Name: mime-detection-routing
Author: xberg-io

Imported from xberg-io/xberg (.ai-rulez/skills/mime-detection-routing/SKILL.md). Install upstream with npx skills add xberg-io/xberg --skill mime-detection-routing. Copyright stays with the author.

MIME Detection & Routing

Detection Flow

Policy -> content and/or extension evidence -> validate_mime_type -> registry.get(mime) -> extractor

Key Functions

Function	Location	Behaviour
`detect_mime_type(path, check_exists: bool)`	`core/mime.rs`	Path-based only — never reads bytes. Lowercased extension → `EXT_TO_MIME`, then tree-sitter extension detection (feature `tree-sitter`), then `mime_guess::from_path`. `check_exists` gates a file-existence check, not content inspection.
`detect_mime_type_from_bytes(bytes)`	`core/mime.rs`	Magic-number detection via the `infer` crate. The only content-sniffing entry point.
`validate_mime_type(mime)`	`core/mime.rs`	Parses the media type, matches its case-insensitive essence against `SUPPORTED_MIME_TYPES`, and returns the registered MIME spelling. Parameters such as `charset` do not affect extractor routing. It does not consult the extractor registry.

The FORMATS registry is the single source of truth

FORMATS: &[FormatEntry { extensions, mime_type, aliases }] in core/mime.rs. EXT_TO_MIME and SUPPORTED_MIME_TYPES are LazyLocks derived from it by iteration — there is no m.insert call site to add to, and hand-editing either is impossible.

The full registry publishes 106 formats, 140 unique extensions, and 53 aliases, verified by scripts/sync_supported_counts.py verify. The published count constants describe that static registry; runtime availability is its intersection with registered extractors. Extension lookup is case-insensitive (the extension is lowercased before the map hit).

Registry Selection

let registry = get_document_extractor_registry();          // plugins/registry/mod.rs
let guard = registry.read()?;
let extractor: Arc<dyn DocumentExtractor> = guard.get(mime_type)?;  // Result, not Option

DocumentExtractorRegistry::get (plugins/registry/extractor.rs) returns the highest-priority() extractor for the MIME type, and returns Err — not None — when none matches.

Wildcard Support

An extractor may register a family: "image/*" matches image/png, image/jpeg, and so on (prefix match on a registered type ending in /*).

Adding a New Format

Add one FormatEntry to FORMATS in crates/xberg/src/core/mime.rs. EXT_TO_MIME and SUPPORTED_MIME_TYPES update automatically.
Run scripts/sync_supported_counts.py sync to update published count claims, then run its verify command.
Implement InternalDocumentExtractor (not DocumentExtractor — see plugin-architecture-patterns) with supported_mime_types() returning the MIME.
Register in crates/xberg/src/extractors/mod.rs::register_default_extractors().

Critical Rules

Call validate_mime_type() before extraction — but do not treat it as proof an extractor exists.
Extension lookup is case-insensitive.
detect_mime_type inspects no content. Extraction defaults to PreferContent, which performs bounded content inspection and falls back to a supported extension. Use ContentOnly when the filename must be ignored; use TrustExtension only for trusted sources.
A specific explicit MIME type is authoritative. application/octet-stream is the exception: it is a generic placeholder and triggers policy-based detection.
Never edit EXT_TO_MIME or SUPPORTED_MIME_TYPES — edit FORMATS.

Install mime-detection-routing and it becomes one more candidate the router can pick - when it fits.

A listing is a routing target with a manifest: what it does, which domains it covers, what it costs and who publishes it. Once installed it sits beside your own models and tools, is scored like any other candidate for each request, and shows up in the trace when it wins. Ratings come from workspaces that installed it, one per account.

{ "ocm": "1", "id": "xberg-io-xberg-mime-detection-routing", "kind": "skill", "name": "mime-detection-routing", "description": "MIME type detection and extractor routing in core/mime.rs — the FORMATS registry that EXT_TO_MIME and SUPPORTED_MIME_TYPES are derived from, the path-based and bytes-based detection functions, priority-based registry selection, wildcard MIME families, and the real procedure for adding a format. Load when adding a format, wiring an extractor to a MIME type, or debugging why a file routes to the wrong (or no) extractor.", "publisher": "xberg-io", "version": "1.0.0", "capabilities": { "domains": [ "general" ], "tags": [ "skill-md", "skills-sh" ], "languages": [ "en" ] }, "quality_prior": 0.6, "examples": [ "MIME type detection and extractor routing in core/mime.rs — the FORMATS registry that EXT_TO_MIME and SUPPORTED_MIME_TYPES are derived from, the path-based and bytes-based detection functions, priority-based registry selection, wildcard MIME families, and the real procedure for adding a format. Load when adding a format, wiring an extractor to a MIME type, or debugging why a file routes to the wrong (or no) extractor." ], "primary": false, "metadata": { "source": { "provider": "skills.sh", "repository": "https://github.com/xberg-io/xberg", "path": ".ai-rulez/skills/mime-detection-routing/SKILL.md", "ref": "HEAD", "url": "https://github.com/xberg-io/xberg/blob/HEAD/.ai-rulez/skills/mime-detection-routing/SKILL.md", "key": "xberg-io/xberg/.ai-rulez/skills/mime-detection-routing/SKILL.md" } }, "instructions": "# MIME Detection & Routing\n\n## Detection Flow\n\n```text\nPolicy -> content and/or extension evidence -> validate_mime_type -> registry.get(mime) -> extractor\n```\n\n## Key Functions\n\n| Function | Location | Behaviour |\n| --- | --- | --- |\n| `detect_mime_type(path, check_exists: bool)` | `core/mime.rs` | **Path-based only** — never reads bytes. Lowercased extension → `EXT_TO_MIME`, then tree-sitter extension detection (feature `tree-sitter`), then `mime_guess::from_path`. `check_exists` gates a file-existence check, not content inspection. |\n| `detect_mime_type_from_bytes(bytes)` | `core/mime.rs` |", "cost": { "context_tokens": 856 } }

mime-detection-routing

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