Check for updates:if github releases with higher tag semvers exist

cmd/ipfs/version.go

 package main
 
 import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"os"
+
 	semver "github.com/coreos/go-semver/semver"
 	"github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/commander"
 	u "github.com/jbenet/go-ipfs/util"
 )
 
 // The IPFS version.
-const Version = "0.1.0"
+const (
+	Version                   = "0.2.0"
+	EndpointURLLatestReleases = "https://api.github.com/repos/jbenet/go-ipfs/tags"
+	VersionErrorShort         = `Warning: You are running version %s of go-ipfs. The latest version is %s.`
+	VersionErrorLong          = `
+	Warning: You are running version %s of go-ipfs. The latest version is %s.
+	Since this is alpha software, it is strongly recommended you update.
+
+	You can update go-ipfs by running
+
+	    ipfs version update
+
+	You can silence this message by running
+
+	    ipfs config update.check ignore
+
+	`
+)
 
 var cmdIpfsVersion = &commander.Command{
 	UsageLine: "version",
@@ -22,7 +44,12 @@ var cmdIpfsVersion = &commander.Command{
 var currentVersion *semver.Version
 
 func init() {
-	currentVersion, _ = semver.NewVersion(Version)
+	var err error
+	currentVersion, err = semver.NewVersion(Version)
+	if err != nil {
+		fmt.Printf("The const Version literal in version.go needs to be in semver format: %s \n", Version)
+		os.Exit(1)
+	}
 	cmdIpfsVersion.Flag.Bool("number", false, "show only the number")
 }
 
@@ -34,3 +61,43 @@ func versionCmd(c *commander.Command, _ []string) error {
 	u.POut("%s\n", Version)
 	return nil
 }
+
+func checkForUpdates() error {
+	resp, err := http.Get(EndpointURLLatestReleases)
+	if err != nil {
+		// can't reach the endpoint, coud be firewall, or no internet connection or something else
+		// will just silently move on
+		return nil
+	}
+	var body interface{}
+	_ = json.NewDecoder(resp.Body).Decode(&body)
+	releases, ok := body.([]interface{})
+	if !ok {
+		// the response body does not seem to meet specified Github API format
+		// https://developer.github.com/v3/repos/#list-tags
+		// will just silently move on
+		return nil
+	}
+	for _, r := range releases {
+		release, ok := r.(map[string]interface{})
+		if !ok {
+			continue
+		}
+		tagName, ok := release["name"].(string)
+		if !ok {
+			continue
+		}
+		if len(tagName) > 0 && tagName[0] == 'v' {
+			// both 'v0.1.0' and '0.1.0' semver tagname conventions can be encountered
+			tagName = tagName[1:]
+		}
+		releaseVersion, err := semver.NewVersion(tagName)
+		if err != nil {
+			continue
+		}
+		if currentVersion.LessThan(*releaseVersion) {
+			return fmt.Errorf(VersionErrorLong, Version, tagName)
+		}
+	}
+	return nil
+}