Registry-wide hardening of the `mcp-name:` ownership-token match, plus
the cargo follow-up fixes from the #1330 review — consolidated here per
maintainer request. Rebased onto current `main` (the merged #1330 cargo
commit drops out), so the diff is just the net-new work.
### Changes
- **PyPI/NuGet: boundary-anchored token match.** Replace
`strings.Contains(readme, "mcp-name: "+name)` with the shared
`containsMCPNameToken`, so a README declaring a longer name
(`…/widget-pro`) no longer satisfies an ownership claim for a shorter
prefix (`…/widget`). (Cargo already got this in #1330; NPM is unaffected
— it compares an exact metadata field.)
- **Matcher: treat the HTML comment close as a boundary.** `<!--
mcp-name: NAME-->` / `<!--mcp-name: NAME-->` (any spacing) validate
again — the documented hidden-comment form for PyPI/NuGet — while a
genuine longer name (`…/widget--pro`) still does not.
- **Cargo hardening (review of #1330):** pin scheme+port (not just host)
on the README fetch and redirects; a rate-limited/failed crate-version
existence probe now reports *transient* instead of "not found"; a 403
with the crate present no longer flatly asserts "no README".
- **Docs:** note the token must be followed by a boundary.
### ⚠️ Behavior change for PyPI/NuGet — read before merging
The match is **strictly stricter** (verified by fuzz, 2.3M execs: it can
only flip pass→fail, never fail→pass). After the comment-close fix, the
**only** forms that newly fail are unusual *inline* ones: the token
ending a sentence (`…/my-mcp.`) or glued to a trailing `/`. The
documented forms (own line, in `<!-- … -->`) are unaffected.
**Correcting an earlier claim:** this re-validates on **edits too**, not
just new versions — `edit.go → UpdateServer → ValidateUpdateRequest →
validateRegistryOwnership` runs the token check on any edit of a live
server (only delete-transitions skip it). So an existing PyPI/NuGet
server whose README uses one of the breaking inline forms would fail on
its next publish *or* edit. Given the v0.1 API-freeze posture, this
should land as a deliberate, noted change.
### Testing
`go build`, `vet`, `gofmt`, `golangci-lint` (prod files),
`check-schema`, `validate-examples` all clean. Hermetic + **live**
PyPI/NuGet/cargo suite passes. New: `TestCargoURLAllowed`, a
combined-fixture probe-429→transient case, comment-form matcher cases,
and `FuzzContainsMCPNameToken` (the strictly-stricter property, 2.3M
execs).
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Follow-up to #1207, addressing items from the cargo validator review.
**Scoped to cargo + shared helpers — no behavior change for existing
npm/pypi/nuget/oci/mcpb publishers.** Safe to merge and promote.
### Changes
**SSRF hardening of the two-call README retrieval**
- Pin the step-2 README URL to an allowed host (`static.crates.io` in
prod; the base host under test) *before* fetching, so a metadata
response can't steer the validator at an internal/attacker host.
- `CheckRedirect` policy pins every redirect hop to the same allowlist
(the initial URL being pinned isn't enough if an upstream 3xx is
followed).
- Cap the README body with `io.LimitReader` (5 MiB).
> Not publisher-exploitable today (the URL comes from crates.io), so
this is defense-in-depth — but it makes the "host is pinned" guarantee
hold in code rather than rely on crates.io's behavior.
**Clearer status handling** (previously any non-5xx/non-200 collapsed to
"not found")
- **429** → reported as transient/retryable, at both the metadata and
README steps.
- **403** → disambiguated via the crate-version endpoint:
genuinely-missing stays "not found"; *exists-but-no-README* gets an
actionable "add a README with `mcp-name` and republish" message (mirrors
the NuGet validator). This continues the 5xx-vs-403 diagnostic split
@P4ST4S started in the #1207 review — thanks!
**Shared `containsMCPNameToken` helper**
Boundary-anchored ownership-token match (prevents prefix confusion, e.g.
a README declaring `io.github.acme/widget-pro` satisfying a claim for
`io.github.acme/widget`), used here **by the cargo validator only**.
Adopting it in PyPI/NuGet is a separate follow-up because it's a
behavior change for those already-live registries.
**Tests & docs**
Hermetic positive `ServerNameFormats`; combined fixture gains a
version-existence endpoint + cases for 403-missing vs 403-no-README,
429, and prefix-confusion rejection; new foreign-README-host (SSRF)
test; internal test for the helper. Docs: list `crates.io` in the
registry-requirements list + the `Package` model doc.
### Testing
`go build`, `go vet`, full `./internal/validators/...` suite (incl. live
cargo positive), `make check-schema`, `validate-examples` all pass. No
new `golangci-lint` findings.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
> **Update — 2026-06-01 (commit 1f3be53)**
>
> - **All @P4ST4S review feedback addressed** — positive-path hermetic
mock + live anchor against `rust-faf-mcp v0.3.1`; 5xx routed as
transient; doc comment qualified. See the [close-out
comment](https://github.com/modelcontextprotocol/registry/pull/1207#issuecomment-4589711057)
for the per-item breakdown.
> - **Runtime-model question RESOLVED** — `package-types.mdx` documents
cargo and MCPB as both first-class Rust MCP distribution paths (cargo
for source-distributed, MCPB for prebuilt-binary). The "Open question"
section below was the original draft framing; the doc now ships the
resolution.
> - **Cargo-specific gotcha discovered and documented** — crates.io
strips HTML comments during README rendering, unlike PyPI/NuGet.
