From 9a5b9253c4bce73a68b08e9f6bd6ac205d8ebc8f Mon Sep 17 00:00:00 2001
From: Alexander Neumann <alexander@bumpern.de>
Date: Fri, 13 Jan 2017 12:33:06 +0100
Subject: [PATCH] LoadBlob: use buffer as scratch space

    benchmark               old bytes     new bytes     delta
    BenchmarkLoadBlob-4     1010128       2256          -99.78%
---
 src/restic/repository/repository.go      | 28 +++++++++---------------
 src/restic/repository/repository_test.go |  3 ++-
 2 files changed, 12 insertions(+), 19 deletions(-)

diff --git a/src/restic/repository/repository.go b/src/restic/repository/repository.go
index 809afb187..cb1e3ad69 100644
--- a/src/restic/repository/repository.go
+++ b/src/restic/repository/repository.go
@@ -81,17 +81,6 @@ func (r *Repository) LoadAndDecrypt(t restic.FileType, id restic.ID) ([]byte, er
 func (r *Repository) loadBlob(id restic.ID, t restic.BlobType, plaintextBuf []byte) (int, error) {
 	debug.Log("load %v with id %v (buf %p, len %d)", t, id.Str(), plaintextBuf, len(plaintextBuf))
 
-	// lookup plaintext size of blob
-	size, err := r.idx.LookupSize(id, t)
-	if err != nil {
-		return 0, err
-	}
-
-	// make sure the plaintext buffer is large enough, extend otherwise
-	if len(plaintextBuf) < int(size) {
-		return 0, errors.Errorf("buffer is too small: %d < %d", len(plaintextBuf), size)
-	}
-
 	// lookup packs
 	blobs, err := r.idx.Lookup(id, t)
 	if err != nil {
@@ -109,8 +98,8 @@ func (r *Repository) loadBlob(id restic.ID, t restic.BlobType, plaintextBuf []by
 
 		// load blob from pack
 		h := restic.Handle{Type: restic.DataFile, Name: blob.PackID.String()}
-		ciphertextBuf := make([]byte, blob.Length)
-		n, err := r.be.Load(h, ciphertextBuf, int64(blob.Offset))
+		plaintextBuf = plaintextBuf[:cap(plaintextBuf)]
+		n, err := r.be.Load(h, plaintextBuf, int64(blob.Offset))
 		if err != nil {
 			debug.Log("error loading blob %v: %v", blob, err)
 			lastError = err
@@ -125,7 +114,7 @@ func (r *Repository) loadBlob(id restic.ID, t restic.BlobType, plaintextBuf []by
 		}
 
 		// decrypt
-		n, err = r.decryptTo(plaintextBuf, ciphertextBuf)
+		n, err = r.decryptTo(plaintextBuf, plaintextBuf)
 		if err != nil {
 			lastError = errors.Errorf("decrypting blob %v failed: %v", id, err)
 			continue
@@ -528,7 +517,9 @@ func (r *Repository) Close() error {
 	return r.be.Close()
 }
 
-// LoadBlob loads a blob of type t from the repository to the buffer.
+// LoadBlob loads a blob of type t from the repository to the buffer. buf must
+// be large enough to hold the encrypted blob, since it is used as scratch
+// space.
 func (r *Repository) LoadBlob(t restic.BlobType, id restic.ID, buf []byte) (int, error) {
 	debug.Log("load blob %v into buf %p", id.Str(), buf)
 	size, err := r.idx.LookupSize(id, t)
@@ -536,8 +527,9 @@ func (r *Repository) LoadBlob(t restic.BlobType, id restic.ID, buf []byte) (int,
 		return 0, err
 	}
 
-	if len(buf) < int(size) {
-		return 0, errors.Errorf("buffer is too small for data blob (%d < %d)", len(buf), size)
+	buf = buf[:cap(buf)]
+	if len(buf) < int(size)+crypto.Extension {
+		return 0, errors.Errorf("buffer is too small for data blob (%d < %d)", len(buf), size+crypto.Extension)
 	}
 
 	n, err := r.loadBlob(id, t, buf)
@@ -571,7 +563,7 @@ func (r *Repository) LoadTree(id restic.ID) (*restic.Tree, error) {
 	}
 
 	debug.Log("size is %d, create buffer", size)
-	buf := make([]byte, size)
+	buf := make([]byte, size+crypto.Extension)
 
 	n, err := r.loadBlob(id, restic.TreeBlob, buf)
 	if err != nil {
diff --git a/src/restic/repository/repository_test.go b/src/restic/repository/repository_test.go
index 34e642abb..978537d7f 100644
--- a/src/restic/repository/repository_test.go
+++ b/src/restic/repository/repository_test.go
@@ -11,6 +11,7 @@ import (
 
 	"restic"
 	"restic/archiver"
+	"restic/crypto"
 	"restic/repository"
 	. "restic/test"
 )
@@ -152,7 +153,7 @@ func BenchmarkLoadBlob(b *testing.B) {
 	defer cleanup()
 
 	length := 1000000
-	buf := make([]byte, length)
+	buf := make([]byte, length, length+crypto.Extension)
 	_, err := io.ReadFull(rnd, buf)
 	OK(b, err)