From 43732bb885ff28d6bcbb15c1ad8b46988fc9e70e Mon Sep 17 00:00:00 2001
From: Alexander Weiss <alex@weissfam.de>
Date: Sat, 10 Oct 2020 21:31:40 +0200
Subject: [PATCH] Add CreateIndexFromPacks()

---
 internal/repository/repository.go | 69 +++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/internal/repository/repository.go b/internal/repository/repository.go
index 051b99252..f40ce9097 100644
--- a/internal/repository/repository.go
+++ b/internal/repository/repository.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"sync"
 
 	"github.com/restic/chunker"
 	"github.com/restic/restic/internal/cache"
@@ -17,6 +18,7 @@ import (
 	"github.com/restic/restic/internal/hashing"
 	"github.com/restic/restic/internal/pack"
 	"github.com/restic/restic/internal/restic"
+	"github.com/restic/restic/internal/ui/progress"
 
 	"github.com/minio/sha256-simd"
 	"golang.org/x/sync/errgroup"
@@ -515,6 +517,73 @@ func (r *Repository) LoadIndex(ctx context.Context) error {
 	return nil
 }
 
+const listPackParallelism = 10
+
+// CreateIndexFromPacks creates a new index by reading all given pack files (with sizes).
+// The index is added to the MasterIndex but not marked as finalized.
+// Returned is the list of pack files which could not be read.
+func (r *Repository) CreateIndexFromPacks(ctx context.Context, packsize map[restic.ID]int64, p *progress.Counter) (invalid restic.IDs, err error) {
+	var m sync.Mutex
+
+	debug.Log("Loading index from pack files")
+
+	// track spawned goroutines using wg, create a new context which is
+	// cancelled as soon as an error occurs.
+	wg, ctx := errgroup.WithContext(ctx)
+
+	type FileInfo struct {
+		restic.ID
+		Size int64
+	}
+	ch := make(chan FileInfo)
+
+	// send list of pack files through ch, which is closed afterwards
+	wg.Go(func() error {
+		defer close(ch)
+		for id, size := range packsize {
+			select {
+			case <-ctx.Done():
+				return nil
+			case ch <- FileInfo{id, size}:
+			}
+		}
+		return nil
+	})
+
+	idx := NewIndex()
+	// a worker receives an pack ID from ch, reads the pack contents, and adds them to idx
+	worker := func() error {
+		for fi := range ch {
+			entries, _, err := r.ListPack(ctx, fi.ID, fi.Size)
+			if err != nil {
+				debug.Log("unable to list pack file %v", fi.ID.Str())
+				m.Lock()
+				invalid = append(invalid, fi.ID)
+				m.Unlock()
+			}
+			idx.StorePack(fi.ID, entries)
+			p.Add(1)
+		}
+
+		return nil
+	}
+
+	// run workers on ch
+	wg.Go(func() error {
+		return RunWorkers(listPackParallelism, worker)
+	})
+
+	err = wg.Wait()
+	if err != nil {
+		return invalid, errors.Fatal(err.Error())
+	}
+
+	// Add idx to MasterIndex
+	r.idx.Insert(idx)
+
+	return invalid, nil
+}
+
 // PrepareCache initializes the local cache. indexIDs is the list of IDs of
 // index files still present in the repo.
 func (r *Repository) PrepareCache(indexIDs restic.IDSet) error {