webseed_test.go | 104 +++++++++++++++++++++++++++++++++++++++++++++++++++++

diff --git a/webseed_test.go b/webseed_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..e709f36e7c74030d40449d8ed060a61cd5c6704c
--- /dev/null
+++ b/webseed_test.go
@@ -0,0 +1,104 @@
+package torrent
+
+import (
+	"crypto/rand"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/anacrolix/torrent/internal/testutil"
+)
+
+// Tests that the client can download a multi-file torrent from two webseeds simultaneously when
+// each webseed only has one of the two files (non-overlapping data). The piece bitmaps are
+// restricted to match the files each server has, and webseedRequestChunkSize is set to pieceLen so
+// each piece is its own webseed slice (preventing requests from spanning into the other server's
+// data due to the alignment of getWebseedRequestEnd).
+func TestDownloadFromTwoNonOverlappingWebseeds(t *testing.T) {
+	// Override webseedRequestChunkSize so each piece maps to its own slice, ensuring requests stay
+	// within the pieces each webseed has.
+	const pieceLen = 2 * defaultChunkSize // 32 KiB; two 16 KiB chunks per piece
+	old := webseedRequestChunkSize
+	webseedRequestChunkSize = uint64(pieceLen)
+	defer func() { webseedRequestChunkSize = old }()
+
+	// Two files, each spanning exactly 2 pieces.
+	fileLen := 2 * pieceLen
+	dataA := make([]byte, fileLen)
+	dataB := make([]byte, fileLen)
+	rand.Read(dataA)
+	rand.Read(dataB)
+
+	tu := testutil.Torrent{
+		Name: "testdata",
+		Files: []testutil.File{
+			{Name: "a.bin", Data: string(dataA)},
+			{Name: "b.bin", Data: string(dataB)},
+		},
+	}
+	mi, info := tu.Generate(int64(pieceLen))
+	numPieces := info.NumPieces() // 4
+	mid := numPieces / 2          // 2; pieces 0-1 = a.bin, pieces 2-3 = b.bin
+
+	// Server 1: serves only a.bin; b.bin returns 404 naturally.
+	dir1 := t.TempDir()
+	require.NoError(t, os.MkdirAll(filepath.Join(dir1, "testdata"), 0o755))
+	require.NoError(t, os.WriteFile(filepath.Join(dir1, "testdata", "a.bin"), dataA, 0o644))
+	srv1 := httptest.NewServer(http.FileServer(http.Dir(dir1)))
+	defer srv1.Close()
+
+	// Server 2: serves only b.bin; a.bin returns 404 naturally.
+	dir2 := t.TempDir()
+	require.NoError(t, os.MkdirAll(filepath.Join(dir2, "testdata"), 0o755))
+	require.NoError(t, os.WriteFile(filepath.Join(dir2, "testdata", "b.bin"), dataB, 0o644))
+	srv2 := httptest.NewServer(http.FileServer(http.Dir(dir2)))
+	defer srv2.Close()
+
+	cfg := TestingConfig(t)
+	cl, err := NewClient(cfg)
+	require.NoError(t, err)
+	defer cl.Close()
+
+	// BEP 19 multi-file webseeds use a trailing slash; the file path is appended automatically.
+	tt, _, err := cl.AddTorrentSpec(&TorrentSpec{
+		AddTorrentOpts: AddTorrentOpts{
+			InfoHash:  mi.HashInfoBytes(),
+			InfoBytes: mi.InfoBytes,
+		},
+		Webseeds: []string{srv1.URL + "/", srv2.URL + "/"},
+	})
+	require.NoError(t, err)
+
+	// Restrict each webseed to only the pieces of its file. Remove pieces that the webseed doesn't
+	// have and decrement their availability counts, so the scheduler doesn't assign wrong pieces
+	// (which would cause a conviction when the missing file returns 404).
+	cl.lock()
+	for _, ws := range tt.webSeeds {
+		var removeStart, removeEnd int
+		if strings.HasPrefix(ws.client.Url, srv1.URL) {
+			removeStart, removeEnd = mid, numPieces // keep [0, mid)
+		} else {
+			removeStart, removeEnd = 0, mid // keep [mid, numPieces)
+		}
+		for i := removeStart; i < removeEnd; i++ {
+			ws.client.Pieces.Remove(uint32(i))
+			tt.decPieceAvailability(pieceIndex(i))
+		}
+	}
+	cl.unlock()
+
+	tt.DownloadAll()
+	require.True(t, cl.WaitAll())
+
+	r := tt.NewReader()
+	defer r.Close()
+	got, err := io.ReadAll(r)
+	require.NoError(t, err)
+	require.Equal(t, append(dataA, dataB...), got)
+}