Return errors from Reader if data downloading won't occur

Chunk write errors to storage can disable data download. Previously Readers would wait indefinitely for the data to become available. This change returns an error instead of stalling.

reader.go

@@ -199,6 +199,10 @@ func (r *reader) waitAvailable(pos, wanted int64, ctxErr *error, wait bool) (ava
 			err = *ctxErr
 			return
 		}
+		if r.t.dataDownloadDisallowed || !r.t.networkingEnabled {
+			err = errors.New("downloading disabled and data not already available")
+			return
+		}
 		if !wait {
 			return
 		}

test/issue377_test.go

@@ -2,6 +2,8 @@ package test
 
 import (
 	"errors"
+	"io"
+	"io/ioutil"
 	"os"
 	"sync"
 	"testing"
@@ -73,7 +75,27 @@ func testReceiveChunkStorageFailure(t *testing.T, seederFast bool) {
 	// Tell the seeder to find the leecher. Is it guaranteed seeders will always try to do this?
 	seederTorrent.AddClientPeer(leecherClient)
 	<-leecherTorrent.GotInfo()
-	assertReadAllGreeting(t, leecherTorrent.NewReader())
+	r := leecherTorrent.Files()[0].NewReader()
+	defer r.Close()
+	// We can't use assertReadAllGreeting here, because the default storage write error handler
+	// disables data downloads, which now causes Readers to error when they're blocked.
+	if false {
+		assertReadAllGreeting(t, leecherTorrent.NewReader())
+	} else {
+		for func() bool {
+			// We don't seem to need to seek, but that's probably just because the storage failure is
+			// happening on the first read.
+			r.Seek(0, io.SeekStart)
+			output, err := ioutil.ReadAll(r)
+			if err != nil {
+				t.Logf("got error while reading: %v", err)
+				return true
+			}
+			assert.EqualValues(t, testutil.GreetingFileContents, output)
+			return false
+		}() {
+		}
+	}
 	// TODO: Check that PeerConns fastEnabled matches seederFast?
 	//select {}
 }

torrent.go

@@ -2024,6 +2024,7 @@ func (t *Torrent) onWriteChunkErr(err error) {
 		go t.userOnWriteChunkErr(err)
 		return
 	}
+	t.logger.WithDefaultLevel(log.Critical).Printf("default chunk write error handler: disabling data download")
 	t.disallowDataDownloadLocked()
 }
 
@@ -2038,12 +2039,14 @@ func (t *Torrent) disallowDataDownloadLocked() {
 	t.iterPeers(func(c *peer) {
 		c.updateRequests()
 	})
+	t.tickleReaders()
 }
 
 func (t *Torrent) AllowDataDownload() {
 	t.cl.lock()
 	defer t.cl.unlock()
 	t.dataDownloadDisallowed = false
+	t.tickleReaders()
 	t.iterPeers(func(c *peer) {
 		c.updateRequests()
 	})