server: add checkupdates command

server/checkupdates_cmd.go

@@ -0,0 +1,63 @@
+package server
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/harfangapps/regis-companion/resp"
+)
+
+type doer interface {
+	Do(req *http.Request) (*http.Response, error)
+}
+
+type checkUpdatesCmd struct {
+	client doer
+}
+
+const githubEndpoint = `https://api.github.com/repos/harfangapps/homebrew-harfangapps/releases/latest`
+
+// CHECKUPDATES
+func (c checkUpdatesCmd) Execute(cmdName string, req []string, s *Server) (interface{}, error) {
+	if len(req) != 1 {
+		return resp.Error(fmt.Sprintf("ERR wrong number of arguments for %v", cmdName)), nil
+	}
+
+	hreq, err := http.NewRequest("GET", githubEndpoint, nil)
+	if err != nil {
+		return resp.Error(fmt.Sprintf("ERR failed to create request: %v", err)), nil
+	}
+
+	res, err := c.client.Do(hreq)
+	if err != nil {
+		return resp.Error(fmt.Sprintf("ERR request failed: %v", err)), nil
+	}
+	defer res.Body.Close()
+
+	v, err := readRelease(res.Body)
+	if err != nil {
+		return resp.Error(fmt.Sprintf("ERR failed to read version: %v", err)), nil
+	}
+
+	// return true if the release is different than the current version
+	// (ideally, should be later than, but in practice different is enough)
+	return v != Version, nil
+}
+
+func readRelease(r io.Reader) (string, error) {
+	var obj struct {
+		TagName string `json:"tag_name"`
+	}
+
+	data, err := ioutil.ReadAll(r)
+	if err != nil {
+		return "", err
+	}
+	if err := json.Unmarshal(data, &obj); err != nil {
+		return "", err
+	}
+	return obj.TagName, nil
+}

server/server.go

@@ -5,6 +5,7 @@ import (
 	"expvar"
 	"fmt"
 	"net"
+	"net/http"
 	"sort"
 	"strings"
 	"sync"
@@ -45,6 +46,9 @@ var (
 
 func init() {
 	supportedCommands = map[string]command{
+		"checkupdates": checkUpdatesCmd{
+			client: &http.Client{Timeout: 10 * time.Second},
+		},
 		"command":       commandCmd{},
 		"gettunneladdr": getTunnelAddrCmd{},
 		"killtunnel":    killTunnelCmd{},