add context cancellation to backup routines

1 files changed, 23 insertions, 12 deletions

diff --git a/system/db/backup.go b/system/db/backup.go
index 735abe4..4a2bf96 100644
--- a/system/db/backup.go
+++ b/system/db/backup.go
@@ -1,6 +1,7 @@
 package db
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"time"
@@ -8,19 +9,29 @@ import (
 	"github.com/boltdb/bolt"
 )
 
-// Backup writes a snapshot of the system.db database to an HTTP response
-func Backup(res http.ResponseWriter) error {
-	err := store.View(func(tx *bolt.Tx) error {
-		ts := time.Now().Unix()
-		disposition := `attachment; filename="system-%d.db.bak"`
+// Backup writes a snapshot of the system.db database to an HTTP response. The
+// output is discarded if we get a cancellation signal.
+func Backup(ctx context.Context, res http.ResponseWriter) error {
+	errChan := make(chan error, 1)
 
-		res.Header().Set("Content-Type", "application/octet-stream")
-		res.Header().Set("Content-Disposition", fmt.Sprintf(disposition, ts))
-		res.Header().Set("Content-Length", fmt.Sprintf("%d", int(tx.Size())))
+	go func() {
+		errChan <- store.View(func(tx *bolt.Tx) error {
+			ts := time.Now().Unix()
+			disposition := `attachment; filename="system-%d.db.bak"`
 
-		_, err := tx.WriteTo(res)
-		return err
-	})
+			res.Header().Set("Content-Type", "application/octet-stream")
+			res.Header().Set("Content-Disposition", fmt.Sprintf(disposition, ts))
+			res.Header().Set("Content-Length", fmt.Sprintf("%d", int(tx.Size())))
+
+			_, err := tx.WriteTo(res)
+			return err
+		})
+	}()
 
-	return err
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case err := <-errChan:
+		return err
+	}
 }