feat(cmd): add source and image subcommands to scan (#1519)

**This change does not break any existing behaviour.**
- Creates `source` and `image` subcommands for `scan`.
- Inserts `source` as the default subcommand if none is provided.
- Removes the `experimental-oci-image` flag and its tests.
- Adds a feedback link to HTML output

For project scanning, users can use the following commands:
- `osv-scanner <file_name>`
- `osv-scanner scan <file_name>`
- `osv-scanner scan source <file_name>`

For docker scanning, users can use the following commands:
- `osv-scanner scan image <docker_image>`
- `osv-scanner scan image --archive <docker_image.tar>`

Help command:
```
NAME:
  osv-scanner - scans various mediums for dependencies and checks them against the OSV database

USAGE:
  osv-scanner [global options] command [command options]

EXAMPLES:
  # Scan a source directory
  $ osv-scanner scan source -r <source_directory>

  # Scan a container image
  $ osv-scanner scan image <image_name>

  # Scan a local image archive (e.g. a tar file) and generate HTML output
  $ osv-scanner scan image --serve --archive <image_name.tar>

  # Fix vulnerabilities in a manifest file and lockfile (non-interactive mode)
  $ osv-scanner fix --non-interactive -M <manifest_file> -L <lockfile>

  For full usage details, please refer to the help command of each subcommand (e.g. osv-scanner scan --help).

VERSION:
  1.9.1

COMMANDS:
  scan     scans projects and container images for dependencies, and checks them against the OSV database.
  fix      [EXPERIMENTAL] scans a manifest and/or lockfile for vulnerabilities and suggests changes for remediating them
  help, h  Shows a list of commands or help for one command


GLOBAL OPTIONS:
    --help, -h  show help  --version, -v  print the version

```

Author: hogo6002

Diff for: cmd/osv-scanner/__snapshots__/main_test.snap

@@ -1,12 +1,12 @@
-package scan
+package helper
 
 var stableCallAnalysisStates = map[string]bool{
 	"go":   true,
 	"rust": false,
 }
 
 // Creates a map to record if languages are enabled or disabled for call analysis.
-func createCallAnalysisStates(enabledCallAnalysis []string, disabledCallAnalysis []string) map[string]bool {
+func CreateCallAnalysisStates(enabledCallAnalysis []string, disabledCallAnalysis []string) map[string]bool {
 	callAnalysisStates := make(map[string]bool)
 
 	for _, language := range enabledCallAnalysis {

Diff for: cmd/osv-scanner/scan/callanalysis_parser.go renamed to cmd/osv-scanner/internal/helper/callanalysis_parser.go

@@ -1,4 +1,4 @@
-package scan
+package helper
 
 import (
 	"reflect"
@@ -55,7 +55,7 @@ func TestCreateCallAnalysisStates(t *testing.T) {
 	}
 
 	for _, testCase := range testCases {
-		actualCallAnalysisStates := createCallAnalysisStates(testCase.enabledCallAnalysis, testCase.disabledCallAnalysis)
+		actualCallAnalysisStates := CreateCallAnalysisStates(testCase.enabledCallAnalysis, testCase.disabledCallAnalysis)
 
 		if !reflect.DeepEqual(actualCallAnalysisStates, testCase.expectedCallAnalysisStates) {
 			t.Errorf("expected call analysis states to be %v, but got %v", testCase.expectedCallAnalysisStates, actualCallAnalysisStates)

Diff for: cmd/osv-scanner/scan/callanalysis_parser_test.go renamed to cmd/osv-scanner/internal/helper/callanalysis_parser_test.go