`package-types.mdx` now spells this out so cargo authors don't ship
invisible mcp-name tokens (which is exactly what happened to
`rust-faf-mcp v0.3.0`; fixed in v0.3.1).
> - **Stale reference removed in this update** — the "Out of scope" line
mentioning `docs/guides/publishing/publish-cargo.md` pointed at a path
that doesn't exist. The canonical per-type doc is
`docs/modelcontextprotocol-io/package-types.mdx`; the Cargo section has
been added there directly.
> - **Two real-world Rust MCP servers queued for day-one register**:
`rust-faf-mcp v0.3.1` (live, end-to-end validated by the new live test)
and `perfetto-mcp-rs` ([@0xZOne](https://github.com/0xZOne) in #1055).
> - **Tests:** 19/19 cargo tests pass (16 existing + 2 hermetic + 1 live
anchor). `make validate` clean. `golangci-lint` 0 issues.
---
Adds support for `registryType: cargo` so Rust MCP servers published to
crates.io can be registered through the
documented validation flow rather than the MCPB binary-packaging
workaround. Closes#1055.
## Motivation and Context
#1055 noted that crates.io has ~1,800 MCP-related packages with no
direct path into the registry — only the MCPB
binary-packaging workaround. This PR adds first-class support for cargo
as a package registry type: schema +
API surface, validator, integration tests, and a documented example. The
publishing guide
(`docs/guides/publishing/publish-cargo.md`) follows on this branch once
the runtime-model direction in
**Additional context** is settled.
## How Has This Been Tested?
- **`make validate`** — clean. Schema-vs-openapi sync verified; 17/17
examples in `generic-server-json.md`
validate against the schema; `expectedServerJSONCount` bumped 16 → 17 to
match the new Cargo example.
- **`go test ./internal/validators/...`** — passes. 16 cargo validator
sub-cases across 4 test functions, run
against real crates.io (~2.5s wall):
- Input validation rejection paths
- Registry-baseURL rejection (4 variants: different host, trailing
slash, http-not-https, subdomain typo)
- Ownership validation against real crates (`serde`, `tokio`, `rand`) —
all correctly rejected for missing
`mcp-name` token
- Server-name format variations (canonical `io.github.OWNER/REPO`,
multi-hyphen, underscore, numeric suffix)
- **Positive-path test** — gated on `rust-faf-mcp` v0.2.3+ being
published with `mcp-name:
io.github.Wolfe-Jam/rust-faf-mcp` in its README. Reserved as a TODO in
`cargo_test.go`; uncomments to become the
live anchor once that publish lands.
- **Local `make test-unit`** — not run due to a Go toolchain version
quirk on my workstation (project
auto-downloads 1.26.0; my local `go` is 1.25.6, causing compile
mismatch). CI will exercise the full
PostgreSQL-backed suite.
## Breaking Changes
None. This is an additive change — `cargo` joins the supported
`registryType` enum alongside
`npm`/`pypi`/`nuget`/`oci`/`mcpb`. Existing publishes continue to work
unchanged.
## Types of changes
- [x] New feature (non-breaking change which adds functionality)
- [x] Documentation update (new Cargo example in
`generic-server-json.md`)
## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed
## Additional context
### Validator design — two-call retrieval on the documented API
`internal/validators/registries/cargo.go` mirrors the PyPI validator's
README-token approach (substring-match
`mcp-name: <serverName>`), with a two-call retrieval pattern to stay on
the documented public crates.io API:
1. `GET /api/v1/crates/{name}/{version}/readme` returns 200 OK with a
JSON pointer (`{"url":
"https://static.crates.io/readmes/.../...html"}`) — crates.io hands us
the URL rather than emitting a 302.
2. Follow the pointer to the rendered HTML; substring-match for the
token.
The two-call pattern stays on the documented public surface. The CDN URL
layout is observed-stable, but treating
it as the entry point would mean depending on an undocumented path. With
two calls, crates.io controls where
the README lives — if they move it, the metadata endpoint hands us the
new URL.
Missing crates and missing versions surface as **403** from the CDN
(S3's default for missing keys), not 404.
The validator treats any non-200 as "not found" and surfaces the actual
status code in the error message.
### Open question — runtime model
Cargo's runtime model is genuinely different from npm/PyPI/NuGet. `cargo
install` is one-time (binary lands on
PATH at `~/.cargo/bin`), not per-invocation like `npx`, `uvx`, or `dnx`
(the new one in .NET 10 SDK Preview 6+).
The new Cargo example in `generic-server-json.md` annotates this
honestly and omits `runtimeHint`.
If a different framing is preferred — e.g. recommending **MCPB**
(prebuilt binary distribution via GitHub
Releases) as the primary path for Rust MCP servers instead of cargo —
happy to adjust the documentation
accordingly. The schema + validator code in this PR is **additive** and
doesn't force a recommendation either
way; a Rust author who chooses cargo can use it, and one who prefers
MCPB still can.
### Out of scope (deferred)
- **`docs/guides/publishing/publish-cargo.md`** — follows on this branch
once the runtime-model direction above
is settled.
- **Publisher CLI `Cargo.toml` autodetect** in
`cmd/publisher/commands/init.go` — separate concern, separate PR.
- **Positive-path validator test** — gated on `rust-faf-mcp` v0.2.3+
publishing as noted in *How Has This Been
Tested?*.
---------
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Radoslav Dimitrov <radoslav@stacklok.com>
Radoslav Dimitrov
Wolfe-James