From 19ce53e69f4b46f9b94dd557ba58aac3fcc44c93 Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Thu, 27 Feb 2020 16:45:57 +1100
Subject: [PATCH] Make io.EOF an expected error from storage.Piece.ReadAt

Fixes #381.
---
 storage/bolt_piece.go |  6 ++++--
 storage/file.go       |  4 ----
 storage/file_test.go  |  6 +++++-
 storage/wrappers.go   | 10 ++--------
 test/transfer_test.go |  1 -
 torrent.go            |  4 +++-
 6 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/storage/bolt_piece.go b/storage/bolt_piece.go
index 179fe3bd..c54a25e9 100644
--- a/storage/bolt_piece.go
+++ b/storage/bolt_piece.go
@@ -2,6 +2,7 @@ package storage
 
 import (
 	"encoding/binary"
+	"io"
 
 	"github.com/anacrolix/missinggo/x"
 	bolt "github.com/etcd-io/bbolt"
@@ -46,15 +47,16 @@ func (me *boltDBPiece) ReadAt(b []byte, off int64) (n int, err error) {
 	err = me.db.View(func(tx *bolt.Tx) error {
 		db := tx.Bucket(dataBucketKey)
 		if db == nil {
-			return nil
+			return io.EOF
 		}
 		ci := off / chunkSize
 		off %= chunkSize
 		for len(b) != 0 {
 			ck := me.chunkKey(int(ci))
 			_b := db.Get(ck[:])
+			// If the chunk is the wrong size, assume it's missing as we can't rely on the data.
 			if len(_b) != chunkSize {
-				break
+				return io.EOF
 			}
 			n1 := copy(b, _b[off:])
 			off = 0
diff --git a/storage/file.go b/storage/file.go
index 415ac5df..013351d7 100644
--- a/storage/file.go
+++ b/storage/file.go
@@ -169,10 +169,6 @@ func (fst fileTorrentImplIO) ReadAt(b []byte, off int64) (n int, err error) {
 				continue
 			}
 			err = err1
-			if err == io.EOF {
-				// Lies.
-				err = io.ErrUnexpectedEOF
-			}
 			return
 		}
 		off -= fi.Length
diff --git a/storage/file_test.go b/storage/file_test.go
index 1a5e1b60..daa28acc 100644
--- a/storage/file_test.go
+++ b/storage/file_test.go
@@ -36,5 +36,9 @@ func TestShortFile(t *testing.T) {
 	p := info.Piece(0)
 	n, err := io.Copy(&buf, io.NewSectionReader(ts.Piece(p), 0, p.Length()))
 	assert.EqualValues(t, 1, n)
-	assert.Equal(t, io.ErrUnexpectedEOF, err)
+	switch err {
+	case nil, io.EOF:
+	default:
+		t.Errorf("expected nil or EOF error from truncated piece, got %v", err)
+	}
 }
diff --git a/storage/wrappers.go b/storage/wrappers.go
index 4fc0e10d..da52c89f 100644
--- a/storage/wrappers.go
+++ b/storage/wrappers.go
@@ -69,16 +69,10 @@ func (p Piece) ReadAt(b []byte, off int64) (n int, err error) {
 	if n > len(b) {
 		panic(n)
 	}
-	off += int64(n)
-	if err == io.EOF && off < p.mip.Length() {
-		err = io.ErrUnexpectedEOF
-	}
-	if err == nil && off >= p.mip.Length() {
-		err = io.EOF
-	}
 	if n == 0 && err == nil {
-		err = io.ErrUnexpectedEOF
+		panic("io.Copy will get stuck")
 	}
+	off += int64(n)
 	if off < p.mip.Length() && err != nil {
 		p.MarkNotComplete()
 	}
diff --git a/test/transfer_test.go b/test/transfer_test.go
index 32b9ed15..4fe9d562 100644
--- a/test/transfer_test.go
+++ b/test/transfer_test.go
@@ -93,7 +93,6 @@ func testClientTransfer(t *testing.T, ps testClientTransferParams) {
 		cfg.DownloadRateLimiter = ps.LeecherDownloadRateLimiter
 	}
 	cfg.Seed = false
-	//cfg.Debug = true
 	if ps.ConfigureLeecher.Config != nil {
 		ps.ConfigureLeecher.Config(cfg)
 	}
diff --git a/torrent.go b/torrent.go
index f6627b2f..42f5636e 100644
--- a/torrent.go
+++ b/torrent.go
@@ -1682,7 +1682,9 @@ func (t *Torrent) pieceHasher(index pieceIndex) {
 	p := t.piece(index)
 	sum, copyErr := t.hashPiece(index)
 	correct := sum == *p.hash
-	if !correct {
+	switch copyErr {
+	case nil, io.EOF:
+	default:
 		log.Fmsg("piece %v (%s) hash failure copy error: %v", p, p.hash.HexString(), copyErr).Log(t.logger)
 	}
 	t.storageLock.RUnlock()