lingochamp/FileDownloader · error · FileDownloadGiveUpRetryException

require with contentLength( ), but the backend response…

Error message

require %s with contentLength(%d), but the backend response contentLength is %d on downloadId[%d]-connectionIndex[%d], please ask your backend dev to fix such problem.

What it means

Error "require %s with contentLength(%d), but the backend response contentLength is %d on downloadId[%d]-connectionIndex[%d], please ask your backend dev to fix such problem." thrown in lingochamp/FileDownloader.

Solutions

1. Ask the backend/CDN to return a Content-Length consistent with the requested Range (start-end) so the delivered length matches the requested length
2. Verify the request's Range header and the library-computed startOffset/endOffset are correct (not corrupted by a previous partial download)
3. Check that no intermediary proxy/cache rewrites the response and strips or alters Content-Length/Content-Range
4. As a workaround, download the file with a single connection from offset 0 or disable range-based multi-connection download for this URL

When it happens

Trigger: Thrown at library/src/main/java/com/liulishuo/filedownloader/download/FetchDataTask.java:104 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of lingochamp/FileDownloader@6237a8cac1 (2026-09-08). Data as JSON: /api/errors/25451b92009c7db0. Report an issue: GitHub.

Appendix: source

Thrown at library/src/main/java/com/liulishuo/filedownloader/download/FetchDataTask.java:104

        if (contentLength == TOTAL_VALUE_IN_CHUNKED_RESOURCE) {
            contentLength = FileDownloadUtils.findContentLengthFromContentRange(connection);
        }
        if (contentLength == 0) {
            throw new FileDownloadGiveUpRetryException(FileDownloadUtils.
                    formatString(
                            "there isn't any content need to download on %d-%d with the "
                                    + "content-length is 0",
                            downloadId, connectionIndex));
        }

        if (this.contentLength > 0 && contentLength != this.contentLength) {
            final String range;
            if (endOffset == ConnectionProfile.RANGE_INFINITE) {
                range = FileDownloadUtils.formatString("range[%d-)", currentOffset);
            } else {
                range = FileDownloadUtils.formatString("range[%d-%d)", currentOffset, endOffset);
            }
            throw new FileDownloadGiveUpRetryException(FileDownloadUtils.
                    formatString("require %s with contentLength(%d), but the "
                                    + "backend response contentLength is %d on "
                                    + "downloadId[%d]-connectionIndex[%d], please ask your backend "
                                    + "dev to fix such problem.",
                            range, this.contentLength, contentLength, downloadId, connectionIndex));
        }

        final long fetchBeginOffset = currentOffset;
        // start fetch
        InputStream inputStream = null;
        FileDownloadOutputStream outputStream = null;

        try {
            final boolean isSupportSeek = CustomComponentHolder.getImpl().isSupportSeek();
            if (hostRunnable != null && !isSupportSeek) {
                throw new IllegalAccessException(
                        "can't using multi-download when the output stream can't support seek");
            }

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