Implementation Guide
Handling large file uploads and multimodal payloads through an AI governance proxy
Treat large and multimodal payloads as their own runtime governance problem.
Follow the payload lifecycle and name the failure mode at each stage
Designing around the payload lifecycle makes enforcement points explicit. Each stage has a control to define and a failure to plan for.
- IngestionSize, format, and transfer-mode checks
- InspectionSensitive data, malware, and injection screening
- Policy decisionAllow, redact, quarantine, or block
- RoutingModel or agent tool receives approved content
- Audit recordHashes, metadata, and decisions retained
| Stage | Control to define | Failure mode |
|---|---|---|
| 1. Ingestion | Enforce maximum size, allowed file types, and accepted transfer modes. Validate the file type from content, not only from the extension or declared header. | Oversized or mislabeled files consume proxy resources or bypass later checks. |
| 2. Inspection | Run sensitive data detection, malware scanning, and injection screening appropriate to each modality, including extraction from embedded or encoded content. | A file type the inspectors cannot parse passes through unexamined. |
| 3. Policy decision | Map inspection results and user, application, or agent identity to allow, redact, quarantine, or block. | Inspection times out and the default behavior is undefined. |
| 4. Model or tool routing | Deliver only the approved or redacted content to the destination, and check that the destination is permitted for that data class. | The original file is forwarded alongside the sanitized version. |
| 5. Audit record | Record what was received, what was decided, and why. | Records either lack detail for investigation or retain excessive sensitive content. |
Define enforcement points, size controls, and fail behavior
Place enforcement where it cannot be bypassed
Place policy enforcement where it cannot be bypassed. If the proxy only governs the model API call while users or agents can attach files through a separate path, the control is incomplete. For reference-based patterns, the key rule is that a reference becomes usable by a model or tool only after the associated inspection result permits it. An asynchronous scan that does not gate use is monitoring, not enforcement, and should be labeled that way in architecture documents.
Set size and format controls at more than one layer
Set size and format controls at more than one layer: at the edge or gateway, at the proxy, and per route. Use an allowlist of file types rather than a blocklist, and validate content against the declared type. Limit recursion depth and expansion for archives and nested documents, since these are common ways to hide content from inspectors. Align timeouts with the inspection mode, so a slow scan produces a defined outcome rather than a dropped connection.
Decide the fail behavior for each route in advance
Decide the fail behavior for each route in advance. When inspection is incomplete, times out, or is unsupported for a file type, the options are fail-open, fail-closed, or quarantine for review. High-risk routes and agent tool inputs usually justify fail-closed or quarantine. Lower-risk internal uses may accept a different choice, but it should be a documented decision by risk owners, not a default left over from configuration.
Questions to assess whether a proxy or gateway can support these patterns
- Which inspection modes are supported for large payloads, and can they be set per route or per policy?
- What are the documented maximum request and file sizes, and how are chunked transfers and timeouts handled?
- Which modalities and file formats can be inspected for sensitive data, malware, and prompt injection, including embedded or encoded content?
- What happens when inspection is incomplete, times out, or is unsupported: fail-open, fail-closed, or quarantine?
- Does the audit record include hashes, metadata, policy decisions, and redaction actions, and can raw content be excluded from retention?
- Can the proxy bind inspection results to references or pre-signed uploads so unapproved content cannot reach a model or tool?
Review your multimodal governance architecture
Talk to Trussed AI about applying runtime policy enforcement and audit logging to AI traffic that includes large files and mixed-modality requests.
Talk to an Expert