dotnet/wpf · error · ArgumentException

SR.Effect_SourceUriMustBeFileOrPack

Error message

SR.Effect_SourceUriMustBeFileOrPack

What it means

PixelShader.UriSource was set to a URI that is neither a file: URI nor a pack: URI, and UriSourcePropertyChangedHook rejected it with ArgumentException(SR.Effect_SourceUriMustBeFileOrPack). The loader only supports reading shader bytecode from the file system or from a WPF pack URI.

Solutions

  1. Copy the shader to a local file (or embed it as a pack Resource/Content) and reference it via file:/pack: URI
  2. Download the remote shader to disk first, then set UriSource to the local path
  3. Use SetStreamSource(Stream) with the byte stream instead of UriSource
  4. Validate the URI scheme before assignment: uri.IsFile || PackUriHelper.IsPackUri(uri)

Example fix

// before
shader.UriSource = new Uri("https://cdn.example.com/shader.ps", UriKind.Absolute); // throws

// after
File.WriteAllText(localPath, downloadedShader); // or ship as pack resource
shader.UriSource = new Uri(localPath, UriKind.Absolute); // file: URI
Defensive patterns

Strategy: validation

Validate before calling

static void ValidateShaderUri(Uri uri)
{
    if (uri == null) throw new ArgumentNullException(nameof(uri));
    bool ok = uri.IsFile || MS.Internal.IO.Packaging.PackUriHelper.IsPackUri(uri);
    if (!ok) throw new ArgumentException("PixelShader.UriSource must be a file or pack URI", nameof(uri));
}

Try / catch

try { shader.UriSource = uri; }
catch (ArgumentException ex) when (ex.Message.Contains("file or pack"))
{
    // copy resource locally or use SetStreamSource instead
}

Prevention

When it happens

Trigger: Assigning pixelShader.UriSource = new Uri("http://...") or any scheme other than file/pack; URIs built from user config with remote or custom schemes.

Common situations: Downloading shaders from a web server and pointing UriSource at the http URL; relative URIs that resolve to unsupported schemes; app settings storing remote shader URLs.

Understand the failure class

Background: "Invalid URL" errors: why new URL(), URI.parse, and reqwest::Url reject your string — missing scheme, whitespace, and bad path format — this error's family across 39 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/1290143ad29a6e3e. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Effects/PixelShader.cs:90

            try {                    
                if (newUri != null)
                {
                    if (!newUri.IsAbsoluteUri)
                    {
                         newUri = BaseUriHelper.GetResolvedUri(BaseUriHelper.BaseUri, newUri);
                    }

                    Debug.Assert(newUri.IsAbsoluteUri);

                    // Now the URI is an absolute URI.

                    //
                    // Only allow file and pack URIs.
                    if (!newUri.IsFile && 
                        !MS.Internal.IO.Packaging.PackUriHelper.IsPackUri(newUri))
                    {
                        throw new ArgumentException(SR.Effect_SourceUriMustBeFileOrPack);
                    }

                    // Security: When loading XPS content, block shader URIs that
                    // escape the current package to prevent SSRF.
                    if (!XpsLoadingContext.IsUriAllowedInCurrentContext(newUri))
                    {
                        throw new FileFormatException(SR.Resource_XpsPackageBoundaryViolation);
                    }

                    stream = WpfWebRequestHelper.CreateRequestAndGetResponseStream(newUri);
                }

                LoadPixelShaderFromStreamIntoMemory(stream);            
            }
            finally
            {
                stream?.Dispose();
            }

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