lingochamp/FileDownloader · error · FileDownloadGiveUpRetryException

fetched length[ ] != content length[ ], range[ , ) offset[…

Error message

fetched length[%d] != content length[%d], range[%d, %d) offset[%d] fetch begin offset[%d]

What it means

FileDownloadGiveUpRetryException thrown by FetchDataTask.run() after a download chunk finishes: the number of bytes actually fetched does not equal the Content-Length advertised by the server (for non-chunked transfers). The library treats this as a server/range inconsistency it cannot recover from, so it aborts rather than retrying.

Solutions

Retry the download; if it fails on the same file repeatedly, the server is serving inconsistent Content-Length — verify with curl -r or wget against the URL
Check for and bypass intermediary proxies/CDN/compression middleware that may alter the body or Range handling
Ensure the server supports HTTP Range requests correctly (responds 206 with exact requested byte range)
Update the filedownloader library version; some edge cases around range/offset bookkeeping were fixed over time
If it only happens on flaky networks, pre-check connectivity and re-issue the download; this exception intentionally disables retry for this attempt

Example fix

// before: single attempt fails hard on flaky network
FileDownloader.getImpl().create(url).setPath(path).start();
// after: catch and re-attempt via listener
FileDownloader.getImpl().create(url).setPath(path)
    .setListener(new FileDownloadListener() {
        @Override public void warn(FileDownloadBase base, FileDownloadSoFar sofar) {}
        @Override public void started(...) {}
        // on error, check if bytes fetched mismatch and re-create the task
    }).start();

Defensive patterns

Strategy: retry

Validate before calling

// before starting the download, probe the server's range support
HttpURLConnection c = (HttpURLConnection) new URL(url).openConnection();
c.setRequestProperty("Range", "bytes=0-");
if (c.getResponseCode() != 206) {
    throw new IllegalStateException("Server does not honor Range; partial download will fail");
}
long declared = c.getContentLength();
if (declared <= 0) {
    throw new IllegalStateException("Server reports no usable Content-Length for range request");
}

Try / catch

try {
    task.start();
} catch (FileDownloadGiveUpRetryException e) {
    // fetched bytes != content-length: server inconsistency
    log.warn("Body length mismatch, re-issuing download", e);
    FileDownloader.getImpl().create(url).setPath(path)
        .setListener(listener).start(); // fresh attempt re-syncs offsets
}

Prevention

Verify the URL returns stable Content-Length and correct 206 responses for Range requests (curl -r 0-99 -I)
Bypass proxies/CDN/gzip middleware that can alter body size between HEAD and GET
Set a path consistent with prior downloads so offsets stay in sync, or clear stale temp files after version changes
Keep the filedownloader library up to date; range bookkeeping bugs were fixed in later versions

When it happens

Trigger: The server's response body length differs from the declared Content-Length for the requested Range [startOffset, endOffset); e.g. server truncates the body, closes the connection early, misreports Content-Length, or returns fewer bytes than promised for a resumed range request.

Common situations: Flaky proxies or CDNs cutting connections mid-body; misconfigured servers behind load balancers that strip/alter Range headers; servers that ignore Range and return a different body than expected; unstable mobile networks that end the stream without an error; buggy server-side compression middleware changing body size.

Understand the failure class

Background: 'Something went wrong' / 'Request failed (500)' / 'HTTP error! status: 404' — what failed HTTP requests actually mean and how to find the real cause — this error's family across 28 libraries.

Related errors

AI-assisted analysis of lingochamp/FileDownloader@6237a8cac1 (2026-09-08). Data as JSON: /api/errors/9e9868dc1e1ae065. Report an issue: GitHub.

Appendix: source

Thrown at library/src/main/java/com/liulishuo/filedownloader/download/FetchDataTask.java:190

            }

            try {
                if (outputStream != null) sync();
            } finally {
                if (outputStream != null) {
                    try {
                        outputStream.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }

        }

        final long fetchedLength = currentOffset - fetchBeginOffset;
        if (contentLength != TOTAL_VALUE_IN_CHUNKED_RESOURCE && contentLength != fetchedLength) {
            throw new FileDownloadGiveUpRetryException(
                    FileDownloadUtils.formatString("fetched length[%d] != content length[%d],"
                                    + " range[%d, %d) offset[%d] fetch begin offset[%d]",
                            fetchedLength, contentLength,
                            startOffset, endOffset, currentOffset, fetchBeginOffset));
        }

        // callback completed
        callback.onCompleted(hostRunnable, startOffset, endOffset);
    }

    private final FileDownloadDatabase database;
    private volatile long lastSyncBytes = 0;
    private volatile long lastSyncTimestamp = 0;

    private void checkAndSync() {
        final long now = SystemClock.elapsedRealtime();
        final long bytesDelta = currentOffset - lastSyncBytes;
        final long timestampDelta = now - lastSyncTimestamp;

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