fix(matrix): stream inbound media downloads to disk (#1436)

pkg/channels/matrix/matrix.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"html"
+	"io"
 	"mime"
 	"net/url"
 	"os"
@@ -726,17 +727,23 @@ func (c *MatrixChannel) downloadMedia(
 	reqCtx, cancel := context.WithTimeout(dlCtx, 20*time.Second)
 	defer cancel()
 
-	data, err := c.client.DownloadBytes(reqCtx, parsed)
+	resp, err := c.client.Download(reqCtx, parsed)
 	if err != nil {
 		return "", err
 	}
+	defer resp.Body.Close()
+
+	reader := resp.Body
+	readerClose := func() error { return nil }
 
 	// Encrypted attachments put URL in msgEvt.File and require client-side decryption.
 	if msgEvt != nil && msgEvt.File != nil && msgEvt.URL == "" {
-		err = msgEvt.File.DecryptInPlace(data)
+		if err = msgEvt.File.PrepareForDecryption(); err != nil {
-		if err != nil {
 			return "", fmt.Errorf("decrypt matrix media: %w", err)
 		}
+		decryptReader := msgEvt.File.DecryptStream(resp.Body)
+		reader = decryptReader
+		readerClose = decryptReader.Close
 	}
 
 	label := matrixMediaLabel(msgEvt, mediaKind)
@@ -749,14 +756,28 @@ func (c *MatrixChannel) downloadMedia(
 	if err != nil {
 		return "", err
 	}
-	defer tmp.Close()
+	tmpPath := tmp.Name()
+	cleanup := true
+	defer func() {
+		_ = tmp.Close()
+		if cleanup {
+			_ = os.Remove(tmpPath)
+		}
+	}()
 
-	if _, err = tmp.Write(data); err != nil {
+	_, err = io.Copy(tmp, reader)
-		_ = os.Remove(tmp.Name())
+	if err != nil {
+		return "", err
+	}
+	if err = readerClose(); err != nil {
+		return "", fmt.Errorf("decrypt matrix media: %w", err)
+	}
+	if err = tmp.Close(); err != nil {
 		return "", err
 	}
 
-	return tmp.Name(), nil
+	cleanup = false
+	return tmpPath, nil
 }
 
 func matrixContentType(msgEvt *event.MessageEventContent) string {

pkg/channels/matrix/matrix_test.go

@@ -2,6 +2,8 @@ package matrix
 
 import (
 	"context"
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"path/filepath"
 	"strings"
@@ -197,6 +199,50 @@ func TestMatrixMediaExt(t *testing.T) {
 	}
 }
 
+func TestDownloadMedia_WritesResponseToTempFile(t *testing.T) {
+	const wantBody = "matrix-media-payload"
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !strings.HasSuffix(r.URL.Path, "/_matrix/client/v1/media/download/matrix.test/abc123") {
+			t.Fatalf("unexpected download path: %s", r.URL.Path)
+		}
+		w.Header().Set("Content-Type", "image/png")
+		_, _ = w.Write([]byte(wantBody))
+	}))
+	defer server.Close()
+
+	client, err := mautrix.NewClient(server.URL, id.UserID("@picoclaw:matrix.test"), "")
+	if err != nil {
+		t.Fatalf("NewClient: %v", err)
+	}
+
+	ch := &MatrixChannel{client: client}
+	msg := &event.MessageEventContent{
+		MsgType: event.MsgImage,
+		Body:    "image.png",
+		URL:     id.ContentURIString("mxc://matrix.test/abc123"),
+		Info:    &event.FileInfo{MimeType: "image/png"},
+	}
+
+	path, err := ch.downloadMedia(context.Background(), msg, "image")
+	if err != nil {
+		t.Fatalf("downloadMedia: %v", err)
+	}
+	defer os.Remove(path)
+
+	if ext := filepath.Ext(path); ext != ".png" {
+		t.Fatalf("temp file extension=%q want=.png", ext)
+	}
+
+	got, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("ReadFile: %v", err)
+	}
+	if string(got) != wantBody {
+		t.Fatalf("file contents=%q want=%q", string(got), wantBody)
+	}
+}
+
 func TestExtractInboundContent_ImageNoURLFallback(t *testing.T) {
 	ch := &MatrixChannel{}
 	msg := &event.MessageEventContent{