Principle:Helicone Helicone Client Request Interception
| Knowledge Sources | |
|---|---|
| Domains | LLM Observability, Proxy Architecture, Request Handling |
| Last Updated | 2026-02-14 00:00 GMT |
Overview
Client request interception is the technique of transparently capturing incoming HTTP requests at the edge before they reach their intended destination, enriching them with contextual metadata for downstream processing.
Description
In an LLM observability pipeline, client request interception serves as the first stage of the data collection lifecycle. When an application sends a request to an LLM provider (such as OpenAI or Anthropic), the request is routed through an intermediary proxy layer that sits between the client and the provider. This proxy must capture the request without materially altering the client's experience, preserving the original semantics, headers, and body content.
The interceptor is responsible for several critical tasks: parsing the raw HTTP request into a structured internal representation, extracting authentication credentials (both for the LLM provider and for the observability platform itself), identifying custom headers that control logging behavior, and buffering the request body so it can be forwarded to the provider while simultaneously being recorded for analytics.
A well-designed interception layer also handles edge cases such as composite authorization headers (where the provider key and the observability key are combined in a single header), proxy key resolution (where the client sends an abstracted key that must be resolved to a real provider key), and URL-embedded authentication tokens. The goal is to present a clean, validated request wrapper to all subsequent stages of the pipeline.
Usage
Use client request interception when building a transparent proxy that must capture request metadata without requiring changes to the client application. This pattern is essential wherever the proxy must authenticate two separate systems (the observability platform and the upstream provider) from a single inbound request, and where the request body must be available both for forwarding and for later analysis.
Theoretical Basis
The pattern is grounded in the Intercepting Filter design pattern from enterprise architecture. In this pattern, a chain of filters processes an incoming request before it reaches the target resource. Each filter can inspect, modify, or reject the request independently.
The theoretical flow is:
- Accept raw HTTP request from the client.
- Parse and normalize headers, separating observability-specific metadata from provider-specific data.
- Resolve authentication: if the request carries a composite or proxy key, translate it to the actual provider credential.
- Buffer the request body into a replayable form, since the body stream can only be consumed once but must serve both forwarding and logging.
- Construct an enriched request envelope that carries the original request alongside extracted metadata (user ID, prompt settings, feature flags, custom properties).
- Return the enriched envelope or an error indicating authentication failure.
This separation of concerns ensures that downstream stages (routing, forwarding, logging) operate on a clean, validated representation rather than raw HTTP primitives.