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import { IService, Request, Response, Service } from "../../../mod.ts";import { createHash } from "./deps.ts";
export class ETagService extends Service implements IService {  #options: { weak: boolean };
  #etags: Map<string, string> = new Map();
  constructor(options: { weak: boolean } = { weak: false }) {    super();    this.#options = options;  }
  runAfterResource(request: Request, response: Response) {    // if response body is empty, send a default etag    if (      response.body === null ||      (typeof response.body === "string" && response.body.length === 0)    ) {      // when it's empty, we want to set a default etag
      // but if etag is already present on request, send a 304      const header = '"0-2jmj7l5rSw0yVb/vlWAYkK/YBwk"';      if (request.headers.get("if-none-match")) {        response.status = 304;        response.body = null;        const existingModifiedDate = this.#etags.get(header) as string; // it will always be set due to this conditional        response.headers.set("last-modified", existingModifiedDate);      } else { // set the NEW default etag        const date = new Date().toUTCString();        response.headers.set("last-modified", date);        this.#etags.set(header, date);      }      response.headers.set("etag", header);      return;    }
    // generate the hash    const body = typeof response.body === "string"      ? new TextEncoder().encode(response.body)      : response.body as Uint8Array;    const hash = createHash("sha1").update(body, "utf8").digest("base64")      .toString().substring(0, 27);    const len = body.byteLength;
    // create the etag value to use    let header = `"${len.toString(16)}-${hash}"`;    if (this.#options.weak === true) {      header = "W/" + header;    }
    response.headers.set("etag", header);
    // check if request already has an etag, if so,    // if its the same as the generated etag from the response body    const incomingRequestIfNoneMatchValue = request.headers.get(      "if-none-match",    );    if (incomingRequestIfNoneMatchValue) { // request inc already has an etag set      // so check if body hash matches      if (header === incomingRequestIfNoneMatchValue) {        // no need to send body, send not modified        response.status = 304;        response.body = null;        response.headers.set(          "last-modified",          this.#etags.get(header) as string,        );        return;      } else {        // res body is new        response.status = 200;        const date = new Date().toUTCString();        this.#etags.set(header, date);        response.headers.set("last-modified", date);        return;      }    }
    // else request doesnt have a new one so generate everything from scratch    response.status = 200;    const date = new Date().toUTCString();    this.#etags.set(header, date);    response.headers.set("last-modified", date);  }}