@@ -0,0 +1,145 @@
+package helper
+
+import (
+	"fmt"
+	"net/http"
+	"os/exec"
+	"runtime"
+	"slices"
+	"strings"
+	"time"
+
+	"github.com/google/osv-scanner/pkg/reporter"
+	"github.com/urfave/cli/v2"
+)
+
+// flags that require network access and values to disable them.
+var OfflineFlags = map[string]string{
+	"skip-git":                             "true",
+	"experimental-offline-vulnerabilities": "true",
+	"experimental-no-resolve":              "true",
+	"experimental-licenses-summary":        "false",
+	// "experimental-licenses": "", // StringSliceFlag has to be manually cleared.
+}
+
+var GlobalScanFlags = []cli.Flag{
+	&cli.StringFlag{
+		Name:      "config",
+		Usage:     "set/override config file",
+		TakesFile: true,
+	},
+	&cli.StringFlag{
+		Name:    "format",
+		Aliases: []string{"f"},
+		Usage:   "sets the output format; value can be: " + strings.Join(reporter.Format(), ", "),
+		Value:   "table",
+		Action: func(_ *cli.Context, s string) error {
+			if slices.Contains(reporter.Format(), s) {
+				return nil
+			}
+
+			return fmt.Errorf("unsupported output format \"%s\" - must be one of: %s", s, strings.Join(reporter.Format(), ", "))
+		},
+	},
+	&cli.BoolFlag{
+		Name:  "serve",
+		Usage: "output as HTML result and serve it locally",
+	},
+	&cli.StringFlag{
+		Name:      "output",
+		Usage:     "saves the result to the given file path",
+		TakesFile: true,
+	},
+	&cli.StringFlag{
+		Name:  "verbosity",
+		Usage: "specify the level of information that should be provided during runtime; value can be: " + strings.Join(reporter.VerbosityLevels(), ", "),
+		Value: "info",
+	},
+	&cli.BoolFlag{
+		Name:  "experimental-offline",
+		Usage: "run in offline mode, disabling any features requiring network access",
+		Action: func(ctx *cli.Context, b bool) error {
+			if !b {
+				return nil
+			}
+			// Disable the features requiring network access.
+			for flag, value := range OfflineFlags {
+				// TODO(michaelkedar): do something if the flag was already explicitly set.
+				if err := ctx.Set(flag, value); err != nil {
+					panic(fmt.Sprintf("failed setting offline flag %s to %s: %v", flag, value, err))
+				}
+			}
+
+			return nil
+		},
+	},
+	&cli.BoolFlag{
+		Name:  "experimental-offline-vulnerabilities",
+		Usage: "checks for vulnerabilities using local databases that are already cached",
+	},
+	&cli.BoolFlag{
+		Name:  "experimental-download-offline-databases",
+		Usage: "downloads vulnerability databases for offline comparison",
+	},
+	&cli.BoolFlag{
+		Name:  "experimental-no-resolve",
+		Usage: "disable transitive dependency resolution of manifest files",
+	},
+	&cli.StringFlag{
+		Name:   "experimental-local-db-path",
+		Usage:  "sets the path that local databases should be stored",
+		Hidden: true,
+	},
+	&cli.BoolFlag{
+		Name:  "experimental-all-packages",
+		Usage: "when json output is selected, prints all packages",
+	},
+	&cli.BoolFlag{
+		Name:  "experimental-licenses-summary",
+		Usage: "report a license summary, implying the --experimental-all-packages flag",
+	},
+	&cli.StringSliceFlag{
+		Name:  "experimental-licenses",
+		Usage: "report on licenses based on an allowlist",
+	},
+}
+
+// openHTML opens the outputted HTML file.
+func OpenHTML(r reporter.Reporter, outputPath string) {
+	// Open the outputted HTML file in the default browser.
+	r.Infof("Opening %s...\n", outputPath)
+	var err error
+	switch runtime.GOOS {
+	case "linux":
+		err = exec.Command("xdg-open", outputPath).Start()
+	case "windows":
+		err = exec.Command("start", "", outputPath).Start()
+	case "darwin": // macOS
+		err = exec.Command("open", outputPath).Start()
+	default:
+		r.Infof("Unsupported OS.\n")
+	}
+
+	if err != nil {
+		r.Errorf("Failed to open: %s.\n Please manually open the outputted HTML file: %s\n", err, outputPath)
+	}
+}
+
+// ServeHTML serves the single HTML file for remote accessing.
+// The program will keep running to serve the HTML report on localhost
+// until the user manually terminates it (e.g. using Ctrl+C).
+func ServeHTML(r reporter.Reporter, outputPath string) {
+	servePort := "8000"
+	localhostURL := fmt.Sprintf("http://localhost:%s/", servePort)
+	r.Infof("Serving HTML report at %s.\nIf you are accessing remotely, use the following SSH command:\n`ssh -L local_port:destination_server_ip:%s ssh_server_hostname`\n", localhostURL, servePort)
+	server := &http.Server{
+		Addr: ":" + servePort,
+		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			http.ServeFile(w, r, outputPath)
+		}),
+		ReadHeaderTimeout: 3 * time.Second,
+	}
+	if err := server.ListenAndServe(); err != nil {
+		r.Errorf("Failed to start server: %v\n", err)
+	}
+}

Diff for: cmd/osv-scanner/internal/helper/helper.go

@@ -42,6 +42,7 @@ func run(args []string, stdout, stderr io.Writer) int {
 			fix.Command(stdout, stderr, &r),
 			update.Command(stdout, stderr, &r),
 		},
+		CustomAppHelpTemplate: getCustomHelpTemplate(),
 	}
 
 	// If ExitErrHandler is not set, cli will use the default cli.HandleExitCoder.
@@ -84,6 +85,41 @@ func run(args []string, stdout, stderr io.Writer) int {
 	return 0
 }
 
