Fix races in Reader

diff --git a/reader.go b/reader.go
index f53c62fba2521132d2a882c1bd52ea9a4108129c..35fb8e4f1bc39bae7fabfb19d9f9ac1ba128022c 100644 (file)
--- a/reader.go
+++ b/reader.go
@@ -3,7 +3,6 @@ package torrent
 import (
        "errors"
        "io"
-       "log"
        "os"
        "sync"
 )
@@ -12,8 +11,12 @@ import (
 type Reader struct {
        t          *Torrent
        responsive bool
-       opMu       sync.Mutex
+       // Ensure operations that change the position are exclusive, like Read()
+       // and Seek().
+       opMu sync.Mutex
 
+       // Required when modifying pos and readahead, or reading them without
+       // opMu.
        mu        sync.Mutex
        pos       int64
        readahead int64
@@ -96,7 +99,9 @@ func (r *Reader) Read(b []byte) (n int, err error) {
                }
                b = b[n1:]
                n += n1
+               r.mu.Lock()
                r.pos += int64(n1)
+               r.mu.Unlock()
        }
        if r.pos >= r.t.torrent.length {
                err = io.EOF
@@ -168,6 +173,9 @@ func (r *Reader) posChanged() {
 }
 
 func (r *Reader) Seek(off int64, whence int) (ret int64, err error) {
+       r.opMu.Lock()
+       defer r.opMu.Unlock()
+
        r.mu.Lock()
        switch whence {
        case os.SEEK_SET:
@@ -181,6 +189,7 @@ func (r *Reader) Seek(off int64, whence int) (ret int64, err error) {
        }
        ret = r.pos
        r.mu.Unlock()
+
        r.posChanged()
        return
 }