Merge Repository.{LoadBlob,loadBlob}

Pushing the allocation logic down into the former loadBlob body means
that fewer allocations have to be performed:

name              old time/op    new time/op    delta
LoadTree-8           478µs ± 1%     481µs ± 2%    ~     (p=0.315 n=9+10)
LoadBlob-8          11.6ms ± 1%    11.6ms ± 2%    ~     (p=0.393 n=10+10)
LoadAndDecrypt-8    13.3ms ± 3%    13.3ms ± 3%    ~     (p=0.905 n=10+9)
LoadIndex-8         33.6ms ± 2%    33.2ms ± 1%  -1.15%  (p=0.028 n=10+9)

name              old alloc/op   new alloc/op   delta
LoadTree-8          41.2kB ± 0%    41.1kB ± 0%  -0.23%  (p=0.000 n=10+10)
LoadBlob-8          2.28kB ± 0%    2.18kB ± 0%  -4.21%  (p=0.000 n=10+10)
LoadAndDecrypt-8    2.10MB ± 0%    2.10MB ± 0%    ~     (all equal)
LoadIndex-8         5.22MB ± 0%    5.22MB ± 0%    ~     (p=0.631 n=10+10)

name              old allocs/op  new allocs/op  delta
LoadTree-8             652 ± 0%       651 ± 0%  -0.15%  (p=0.000 n=10+10)
LoadBlob-8            24.0 ± 0%      23.0 ± 0%  -4.17%  (p=0.000 n=10+10)
LoadAndDecrypt-8      30.0 ± 0%      30.0 ± 0%    ~     (all equal)
LoadIndex-8          30.2k ± 0%     30.2k ± 0%    ~     (p=0.610 n=10+10)

name              old speed      new speed      delta
LoadBlob-8        86.4MB/s ± 1%  85.9MB/s ± 2%    ~     (p=0.393 n=10+10)
LoadAndDecrypt-8  75.4MB/s ± 3%  75.4MB/s ± 3%    ~     (p=0.858 n=10+9)

internal/repository/repository.go

@@ -130,17 +130,16 @@ func (r *Repository) sortCachedPacks(blobs []restic.PackedBlob) []restic.PackedB
 	return append(cached, noncached...)
 }
 
-// loadBlob tries to load and decrypt content identified by t and id from a
+// LoadBlob loads a blob of type t from the repository.
-// pack from the backend, the result is stored in plaintextBuf, which must be
+// It may use all of buf[:cap(buf)] as scratch space.
-// large enough to hold the complete blob.
+func (r *Repository) LoadBlob(ctx context.Context, t restic.BlobType, id restic.ID, buf []byte) ([]byte, error) {
-func (r *Repository) loadBlob(ctx context.Context, id restic.ID, t restic.BlobType, plaintextBuf []byte) (int, error) {
+	debug.Log("load %v with id %v (buf len %v, cap %d)", t, id, len(buf), cap(buf))
-	debug.Log("load %v with id %v (buf len %v, cap %d)", t, id, len(plaintextBuf), cap(plaintextBuf))
 
 	// lookup packs
 	blobs, found := r.idx.Lookup(id, t)
 	if !found {
 		debug.Log("id %v not found in index", id)
-		return 0, errors.Errorf("id %v not found in repository", id)
+		return nil, errors.Errorf("id %v not found in repository", id)
 	}
 
 	// try cached pack files first
@@ -157,13 +156,14 @@ func (r *Repository) loadBlob(ctx context.Context, id restic.ID, t restic.BlobTy
 		// load blob from pack
 		h := restic.Handle{Type: restic.DataFile, Name: blob.PackID.String()}
 
-		if uint(cap(plaintextBuf)) < blob.Length {
+		switch {
-			return 0, errors.Errorf("buffer is too small: %v < %v", cap(plaintextBuf), blob.Length)
+		case cap(buf) < int(blob.Length):
+			buf = make([]byte, blob.Length)
+		case len(buf) != int(blob.Length):
+			buf = buf[:blob.Length]
 		}
 
