Slightly refactor nanokvm code

* Add ability to properly configure logrus (e.x. specify output file)
 * Make the code slightly more ideomatic (sort imports, etc)
 * Replace some of the shell calls with equivalent native code
 * Fix update process
 * Improve error handling (handle 2 previously unhandled errors)
 * Add locking for HID operations and make a HID-operations struct a singleton

server/utils/http.go

@@ -2,34 +2,48 @@ package utils
 
 import (
 	"errors"
-	log "github.com/sirupsen/logrus"
 	"io"
 	"net/http"
 	"os"
+	"path/filepath"
+
+	log "github.com/sirupsen/logrus"
 )
 
 func Download(req *http.Request, target string) error {
-	out, err := os.OpenFile(target, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0755)
+	log.Debugf("downloading %s to %s", req.URL.String(), target)
+	err := os.MkdirAll(filepath.Dir(target), 0o755)
 	if err != nil {
-		log.Errorf("create file %s err: %s", target, err)
+		log.Errorf("create dir %s err: %s", filepath.Dir(target), err)
 		return err
 	}
-	defer out.Close()
+	out, err := os.OpenFile(target, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0o755)
+	if err != nil {
+		log.Errorf("cannot create file '%s', error: %s", target, err)
+		return err
+	}
+	defer func() {
+		_ = out.Close()
+	}()
 
 	resp, err := (&http.Client{}).Do(req)
 	if err != nil {
-		log.Errorf("download file err: %s", err)
+		log.Errorf("request error: %s", err)
 		return err
 	}
-	defer resp.Body.Close()
+	defer func() {
+		_ = resp.Body.Close()
+	}()
 
 	if resp.StatusCode != http.StatusOK {
-		return errors.New("request error")
+		log.Errorf("request failed, status code: %d", resp.StatusCode)
+		return errors.New("update website is inaccessible right now")
 	}
 
 	contentType := resp.Header.Get("Content-Type")
 	if contentType != "application/octet-stream" && contentType != "application/zip" {
-		return errors.New("download error")
+		log.Debugf("unexpected content-type, it should be either octet-stream or zip, but got: %s", contentType)
+		return errors.New("unsupported content type")
 	}
 
 	_, err = io.Copy(out, resp.Body)