feat(server): add transparent HTTP proxy routing

[Pouyanpi]

Description

Phase A establishes the private provider-neutral foundations for transparent provider proxying. This PR binds buffered guarded operations to a private FastAPI HTTP surface while keeping outbound dispatch and provider behavior injected.

It adds:

• guarded routes registered before a transparent catch-all;
• fail-closed handling for wrong methods, trailing slashes, and repeated slashes so guarded operations cannot enter unguarded forwarding;
• prefix-safe guarded and reserved-path classification when the router is mounted below an application path;
• rejection of overlapping guarded declarations for the same method;
• GuardedOperationPath ownership for guarded path variants;
• protection for application-owned routes from the proxy catch-all;
• buffered preservation of request method, path, raw path, query, headers, and body;
• buffered preservation of response status, headers, and body;
• declared and observed request limits plus bounded provider responses, with defaults of 1 MiB and 10 MiB;
• malformed, negative, and repeated Content-Length rejection before body consumption;
• canonical percent-encoded path fallback when ASGI does not provide raw_path;
• injected outbound dispatch and semantic outcome-rendering seams;
• typed outbound dispatch failures without reclassifying programming errors.

Stable and temporary parts

Route precedence, guarded-path ownership, bypass resistance, buffered HTTP preservation, and body-limit behavior are intended to remain.

Several composition seams are deliberately narrower than their final owners:

• HttpDispatch is only an injected callable here; application-owned transport later supplies URL construction, outbound header policy, connection pooling, streaming, cancellation, response closure, and client lifecycle;
• OutcomeRenderer is only an injection seam here; provider integration later supplies one provider-owned mapping shared by runtime responses and OpenAPI documentation;
• create_http_proxy_router() temporarily combines guarded routes and catch-all ownership to prove precedence in isolation; application composition later separates reusable guarded-route registration from catch-all ownership;
• application-owned routes must be registered before this temporary catch-all; the later application composition layer owns and enforces that ordering;
• catch-all forwarding is buffered in this PR; provider pass-through later streams request and response bodies while guarded operations remain bounded.

Review focus

• Can any guarded path variant bypass checking through the catch-all?
• Are application-owned routes kept outside proxy ownership?
• Is transparent HTTP fidelity preserved within the buffered model?
• Do body limits, malformed lengths, encoded paths, and typed dispatch failures fail closed without hiding programming errors?
• Are the temporary dispatch, rendering, and combined-router seams explicit enough not to be mistaken for final application ownership?

Non-goals

• upstream URL resolution, outbound header filtering, connection pooling, or client lifecycle;
• provider payload models or contracts;
• streaming;
• Rails configuration resolution;
• safe replacement;
• a public provider-extension API.

Phase A stack

Review every PR against its parent branch rather than against develop, except for PR 1.

Order	PR	Branch	Base
1	#2404	pouyanpi/transparent-proxy-kernel-1	develop
2	#2405	pouyanpi/transparent-proxy-buffered-kernel-2	pouyanpi/transparent-proxy-kernel-1
3	#2406	pouyanpi/transparent-proxy-http-kernel-3	pouyanpi/transparent-proxy-buffered-kernel-2
4	#2407	pouyanpi/transparent-proxy-projection-outcomes-4	pouyanpi/transparent-proxy-http-kernel-3

AI Assistance

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• AI tools were used; a human reviewed and can explain every change.

Checklist

• I've read the CONTRIBUTING guidelines.
• This is maintainer-led work tracked internally.
• The PR title follows the project commit convention.
• Public documentation is not applicable to this private HTTP-routing change.
• Tests cover the introduced behavior.
• Verification and checks not run are documented.
• Generated changelog files were not edited manually.
• All automated and human review comments are addressed or answered.
• The responsible reviewer or team is mentioned.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[greptile-apps]

Confidence Score: 4/5

[Medium risk] Adds HTTP proxy routing for guarded operations.

The PR does not appear safe to merge until disjoint typed routes can be registered and the new overlap tests pass.

Findings

1.  Disjoint routes rejected ▶

Fix with agent prompt

### Issue 1
nemoguardrails/server/experimental/_http_kernel.py:223
When same-method operations use `/v1/{key:int}` and `/v1/{identifier:uuid}`, this comparison treats them as overlapping even though their accepted path strings are disjoint. Router creation then raises `ValueError` instead of registering both operations. The new test cases at `tests/server/experimental/test_http_kernel.py:484-485` also use an unhyphenated UUID witness, so their match assertion fails before route registration is tested.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Summary

The PR adds private FastAPI routes for buffered guarded operations and transparent provider forwarding, with path-ownership checks, body limits, response framing, and routing tests.

