --runtime-args]"
 	c.Description = "DESTINATION points to the host path underneath which the nvidia-container-toolkit should be installed.\nIt will be installed at ${DESTINATION}/toolkit"
 	c.Version = Version
 	c.Action = func(ctx *cli.Context) error {
@@ -82,17 +85,17 @@ func main() {
 			Destination: &options.runtimeArgs,
 			EnvVars:     []string{"RUNTIME_ARGS"},
 		},
+		&cli.StringFlag{
+			Name:        "root",
+			Value:       root,
+			Usage:       "the folder where the NVIDIA Container Toolkit is to be installed. It will be installed to `ROOT`/toolkit",
+			Destination: &options.root,
+			EnvVars:     []string{"ROOT"},
+		},
 	}
 
 	// Run the CLI
 	log.Infof("Starting %v", c.Name)
-
-	remainingArgs, err := ParseArgs(os.Args, &options)
-	if err != nil {
-		log.Errorf("Error: unable to parse arguments: %v", err)
-		os.Exit(1)
-	}
-
 	if err := c.Run(remainingArgs); err != nil {
 		log.Errorf("error running nvidia-toolkit: %v", err)
 		os.Exit(1)
@@ -139,44 +142,40 @@ func Run(c *cli.Context, o *options) error {
 	return nil
 }
 
-// ParseArgs parses the command line arguments and returns the remaining arguments
-func ParseArgs(args []string, o *options) ([]string, error) {
+// ParseArgs checks if a single positional argument was defined and extracts this the root.
+// If no positional arguments are defined, the it is assumed that the root is specified as a flag.
+func ParseArgs(args []string) ([]string, string, error) {
 	log.Infof("Parsing arguments")
 
-	numPositionalArgs := 2 // Includes command itself
-
-	if len(args) < numPositionalArgs {
-		return nil, fmt.Errorf("missing arguments")
+	if len(args) < 2 {
+		return args, "", nil
 	}
 
-	for _, arg := range args {
-		if arg == "--help" || arg == "-h" {
-			return []string{args[0], arg}, nil
-		}
-		if arg == "--version" || arg == "-v" {
-			return []string{args[0], arg}, nil
-		}
-	}
-
-	for _, arg := range args[:numPositionalArgs] {
+	var lastPositionalArg int
+	for i, arg := range args {
 		if strings.HasPrefix(arg, "-") {
-			return nil, fmt.Errorf("unexpected flag where argument should be")
+			break
 		}
+		lastPositionalArg = i
 	}
 
-	for _, arg := range args[numPositionalArgs:] {
-		if !strings.HasPrefix(arg, "-") {
-			return nil, fmt.Errorf("unexpected argument where flag should be")
-		}
+	if lastPositionalArg == 0 {
+		return args, "", nil
 	}
 
-	o.root = args[1]
+	if lastPositionalArg == 1 {
+		return append([]string{args[0]}, args[2:]...), args[1], nil
+	}
 
-	return append([]string{args[0]}, args[numPositionalArgs:]...), nil
+	return nil, "", fmt.Errorf("unexpected positional argument(s) %v", args[2:lastPositionalArg+1])
 }
 
 func verifyFlags(o *options) error {
 	log.Infof("Verifying Flags")
+	if o.root == "" {
+		return fmt.Errorf("the install root must be specified")
+	}
+
 	if _, exists := availableRuntimes[o.runtime]; !exists {
 		return fmt.Errorf("unknown runtime: %v", o.runtime)
 	}

tools/container/nvidia-toolkit/run_test.go

@@ -0,0 +1,84 @@
+/**
+# Copyright (c) 2022, NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+**/
+
+package main
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseArgs(t *testing.T) {
+	testCases := []struct {
+		args              []string
+		expectedRemaining []string
+		expectedRoot      string
+		expectedError     error
+	}{
+		{
+			args:              []string{},
+			expectedRemaining: []string{},
+			expectedRoot:      "",
+			expectedError:     nil,
+		},
+		{
+			args:              []string{"app"},
+			expectedRemaining: []string{"app"},
+		},
+		{
+			args:              []string{"app", "root"},
+			expectedRemaining: []string{"app"},
+			expectedRoot:      "root",
+		},
+		{
+			args:              []string{"app", "--flag"},
+			expectedRemaining: []string{"app", "--flag"},
+		},
+		{
+			args:              []string{"app", "root", "--flag"},
+			expectedRemaining: []string{"app", "--flag"},
+			expectedRoot:      "root",
+		},
+		{
+			args:          []string{"app", "root", "not-root", "--flag"},
+			expectedError: fmt.Errorf("unexpected positional argument(s) [not-root]"),
+		},
+		{
+			args:          []string{"app", "root", "not-root"},
+			expectedError: fmt.Errorf("unexpected positional argument(s) [not-root]"),
+		},
+		{
+			args:          []string{"app", "root", "not-root", "also"},
+			expectedError: fmt.Errorf("unexpected positional argument(s) [not-root also]"),
+		},
+	}
+
+	for i, tc := range testCases {
+		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
+			remaining, root, err := ParseArgs(tc.args)
+			if tc.expectedError != nil {
+				require.EqualError(t, err, tc.expectedError.Error())
+			} else {
+				require.NoError(t, err)
+			}
+
+			require.ElementsMatch(t, tc.expectedRemaining, remaining)
+			require.Equal(t, tc.expectedRoot, root)
+		})
+	}
+}