fix(sglang): validate diffusion input_reference and bound media fetches

[nnshah1]

Overview:

The sglang image-diffusion and video-generation handlers passed the client-supplied input_reference through to the generator's image_path after only a non-empty check. This validates it first and, for remote references, materializes it locally before the generator sees it — so the generator is always handed a trusted local path.

The sibling vLLM/omni and trtllm backends already validate this same field; this brings the sglang diffusion path in line with them.

Behavior note: local I2I/I2V references now require DYN_MM_LOCAL_PATH to be set to the allowed directory (previously any path was accepted).

Rebased onto #14563. That PR consolidated common/http to a single aiohttp backend and has merged. This branch now carries main. Three paths conflicted: httpx_client.py and its test were modify/delete — the edits here were the httpx-side half of the max_bytes plumbing, so the deletion wins and the capability lives on the aiohttp side — and test_http_facade.py conflicted on its import line only. base.py, aiohttp_client.py, __init__.py and url_validator.py auto-merged, including the fetch_bytes signature both PRs rewrote; both sides were confirmed to have survived rather than trusting the merge, and the download cap was re-measured on the merged tree.

Details:

Validation and materialization

• validate_media_reference (common/http/url_validator.py) — like validate_media_url, but returns a plain filesystem path for local references, which is what the generator expects. file:// paths are percent-decoded; a bare path stays literal.
• local_media_reference (common/http/media_reference.py) — an async context manager yielding a trusted local path. Remote references are fetched through fetch_bytes(policy=...), which revalidates every redirect hop, into a temp file removed on exit; local references pass through. data: is rejected: validate_url allows it, but it is a URI, not a path, and would reach the generator as one.
• Both handlers are wired to it through an AsyncExitStack, so the temp file outlives generation and is cleaned afterwards.

Bounds, because this path now handles client input it did not before

• The download is capped (MAX_MEDIA_BYTES, 64 MiB). SGLang's get_image_bytes streams an http(s) image_path through download_remote_media under media_url_max_file_size_mb (default 64, server_args.py:2804); handing it a local path takes the plain open() branch, where that limit never runs. fetch_bytes gained max_bytes and the client streams through collect_capped — a declared Content-Length is caller-controlled and absent when chunked, and aiohttp's read(n) returns at most n bytes, so neither a header check nor a single capped read is sufficient. The cap is operator-tunable via DYN_MM_MAX_FILE_SIZE_MB (megabytes), matching both the SGLang arg it replaces and trtllm's DYN_TRTLLM_MAX_FILE_SIZE_MB; carrying the default across without the knob would have left this path less configurable than what it replaced. Empty, unparseable or non-positive falls back to 64 with a warning — a malformed value must not take the worker down, and non-positive must not read as unlimited.
• collect_capped is handed an explicit read granularity (iter_chunked), which is what keeps the cap an allocation bound rather than only a rejection. Against a 128 MiB-decoded gzip body (130,479 bytes on the wire) with the 64 MiB cap, peak traced allocation is 68,032,217 B — the cap plus roughly one chunk — instead of the whole decompressed body.
• Messages built from caller input are bounded with the repo's existing describe_media_source, which moved from multimodal/media_source.py (it pulls in torch, so common/http could not import it) to url_validator.py and is re-exported from its old home. It is a no-op below 120 characters, so existing messages are unchanged.
• validate_local_path interpolated the raw OSError, whose text repeats the filename, so the label bound only held while the path failed before reaching the filesystem. Under an existing parent the name reaches lstat() and the message carried it in full — 200,234 characters for a 200,000-character name, into the response and the log both. Now exc.strerror (the errno text alone), with bounded str(exc) as the fallback: 183.
• describe_media_source elided a data: payload but returned the media-type field whole, and everything before the comma is that field, so a large metadata field produced a 200,036-character label with the payload already elided. Bounded like any other source: 174.
• The temp-file suffix comes from the reference's path, so only a short alphanumeric extension survives; a long one previously reached mkstemp and raised OSError: File name too long, carrying the server's temp directory back to the caller.
• The configured allowed directory is no longer named in either rejection message.
• HttpStatusError bounds both halves of its message: aiohttp's ClientResponseError text repeats the URL (str(e) is 3,055 characters for a 3,000-character URL and contains it, while .message is the 9-character reason phrase), and the video handler places str(exc) directly in its response body. Re-measured on the consolidated client with a 400-character marker in the URL, across 404 / refused / timeout: marker absent from all three, lengths 159 / 255 / 151.
• The bound is applied to the .message attribute, not only the rendered string: errors.rs::extract_http_like_error reads .status and .message off this class by name — its doc comment names it — and per the SECURITY note there forwards .message verbatim on a 4xx, without calling str(). Same input: str(e) 289 characters but .message 40,010 before, 141 after. This also covers image_loader.py:154,164, which build that message themselves. .url is not part of that protocol and keeps its full value.
• The backend exception text those messages interpolate is bounded head-and-tail rather than head-only: aiohttp renders the host before the errno, so truncating from the front would drop the diagnosis. Growing the hostname through the real client — 241 → 237, 5,355 → 303, 41,056 → 305 at 58 / 5,107 / 40,807 characters, with the errno still present at every size.
• describe_media_source copies its input, so building the label above validate_url's data: early return made that path linear in the payload — 1.351 ms for a 32 MiB inline image, against 0.029 ms now. That path is the mainline for every base64-inline image through validate_media_url, not just diffusion.

