cmd: Refactor subcommands, add help, make them pluggable

* cli: Change command structure, add help subcommand (#328)

* cli: improve subcommand structure

- make help command as normal subcommand
- add flag usage message for each command

* cmd: Refactor subcommands and command line help; make commands pluggable

3 files changed, 671 insertions, 347 deletions

diff --git a/cmd/commandfuncs.go b/cmd/commandfuncs.go
new file mode 100644
index 0000000..be9da93
--- /dev/null
+++ b/cmd/commandfuncs.go
@@ -0,0 +1,391 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// 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 caddycmd
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"net"
+	"net/http"
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/caddyconfig"
+	"github.com/keybase/go-ps"
+	"github.com/mholt/certmagic"
+)
+
+func cmdStart(fl Flags) (int, error) {
+	startCmdConfigFlag := fl.String("config")
+	startCmdConfigAdapterFlag := fl.String("config-adapter")
+
+	// open a listener to which the child process will connect when
+	// it is ready to confirm that it has successfully started
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("opening listener for success confirmation: %v", err)
+	}
+	defer ln.Close()
+
+	// craft the command with a pingback address and with a
+	// pipe for its stdin, so we can tell it our confirmation
+	// code that we expect so that some random port scan at
+	// the most unfortunate time won't fool us into thinking
+	// the child succeeded (i.e. the alternative is to just
+	// wait for any connection on our listener, but better to
+	// ensure it's the process we're expecting - we can be
+	// sure by giving it some random bytes and having it echo
+	// them back to us)
+	cmd := exec.Command(os.Args[0], "run", "--pingback", ln.Addr().String())
+	if startCmdConfigFlag != "" {
+		cmd.Args = append(cmd.Args, "--config", startCmdConfigFlag)
+	}
+	if startCmdConfigAdapterFlag != "" {
+		cmd.Args = append(cmd.Args, "--config-adapter", startCmdConfigAdapterFlag)
+	}
+	stdinpipe, err := cmd.StdinPipe()
+	if err != nil {
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("creating stdin pipe: %v", err)
+	}
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	// generate the random bytes we'll send to the child process
+	expect := make([]byte, 32)
+	_, err = rand.Read(expect)
+	if err != nil {
+		return caddy.ExitCodeFailedStartup, fmt.Errorf("generating random confirmation bytes: %v", err)
+	}
+
+	// begin writing the confirmation bytes to the child's
+	// stdin; use a goroutine since the child hasn't been
+	// started yet, and writing sychronously would result
+	// in a deadlock
+	go func() {
+		stdinpipe.Write(expect)
+		stdinpipe.Close()
+	}()
+
+	// start the process
+	err = cmd.Start()
+	if err != nil {
+		return caddy.ExitCodeFailedStartup, fmt.Errorf("starting caddy process: %v", err)
+	}
+
+	// there are two ways we know we're done: either
+	// the process will connect to our listener, or
+	// it will exit with an error
+	success, exit := make(chan struct{}), make(chan error)
+
+	// in one goroutine, we await the success of the child process
+	go func() {
+		for {
+			conn, err := ln.Accept()
+			if err != nil {
+				if !strings.Contains(err.Error(), "use of closed network connection") {
+					log.Println(err)
+				}
+				break
+			}
+			err = handlePingbackConn(conn, expect)
+			if err == nil {
+				close(success)
+				break
+			}
+			log.Println(err)
+		}
+	}()
+
+	// in another goroutine, we await the failure of the child process
+	go func() {
+		err := cmd.Wait() // don't send on this line! Wait blocks, but send starts before it unblocks
+		exit <- err       // sending on separate line ensures select won't trigger until after Wait unblocks
+	}()
+
+	// when one of the goroutines unblocks, we're done and can exit
+	select {
+	case <-success:
