Edge Security Acceleration:Fetch API

Fetch API methods

Fetch supports asynchronous calls. Fetch does not block script execution as long as you do not use the await keyword. Fetch allows you to send up to four subrequests at a time. The underlying layer uses persistent connections, ensuring stable performance without requiring you to manage connection pools.

You can call the Fetch API to send HTTP or HTTPS requests. Each redirect is considered one request. Each Fetch API request supports up to 12 redirect operations.

• Method definition

  fetch(arg, init) is used as the Fetch method. For more information, see WorkerOrGlobalScope.fetch().

• Method limits

  • The Fetch API supports domain names but does not support IP addresses. HTTP requests use port 80 and HTTPS requests use port 443.

  • The init parameter's internal credentials, referrer, referrerPolicy, cache and integrity parameters are not in use.

  • By default, the redirect parameter is set to follow, which specifies that fetch requests follow 3xx redirects. If you don't want fetch requests to follow 3xx redirects, set the redirect parameter to manual.

  Note

  • Browsers process fetch requests the same way across different modes. For example, you can use CROS fetch to retrieve resources from any origin servers by using Alibaba Cloud CDN, DCDN, or ESA.

  • To send more than four subrequests at a time, submit a ticket to request a quota increase.

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

  • If you use Fetch to obtain resources that are compressed in Gzip, these resources are automatically decompressed before they are returned. If you do not want the resources to be decompressed by default, you can set the decompress parameter to manual as described in the Decompress section.

• Configure a timeout period

  • Timeout

    /**
     * Deploy request timeout
     *
     * @param {Number} timeout. Timeout period. Unit: ms.
     * @param {Object} config. Timeout configuration.
     *   - @param {Object|Funtion} handler. Return value if the operation times out.
     * @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);
      });
    };

  • Sample request

    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

• Description

  For more information about the Request operation, see Request.

• Limits

  The following properties of the Request object are not in use in the CDN/DCDN/ESA context.

  • context

  • credentials

  • destination

  • integrity

  • mode

  • referrer

  • referrerPolicy

  • cache

• Use cases

  • Fetches the request method: request.method.

  • Fetches the request URL: request.url.

  • Fetches the request header: request.headers.

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

  • Fetches JSON data: await request.json().

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

  • Fetches strings encoded in UTF-8: await request.text().

  The Request operation is a standard API operation. The Request operation ignores the body when it fetches all values of the body without the need to consume the memory resources of ER. This minimizes the garbage collection (GC) pause time and ensures that all values of the request body are fetched from the underlying sockets. For await request.ignore(), if you do not need to read the fetched body or are not interested in it, we recommend that you call request.ignore for all fetch requests to improve performance. This is because the runtime automatically sends requests with fully read bodies to the connection pool for future use.

Response

• Description

  For more information about the Response operation, see Response.

• Limits

  The useFinalURLS and error properties of the Response object are not implemented and have no meaning in the CDN/DCDN/ESA context.

• Use cases

  • Fetches the response code: response.status.

  • Fetches the reason phrase of a response: response.statusText.

  • Fetches the response header: response.headers.

  • Fetches the response URL: response.url, which indicates the URL to which the response was sent.

  • Fetches a list of all redirect URLs (non-standard): response.urlList. Similar to how the Request object implements the body mixin, you can use similar methods to obtain 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.