Error mapping

• A rejected input_reference raises InvalidArgument explicitly. Correction to an earlier version of this description and to 1d215cd94e's commit message: this changes neither the status nor the text. UrlValidationError is a ValueError, and backend.rs:1694 already maps a bare PyValueError to BackendError::InvalidArgument carrying err.to_string(), which openai.rs:276 turns into a 400. The mapping states the intent at the call site instead of relying on that fallback — which also means those messages already reached callers before this series, on every media path, so the bounding above is what closed the echo, not the mapping. (Read from the Rust at those two line numbers; the binding was not exercised.)
• A 4xx from the chosen origin is also an InvalidArgument, carrying the status but not the URL. image_loader.py:162 already takes that line for an unreachable caller-supplied URL. 5xx and transport failures propagate unchanged.
• An embedded NUL makes Path.resolve() raise ValueError, not OSError, and percent-decoding made %00 reach it. image_loader.py and video_loader.py both key their 4xx-vs-5xx decision on the UrlValidationError type and say so in comments, so validate_local_path now catches it.

Where should the reviewer start?

1. components/src/dynamo/common/http/media_reference.py — the new module; the invariant is "yields a local path, never a URL".
2. components/src/dynamo/common/http/base.py — collect_capped and the max_bytes threading. This changes the _fetch_simple / _fetch_body_or_redirect abstract signatures, so it is the widest-reaching change here. max_bytes defaults to None, leaving every existing caller unchanged.
3. components/src/dynamo/common/http/url_validator.py — validate_media_reference, the ValueError catch, and the bounded messages.
4. The two handlers, then their tests.

Related Issues

🚫 This PR is NOT linked to an issue:

• Confirmed — no related issue

Connect-time address pinning is separate work, tracked in #14474; it is narrower now that the fetch goes through Dynamo's own client, which is what that work governs.

Validation

Python-only change; sglang/torch paths were run in …/dynamo:<sha>-sglang-runtime-test on an AMD64 GPU box, the rest on macOS ARM64.

• 96 passed in common/tests/http/ on the merged tree (up from 67 on main alone); mypy and ruff clean on the changed package. The wider in-container sweep — 403 passed, 4 skipped across common/tests/multimodal/, both diffusion handler test files, sglang/tests/test_sglang_multimodal_utils.py and trtllm/tests/ — was run before the refactor(http): consolidate to a single aiohttp backend; remove httpx #14563 merge and has not been repeated since.
• Redirect handling — a local origin returning a 302 to a blocked address is refused at the hop, before any connection to it; a same-origin 302 still resolves and its temp file is cleaned.
• Download cap — against a real server, 64 MiB with a declared Content-Length and 64 MiB chunked are both refused, with peak RSS flat (72 → 74 MB, against 72 → 214 MB before the cap).
• The cap knob — DYN_MM_MAX_FILE_SIZE_MB=128 makes fetch_bytes receive 134,217,728 where it previously received 67,108,864; unset, invalid, 0 and -5 all resolve to 64 MiB. Verified on an AMD64 GPU box inside the runtime-test image with the PR tree overlaid on PYTHONPATH: 107 passed in common/tests/http/.
• Path confinement — references outside DYN_MM_LOCAL_PATH, and absolute paths, are rejected before the generator is called, on the image and video handlers.
• Bounds — a 200 KB input_reference produced a 200 KB error string reaching both the response and the error log; it is under 500 characters now. Same for the two malformed-URL shapes (200,038 → 167 and 200,025 → 163).
• Percent-decoding — file://<dir>/my%20image.png resolves to my image.png; encoded parent-directory segments are still rejected; %00 is a UrlValidationError again instead of a bare ValueError.
• Every added test was run against the pre-fix tree and fails there. The video-handler tests cover behavior that already existed but was untested, so they pass pre-fix by design — confirmed meaningful by deleting the validation from that handler and watching three of the four fail.

Where verification stops: the sglang handler tests were not re-run locally after the merge — they need torch, which the machine used for this pass does not have. Every symbol they import from dynamo.common was confirmed to still resolve on the merged tree, but the tests themselves are on CI. Separately, the SGLang chain load_image → get_image_bytes → download_remote_media is read from 0.5.18 source, not executed — no diffusion model was loaded. What is executed is the branch decision in get_image_bytes (http(s) → capped stream, file:// or / → plain open), which is what makes the cap this PR restores necessary.

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Walkthrough

The image diffusion handler now validates image-to-image input references before generation. Local paths must comply with the configured path policy. URLs undergo URL validation. Tests cover accepted paths and rejected paths outside the allowed directory.