+		fmt.Printf("Successfully started Caddy (pid=%d)\n", cmd.Process.Pid)
+	case err := <-exit:
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("caddy process exited with error: %v", err)
+	}
+
+	return caddy.ExitCodeSuccess, nil
+}
+
+func cmdRun(fl Flags) (int, error) {
+	runCmdConfigFlag := fl.String("config")
+	runCmdConfigAdapterFlag := fl.String("config-adapter")
+	runCmdPrintEnvFlag := fl.Bool("print-env")
+	runCmdPingbackFlag := fl.String("pingback")
+
+	// if we are supposed to print the environment, do that first
+	if runCmdPrintEnvFlag {
+		printEnvironment()
+	}
+
+	// get the config in caddy's native format
+	config, err := loadConfig(runCmdConfigFlag, runCmdConfigAdapterFlag)
+	if err != nil {
+		return caddy.ExitCodeFailedStartup, err
+	}
+
+	// set a fitting User-Agent for ACME requests
+	goModule := caddy.GoModule()
+	cleanModVersion := strings.TrimPrefix(goModule.Version, "v")
+	certmagic.UserAgent = "Caddy/" + cleanModVersion
+
+	// start the admin endpoint along with any initial config
+	err = caddy.StartAdmin(config)
+	if err != nil {
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("starting caddy administration endpoint: %v", err)
+	}
+	defer caddy.StopAdmin()
+
+	// if we are to report to another process the successful start
+	// of the server, do so now by echoing back contents of stdin
+	if runCmdPingbackFlag != "" {
+		confirmationBytes, err := ioutil.ReadAll(os.Stdin)
+		if err != nil {
+			return caddy.ExitCodeFailedStartup,
+				fmt.Errorf("reading confirmation bytes from stdin: %v", err)
+		}
+		conn, err := net.Dial("tcp", runCmdPingbackFlag)
+		if err != nil {
+			return caddy.ExitCodeFailedStartup,
+				fmt.Errorf("dialing confirmation address: %v", err)
+		}
+		defer conn.Close()
+		_, err = conn.Write(confirmationBytes)
+		if err != nil {
+			return caddy.ExitCodeFailedStartup,
+				fmt.Errorf("writing confirmation bytes to %s: %v", runCmdPingbackFlag, err)
+		}
+	}
+
+	select {}
+}
+
+func cmdStop(_ Flags) (int, error) {
+	processList, err := ps.Processes()
+	if err != nil {
+		return caddy.ExitCodeFailedStartup, fmt.Errorf("listing processes: %v", err)
+	}
+	thisProcName := getProcessName()
+	var found bool
+	for _, p := range processList {
+		// the process we're looking for should have the same name but different PID
+		if p.Executable() == thisProcName && p.Pid() != os.Getpid() {
+			found = true
+			fmt.Printf("pid=%d\n", p.Pid())
+
+			if err := gracefullyStopProcess(p.Pid()); err != nil {
+				return caddy.ExitCodeFailedStartup, err
+			}
+		}
+	}
+	if !found {
+		return caddy.ExitCodeFailedStartup, fmt.Errorf("Caddy is not running")
+	}
+	fmt.Println(" success")
+	return caddy.ExitCodeSuccess, nil
+}
+
+func cmdReload(fl Flags) (int, error) {
+	reloadCmdConfigFlag := fl.String("config")
+	reloadCmdConfigAdapterFlag := fl.String("config-adapter")
+	reloadCmdAddrFlag := fl.String("address")
+
+	// a configuration is required
+	if reloadCmdConfigFlag == "" {
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("no configuration to load (use --config)")
+	}
+
+	// get the config in caddy's native format
+	config, err := loadConfig(reloadCmdConfigFlag, reloadCmdConfigAdapterFlag)
+	if err != nil {
+		return caddy.ExitCodeFailedStartup, err
+	}
+
+	// get the address of the admin listener and craft endpoint URL
+	adminAddr := reloadCmdAddrFlag
+	if adminAddr == "" {
+		var tmpStruct struct {
+			Admin caddy.AdminConfig `json:"admin"`
+		}
+		err = json.Unmarshal(config, &tmpStruct)
+		if err != nil {
+			return caddy.ExitCodeFailedStartup,
+				fmt.Errorf("unmarshaling admin listener address from config: %v", err)
+		}
+		adminAddr = tmpStruct.Admin.Listen
+	}
+	if adminAddr == "" {
+		adminAddr = caddy.DefaultAdminListen
+	}
+	adminEndpoint := fmt.Sprintf("http://%s/load", adminAddr)
+
+	// send the configuration to the instance
+	resp, err := http.Post(adminEndpoint, "application/json", bytes.NewReader(config))
