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format_media_type.ts
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format_media_type.ts
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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
import { isIterator, isToken, needsEncoding } from "./_util.ts";
/** Serializes the media type and the optional parameters as a media type
* conforming to RFC 2045 and RFC 2616.
*
* The type and parameter names are written in lower-case.
*
* When any of the arguments results in a standard violation then the return
* value will be an empty string (`""`).
*
* @example
* ```ts
* import { formatMediaType } from "https://deno.land/std@$STD_VERSION/media_types/format_media_type.ts";
*
* formatMediaType("text/plain", { charset: "UTF-8" }); // "text/plain; charset=UTF-8"
* ```
*/
export function formatMediaType(
type: string,
param?: Record<string, string> | Iterable<[string, string]>,
): string {
let b = "";
const [major = "", sub] = type.split("/");
if (!sub) {
if (!isToken(type)) {
return "";
}
b += type.toLowerCase();
} else {
if (!isToken(major) || !isToken(sub)) {
return "";
}
b += `${major.toLowerCase()}/${sub.toLowerCase()}`;
}
if (param) {
param = isIterator(param) ? Object.fromEntries(param) : param;
const attrs = Object.keys(param);
attrs.sort();
for (const attribute of attrs) {
if (!isToken(attribute)) {
return "";
}
const value = param[attribute]!;
b += `; ${attribute.toLowerCase()}`;
const needEnc = needsEncoding(value);
if (needEnc) {
b += "*";
}
b += "=";
if (needEnc) {
b += `utf-8''${encodeURIComponent(value)}`;
continue;
}
if (isToken(value)) {
b += value;
continue;
}
b += `"${value.replace(/["\\]/gi, (m) => `\\${m}`)}"`;
}
}
return b;
}