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fix(cargo): harden README fetch, clarify status handling, strengthen tests (#1330)

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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>
This commit is contained in:
Radoslav Dimitrov 2026-06-04 17:34:54 -04:00 • committed by GitHub
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7
pkg/model/types.go
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@ -22,12 +22,13 @@ type Transport struct {
// - NPM: RegistryType, Identifier (package name), Version, RegistryBaseURL (optional)
// - PyPI: RegistryType, Identifier (package name), Version, RegistryBaseURL (optional)
// - NuGet: RegistryType, Identifier (package ID), Version, RegistryBaseURL (optional)
// - Cargo: RegistryType, Identifier (crate name), Version, RegistryBaseURL (optional)
// - OCI: RegistryType, Identifier (full image reference like "ghcr.io/owner/repo:tag")
// - MCPB: RegistryType, Identifier (download URL), Version (optional), FileSHA256 (required)
type Package struct {
// RegistryType indicates how to download packages (e.g., "npm", "pypi", "oci", "nuget", "mcpb")
RegistryType string `json:"registryType" minLength:"1" doc:"Registry type indicating how to download packages (e.g., 'npm', 'pypi', 'oci', 'nuget', 'mcpb')" example:"npm"`
// RegistryBaseURL is the base URL of the package registry (used by npm, pypi, nuget; not used by oci, mcpb)
// RegistryType indicates how to download packages (e.g., "npm", "pypi", "cargo", "oci", "nuget", "mcpb")
RegistryType string `json:"registryType" minLength:"1" doc:"Registry type indicating how to download packages (e.g., 'npm', 'pypi', 'cargo', 'oci', 'nuget', 'mcpb')" example:"npm"`
// RegistryBaseURL is the base URL of the package registry (used by npm, pypi, nuget, cargo; not used by oci, mcpb)
RegistryBaseURL string `json:"registryBaseUrl,omitempty" format:"uri" doc:"Base URL of the package registry" example:"https://registry.npmjs.org"`
// Identifier is the package identifier:
// - For NPM/PyPI/NuGet: package name or ID