error-pages/internal/cli/serve/command.go

package serve

import (
	"context"
	"errors"
	"fmt"
	"net"
	"os"
	"strings"
	"time"

	"github.com/urfave/cli/v2"
	"go.uber.org/zap"

	"gh.tarampamp.am/error-pages/internal/breaker"
	"gh.tarampamp.am/error-pages/internal/cli/shared"
	"gh.tarampamp.am/error-pages/internal/config"
	"gh.tarampamp.am/error-pages/internal/env"
	appHttp "gh.tarampamp.am/error-pages/internal/http"
	"gh.tarampamp.am/error-pages/internal/options"
	"gh.tarampamp.am/error-pages/internal/pick"
)

type command struct {
	c *cli.Command
}

const (
	templateNameFlagName     = "template-name"
	defaultErrorPageFlagName = "default-error-page"
	defaultHTTPCodeFlagName  = "default-http-code"
	showDetailsFlagName      = "show-details"
	proxyHTTPHeadersFlagName = "proxy-headers"
	disableL10nFlagName      = "disable-l10n"
)

const (
	useRandomTemplate              = "random"
	useRandomTemplateOnEachRequest = "i-said-random"
	useRandomTemplateDaily         = "random-daily"
	useRandomTemplateHourly        = "random-hourly"
)

// NewCommand creates `serve` command.
func NewCommand(log *zap.Logger) *cli.Command { //nolint:funlen
	var cmd = command{}

	cmd.c = &cli.Command{
		Name:    "serve",
		Aliases: []string{"s", "server"},
		Usage:   "Start HTTP server",
		Action: func(c *cli.Context) error {
			var cfg *config.Config

			if configPath := c.String(shared.ConfigFileFlag.Name); configPath == "" { // load config from file
				return errors.New("path to the config file is required for this command")
			} else if loadedCfg, err := config.FromYamlFile(c.String(shared.ConfigFileFlag.Name)); err != nil {
				return err
			} else {
				cfg = loadedCfg
			}

			var (
				ip   = c.String(shared.ListenAddrFlag.Name)
				port = uint16(c.Uint(shared.ListenPortFlag.Name))
				o    options.ErrorPage
			)

			if net.ParseIP(ip) == nil {
				return fmt.Errorf("wrong IP address [%s] for listening", ip)
			}

			{ // fill options
				o.Template.Name = c.String(templateNameFlagName)
				o.L10n.Disabled = c.Bool(disableL10nFlagName)
				o.Default.PageCode = c.String(defaultErrorPageFlagName)
				o.Default.HTTPCode = uint16(c.Uint(defaultHTTPCodeFlagName))
				o.ShowDetails = c.Bool(showDetailsFlagName)

				if headers := c.String(proxyHTTPHeadersFlagName); headers != "" { //nolint:nestif
					var m = make(map[string]struct{})

					// make unique and ignore empty strings
					for _, header := range strings.Split(headers, ",") {
						if h := strings.TrimSpace(header); h != "" {
							if strings.ContainsRune(h, ' ') {
								return fmt.Errorf("whitespaces in the HTTP headers for proxying [%s] are not allowed", header)
							}

							if _, ok := m[h]; !ok {
								m[h] = struct{}{}
							}
						}
					}

					// convert map into slice
					o.ProxyHTTPHeaders = make([]string, 0, len(m))
					for h := range m {
						o.ProxyHTTPHeaders = append(o.ProxyHTTPHeaders, h)
					}
				}
			}

			if o.Default.HTTPCode > 599 { //nolint:gomnd
				return fmt.Errorf("wrong default HTTP response code [%d]", o.Default.HTTPCode)
			}