-		plaintextBuf = plaintextBuf[:blob.Length]
+		n, err := restic.ReadAt(ctx, r.be, h, int64(blob.Offset), buf)
-
-		n, err := restic.ReadAt(ctx, r.be, h, int64(blob.Offset), plaintextBuf)
 		if err != nil {
 			debug.Log("error loading blob %v: %v", blob, err)
 			lastError = err
@@ -178,7 +178,7 @@ func (r *Repository) loadBlob(ctx context.Context, id restic.ID, t restic.BlobTy
 		}
 
 		// decrypt
-		nonce, ciphertext := plaintextBuf[:r.key.NonceSize()], plaintextBuf[r.key.NonceSize():]
+		nonce, ciphertext := buf[:r.key.NonceSize()], buf[r.key.NonceSize():]
 		plaintext, err := r.key.Open(ciphertext[:0], nonce, ciphertext, nil)
 		if err != nil {
 			lastError = errors.Errorf("decrypting blob %v failed: %v", id, err)
@@ -191,16 +191,16 @@ func (r *Repository) loadBlob(ctx context.Context, id restic.ID, t restic.BlobTy
 			continue
 		}
 
-		// move decrypted data to the start of the provided buffer
+		// move decrypted data to the start of the buffer
-		copy(plaintextBuf[0:], plaintext)
+		copy(buf, plaintext)
-		return len(plaintext), nil
+		return buf[:len(plaintext)], nil
 	}
 
 	if lastError != nil {
-		return 0, lastError
+		return nil, lastError
 	}
 
-	return 0, errors.Errorf("loading blob %v from %v packs failed", id.Str(), len(blobs))
+	return nil, errors.Errorf("loading blob %v from %v packs failed", id.Str(), len(blobs))
 }
 
 // LoadJSONUnpacked decrypts the data and afterwards calls json.Unmarshal on
@@ -670,30 +670,6 @@ func (r *Repository) Close() error {
 	return r.be.Close()
 }
 
-// LoadBlob loads a blob of type t from the repository.
-// It may use all of buf[:cap(buf)] as scratch space.
-func (r *Repository) LoadBlob(ctx context.Context, t restic.BlobType, id restic.ID, buf []byte) ([]byte, error) {
-	debug.Log("load blob %v into buf (len %v, cap %v)", id, len(buf), cap(buf))
-	size, found := r.idx.LookupSize(id, t)
-	if !found {
-		return nil, errors.Errorf("id %v not found in repository", id)
-	}
-
-	if cap(buf) < restic.CiphertextLength(int(size)) {
-		buf = restic.NewBlobBuffer(int(size))
-	}
-
-	n, err := r.loadBlob(ctx, id, t, buf)
-	if err != nil {
-		return nil, err
-	}
-	buf = buf[:n]
-
-	debug.Log("loaded %d bytes into buf %p", len(buf), buf)
-
-	return buf, err
-}
-
 // SaveBlob saves a blob of type t into the repository. If id is the null id, it
 // will be computed and returned.
 func (r *Repository) SaveBlob(ctx context.Context, t restic.BlobType, buf []byte, id restic.ID) (restic.ID, error) {
@@ -708,19 +684,10 @@ func (r *Repository) SaveBlob(ctx context.Context, t restic.BlobType, buf []byte
 func (r *Repository) LoadTree(ctx context.Context, id restic.ID) (*restic.Tree, error) {
 	debug.Log("load tree %v", id)
 
-	size, found := r.idx.LookupSize(id, restic.TreeBlob)
+	buf, err := r.LoadBlob(ctx, restic.TreeBlob, id, nil)
-	if !found {
-		return nil, errors.Errorf("tree %v not found in repository", id)
-	}
-
-	debug.Log("size is %d, create buffer", size)
-	buf := restic.NewBlobBuffer(int(size))
-
-	n, err := r.loadBlob(ctx, id, restic.TreeBlob, buf)
 	if err != nil {
 		return nil, err
 	}
-	buf = buf[:n]
 
 	t := &restic.Tree{}
 	err = json.Unmarshal(buf, t)