Edge Security Acceleration:Fetch API

Fetch API method definition

Fetch is fully asynchronous. It does not block script execution unless you use await. You can send up to four subrequests at a time. The underlying layer uses persistent connections, so you do not need to manage connection pools.

Fetch can make HTTP or HTTPS requests. Each redirect counts as one request. Each fetch request supports a maximum of 12 redirect operations.

• Method definition

  fetch(arg, init). For more information, see the MDN documentation for WorkerOrGlobalScope.fetch().

• Method limits

  • The Fetch API supports only domain names, not IP addresses. The default port for HTTP requests is 80, and the default port for HTTPS requests is 443.

  • The credentials, referrer, referrerPolicy, cache, and integrity properties of the init parameter have no effect.

  • The default value for redirect is follow, which means that fetch follows 3xx responses from the origin server. To prevent fetch from following 3xx responses, set redirect to manual.

  Note

  • The various Fetch modes available in a browser do not apply. For example, on CDN, DCDN, or ESA, you can use CROS fetch to retrieve data from any origin server.

  • To send four or more subrequests, submit a ticket to request a quota increase.

  • The total length of a request URL cannot exceed 4 KB.

  • Gzip-compressed resources that a function retrieves using Fetch are decompressed by default. To prevent default decompression, add the manual parameter. For more information, see the Decompress section.

• Set a timeout period

  • Timeout function

    /**
     * Request timeout control implementation
     *
     * @param {Number} timeout Timeout period, in ms
     * @param {Object} config Timeout configuration
     *   - @param {Object|Funtion} handler Value to return on timeout
     * @returns
     */
    const RequestTimeout = (timeout, config) => {
      return new Promise((resolve) => {
        const { handler = null } = config;
        let timer = setTimeout(() => {
          clearTimeout(timer);
          timer = null;
    
          const defaultRes = (typeof handler === 'function' ? handler() : handler) || {};
          resolve(defaultRes);
        }, timeout);
      });
    };

  • Example call

    const KV_TIMEOUT = 1000;
    let edgekv = new EdgeKV({
      namespace: KV_NS,
    });
    
    let kvRequest = edgekv.get(key, getType);
    let timeoutPromise = RequestTimeout(KV_TIMEOUT, {
      handler: {
        res: {},
        errorMessage: `kv request timeout (${KV_TIMEOUT}ms)`,
      }
    });
    
    let resp = await Promise.race([
      kvRequest,
      timeoutPromise,
    ]);
    
    if (resp === undefined) {
      return "kv not found, key = " + key;
    } else {
      return resp;
    }

Redirect

Decompress

content-length

Headers

• Definition

  For more information about the Headers object, see Headers.

• Limits

  A header records the amount of memory resources that are consumed. The maximum size of a Headers object is 8 KB. If the size of a Headers object exceeds this limit, a JavaScript exception is thrown.

• Blacklist

  The Fetch API uses a header blacklist. If you attempt to read or write a header that is in the blacklist, an exception is thrown. The following table describes the headers that are included in the blacklist.

  • expect

  • te

  • trailer

  • upgrade

  • proxy-connection

  • connection

  • keep-alive

  • dnt

  • host

  • Reserved headers

Request

• Definition

  For more information, see the MDN documentation for Request.

• Limits

  The following properties of the Request object are not implemented and do not apply in the CDN, DCDN, or ESA context.

  • context

  • credentials

  • destination

  • integrity

  • mode

  • referrer

  • referrerPolicy

  • cache

• Common uses

  • Retrieve the request method: request.method.

  • Retrieve the request URL: request.url.

  • Retrieve the request headers: request.headers.

  • Retrieve the request payload: request.body. The body is a ReadableStream object.

  • Retrieve JSON: await request.json().

  • Retrieve form data: await request.formData().

  • Retrieve a UTF-8 string: await request.text().

  The Request interface is an extension of the standard. It lets you ignore the request body while ensuring the body stream is fully read from the underlying socket. The body is not read into the memory of the JavaScript virtual machine, which avoids garbage collection (GC) delays. If you do not need to read the body of a Fetch request, call request.ignore. For example, await request.ignore(). This improves performance because the runtime automatically returns the connection to the connection pool for reuse after the body is fully read.

Response

• Definition

  For more information, see the MDN documentation for Response.

• Limits

  The useFinalURLS and error properties of the Response object are not implemented and do not apply in the CDN, DCDN, or ESA context.

• Common uses

  • Retrieve the response code: response.status.

  • Retrieve the response reason phrase: response.statusText.

  • Retrieve the response headers: response.headers.

  • Retrieve the response URL: response.url. This is the final URL after all redirects.

  • Retrieve a list of all redirect URLs (non-standard): response.urlList. The Response object implements a body mixin, similar to the Request object. You can use similar methods to retrieve the body object.

FormData

• Definition

  For more information about the FormData operation, see FormData.

• Limits

  The FormData operation is similar to the Headers operation. FormData limits the size of headers. If the size of a header exceeds the upper limit, an exception is thrown. If you send FormData as an HTTP request body, content-type is set to form-data/multipart by default.

URLSearchParams

• Definition

  For more information about the URLSearchParams operation, see URLSearchParams().

• Limits

  If you send URLSearchParams as an HTTP request body, content-type is set to application/x-www-form-urlencode by default. The data size cannot exceed 1,000 bytes.

Blob and File

• Definition

  • For more information about the Blob operation, see Blob.

  • For more information about the File operation, see File.

• Limits

  ER supports the Blob and File classes, which meet the standards of the Blob and File operations. ER cannot read or write files. You can pass the Blob and File classes supported by ER to the response body. The value of the content-type header is the same as the MIME type in the Blob or File operation.