			return cmd.Run(c.Context, log, cfg, ip, port, o)
		},
		Flags: []cli.Flag{
			shared.ConfigFileFlag,
			shared.ListenPortFlag,
			shared.ListenAddrFlag,
			&cli.StringFlag{
				Name:    templateNameFlagName,
				Aliases: []string{"t"},
				Usage: fmt.Sprintf(
					"template name (set \"%s\" to use a randomized or \"%s\" to use a randomized template on "+
						"each request or \"%s/%s\" daily/hourly randomized)",
					useRandomTemplate,
					useRandomTemplateOnEachRequest,
					useRandomTemplateDaily,
					useRandomTemplateHourly,
				),
				EnvVars: []string{env.TemplateName.String()},
			},
			&cli.StringFlag{
				Name:    defaultErrorPageFlagName,
				Value:   "404",
				Usage:   "default error page",
				EnvVars: []string{env.DefaultErrorPage.String()},
			},
			&cli.UintFlag{
				Name:    defaultHTTPCodeFlagName,
				Value:   404, //nolint:gomnd
				Usage:   "default HTTP response code",
				EnvVars: []string{env.DefaultHTTPCode.String()},
			},
			&cli.BoolFlag{
				Name:    showDetailsFlagName,
				Usage:   "show request details in response",
				EnvVars: []string{env.ShowDetails.String()},
			},
			&cli.StringFlag{
				Name:    proxyHTTPHeadersFlagName,
				Usage:   "proxy HTTP request headers list (comma-separated)",
				EnvVars: []string{env.ProxyHTTPHeaders.String()},
			},
			&cli.BoolFlag{
				Name:    disableL10nFlagName,
				Usage:   "disable error pages localization",
				EnvVars: []string{env.DisableL10n.String()},
			},
		},
	}

	return cmd.c
}

// Run current command.
func (cmd *command) Run( //nolint:funlen
	parentCtx context.Context, log *zap.Logger, cfg *config.Config, ip string, port uint16, opt options.ErrorPage,
) error {
	var (
		ctx, cancel = context.WithCancel(parentCtx) // serve context creation
		oss         = breaker.NewOSSignals(ctx)     // OS signals listener
	)

	// subscribe for system signals
	oss.Subscribe(func(sig os.Signal) {
		log.Warn("Stopping by OS signal..", zap.String("signal", sig.String()))

		cancel()
	})

	defer func() {
		cancel()   // call the cancellation function after all
		oss.Stop() // stop system signals listening
	}()

	var (
		templateNames = cfg.TemplateNames()
		picker        interface{ Pick() string }
	)

	switch opt.Template.Name {
	case useRandomTemplate:
		log.Info("A random template will be used")

		picker = pick.NewStringsSlice(templateNames, pick.RandomOnce)

	case useRandomTemplateOnEachRequest:
		log.Info("A random template on EACH request will be used")

		picker = pick.NewStringsSlice(templateNames, pick.RandomEveryTime)

	case useRandomTemplateDaily:
		log.Info("A random template will be used and changed once a day")

		picker = pick.NewStringsSliceWithInterval(templateNames, pick.RandomEveryTime, time.Hour*24) //nolint:gomnd

	case useRandomTemplateHourly:
		log.Info("A random template will be used and changed hourly")

		picker = pick.NewStringsSliceWithInterval(templateNames, pick.RandomEveryTime, time.Hour)

	case "":
		log.Info("The first template (ordered by name) will be used")

		picker = pick.NewStringsSlice(templateNames, pick.First)

	default:
		if t, found := cfg.Template(opt.Template.Name); found {
			log.Info("We will use the requested template", zap.String("name", t.Name()))
			picker = pick.NewStringsSlice([]string{t.Name()}, pick.First)
		} else {
			return errors.New("requested nonexistent template: " + opt.Template.Name)
		}
	}

	// create HTTP server
	server := appHttp.NewServer(log)

	// register server routes, middlewares, etc.
	if err := server.Register(cfg, picker, opt); err != nil {
		return err
	}

	startedAt, startingErrCh := time.Now(), make(chan error, 1) // channel for server starting error

	// start HTTP server in separate goroutine
	go func(errCh chan<- error) {
		defer close(errCh)

		log.Info("Server starting",
			zap.String("addr", ip),
			zap.Uint16("port", port),
			zap.String("default error page", opt.Default.PageCode),
			zap.Uint16("default HTTP response code", opt.Default.HTTPCode),
			zap.Strings("proxy headers", opt.ProxyHTTPHeaders),
			zap.Bool("show request details", opt.ShowDetails),
			zap.Bool("localization disabled", opt.L10n.Disabled),
		)

		if err := server.Start(ip, port); err != nil {
			errCh <- err
		}
	}(startingErrCh)

	// and wait for...
	select {
	case err := <-startingErrCh: // ..server starting error
		return err

	case <-ctx.Done(): // ..or context cancellation
		log.Info("Gracefully server stopping", zap.Duration("uptime", time.Since(startedAt)))

		if p, ok := picker.(interface{ Close() error }); ok {
			if err := p.Close(); err != nil {
				return err
			}
		}

		// stop the server using created context above
		if err := server.Stop(); err != nil {
			return err
		}
	}

	return nil
}