+	if err != nil {
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("sending configuration to instance: %v", err)
+	}
+	defer resp.Body.Close()
+
+	// if it didn't work, let the user know
+	if resp.StatusCode >= 400 {
+		respBody, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1024*10))
+		if err != nil {
+			return caddy.ExitCodeFailedStartup,
+				fmt.Errorf("HTTP %d: reading error message: %v", resp.StatusCode, err)
+		}
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("caddy responded with error: HTTP %d: %s", resp.StatusCode, respBody)
+	}
+
+	return caddy.ExitCodeSuccess, nil
+}
+
+func cmdVersion(_ Flags) (int, error) {
+	goModule := caddy.GoModule()
+	if goModule.Sum != "" {
+		// a build with a known version will also have a checksum
+		fmt.Printf("%s %s\n", goModule.Version, goModule.Sum)
+	} else {
+		fmt.Println(goModule.Version)
+	}
+	return caddy.ExitCodeSuccess, nil
+}
+
+func cmdListModules(_ Flags) (int, error) {
+	for _, m := range caddy.Modules() {
+		fmt.Println(m)
+	}
+	return caddy.ExitCodeSuccess, nil
+}
+
+func cmdEnviron(_ Flags) (int, error) {
+	printEnvironment()
+	return caddy.ExitCodeSuccess, nil
+}
+
+func cmdAdaptConfig(fl Flags) (int, error) {
+	adaptCmdAdapterFlag := fl.String("adapter")
+	adaptCmdInputFlag := fl.String("input")
+	adaptCmdPrettyFlag := fl.Bool("pretty")
+
+	if adaptCmdAdapterFlag == "" || adaptCmdInputFlag == "" {
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("usage: caddy adapt-config --adapter <name> --input <file>")
+	}
+
+	cfgAdapter := caddyconfig.GetAdapter(adaptCmdAdapterFlag)
+	if cfgAdapter == nil {
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("unrecognized config adapter: %s", adaptCmdAdapterFlag)
+	}
+
+	input, err := ioutil.ReadFile(adaptCmdInputFlag)
+	if err != nil {
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("reading input file: %v", err)
+	}
+
+	opts := make(map[string]interface{})
+	if adaptCmdPrettyFlag {
+		opts["pretty"] = "true"
+	}
+
+	adaptedConfig, warnings, err := cfgAdapter.Adapt(input, opts)
+	if err != nil {
+		return caddy.ExitCodeFailedStartup, err
+	}
+
+	// print warnings to stderr
+	for _, warn := range warnings {
+		msg := warn.Message
+		if warn.Directive != "" {
+			msg = fmt.Sprintf("%s: %s", warn.Directive, warn.Message)
+		}
+		log.Printf("[WARNING][%s] %s:%d: %s", adaptCmdAdapterFlag, warn.File, warn.Line, msg)
+	}
+
+	// print result to stdout
+	fmt.Println(string(adaptedConfig))
+
+	return caddy.ExitCodeSuccess, nil
+}
+
+func cmdHelp(fl Flags) (int, error) {
+	const fullDocs = `Full documentation is available at:
+https://github.com/caddyserver/caddy/wiki/v2:-Documentation`
+
+	args := fl.Args()
+	if len(args) == 0 {
+		s := `Caddy is an extensible server platform.
+
+usage:
+  caddy <command> [<args...>]
+
+commands:
+`
+		for _, cmd := range commands {
+			s += fmt.Sprintf("  %-15s %s\n", cmd.Name, cmd.Short)
+		}
+
+		s += "\nUse 'caddy help <command>' for more information about a command.\n"
+		s += "\n" + fullDocs + "\n"
+
+		fmt.Print(s)
+
+		return caddy.ExitCodeSuccess, nil
+	} else if len(args) > 1 {
+		return caddy.ExitCodeFailedStartup, fmt.Errorf("can only give help with one command")
+	}
+
+	subcommand, ok := commands[args[0]]
+	if !ok {
+		return caddy.ExitCodeFailedStartup, fmt.Errorf("unknown command: %s", args[0])
+	}
+
+	result := fmt.Sprintf("%s\n\nusage:\n  caddy %s %s\n",
+		strings.TrimSpace(subcommand.Long),
+		subcommand.Name,
+		strings.TrimSpace(subcommand.Usage),
+	)
+
+	if help := flagHelp(subcommand.Flags); help != "" {
+		result += fmt.Sprintf("\nflags:\n%s", help)
+	}
+
+	result += "\n" + fullDocs + "\n"
+
+	fmt.Print(result)
+
+	return caddy.ExitCodeSuccess, nil
+}
diff --git a/cmd/commands.go b/cmd/commands.go
index 2526e45..8a9d482 100644
--- a/cmd/commands.go
+++ b/cmd/commands.go
@@ -15,343 +15,204 @@
 package caddycmd
 
