[MM-16700] Add InstallPluginFromUrl helper method (#12994)

Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>

plugin/helpers_plugin.go

@@ -0,0 +1,56 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package plugin
+
+import (
+	"net/http"
+	"net/url"
+	"time"
+
+	"github.com/blang/semver"
+	"github.com/mattermost/mattermost-server/v5/model"
+	"github.com/pkg/errors"
+)
+
+// InstallPluginFromURL implements Helpers.InstallPluginFromURL.
+func (p *HelpersImpl) InstallPluginFromURL(downloadURL string, replace bool) (*model.Manifest, error) {
+	err := p.ensureServerVersion("5.18.0")
+	if err != nil {
+		return nil, err
+	}
+
+	parsedURL, err := url.Parse(downloadURL)
+	if err != nil {
+		return nil, errors.Wrap(err, "error while parsing url")
+	}
+
+	client := &http.Client{Timeout: time.Hour}
+	response, err := client.Get(parsedURL.String())
+	if err != nil {
+		return nil, errors.Wrap(err, "unable to download the plugin")
+	}
+	defer response.Body.Close()
+
+	if response.StatusCode != http.StatusOK {
+		return nil, errors.Errorf("received %d status code while downloading plugin from server", response.StatusCode)
+	}
+
+	manifest, installError := p.API.InstallPlugin(response.Body, replace)
+	if installError != nil {
+		return nil, errors.Wrap(err, "unable to install plugin on server")
+	}
+
+	return manifest, nil
+}
+
+func (p *HelpersImpl) ensureServerVersion(required string) error {
+	serverVersion := p.API.GetServerVersion()
+	currentVersion := semver.MustParse(serverVersion)
+	requiredVersion := semver.MustParse(required)
+
+	if currentVersion.LT(requiredVersion) {
+		return errors.Errorf("incompatible server version for plugin, minimum required version: %s, current version: %s", required, serverVersion)
+	}
+	return nil
+}