1 files changed, 126 insertions, 0 deletions
diff --git a/runsc/cmd/help.go b/runsc/cmd/help.go
new file mode 100644
index 000000000..ff4f901cb
--- /dev/null
+++ b/runsc/cmd/help.go
@@ -0,0 +1,126 @@
+// Copyright 2018 Google LLC
+//
+// 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 cmd
+
+import (
+	"context"
+	"fmt"
+
+	"flag"
+	"github.com/google/subcommands"
+)
+
+// NewHelp returns a help command for the given commander.
+func NewHelp(cdr *subcommands.Commander) *Help {
+	return &Help{
+		cdr: cdr,
+	}
+}
+
+// Help implements subcommands.Command for the "help" command. The 'help'
+// command prints help for commands registered to a Commander but also allows for
+// registering additional help commands that print other documentation.
+type Help struct {
+	cdr      *subcommands.Commander
+	commands []subcommands.Command
+	help     bool
+}
+
+// Name implements subcommands.Command.Name.
+func (*Help) Name() string {
+	return "help"
+}
+
+// Synopsis implements subcommands.Command.Synopsis.
+func (*Help) Synopsis() string {
+	return "Print help documentation."
+}
+
+// Usage implements subcommands.Command.Usage.
+func (*Help) Usage() string {
+	return `help [<subcommand>]:
+	With an argument, prints detailed information on the use of
+	the specified topic or subcommand. With no argument, print a list of
+	all commands and a brief description of each.
+`
+}
+
+// SetFlags implements subcommands.Command.SetFlags.
+func (h *Help) SetFlags(f *flag.FlagSet) {}
+
+// Execute implements subcommands.Command.Execute.
+func (h *Help) Execute(ctx context.Context, f *flag.FlagSet, args ...interface{}) subcommands.ExitStatus {
+	switch f.NArg() {
+	case 0:
+		fmt.Fprintf(h.cdr.Output, "Usage: %s <flags> <subcommand> <subcommand args>\n\n", h.cdr.Name())
+		fmt.Fprintf(h.cdr.Output, `runsc is a command line client for running applications packaged in the Open
+Container Initiative (OCI) format. Applications run by runsc are run in an
+isolated gVisor sandbox that emulates a Linux environment.
+
+gVisor is a user-space kernel, written in Go, that implements a substantial
+portion of the Linux system call interface. It provides an additional layer
+of isolation between running applications and the host operating system.
+
+Functionality is provided by subcommands. For additonal help on individual
+subcommands use "%s %s <subcommand>".
+
+`, h.cdr.Name(), h.Name())
+		h.cdr.VisitGroups(func(g *subcommands.CommandGroup) {
+			h.cdr.ExplainGroup(h.cdr.Output, g)
+		})
+
+		fmt.Fprintf(h.cdr.Output, "Additional help topics (Use \"%s %s <topic>\" to see help on the topic):\n", h.cdr.Name(), h.Name())
+		for _, cmd := range h.commands {
+			fmt.Fprintf(h.cdr.Output, "\t%-15s  %s\n", cmd.Name(), cmd.Synopsis())
+		}
+		fmt.Fprintf(h.cdr.Output, "\nUse \"%s flags\" for a list of top-level flags\n", h.cdr.Name())
+		return subcommands.ExitSuccess
+	default:
+		// Look for commands registered to the commander and print help explanation if found.
+		found := false
+		h.cdr.VisitCommands(func(g *subcommands.CommandGroup, cmd subcommands.Command) {
+			if f.Arg(0) == cmd.Name() {
+				h.cdr.ExplainCommand(h.cdr.Output, cmd)
+				found = true
+			}
+		})
+		if found {
+			return subcommands.ExitSuccess
+		}
+
+		// Next check commands registered to the help command.
+		for _, cmd := range h.commands {
+			if f.Arg(0) == cmd.Name() {
+				fs := flag.NewFlagSet(f.Arg(0), flag.ContinueOnError)
+				fs.Usage = func() { h.cdr.ExplainCommand(h.cdr.Error, cmd) }
+				cmd.SetFlags(fs)
+				if fs.Parse(f.Args()[1:]) != nil {
+					return subcommands.ExitUsageError
+				}
+				return cmd.Execute(ctx, f, args...)
+			}
+		}
+
+		fmt.Fprintf(h.cdr.Error, "Subcommand %s not understood\n", f.Arg(0))
+	}
+
+	f.Usage()
+	return subcommands.ExitUsageError
+}
+
+// Register registers a new help command.
+func (h *Help) Register(cmd subcommands.Command) {
+	h.commands = append(h.commands, cmd)
+}