From db50bae0c442d316cb2411ad05f25f7830cf5d5d Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <brad@danga.com>
Date: Mon, 7 Nov 2016 21:56:15 -0800
Subject: [PATCH] pkg/index: read blob before acquiring index mutex

For #878

Change-Id: I8abaf5d923fc6dee7e8a9a3e84f82d4cf7484329
---
 pkg/index/kvfile_test.go |  6 ++++--
 pkg/index/receive.go     | 29 ++++++++++++++++-------------
 2 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/pkg/index/kvfile_test.go b/pkg/index/kvfile_test.go
index 691c344d9..69dfbab21 100644
--- a/pkg/index/kvfile_test.go
+++ b/pkg/index/kvfile_test.go
@@ -57,8 +57,10 @@ func indexTest(t *testing.T,
 	sortedGenfn func(t *testing.T) (sorted.KeyValue, func()),
 	tfn func(*testing.T, func() *index.Index)) {
 	defer test.TLog(t)()
-	var mu sync.Mutex // guards cleanups
-	var cleanups []func()
+	var (
+		mu       sync.Mutex // guards cleanups
+		cleanups []func()
+	)
 	defer func() {
 		mu.Lock() // never unlocked
 		for _, fn := range cleanups {
diff --git a/pkg/index/receive.go b/pkg/index/receive.go
index c87a740ad..765b8b441 100644
--- a/pkg/index/receive.go
+++ b/pkg/index/receive.go
@@ -189,8 +189,14 @@ func (ix *Index) removeAllMissingEdges(br blob.Ref) {
 	}
 }
 
-func (ix *Index) ReceiveBlob(blobRef blob.Ref, source io.Reader) (retsb blob.SizedRef, err error) {
-	ctx := context.TODO()
+func (ix *Index) ReceiveBlob(blobRef blob.Ref, source io.Reader) (blob.SizedRef, error) {
+	// Read from source before acquiring ix.Lock (Issue 878):
+	sniffer := NewBlobSniffer(blobRef)
+	written, err := io.Copy(sniffer, source)
+	if err != nil {
+		return blob.SizedRef{}, err
+	}
+	sbr := blob.SizedRef{Ref: blobRef, Size: uint32(written)}
 
 	ix.Lock()
 	defer ix.Unlock()
@@ -204,14 +210,10 @@ func (ix *Index) ReceiveBlob(blobRef blob.Ref, source io.Reader) (retsb blob.Siz
 			}
 		}
 	}()
-	sniffer := NewBlobSniffer(blobRef)
-	written, err := io.Copy(sniffer, source)
-	if err != nil {
-		return
-	}
+
 	if haveVal, haveErr := ix.s.Get("have:" + blobRef.String()); haveErr == nil {
 		if strings.HasSuffix(haveVal, "|indexed") {
-			return blob.SizedRef{Ref: blobRef, Size: uint32(written)}, nil
+			return sbr, nil
 		}
 	}
 
@@ -221,10 +223,11 @@ func (ix *Index) ReceiveBlob(blobRef blob.Ref, source io.Reader) (retsb blob.Siz
 		fetcher: ix.blobSource,
 	}
 
+	ctx := context.TODO()
 	mm, err := ix.populateMutationMap(ctx, fetcher, blobRef, sniffer)
 	if err != nil {
 		if err != errMissingDep {
-			return
+			return blob.SizedRef{}, err
 		}
 		fetcher.mu.Lock()
 		defer fetcher.mu.Unlock()
@@ -243,18 +246,18 @@ func (ix *Index) ReceiveBlob(blobRef blob.Ref, source io.Reader) (retsb blob.Siz
 			// successfully recorded that the blob isn't
 			// indexed, but we'll reindex it later once
 			// the dependent blobs arrive.
-			return blob.SizedRef{Ref: blobRef, Size: uint32(written)}, nil
+			return sbr, nil
 		}
-		return
+		return blob.SizedRef{}, err
 	}
 
 	if err := ix.commit(mm); err != nil {
-		return retsb, err
+		return blob.SizedRef{}, err
 	}
 
 	if c := ix.corpus; c != nil {
 		if err = c.addBlob(ctx, blobRef, mm); err != nil {
-			return
+			return blob.SizedRef{}, err
 		}
 	}