 import (
-	"bytes"
-	"crypto/rand"
-	"encoding/json"
 	"flag"
-	"fmt"
-	"io"
-	"io/ioutil"
-	"log"
-	"net"
-	"net/http"
-	"os"
-	"os/exec"
-
-	"strings"
-
-	"github.com/caddyserver/caddy/v2"
-	"github.com/caddyserver/caddy/v2/caddyconfig"
-	"github.com/keybase/go-ps"
-	"github.com/mholt/certmagic"
+	"regexp"
 )
 
-func cmdStart() (int, error) {
-	startCmd := flag.NewFlagSet("start", flag.ExitOnError)
-	startCmdConfigFlag := startCmd.String("config", "", "Configuration file")
-	startCmdConfigAdapterFlag := startCmd.String("config-adapter", "", "Name of config adapter to apply")
-	startCmd.Parse(os.Args[2:])
+// Command represents a subcommand. All fields
+// are required to be set except for Flags if
+// there are no flags and Usage if there are
+// no flags or arguments.
+type Command struct {
+	Name string
 
-	// open a listener to which the child process will connect when
-	// it is ready to confirm that it has successfully started
-	ln, err := net.Listen("tcp", "127.0.0.1:0")
-	if err != nil {
-		return caddy.ExitCodeFailedStartup,
-			fmt.Errorf("opening listener for success confirmation: %v", err)
-	}
-	defer ln.Close()
+	// Run is a function that executes a subcommand.
+	// It returns an exit code and any associated error.
+	// Takes non-flag commandline arguments as args.
+	// Flag must be parsed before Run is executed.
+	Func CommandFunc
 
-	// craft the command with a pingback address and with a
-	// pipe for its stdin, so we can tell it our confirmation
-	// code that we expect so that some random port scan at
-	// the most unfortunate time won't fool us into thinking
-	// the child succeeded (i.e. the alternative is to just
-	// wait for any connection on our listener, but better to
-	// ensure it's the process we're expecting - we can be
-	// sure by giving it some random bytes and having it echo
-	// them back to us)
-	cmd := exec.Command(os.Args[0], "run", "--pingback", ln.Addr().String())
-	if *startCmdConfigFlag != "" {
-		cmd.Args = append(cmd.Args, "--config", *startCmdConfigFlag)
-	}
-	if *startCmdConfigAdapterFlag != "" {
-		cmd.Args = append(cmd.Args, "--config-adapter", *startCmdConfigAdapterFlag)
-	}
-	stdinpipe, err := cmd.StdinPipe()
-	if err != nil {
-		return caddy.ExitCodeFailedStartup,
-			fmt.Errorf("creating stdin pipe: %v", err)
-	}
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
+	// Usage is the one-line message explaining args, flags.
+	Usage string
 
-	// generate the random bytes we'll send to the child process
-	expect := make([]byte, 32)
-	_, err = rand.Read(expect)
-	if err != nil {
-		return caddy.ExitCodeFailedStartup, fmt.Errorf("generating random confirmation bytes: %v", err)
-	}
+	// Short is the short description for command.
+	Short string
 
-	// begin writing the confirmation bytes to the child's
-	// stdin; use a goroutine since the child hasn't been
-	// started yet, and writing sychronously would result
-	// in a deadlock
-	go func() {
-		stdinpipe.Write(expect)
-		stdinpipe.Close()
-	}()
+	// Long is the message for 'caddy help <command>'
+	Long string
 
-	// start the process
-	err = cmd.Start()
-	if err != nil {
-		return caddy.ExitCodeFailedStartup, fmt.Errorf("starting caddy process: %v", err)
-	}
-
-	// there are two ways we know we're done: either
-	// the process will connect to our listener, or
-	// it will exit with an error
-	success, exit := make(chan struct{}), make(chan error)
-
-	// in one goroutine, we await the success of the child process
-	go func() {
-		for {
-			conn, err := ln.Accept()
-			if err != nil {
-				if !strings.Contains(err.Error(), "use of closed network connection") {
-					log.Println(err)
-				}
-				break
-			}
-			err = handlePingbackConn(conn, expect)
-			if err == nil {
-				close(success)
-				break
-			}
-			log.Println(err)
-		}
-	}()
-
-	// in another goroutine, we await the failure of the child process
-	go func() {
-		err := cmd.Wait() // don't send on this line! Wait blocks, but send starts before it unblocks
-		exit <- err       // sending on separate line ensures select won't trigger until after Wait unblocks
-	}()
-
-	// when one of the goroutines unblocks, we're done and can exit
-	select {
-	case <-success:
-		fmt.Printf("Successfully started Caddy (pid=%d)\n", cmd.Process.Pid)
-	case err := <-exit:
-		return caddy.ExitCodeFailedStartup,
-			fmt.Errorf("caddy process exited with error: %v", err)
-	}
-
-	return caddy.ExitCodeSuccess, nil
+	// Flags is flagset for command.
+	Flags *flag.FlagSet
 }
 
