@remix-run/headers/src/lib/accept-encoding.ts

A toolkit for working with HTTP headers in JavaScript

import { type HeaderValue } from './header-value.ts'
import { parseParams } from './param-values.ts'
import { isIterable } from './utils.ts'

/**
 * Initializer for an `Accept-Encoding` header value.
 */
export type AcceptEncodingInit = Iterable<string | [string, number]> | Record<string, number>

/**
 * The value of a `Accept-Encoding` HTTP header.
 *
 * [MDN `Accept-Encoding` Reference](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Encoding)
 *
 * [HTTP/1.1 Specification](https://datatracker.ietf.org/doc/html/rfc7231#section-5.3.4)
 */
export class AcceptEncoding implements HeaderValue, Iterable<[string, number]> {
  #map: Map<string, number>

  /**
   * @param init A string, iterable, or record to initialize the header
   */
  constructor(init?: string | AcceptEncodingInit) {
    this.#map = new Map()

    if (init) {
      if (typeof init === 'string') {
        for (let piece of init.split(/\s*,\s*/)) {
          let params = parseParams(piece)
          if (params.length < 1) continue

          let encoding = params[0][0]
          let weight = 1

          for (let i = 1; i < params.length; i++) {
            let [key, value] = params[i]
            if (key === 'q') {
              weight = Number(value)
              break
            }
          }

          this.#map.set(encoding.toLowerCase(), weight)
        }
      } else if (isIterable(init)) {
        for (let value of init) {
          if (Array.isArray(value)) {
            this.#map.set(value[0].toLowerCase(), value[1])
          } else {
            this.#map.set(value.toLowerCase(), 1)
          }
        }
      } else {
        for (let encoding of Object.getOwnPropertyNames(init)) {
          this.#map.set(encoding.toLowerCase(), init[encoding])
        }
      }

      this.#sort()
    }
  }

  #sort() {
    this.#map = new Map([...this.#map].sort((a, b) => b[1] - a[1]))
  }

  /**
   * An array of all encodings in the header.
   */
  get encodings(): string[] {
    return Array.from(this.#map.keys())
  }

  /**
   * An array of all weights (q values) in the header.
   */
  get weights(): number[] {
    return Array.from(this.#map.values())
  }

  /**
   * The number of encodings in the header.
   */
  get size(): number {
    return this.#map.size
  }

  /**
   * Returns `true` if the header matches the given encoding (i.e. it is "acceptable").
   *
   * @param encoding The encoding to check
   * @return `true` if the encoding is acceptable, `false` otherwise
   */
  accepts(encoding: string): boolean {
    return encoding.toLowerCase() === 'identity' || this.getWeight(encoding) > 0
  }

  /**
   * Gets the weight an encoding. Performs wildcard matching so `*` matches all encodings.
   *
   * @param encoding The encoding to get
   * @return The weight of the encoding, or `0` if it is not in the header
   */
  getWeight(encoding: string): number {
    let lower = encoding.toLowerCase()

    for (let [enc, weight] of this) {
      if (enc === lower || enc === '*' || lower === '*') {
        return weight
      }
    }

    return 0
  }

  /**
   * Returns the most preferred encoding from the given list of encodings.
   *
   * @param encodings The encodings to choose from
   * @return The most preferred encoding or `null` if none match
   */
  getPreferred<encoding extends string>(encodings: readonly encoding[]): encoding | null {
    let sorted = encodings
      .map((encoding) => [encoding, this.getWeight(encoding)] as const)
      .sort((a, b) => b[1] - a[1])

    let first = sorted[0]

    return first !== undefined && first[1] > 0 ? first[0] : null
  }

  /**
   * Gets the weight of an encoding. If it is not in the header verbatim, this returns `null`.
   *
   * @param encoding The encoding to get
   * @return The weight of the encoding, or `null` if it is not in the header
   */
  get(encoding: string): number | null {
    return this.#map.get(encoding.toLowerCase()) ?? null
  }

  /**
   * Sets an encoding with the given weight.
   *
   * @param encoding The encoding to set
   * @param weight The weight of the encoding (default: `1`)
   */
  set(encoding: string, weight = 1): void {
    this.#map.set(encoding.toLowerCase(), weight)
    this.#sort()
  }

  /**
   * Removes the given encoding from the header.
   *
   * @param encoding The encoding to remove
   */
  delete(encoding: string): void {
    this.#map.delete(encoding.toLowerCase())
  }

  /**
   * Checks if the header contains a given encoding.
   *
   * @param encoding The encoding to check
   * @return `true` if the encoding is in the header, `false` otherwise
   */
  has(encoding: string): boolean {
    return this.#map.has(encoding.toLowerCase())
  }

  /**
   * Removes all encodings from the header.
   */
  clear(): void {
    this.#map.clear()
  }

  /**
   * Returns an iterator of all encoding and weight pairs.
   *
   * @return An iterator of `[encoding, weight]` tuples
   */
  entries(): IterableIterator<[string, number]> {
    return this.#map.entries()
  }

  [Symbol.iterator](): IterableIterator<[string, number]> {
    return this.entries()
  }

  /**
   * Invokes the callback for each encoding and weight pair.
   *
   * @param callback The function to call for each pair
   * @param thisArg The value to use as `this` when calling the callback
   */
  forEach(
    callback: (encoding: string, weight: number, header: AcceptEncoding) => void,
    thisArg?: any,
  ): void {
    for (let [encoding, weight] of this) {
      callback.call(thisArg, encoding, weight, this)
    }
  }

  /**
   * Returns the string representation of the header value.
   *
   * @return The header value as a string
   */
  toString(): string {
    let pairs: string[] = []

    for (let [encoding, weight] of this.#map) {
      pairs.push(`${encoding}${weight === 1 ? '' : `;q=${weight}`}`)
    }

    return pairs.join(',')
  }
}