mediaapi/fileutils: Comment truncation of data when reading

src/github.com/matrix-org/dendrite/mediaapi/fileutils/fileutils.go

@@ -111,6 +111,7 @@ func WriteTempFile(reqReader io.Reader, maxFileSizeBytes types.FileSizeBytes, ab
 	}
 	defer tmpFile.Close()
 
+	// The amount of data read is limited to maxFileSizeBytes. At this point, if there is more data it will be truncated.
 	limitedReader := io.LimitReader(reqReader, int64(maxFileSizeBytes))
 	// Hash the file data. The hash will be returned. The hash is useful as a
 	// method of deduplicating files to save storage, as well as a way to conduct

src/github.com/matrix-org/dendrite/mediaapi/writers/upload.go

@@ -108,6 +108,7 @@ func (r *uploadRequest) doUpload(reqReader io.Reader, cfg *config.MediaAPI, db *
 	// The file data is hashed and the hash is used as the MediaID. The hash is useful as a
 	// method of deduplicating files to save storage, as well as a way to conduct
 	// integrity checks on the file data in the repository.
+	// Data is truncated to maxFileSizeBytes. Content-Length was reported as 0 < Content-Length <= maxFileSizeBytes so this is OK.
 	hash, bytesWritten, tmpDir, err := fileutils.WriteTempFile(reqReader, cfg.MaxFileSizeBytes, cfg.AbsBasePath)
 	if err != nil {
 		r.Logger.WithError(err).WithFields(log.Fields{