dotnet/wpf · error · InvalidOperationException

SR.RequestAlreadyStarted

Error message

SR.RequestAlreadyStarted

What it means

The ByteRangeDownloader.Proxy property is immutable once the first HTTP request has been made (_firstRequestMade). Setting Proxy afterwards throws InvalidOperationException(SR.RequestAlreadyStarted) because the download pipeline is already configured and running.

Solutions

1. Set Proxy immediately after construction, before any RequestByteRanges call
2. Create a new ByteRangeDownloader instance if the proxy must change
3. Serialize configuration: gather all settings first, then start downloading

Example fix

// before
var d = new ByteRangeDownloader(uri, handle, temp);
d.RequestByteRanges(ranges);
d.Proxy = newProxy; // throws
// after
var d = new ByteRangeDownloader(uri, handle, temp);
d.Proxy = newProxy; // before first request
d.RequestByteRanges(ranges);

if (!proxyConfigured && firstRequestAlreadyMade)
    throw new InvalidOperationException("Set Proxy before starting downloads");
// configure before first RequestByteRanges call

try {
    downloader.Proxy = newProxy;
} catch (InvalidOperationException ex) when (ex.Message.Contains("Request")) {
    downloader = new ByteRangeDownloader(uri, handle, tempFile) { Proxy = newProxy };
}

When it happens

Trigger: Assigning downloader.Proxy after a prior RequestByteRanges call has kicked off the first request.

Common situations: Reconfiguring a downloader mid-download, or reusing a cached downloader instance across requests with different proxy settings.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• Cannot remove signature from read-only file.
• SchemaInvalidForTransport
• SR.ByteRangeDownloaderDisposed
• SR.Image_EndInitWithoutBeginInit
• SR.Image_OnlyOneInit

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/aa1841604d05cac4. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/IO/Packaging/ByteRangeDownloader.cs:302

        #region Internal Properties

        /// <summary>
        /// Proxy for all requests to ByteRangeDownloader
        /// </summary>
        internal IWebProxy Proxy
        {
            set
            {
                CheckDisposed();
                ArgumentNullException.ThrowIfNull(value);

                if (!_firstRequestMade)
                {
                    _proxy = value;
                }
                else    // Once first request is made it cannot change
                {
                    throw new InvalidOperationException(SR.RequestAlreadyStarted);
                }
            }
        }

        /// <summary>
        /// Authentication information for all requests to ByteRangeDownloader
        /// </summary>
        internal ICredentials Credentials
        {
            set
            {
                CheckDisposed();
                _credentials = value;
            }
        }

        /// <summary>
        /// Cache Policy for all requests to ByteRangeDownloader

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