-func cmdRun() (int, error) {
-	runCmd := flag.NewFlagSet("run", flag.ExitOnError)
-	runCmdConfigFlag := runCmd.String("config", "", "Configuration file")
-	runCmdConfigAdapterFlag := runCmd.String("config-adapter", "", "Name of config adapter to apply")
-	runCmdPrintEnvFlag := runCmd.Bool("print-env", false, "Print environment")
-	runCmdPingbackFlag := runCmd.String("pingback", "", "Echo confirmation bytes to this address on success")
-	runCmd.Parse(os.Args[2:])
-
-	// if we are supposed to print the environment, do that first
-	if *runCmdPrintEnvFlag {
-		exitCode, err := cmdEnviron()
-		if err != nil {
-			return exitCode, err
-		}
-	}
-
-	// get the config in caddy's native format
-	config, err := loadConfig(*runCmdConfigFlag, *runCmdConfigAdapterFlag)
-	if err != nil {
-		return caddy.ExitCodeFailedStartup, err
-	}
-
-	// set a fitting User-Agent for ACME requests
-	goModule := caddy.GoModule()
-	cleanModVersion := strings.TrimPrefix(goModule.Version, "v")
-	certmagic.UserAgent = "Caddy/" + cleanModVersion
-
-	// start the admin endpoint along with any initial config
-	err = caddy.StartAdmin(config)
-	if err != nil {
-		return caddy.ExitCodeFailedStartup,
-			fmt.Errorf("starting caddy administration endpoint: %v", err)
-	}
-	defer caddy.StopAdmin()
-
-	// if we are to report to another process the successful start
-	// of the server, do so now by echoing back contents of stdin
-	if *runCmdPingbackFlag != "" {
-		confirmationBytes, err := ioutil.ReadAll(os.Stdin)
-		if err != nil {
-			return caddy.ExitCodeFailedStartup,
-				fmt.Errorf("reading confirmation bytes from stdin: %v", err)
-		}
-		conn, err := net.Dial("tcp", *runCmdPingbackFlag)
-		if err != nil {
-			return caddy.ExitCodeFailedStartup,
-				fmt.Errorf("dialing confirmation address: %v", err)
-		}
-		defer conn.Close()
-		_, err = conn.Write(confirmationBytes)
-		if err != nil {
-			return caddy.ExitCodeFailedStartup,
-				fmt.Errorf("writing confirmation bytes to %s: %v", *runCmdPingbackFlag, err)
-		}
-	}
-
-	select {}
+// CommandFunc is a command's function. It runs the
+// command and returns the proper exit code along with
+// any error that occurred.
+type CommandFunc func(Flags) (int, error)
+
+var commands = map[string]Command{
+	"start": {
+		Name:  "start",
+		Func:  cmdStart,
+		Usage: "[--config <path>] [--config-adapter <name>]",
+		Short: "Starts the Caddy process and returns after server has started.",
+		Long: `
+Starts the Caddy process, optionally bootstrapped with an initial
+config file. Blocks until server is successfully running (or fails to run),
+then returns. On Windows, the child process will remain attached to the
+terminal, so closing the window will forcefully stop Caddy. See run for more
+details.`,
+		Flags: func() *flag.FlagSet {
+			fs := flag.NewFlagSet("start", flag.ExitOnError)
+			fs.String("config", "", "Configuration file")
+			fs.String("config-adapter", "", "Name of config adapter to apply")
+			return fs
+		}(),
+	},
+
+	"run": {
+		Name:  "run",
+		Func:  cmdRun,
+		Usage: "[--config <path>] [--config-adapter <name>] [--print-env]",
+		Short: `Starts the Caddy process and blocks indefinitely.`,
+		Long: `
+Same as start, but blocks indefinitely; i.e. runs Caddy in "daemon" mode. On
+Windows, this is recommended over caddy start when running Caddy manually since
+it will be more obvious that Caddy is still running and bound to the terminal
+window.
+
+If a config file is specified, it will be applied immediately after the process
+is running. If the config file is not in Caddy's native JSON format, you can
+specify an adapter with --config-adapter to adapt the given config file to
+Caddy's native format. The config adapter must be a registered module. Any
+warnings will be printed to the log, but beware that any adaptation without
+errors will immediately be used. If you want to review the results of the
+adaptation first, use adapt-config.
+
+As a special case, if the current working directory has a file called
+"Caddyfile" and the caddyfile config adapter is plugged in (default), then that
+file will be loaded and used to configure Caddy, even without any command line
+flags.
+
+If --print-env is specified, the environment as seen by the Caddy process will
+be printed before starting. This is the same as the environ command but does
+not quit after printing.`,
+		Flags: func() *flag.FlagSet {
+			fs := flag.NewFlagSet("run", flag.ExitOnError)
+			fs.String("config", "", "Configuration file")
+			fs.String("config-adapter", "", "Name of config adapter to apply")
+			fs.Bool("print-env", false, "Print environment")
+			fs.String("pingback", "", "Echo confirmation bytes to this address on success")
+			return fs
+		}(),
+	},
+
+	"stop": {
+		Name:  "stop",
+		Func:  cmdStop,
+		Short: "Gracefully stops the running Caddy process",
+		Long: `Gracefully stops the running Caddy process. (Note: this will stop any process
+named the same as the executable.) On Windows, this stop is forceful and Caddy
+will not have an opportunity to clean up any active locks; for a graceful
+shutdown on Windows, use Ctrl+C or the /stop endpoint.`,
+	},
+
+	"reload": {
+		Name:  "reload",
+		Func:  cmdReload,
+		Usage: "--config <path> [--config-adapter <name>] [--address <interface>]",
+		Short: "Gives the running Caddy instance a new configuration",
+		Long: `Gives the running Caddy instance a new configuration. This has the same effect
+as POSTing a document to the /load endpoint, but is convenient for simple
+workflows revolving around config files. Since the admin endpoint is
+configurable, the endpoint configuration is loaded from the --address flag if
+specified; otherwise it is loaded from the given config file; otherwise the
+default is assumed.`,
+		Flags: func() *flag.FlagSet {
+			fs := flag.NewFlagSet("load", flag.ExitOnError)
+			fs.String("config", "", "Configuration file")
+			fs.String("config-adapter", "", "Name of config adapter to apply")
+			fs.String("address", "", "Address of the administration listener, if different from config")
+			return fs
+		}(),
+	},
+
+	"version": {
+		Name:  "version",
+		Func:  cmdVersion,
+		Short: "Prints the version.",
+		Long:  `Prints the version.`,
+	},
+
+	"list-modules": {
+		Name:  "list-modules",
+		Func:  cmdListModules,
+		Short: "List installed Caddy modules.",
+		Long:  `List installed Caddy modules.`,
+	},
+
+	"environ": {
+		Name:  "environ",
+		Func:  cmdEnviron,
+		Short: "Prints the environment as seen by Caddy.",
+		Long:  `Prints the environment as seen by Caddy.`,
+	},
+
+	"adapt-config": {
+		Name:  "adapt-config",
+		Func:  cmdAdaptConfig,
+		Usage: "--input <path> --adapter <name> [--pretty]",
+		Short: "Adapts a configuration to Caddy's native JSON config structure",
+		Long: `
+Adapts a configuration to Caddy's native JSON config structure and writes the
+output to stdout, along with any warnings to stderr. If --pretty is specified,
+the output will be formatted with indentation for human readability.`,
+	},
 }
 
