feat: add download link to create a zip archive of restored files

internal/api/downloadhandler.go

@@ -0,0 +1,84 @@
+package api
+
+import (
+	"archive/zip"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	v1 "github.com/garethgeorge/backrest/gen/go/v1"
+	"github.com/garethgeorge/backrest/internal/oplog"
+	"go.uber.org/zap"
+)
+
+func NewDownloadHandler(oplog *oplog.OpLog) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		p := r.URL.Path[1:]
+		sep := strings.Index(p, "/")
+		if sep == -1 {
+			http.Error(w, "invalid path", http.StatusBadRequest)
+			return
+		}
+		restoreID := p[:sep]
+		filePath := p[sep+1:]
+		opID, err := strconv.ParseInt(restoreID, 16, 64)
+		if err != nil {
+			http.Error(w, "invalid restore ID: "+err.Error(), http.StatusBadRequest)
+			return
+		}
+		op, err := oplog.Get(int64(opID))
+		if err != nil {
+			http.Error(w, "restore not found", http.StatusNotFound)
+			return
+		}
+		restoreOp, ok := op.Op.(*v1.Operation_OperationRestore)
+		if !ok {
+			http.Error(w, "restore not found", http.StatusNotFound)
+			return
+		}
+		targetPath := restoreOp.OperationRestore.GetTarget()
+		if targetPath == "" {
+			http.Error(w, "restore target not found", http.StatusNotFound)
+			return
+		}
+		fullPath := filepath.Join(targetPath, filePath)
+
+		w.Header().Set("Content-Disposition", "attachment; filename=archive.zip")
+		w.Header().Set("Content-Type", "application/zip")
+		w.Header().Set("Content-Transfer-Encoding", "binary")
+
+		z := zip.NewWriter(w)
+		zap.L().Info("creating zip archive", zap.String("path", fullPath))
+		if err := filepath.Walk(fullPath, func(path string, info os.FileInfo, err error) error {
+			if err != nil {
+				return err
+			}
+			if info.IsDir() {
+				return nil
+			}
+			file, err := os.OpenFile(path, os.O_RDONLY, 0)
+			if err != nil {
+				zap.L().Warn("error opening file", zap.String("path", path), zap.Error(err))
+				return nil
+			}
+			defer file.Close()
+			f, err := z.Create(path[len(fullPath)+1:])
+			if err != nil {
+				return fmt.Errorf("add file to zip archive: %w", err)
+			}
+			io.Copy(f, file)
+			return nil
+		}); err != nil {
+			zap.S().Errorf("error creating zip archive: %v", err)
+			http.Error(w, "error creating zip archive", http.StatusInternalServerError)
+		}
+		if err := z.Close(); err != nil {
+			zap.S().Errorf("error closing zip archive: %v", err)
+			http.Error(w, "error closing zip archive", http.StatusInternalServerError)
+		}
+	})
+}