update: Change update notifier for new style banner. (#3289)

For binary releases and operating systems it would be

All operating systems.
```
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Minio is 25 days 12 hours 30 minutes old                           ┃
┃ Update: https://dl.minio.io/server/minio/release/linux-amd64/minio ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
```

On docker.
```
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Minio is 25 days 12 hours 32 minutes old ┃
┃ Update: docker pull minio/minio          ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
```

cmd/update-main.go

@@ -18,7 +18,6 @@ package cmd
 
 import (
 	"bytes"
-	"encoding/json"
 	"errors"
 	"io/ioutil"
 	"net/http"
@@ -74,10 +73,9 @@ const (
 
 // updateMessage container to hold update messages.
 type updateMessage struct {
-	Status   string `json:"status"`
-	Update   bool   `json:"update"`
-	Download string `json:"downloadURL"`
-	Version  string `json:"version"`
+	Update    bool          `json:"update"`
+	Download  string        `json:"downloadURL"`
+	NewerThan time.Duration `json:"newerThan"`
 }
 
 // String colorized update message.
@@ -86,19 +84,10 @@ func (u updateMessage) String() string {
 		updateMessage := color.New(color.FgGreen, color.Bold).SprintfFunc()
 		return updateMessage("You are already running the most recent version of ‘minio’.")
 	}
-	msg := colorizeUpdateMessage(u.Download)
+	msg := colorizeUpdateMessage(u.Download, u.NewerThan)
 	return msg
 }
 
-// JSON jsonified update message.
-func (u updateMessage) JSON() string {
-	u.Status = "success"
-	updateMessageJSONBytes, err := json.Marshal(u)
-	fatalIf((err), "Unable to marshal into JSON.")
-
-	return string(updateMessageJSONBytes)
-}
-
 func parseReleaseData(data string) (time.Time, error) {
 	releaseStr := strings.Fields(data)
 	if len(releaseStr) < 2 {
@@ -149,6 +138,34 @@ func isDocker() bool {
 	return bytes.Contains(cgroup, []byte("docker"))
 }
 
+// Check if the minio server binary was built with source.
+func isSourceBuild() bool {
+	return Version == "DEVELOPMENT.GOGET"
+}
+
+// Fetch the current version of the Minio server binary.
+func getCurrentMinioVersion() (current time.Time, err error) {
+	// For development builds we check for binary modTime
+	// to validate against latest minio server release.
+	if Version != "DEVELOPMENT.GOGET" {
+		// Parse current minio version into RFC3339.
+		current, err = time.Parse(time.RFC3339, Version)
+		if err != nil {
+			return time.Time{}, err
+		}
+		return current, nil
+	} // else {
+	// For all development builds through `go get`.
+	// fall back to looking for version of the build
+	// date of the binary itself.
+	var fi os.FileInfo
+	fi, err = os.Stat(os.Args[0])
+	if err != nil {
+		return time.Time{}, err
+	}
+	return fi.ModTime(), nil
+}
+
 // verify updates for releases.
 func getReleaseUpdate(updateURL string, duration time.Duration) (updateMsg updateMessage, errMsg string, err error) {
 	// Construct a new update url.
@@ -157,19 +174,22 @@ func getReleaseUpdate(updateURL string, duration time.Duration) (updateMsg updat
 
 	// Get the downloadURL.
 	var downloadURL string
-	switch runtime.GOOS {
-	case "windows":
-		// For windows.
-		downloadURL = newUpdateURLPrefix + "/minio.exe"
-	default:
-		// For all other operating systems.
-		downloadURL = newUpdateURLPrefix + "/minio"
+	if isDocker() {
+		downloadURL = "docker pull minio/minio"
+	} else {
+		switch runtime.GOOS {
+		case "windows":
+			// For windows.
+			downloadURL = newUpdateURLPrefix + "/minio.exe"
+		default:
+			// For all other operating systems.
+			downloadURL = newUpdateURLPrefix + "/minio"
+		}
 	}
 
 	// Initialize update message.
 	updateMsg = updateMessage{
 		Download: downloadURL,
-		Version:  Version,
 	}
 
 	// Instantiate a new client with 3 sec timeout.
@@ -177,17 +197,9 @@ func getReleaseUpdate(updateURL string, duration time.Duration) (updateMsg updat
 		Timeout: duration,
 	}
 
-	// Parse current minio version into RFC3339.
-	current, err := time.Parse(time.RFC3339, Version)
+	current, err := getCurrentMinioVersion()
 	if err != nil {
-		errMsg = "Unable to parse version string as time."
-		return
-	}
-
-	// Verify if current minio version is zero.
-	if current.IsZero() {
-		err = errors.New("date should not be zero")
-		errMsg = "Updates mechanism is not supported for custom builds. Please download official releases from https://minio.io/#minio"
+		errMsg = "Unable to fetch the current version of Minio server."
 		return
 	}
 
@@ -198,10 +210,22 @@ func getReleaseUpdate(updateURL string, duration time.Duration) (updateMsg updat
 	}
 
 	userAgentPrefix := func() string {
+		prefix := "Minio (" + runtime.GOOS + "; " + runtime.GOARCH
+		// if its a source build.
+		if isSourceBuild() {
+			if isDocker() {
+				prefix = prefix + "; " + "docker; source) "
+			} else {
+				prefix = prefix + "; " + "source) "
+			}
+			return prefix
+		} // else { not source.
 		if isDocker() {
-			return "Minio (" + runtime.GOOS + "; " + runtime.GOARCH + "; " + "docker) "
+			prefix = prefix + "; " + "docker) "
+		} else {
+			prefix = prefix + ") "
 		}
-		return "Minio (" + runtime.GOOS + "; " + runtime.GOARCH + ") "
+		return prefix
 	}()
 
 	// Set user agent.
@@ -239,13 +263,14 @@ func getReleaseUpdate(updateURL string, duration time.Duration) (updateMsg updat
 
 	// Verify if the date is not zero.
 	if latest.IsZero() {
-		err = errors.New("date should not be zero")
+		err = errors.New("Release date cannot be zero. Please report this issue at https://github.com/minio/minio/issues")
 		return
 	}
 
 	// Is the update latest?.
 	if latest.After(current) {
 		updateMsg.Update = true
+		updateMsg.NewerThan = latest.Sub(current)
 	}
 
 	// Return update message.
@@ -254,11 +279,6 @@ func getReleaseUpdate(updateURL string, duration time.Duration) (updateMsg updat
 
 // main entry point for update command.
 func mainUpdate(ctx *cli.Context) {
-	// Error out if 'update' command is issued for development based builds.
-	if Version == "DEVELOPMENT.GOGET" {
-		fatalIf(errors.New(""), "Update mechanism is not supported for ‘go get’ based binary builds. Please download official releases from https://minio.io/#minio")
-	}
-
 	// Check for update.
 	var updateMsg updateMessage
 	var errMsg string