Changes

Image reference validation

Layer / File(s)	Summary
Input reference validation components/src/dynamo/sglang/request_handlers/image_diffusion/image_diffusion_handler.py	The handler validates local references against the configured local-path policy and validates other references asynchronously as URLs.
Validated generation integration components/src/dynamo/sglang/request_handlers/image_diffusion/image_diffusion_handler.py, components/src/dynamo/sglang/tests/test_sglang_image_diffusion_handler.py	Image generation uses the validated path. Tests cover accepted paths and reject paths outside DYN_MM_LOCAL_PATH without calling the generator.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🟡 Moderate · up to ec5be

Remote image references can still reach internal services through DNS rebinding. Bind validation to the actual fetch before merging this SSRF mitigation.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 2 files.
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.
Title check	✅ Passed	The title clearly and concisely describes the main change: validation of SGLang diffusion input references and bounded media fetching.
Description check	✅ Passed	The description includes the required Overview, Details, reviewer guidance, and Related Issues sections. It explains the validation behavior, security bounds, testing, and verification limits. The no-…

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Inline comments:
In
`@components/src/dynamo/sglang/request_handlers/image_diffusion/image_diffusion_handler.py`:
- Line 202: Update _validate_input_reference and the DiffGenerator input flow so
remote URLs are fetched through a controlled client that validates the connected
peer IP and every redirect, preventing DNS rebinding; store the validated
response in a confined local file and pass that file path as image_path instead
of allowing DiffGenerator to fetch the original hostname. Add regression tests
covering DNS rebinding and unsafe redirects.

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• components/src/dynamo/sglang/request_handlers/image_diffusion/image_diffusion_handler.py
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[dmitry-tokarev-nv]

I took over this PR to drive it to mergable state. Addressed all comments and CI failures.

[rmccorm4]

Four P2 findings reproduced locally on ec106be.

[dmitry-tokarev-nv]

@nnshah1 I took the merge-with-main so it's off your plate after all — you had offered to own it, so say the word if you'd rather redo it your way and I'll stay out. Branch is MERGEABLE again (was CONFLICTING/DIRTY).

I used a merge, not a rebase — it's additive, so nothing here force-pushes over work in progress, and the branch already carried three main merges.

The three conflicts were exactly the ones you called:

• httpx_client.py + test_httpx_client.py — modify/delete. Took the deletion. The edits this branch had there (the max_bytes/collect_capped plumbing, the aiter_bytes chunk size, the stream=True assertion) were httpx-side implementations of a capability that already exists on the aiohttp side.
• test_http_facade.py — content conflict, and it turned out to be the import line only: kept base (this branch's new tests reach into it), dropped HttpxClient.

base.py, aiohttp_client.py, __init__.py and url_validator.py auto-merged — including the fetch_bytes signature you flagged. That's the case worth distrusting, so I checked both directions rather than the merge exit code:

• this branch survived — collect_capped, fetch_bytes(max_bytes=...), and both abstract methods still carry max_bytes; aiohttp_client applies it through collect_capped(response.content.iter_chunked(_READ_CHUNK), url, max_bytes) on the simple path and the redirect-revalidation path.
• refactor(http): consolidate to a single aiohttp backend; remove httpx #14563 survived — the aiohttp-only _create_client (warn and fall back, no httpx branch), _effective_timeout's sock_connect, the trust_env=True session, and the allow_redirects split.

Measured on the merged tree, since a clean textual merge proves neither:

no policy:   3 MiB chunked, no cap        -> OK 3145728 bytes
             3 MiB chunked, cap 1 MiB     -> Media exceeds the 1048576 byte download limit
             8 MiB gzip-bomb, cap 1 MiB   -> same cap trips (still counting decompressed bytes)
             CONTROL 1000 B, cap 1 MiB    -> OK
policy path: 3 MiB chunked, cap 1 MiB     -> same limit error
             CONTROL 1000 B, cap 1 MiB    -> OK

93 tests pass in common/tests/http (67 on main alone). ruff check clean, mypy clean on the http package. The two ruff format diffs are my local ruff 0.15.22 against the repo's pinned v0.5.2 — one of them is pre-existing on main, and pre-commit has passed on this branch with the other line since 6ffa3327.

One thing I changed beyond the mechanical merge: two comments justified the message bounding by citing httpx's HTTPStatusError repeating the URL. That backend is gone, so I reworded them to aiohttp — after measuring that it has the same property: str(ClientResponseError) is 3055 chars for a 3000-char URL and contains it, while .message is just the 9-char reason phrase. The bounding rationale is unchanged, only the backend name was stale.

Not verified locally: the sglang handler tests need torch, which this machine doesn't have. I confirmed every symbol they import from dynamo.common still resolves in the merged tree (local_media_reference, HttpStatusError, UrlValidationError/Policy, describe_error_detail), but the tests themselves are on CI to prove.

[Aphoh]

lgtm

[KrishnanPrash]

Approved to unblock