+func getCustomHelpTemplate() string {
+	return `
+NAME:
+	{{.Name}} - {{.Usage}}
+
+USAGE:
+	{{.Name}} {{if .VisibleFlags}}[global options]{{end}}{{if .Commands}} command [command options]{{end}}
+
+EXAMPLES:
+	# Scan a source directory
+	$ {{.Name}} scan source -r <source_directory>
+
+	# Scan a container image
+	$ {{.Name}} scan image <image_name>
+
+	# Scan a local image archive (e.g. a tar file) and generate HTML output
+	$ {{.Name}} scan image --serve --archive <image_name.tar>
+
+	# Fix vulnerabilities in a manifest file and lockfile (non-interactive mode)
+	$ {{.Name}} fix --non-interactive -M <manifest_file> -L <lockfile>
+
+	For full usage details, please refer to the help command of each subcommand (e.g. {{.Name}} scan --help).
+
+VERSION:
+	{{.Version}}
+
+COMMANDS:
+{{range .Commands}}{{if and (not .HideHelp) (not .Hidden)}}  {{join .Names ", "}}{{ "\t"}}{{.Usage}}{{ "\n" }}{{end}}{{end}}
+{{if .VisibleFlags}}
+GLOBAL OPTIONS:
+	{{range .VisibleFlags}}  {{.}}{{end}}
+{{end}}
+`
+}
+
 // Gets all valid commands and global options for OSV-Scanner.
 func getAllCommands(commands []*cli.Command) []string {
 	// Adding all subcommands
@@ -108,24 +144,60 @@ func getAllCommands(commands []*cli.Command) []string {
 	return allCommands
 }
 
+// warnIfCommandAmbiguous warns the user if the command they are trying to run
+// exists as both a subcommand and as a file on the filesystem.
+// If this is the case, the command is assumed to be a subcommand.
+func warnIfCommandAmbiguous(command string, stdout, stderr io.Writer) {
+	if _, err := os.Stat(command); err == nil {
+		r := reporter.NewJSONReporter(stdout, stderr, reporter.InfoLevel)
+		r.Warnf("Warning: `%[1]s` exists as both a subcommand of OSV-Scanner and as a file on the filesystem. `%[1]s` is assumed to be a subcommand here. If you intended for `%[1]s` to be an argument to `%[1]s`, you must specify `%[1]s %[1]s` in your command line.\n", command)
+	}
+}
+
 // Inserts the default command to args if no command is specified.
 func insertDefaultCommand(args []string, commands []*cli.Command, defaultCommand string, stdout, stderr io.Writer) []string {
+	// Do nothing if no command or file name is provided.
 	if len(args) < 2 {
 		return args
 	}
 
 	allCommands := getAllCommands(commands)
-	if !slices.Contains(allCommands, args[1]) {
+	command := args[1]
+	// If no command is provided, use the default command and subcommand.
+	if !slices.Contains(allCommands, command) {
 		// Avoids modifying args in-place, as some unit tests rely on its original value for multiple calls.
-		argsTmp := make([]string, len(args)+1)
-		copy(argsTmp[2:], args[1:])
+		argsTmp := make([]string, len(args)+2)
+		copy(argsTmp[3:], args[1:])
 		argsTmp[1] = defaultCommand
+		// Set the default subCommand of Scan
+		argsTmp[2] = scan.DefaultSubcommand
 
 		// Executes the cli app with the new args.
 		return argsTmp
-	} else if _, err := os.Stat(args[1]); err == nil {
-		r := reporter.NewJSONReporter(stdout, stderr, reporter.InfoLevel)
-		r.Warnf("Warning: `%[1]s` exists as both a subcommand of OSV-Scanner and as a file on the filesystem. `%[1]s` is assumed to be a subcommand here. If you intended for `%[1]s` to be an argument to `%[1]s`, you must specify `%[1]s %[1]s` in your command line.\n", args[1])
+	}
+
+	warnIfCommandAmbiguous(command, stdout, stderr)
+
+	// If only the default command is provided without its subcommand, append the subcommand.
+	if command == defaultCommand {
+		if len(args) < 3 {
+			// Indicates that only "osv-scanner scan" was provided, without a subcommand or filename
+			return args
+		}
+
+		subcommand := args[2]
+		// Default to the "source" subcommand if none is provided.
+		if !slices.Contains(scan.Subcommands, subcommand) {
+			argsTmp := make([]string, len(args)+1)
+			copy(argsTmp[3:], args[2:])
+			argsTmp[1] = defaultCommand
+			argsTmp[2] = scan.DefaultSubcommand
+
+			return argsTmp
+		}
+
+		// Print a warning message if subcommand exist on the filesystem.
+		warnIfCommandAmbiguous(subcommand, stdout, stderr)
 	}
 
 	return args