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// Copyright 2018-2024 the oak authors. All rights reserved. MIT license.
/** * A collection of oak specific APIs for management of ETags. * * @module */
import type { State } from "./application.ts";import type { Context } from "./context.ts";import { calculate, type ETagOptions } from "./deps.ts";import type { Middleware } from "./middleware.ts";import { BODY_TYPES, isAsyncIterable, isReader } from "./util.ts";
// re-exports to maintain backwards compatibilityexport {  calculate,  type ETagOptions,  type FileInfo,  ifMatch,  ifNoneMatch,} from "./deps.ts";
// This is to work around issue introduced in Deno 1.40// See: https://github.com/denoland/deno/issues/22115function isFsFile(value: unknown): value is Deno.FsFile {  return !!(value && typeof value === "object" && "stat" in value &&    typeof value.stat === "function");}
/** For a given Context, try to determine the response body entity that an ETag * can be calculated from. */// deno-lint-ignore no-explicit-anyexport function getEntity<S extends State = Record<string, any>>(  context: Context<S>,): Promise<string | Uint8Array | Deno.FileInfo | undefined> {  const { body } = context.response;  if (isFsFile(body)) {    return body.stat();  }  if (body instanceof Uint8Array) {    return Promise.resolve(body);  }  if (BODY_TYPES.includes(typeof body)) {    return Promise.resolve(String(body));  }  if (isAsyncIterable(body) || isReader(body)) {    return Promise.resolve(undefined);  }  if (typeof body === "object" && body !== null) {    try {      const bodyText = JSON.stringify(body);      return Promise.resolve(bodyText);    } catch {      // We don't really care about errors here    }  }  return Promise.resolve(undefined);}
/** * Create middleware that will attempt to decode the response.body into * something that can be used to generate an `ETag` and add the `ETag` header to * the response. */// deno-lint-ignore no-explicit-anyexport function factory<S extends State = Record<string, any>>(  options?: ETagOptions,): Middleware<S> {  return async function etag(context: Context<S>, next) {    await next();    if (!context.response.headers.has("ETag")) {      const entity = await getEntity(context);      if (entity) {        const etag = await calculate(entity, options);        if (etag) {          context.response.headers.set("ETag", etag);        }      }    }  };}