• Changes since the previous review replace sampled-path overlap detection with converter and route-boundary comparisons.
• That comparison rejects disjoint typed routes, and two new overlap tests use invalid UUID witnesses.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[HTTP request] --> B{Guarded route match?}
  B -->|Yes| C[Buffer and check input]
  C --> D[Injected dispatch]
  D --> E[Check output and render]
  B -->|No| F{Guarded or reserved path variant?}
  F -->|Yes| G[Render route rejection]
  F -->|No| H[Buffer and forward]

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_{Reviews (8) · Last reviewed commit: "fix(server): conservatively reject guard..." · Reviewed by Greptile}

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📝 Walkthrough

Walkthrough

The change adds an experimental HTTP proxy router. It content-checks guarded provider routes and forwards other provider paths without content checks. The router buffers request and response bodies, enforces configured size limits, and renders typed failures.

Changes

Experimental HTTP proxy

Layer / File(s)	Summary
Checker support and HTTP route contracts nemoguardrails/server/experimental/_buffered_kernel.py, nemoguardrails/server/experimental/_http_kernel.py, tests/server/experimental/test_import_boundaries.py	The buffered operation executor accepts raw or resolved checkers. The HTTP module adds operation and failure types, validates route definitions, and registers guarded routes and a catch-all. Tests cover route ownership, method handling, route validation, and independent module importability.
Buffered request and response handling nemoguardrails/server/experimental/_http_kernel.py, tests/server/experimental/test_http_kernel.py	The router buffers request and response data, checks guarded operations, and forwards unmatched provider paths without content checks. It enforces body limits and renders request, response, and dispatch failures. Tests cover checking outcomes, forwarding, body limits, malformed content lengths, dispatch errors, and Unicode paths.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant HttpProxyRouter
  participant ContentChecker
  participant ProviderDispatch
  participant OutcomeRenderer
  Client->>HttpProxyRouter: Send request
  alt Guarded route
    HttpProxyRouter->>ContentChecker: Check request content
    ContentChecker-->>HttpProxyRouter: Return check outcome
    HttpProxyRouter->>ProviderDispatch: Dispatch permitted request
    ProviderDispatch-->>HttpProxyRouter: Return buffered response
    HttpProxyRouter->>ContentChecker: Check response content
    ContentChecker-->>HttpProxyRouter: Return check outcome
  else Other provider path
    HttpProxyRouter->>ProviderDispatch: Forward request without content checks
    ProviderDispatch-->>HttpProxyRouter: Return buffered response
  end
  HttpProxyRouter->>OutcomeRenderer: Render response or failure outcome
  OutcomeRenderer-->>Client: Return rendered HTTP response

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Merge Risk: 🟡 Moderate · up to 7a731

When the proxy router is installed under a URL prefix, some requests for guarded operations can be forwarded without inspection. Fix path classification before merging that configuration.

🚥 Pre-merge checks | ✅ 5 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 58.18% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 55 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Test Results For Major Changes	✅ Passed	The PR is a major feature change, and its description documents testing results: 65 experimental tests passed, plus 362 server tests passed with 10 skipped. The diff also adds focused HTTP proxy cover…
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding transparent HTTP proxy routing in the server.

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Actionable comments posted: 1

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Inline comments:
In `@nemoguardrails/server/experimental/_http_kernel.py`:
- Around line 339-364: Normalize the catch-all route’s `path` parameter instead
of `request.url.path` when classifying requests against `guarded_matchers` and
`reserved_matchers`; this excludes the router prefix while preserving slash
normalization and trailing-slash handling.

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📥 Commits

Reviewing files that changed from the base of the PR and between f4902d0 and 7a731d7.

📒 Files selected for processing (4)

• nemoguardrails/server/experimental/_buffered_kernel.py
• nemoguardrails/server/experimental/_http_kernel.py
• tests/server/experimental/test_http_kernel.py
• tests/server/experimental/test_import_boundaries.py

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[tgasser-nv]

Looks good, there are a few issues in the PR that need addressing:

1. Can you add tests to get the line coverage up to 100%?
2. Could you use the OutcomeRenderer in the catch-all Rejections rather than direct HTTP error/code

[Pouyanpi]

Thanks @tgasser-nv, addressed these:

• fixed path classification and forwarding mismatches, with regression tests.
• validated request framing and rebuilt buffered response framing.
• added reserved route validation while keeping valid application routes supported.
• routed catch-all rejections through the renderer, with native openai mapping in feat(server): integrate OpenAI Chat buffered proxy #2414.
• added tests for the missing cases; local http kernel line coverage is now 100%.

outbound header filtering and fixed upstream origins are handled by the later transport. the path/framing fixes are boundary hardening; we haven't demonstrated an end-to-end bypass, ssrf, or request smuggling through the intended deployment.

[tgasser-nv]

Looks good, thanks for making the updates!

There are a couple of nits on the path parsing I missed originally before merging:

• /v1/models/../generate is checked as models.generate and runs /v1/generate
• /v1%252Fgenerate passes the catch-all as an unguarded path, but the upstream will run /v1/generate without a check.

[Pouyanpi]

@tgasser-nv, thanks for catching those cases. It's addressed now 👍🏻