detection/from-extension

Purpose

Detects the MIME type from a file extension or full filename. Strips path components and leading dots, normalizes to lowercase, and looks up the result in the built-in MIME database. Returns a DetectionResult with source: "extension" and a confidence weight of 0.7 in the unified detect() function.

Features

Accepts both raw extensions (.png, png) and full filenames (photo.jpeg)
Strips directory path components automatically
Normalizes extensions to lowercase before lookup
Handles multiple dots in filenames correctly (uses the last extension)
Returns undefined for unknown extensions instead of throwing
Wraps the database entry in a DetectionResult envelope

Usage: Basic Example

import { detectFromExtension } from "@suaveplan/mime/detection/from-extension";

const result = detectFromExtension("photo.jpg");
console.log(result?.mime);   // "image/jpeg"
console.log(result?.source); // "extension"

// Just an extension without filename
const svg = detectFromExtension(".svg");
console.log(svg?.mime); // "image/svg+xml"

Usage: Advanced Example

import { detectFromExtension } from "@suaveplan/mime/detection/from-extension";

function getMimeForUpload(filename: string): string {
    const detected = detectFromExtension(filename);
    // Fall back to binary stream for unknown extensions
    return detected?.mime ?? "application/octet-stream";
}

// Handles paths with directories
console.log(detectFromExtension("/uploads/2024/report.pdf")?.mime); // "application/pdf"

// Unknown extension returns undefined
console.log(detectFromExtension("file.xyz")); // undefined

API Reference

`detectFromExtension(input: string): DetectionResult | undefined`

Parameter	Type	Description
`input`	`string`	File extension (with or without dot) or full filename/path.

Returns: DetectionResult with source: "extension" and the matched mime, or undefined when the extension is not in the database.

Throws: Never.

Implementation Notes

The function extracts the extension by splitting on . and taking the last segment, then looking up getEntryByExtension. The split also handles filenames with no extension (returns undefined) and filenames starting with a dot (treated as hidden files with no extension, e.g. .gitignore). Path components are stripped by looking only at the basename portion after the last / or \. Lookup is O(1) via the registry's Map<string, MimeEntry> index.

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