-func cmdStop() (int, error) {
-	processList, err := ps.Processes()
-	if err != nil {
-		return caddy.ExitCodeFailedStartup, fmt.Errorf("listing processes: %v", err)
-	}
-	thisProcName := getProcessName()
-	var found bool
-	for _, p := range processList {
-		// the process we're looking for should have the same name but different PID
-		if p.Executable() == thisProcName && p.Pid() != os.Getpid() {
-			found = true
-			fmt.Printf("pid=%d\n", p.Pid())
-
-			if err := gracefullyStopProcess(p.Pid()); err != nil {
-				return caddy.ExitCodeFailedStartup, err
-			}
-		}
-	}
-	if !found {
-		return caddy.ExitCodeFailedStartup, fmt.Errorf("Caddy is not running")
+func init() {
+	// the help command is special in that its func
+	// refers to the commands map; thus, defining it
+	// inline with the commands map's initialization
+	// yields a compile-time error, so we have to
+	// define this command separately
+	commands["help"] = Command{
+		Name:  "help",
+		Func:  cmdHelp,
+		Usage: "<command>",
+		Short: "Shows help for a Caddy subcommand.",
 	}
-	fmt.Println(" success")
-	return caddy.ExitCodeSuccess, nil
 }
 
-func cmdReload() (int, error) {
-	reloadCmd := flag.NewFlagSet("load", flag.ExitOnError)
-	reloadCmdConfigFlag := reloadCmd.String("config", "", "Configuration file")
-	reloadCmdConfigAdapterFlag := reloadCmd.String("config-adapter", "", "Name of config adapter to apply")
-	reloadCmdAddrFlag := reloadCmd.String("address", "", "Address of the administration listener, if different from config")
-	reloadCmd.Parse(os.Args[2:])
-
-	// a configuration is required
-	if *reloadCmdConfigFlag == "" {
-		return caddy.ExitCodeFailedStartup,
-			fmt.Errorf("no configuration to load (use --config)")
-	}
-
-	// get the config in caddy's native format
-	config, err := loadConfig(*reloadCmdConfigFlag, *reloadCmdConfigAdapterFlag)
-	if err != nil {
-		return caddy.ExitCodeFailedStartup, err
-	}
-
-	// get the address of the admin listener and craft endpoint URL
-	adminAddr := *reloadCmdAddrFlag
-	if adminAddr == "" {
-		var tmpStruct struct {
-			Admin caddy.AdminConfig `json:"admin"`
-		}
-		err = json.Unmarshal(config, &tmpStruct)
-		if err != nil {
-			return caddy.ExitCodeFailedStartup,
-				fmt.Errorf("unmarshaling admin listener address from config: %v", err)
-		}
-		adminAddr = tmpStruct.Admin.Listen
+// RegisterCommand registers the command cmd.
+// cmd.Name must be unique and conform to the
+// following format:
+//
+//    - lowercase
+//    - alphanumeric and hyphen characters only
+//    - cannot start or end with a hyphen
+//    - hyphen cannot be adjacent to another hyphen
+//
+// This function panics if the name is already registered,
+// if the name does not meet the described format, or if
+// any of the fields are missing from cmd.
+func RegisterCommand(cmd Command) {
+	if cmd.Name == "" {
+		panic("command name is required")
 	}
-	if adminAddr == "" {
-		adminAddr = caddy.DefaultAdminListen
+	if cmd.Func == nil {
+		panic("command function missing")
 	}
-	adminEndpoint := fmt.Sprintf("http://%s/load", adminAddr)
-
-	// send the configuration to the instance
-	resp, err := http.Post(adminEndpoint, "application/json", bytes.NewReader(config))
-	if err != nil {
-		return caddy.ExitCodeFailedStartup,
-			fmt.Errorf("sending configuration to instance: %v", err)
