arduino/Arduino · error · IOException

Received invalid http status code from server: {resp}

Error message

Received invalid http status code from server: {resp}

What it means

FileDownloader throws this IOException when the HTTP response code of the download request falls outside the 200-299 range. The partial output file is deleted first so no corrupt download remains, then the error names the exact status code received.

Source

Thrown at arduino-core/src/cc/arduino/utils/network/FileDownloader.java:222

    }
    return Optional.empty();
  }

  private void openConnectionAndFillTheFile(boolean noResume) throws Exception {
    initialSize = outputFile.length();
    if (noResume && initialSize > 0) {
      // delete file and restart downloading
      Files.deleteIfExists(outputFile.toPath());
      initialSize = 0;
    }

    final HttpURLConnection connection = new HttpConnectionManager(downloadUrl)
      .makeConnection((c) -> setDownloaded(0));
    final int resp = connection.getResponseCode();

    if (resp < 200 || resp >= 300) {
      Files.deleteIfExists(outputFile.toPath());
      throw new IOException("Received invalid http status code from server: " + resp);
    }

    RandomAccessFile randomAccessOutputFile = null;
    try {
      // Open file and seek to the end of it
      randomAccessOutputFile = new RandomAccessFile(outputFile, "rw");
      randomAccessOutputFile.seek(initialSize);
      readStreamCopyTo(randomAccessOutputFile, connection);
    } finally {
      IOUtils.closeQuietly(randomAccessOutputFile);
    }

  }

  private void readStreamCopyTo(RandomAccessFile randomAccessOutputFile, HttpURLConnection connection) throws Exception {
    InputStream stream = null;
    try {
      // Check for valid content length.

View on GitHub (pinned to a0df6e0e83)

Solutions

1. Verify the download URL is correct and reachable (open it in a browser or curl -I)
2. Check proxy settings in Arduino preferences if behind a corporate proxy
3. Retry after a delay for transient 5xx responses
4. Check authentication/firewall rules if the server returns 403

Example fix

// before: no pre-check
downloader.downloadFile(new URL(url), file, false);
// after: HEAD-check and retry
HttpURLConnection c = (HttpURLConnection) new URL(url).openConnection();
c.setRequestMethod("HEAD");
if (c.getResponseCode() < 200 || c.getResponseCode() >= 300) throw new IOException("URL unavailable: " + c.getResponseCode());
downloader.downloadFile(new URL(url), file, false);

HttpURLConnection c = (HttpURLConnection) url.openConnection();
c.setRequestMethod("HEAD");
if (c.getResponseCode() < 200 || c.getResponseCode() >= 300)
  throw new IllegalStateException("URL not downloadable: " + c.getResponseCode());

try {
  downloader.downloadFile(url, file, false);
} catch (IOException e) {
  if (e.getMessage().contains("Received invalid http status code")) {
    // check proxy settings / retry with backoff
    configureProxy();
    downloader.downloadFile(url, file, false);
  } else throw e;
}

When it happens

Trigger: downloadFile() calls openConnectionAndFillTheFile(), which calls HttpConnectionManager.makeConnection(); connection.getResponseCode() returns < 200 or >= 300 (e.g. 403 Forbidden, 404 Not Found, 500, or a non-handled 3xx).

Common situations: Download URL points to a moved/removed resource (404); server or CDN blocks the client (403); proxy misconfiguration (CustomProxySelector) returning an error page; transient 5xx during heavy load.

Related errors

• Error downloading {0}
• CRC doesn't match, file is corrupted. It may be a temporary
• Unable to fetch PAC file at {pac}. Response code is {respons
• Incomplete download
• Too many redirect {requestURL}

AI-assisted analysis of arduino/Arduino@a0df6e0e83 (2026-09-06). Data as JSON: /api/errors/e42983c32c2b061e. Report an issue: GitHub.