Example of self-updating from a nexus repository

selfupdate_example.go

package main

import (
	"context"
	"crypto/tls"
	"fmt"
	"io"
	"net/http"
	"os"
	"regexp"
	"runtime"
	"sort"
	"time"

	"github.com/Masterminds/semver/v3"
	"github.com/apex/log"
	"github.com/fynelabs/selfupdate"
)

var reVersion = regexp.MustCompile(`(?m)<a href="(?P<version>\d+\.\d+\.\d+[a-zA-Z0-9._+~]*)/">`)

// Pulled from main.go
type Flags struct {
	// Wrap global flags and configurations to add sub-command logic.
	*models.Flags

	Login  CommandLogin  `command:"login"  description:"login to example"`
	Update CommandUpdate `command:"update" description:"update example-cli"`

	Get struct {
		// TRUNCATED
	} `command:"get" description:"get information about a resource"`
}

type CommandUpdate struct {
	NexusURL        string `long:"nexus-url"        description:"URL to use for nexus"    default:"https://nexus.example.com"`
	NexusRepository string `long:"nexus-repository" description:"Nexus repository to use" default:"some-repository-name"`
	TLSSkipVerify   bool   `long:"tls-skip-verify"  description:"Skip TLS verification"`
	AllowPrerelease bool   `long:"allow-prerelease" description:"Allow updating to prerelease versions"`

	client *http.Client
}

func (c *CommandUpdate) Execute(args []string) error {
	c.initClient()

	newVersion := c.needsUpdate(context.Background(), true)
	if newVersion == nil {
		logger.Info("example-cli is up to date")
		os.Exit(0)
	}

	binary := fmt.Sprintf("example_%s_%s", runtime.GOOS, runtime.GOARCH)
	if runtime.GOOS == "windows" {
		binary += ".exe"
	}

	uri := fmt.Sprintf(
		"%s/repository/%s/%s/%s/%s/%s",
		c.NexusURL,
		c.NexusRepository,
		productName,
		applicationName,
		newVersion.Original(),
		binary,
	)

	logger.WithField("uri", uri).Info("downloading update")

	resp, err := c.client.Get(uri)
	if err != nil {
		logger.WithError(err).Fatal("error downloading update")
	}

	err = selfupdate.Apply(resp.Body, selfupdate.Options{})
	resp.Body.Close()

	if err != nil {
		logger.WithError(err).Error("error applying update")

		if rerr := selfupdate.RollbackError(err); rerr != nil {
			logger.WithError(rerr).Error("error rolling back update")
		}

		os.Exit(1)
	}

	logger.WithField("new-version", newVersion.String()).Info("example-cli updated successfully")
	return nil
}

func (c *CommandUpdate) initClient() {
	if c.client != nil {
		return
	}

	c.client = &http.Client{
		Timeout: time.Second * 10,
		Transport: &http.Transport{
			TLSClientConfig: &tls.Config{
				InsecureSkipVerify: c.TLSSkipVerify,
			},
		},
	}
}

// needsUpdate checks if an update is available. If required is set, and an update
// check can't be done, this will exit the program with an error. If newVersion is
// nil, no update is available.
func (c *CommandUpdate) needsUpdate(ctx context.Context, required bool) *semver.Version {
	c.initClient()

	logger.WithField("current-version", version).Debug("checking for updates")

	// Fetch versions.
	current, versions, err := c.fetchVersions(ctx)
	if err != nil {
		if !required {
			logger.WithError(err).Debug("error fetching versions")
			return nil
		}
		logger.WithError(err).Fatal("error fetching versions")
	}

	// Check if we're up to date.
	if !current.LessThan(versions[0]) {
		return nil
	}

	return versions[0]
}

func (c *CommandUpdate) fetchVersions(ctx context.Context) (current *semver.Version, versions []*semver.Version, err error) {
	current, err = semver.NewVersion(version)
	if err != nil {
		return nil, nil, fmt.Errorf("error parsing current version %q: %w", version, err)
	}

	uri := fmt.Sprintf(
		"%s/service/rest/repository/browse/%s/%s/%s/",
		c.NexusURL,
		c.NexusRepository,
		productName,
		applicationName,
	)

	logger.WithField("uri", uri).Debug("fetching versions")

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, uri, http.NoBody)
	if err != nil {
		return current, nil, fmt.Errorf("error creating version check request: %w", err)
	}

	req.Header.Set("Accept", "text/html,application/xhtml+xml,application/xml")
	req.Header.Set("Cache-Control", "no-cache")
	req.Header.Set("User-Agent", fmt.Sprintf("%s/%s/%s", productName, applicationName, version))

	resp, err := c.client.Do(req)
	if err != nil {
		return current, nil, fmt.Errorf("error performing version check request: %w", err)
	}
	defer resp.Body.Close()

	data, err := io.ReadAll(resp.Body)
	if err != nil {
		return current, nil, fmt.Errorf("error parsing version response: %w", err)
	}

	logger.WithFields(log.Fields{
		"status": resp.Status,
		"body":   string(data),
	}).Debug("version check response")

	if resp.StatusCode != http.StatusOK {
		return current, nil, fmt.Errorf("error performing version check request: %s", resp.Status)
	}

	for _, result := range reVersion.FindAllStringSubmatch(string(data), -1) {
		v, err := semver.NewVersion(result[1])
		if err != nil {
			logger.WithError(err).WithField("version", result[1]).Warn("error parsing version, skipping")
			continue
		}

		if !c.AllowPrerelease && v.Prerelease() != "" {
			logger.WithField("version", result[1]).Debug("skipping prerelease version")
			continue
		}

		logger.WithField("version", v.String()).Debug("found version")

		versions = append(versions, v)
	}

	if len(versions) == 0 {
		return current, nil, fmt.Errorf("no versions found")
	}

	sort.Sort(sort.Reverse(semver.Collection(versions)))

	return current, versions, nil
}