From 43418e9f65dc111f1c409a4a5cc10727823df239 Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Mon, 7 Oct 2013 18:58:33 +1100
Subject: [PATCH] Fix bugs in the new WriteSectionTo hashing implementation

---
 client.go    | 5 +++--
 mmap_span.go | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/client.go b/client.go
index 1eb15b9d..af67137c 100644
--- a/client.go
+++ b/client.go
@@ -8,6 +8,7 @@ import (
 	"crypto/rand"
 	"encoding"
 	"errors"
+	"fmt"
 	metainfo "github.com/nsf/libtorgo/torrent"
 	"io"
 	"launchpad.net/gommap"
@@ -231,12 +232,12 @@ func (t *Torrent) PieceSize(piece int) (size int64) {
 
 func (t *Torrent) HashPiece(piece int) (ps pieceSum) {
 	hash := PieceHash.New()
-	n, err := t.Data.WriteSectionTo(hash, int64(piece)*t.MetaInfo.PieceLength, int64(piece)*t.MetaInfo.PieceLength)
+	n, err := t.Data.WriteSectionTo(hash, int64(piece)*t.MetaInfo.PieceLength, t.MetaInfo.PieceLength)
 	if err != nil {
 		panic(err)
 	}
 	if n != t.PieceSize(piece) {
-		panic("hashed wrong number of bytes")
+		panic(fmt.Sprintf("hashed wrong number of bytes: expected %d; did %d; piece %d", t.PieceSize(piece), n, piece))
 	}
 	copyHashSum(ps[:], hash.Sum(nil))
 	return
diff --git a/mmap_span.go b/mmap_span.go
index fcc5cd4e..37f97720 100644
--- a/mmap_span.go
+++ b/mmap_span.go
@@ -61,7 +61,7 @@ func (me MMapSpan) WriteSectionTo(w io.Writer, off, n int64) (written int64, err
 		if err != nil {
 			return true
 		}
-		return n != 0
+		return n == 0
 	})
 	return
 }