+	if cmd.Short == "" {
+		panic("command short string is required")
 	}
-	defer resp.Body.Close()
-
-	// if it didn't work, let the user know
-	if resp.StatusCode >= 400 {
-		respBody, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1024*10))
-		if err != nil {
-			return caddy.ExitCodeFailedStartup,
-				fmt.Errorf("HTTP %d: reading error message: %v", resp.StatusCode, err)
-		}
-		return caddy.ExitCodeFailedStartup,
-			fmt.Errorf("caddy responded with error: HTTP %d: %s", resp.StatusCode, respBody)
+	if _, exists := commands[cmd.Name]; exists {
+		panic("command already registered: " + cmd.Name)
 	}
-
-	return caddy.ExitCodeSuccess, nil
-}
-
-func cmdVersion() (int, error) {
-	goModule := caddy.GoModule()
-	if goModule.Sum != "" {
-		// a build with a known version will also have a checksum
-		fmt.Printf("%s %s\n", goModule.Version, goModule.Sum)
-	} else {
-		fmt.Println(goModule.Version)
-	}
-	return caddy.ExitCodeSuccess, nil
-}
-
-func cmdListModules() (int, error) {
-	for _, m := range caddy.Modules() {
-		fmt.Println(m)
-	}
-	return caddy.ExitCodeSuccess, nil
-}
-
-func cmdEnviron() (int, error) {
-	for _, v := range os.Environ() {
-		fmt.Println(v)
+	if !commandNameRegex.MatchString(cmd.Name) {
+		panic("invalid command name")
 	}
-	return caddy.ExitCodeSuccess, nil
+	commands[cmd.Name] = cmd
 }
 
-func cmdAdaptConfig() (int, error) {
-	adaptCmd := flag.NewFlagSet("adapt", flag.ExitOnError)
-	adaptCmdAdapterFlag := adaptCmd.String("adapter", "", "Name of config adapter")
-	adaptCmdInputFlag := adaptCmd.String("input", "", "Configuration file to adapt")
-	adaptCmdPrettyFlag := adaptCmd.Bool("pretty", false, "Format the output for human readability")
-	adaptCmd.Parse(os.Args[2:])
-
-	if *adaptCmdAdapterFlag == "" || *adaptCmdInputFlag == "" {
-		return caddy.ExitCodeFailedStartup,
-			fmt.Errorf("usage: caddy adapt-config --adapter <name> --input <file>")
-	}
-
-	cfgAdapter := caddyconfig.GetAdapter(*adaptCmdAdapterFlag)
-	if cfgAdapter == nil {
-		return caddy.ExitCodeFailedStartup,
-			fmt.Errorf("unrecognized config adapter: %s", *adaptCmdAdapterFlag)
-	}
-
-	input, err := ioutil.ReadFile(*adaptCmdInputFlag)
-	if err != nil {
-		return caddy.ExitCodeFailedStartup,
-			fmt.Errorf("reading input file: %v", err)
-	}
-
-	opts := make(map[string]interface{})
-	if *adaptCmdPrettyFlag {
-		opts["pretty"] = "true"
-	}
-
-	adaptedConfig, warnings, err := cfgAdapter.Adapt(input, opts)
-	if err != nil {
-		return caddy.ExitCodeFailedStartup, err
-	}
-
-	// print warnings to stderr
-	for _, warn := range warnings {
-		msg := warn.Message
-		if warn.Directive != "" {
-			msg = fmt.Sprintf("%s: %s", warn.Directive, warn.Message)
-		}
-		log.Printf("[WARNING][%s] %s:%d: %s", *adaptCmdAdapterFlag, warn.File, warn.Line, msg)
-	}
-
-	// print result to stdout
-	fmt.Println(string(adaptedConfig))
-
-	return caddy.ExitCodeSuccess, nil
-}
+var commandNameRegex = regexp.MustCompile(`^[a-z0-9]$|^([a-z0-9]+-?[a-z0-9]*)+[a-z0-9]$`)
diff --git a/cmd/main.go b/cmd/main.go
index 5b97992..aea020f 100644
--- a/cmd/main.go
+++ b/cmd/main.go
@@ -23,6 +23,9 @@ import (
 	"log"
 	"net"
 	"os"
+	"strconv"
+	"strings"
+	"time"
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/caddyconfig"
@@ -33,45 +36,43 @@ import (
 func Main() {
 	caddy.TrapSignals()
 
-	if len(os.Args) < 2 {
-		fmt.Println(usageString())
-		return
+	switch len(os.Args) {
+	case 0:
+		log.Printf("[FATAL] no arguments provided by OS; args[0] must be command")
+		os.Exit(caddy.ExitCodeFailedStartup)
+	case 1:
+		os.Args = append(os.Args, "help")
 	}
 
-	subcommand, ok := commands[os.Args[1]]
+	subcommandName := os.Args[1]
+	subcommand, ok := commands[subcommandName]
 	if !ok {
-		fmt.Printf("%q is not a valid command\n", os.Args[1])
+		if strings.HasPrefix(os.Args[1], "-") {
+			// user probably forgot to type the subcommand
+			log.Println("[ERROR] first argument must be a subcommand; see 'caddy help'")
+		} else {
+			log.Printf("[ERROR] '%s' is not a recognized subcommand; see 'caddy help'", os.Args[1])
+		}
 		os.Exit(caddy.ExitCodeFailedStartup)
 	}
 
-	if exitCode, err := subcommand(); err != nil {
+	fs := subcommand.Flags
+	if fs == nil {
+		fs = flag.NewFlagSet(subcommand.Name, flag.ExitOnError)
+	}
+
+	err := fs.Parse(os.Args[2:])
+	if err != nil {
 		log.Println(err)
-		os.Exit(exitCode)
+		os.Exit(caddy.ExitCodeFailedStartup)
 	}
-}
 
-// commandFunc is a function that executes
-// a subcommand. It returns an exit code and
-// any associated error.
-type commandFunc func() (int, error)
-
-var commands = map[string]commandFunc{
-	"start":        cmdStart,
-	"run":          cmdRun,
-	"stop":         cmdStop,
-	"reload":       cmdReload,
-	"version":      cmdVersion,
-	"list-modules": cmdListModules,
-	"environ":      cmdEnviron,
-	"adapt-config": cmdAdaptConfig,
-}
+	exitCode, err := subcommand.Func(Flags{fs})
+	if err != nil {
+		log.Printf("%s: %v", subcommand.Name, err)
+	}
 
-func usageString() string {
-	buf := new(bytes.Buffer)
-	buf.WriteString("usage: caddy <command> [<args>]")
-	flag.CommandLine.SetOutput(buf)
-	flag.CommandLine.PrintDefaults()
-	return buf.String()
+	os.Exit(exitCode)
 }
 
 // handlePingbackConn reads from conn and ensures it matches
@@ -156,3 +157,74 @@ func loadConfig(configFile, adapterName string) ([]byte, error) {
 
 	return config, nil
 }
+
+// Flags wraps a FlagSet so that typed values
+// from flags can be easily retrieved.
+type Flags struct {
+	*flag.FlagSet
+}
+
+// String returns the string representation of the
+// flag given by name. It panics if the flag is not
+// in the flag set.
+func (f Flags) String(name string) string {
+	return f.FlagSet.Lookup(name).Value.String()
+}
+
+// Bool returns the boolean representation of the
+// flag given by name. It returns false if the flag
+// is not a boolean type. It panics if the flag is
+// not in the flag set.
+func (f Flags) Bool(name string) bool {
+	val, _ := strconv.ParseBool(f.String(name))
+	return val
+}
+
+// Int returns the integer representation of the
+// flag given by name. It returns 0 if the flag
+// is not an integer type. It panics if the flag is
+// not in the flag set.
+func (f Flags) Int(name string) int {
+	val, _ := strconv.ParseInt(f.String(name), 0, strconv.IntSize)
+	return int(val)
+}
+
+// Float64 returns the float64 representation of the
+// flag given by name. It returns false if the flag
+// is not a float63 type. It panics if the flag is
+// not in the flag set.
+func (f Flags) Float64(name string) float64 {
+	val, _ := strconv.ParseFloat(f.String(name), 64)
+	return val
+}
+
+// Duration returns the duration representation of the
+// flag given by name. It returns false if the flag
+// is not a duration type. It panics if the flag is
+// not in the flag set.
+func (f Flags) Duration(name string) time.Duration {
+	val, _ := time.ParseDuration(f.String(name))
+	return val
+}
+
+// flagHelp returns the help text for fs.
+func flagHelp(fs *flag.FlagSet) string {
+	if fs == nil {
+		return ""
+	}
+
+	// temporarily redirect output
+	out := fs.Output()
+	defer fs.SetOutput(out)
+
+	buf := new(bytes.Buffer)
+	fs.SetOutput(buf)
+	fs.PrintDefaults()
+	return buf.String()
+}
+
+func printEnvironment() {
+	for _, v := range os.Environ() {
+		fmt.Println(v)
+	}
+}