FAQ about the Fetch operation of ER - - Alibaba Cloud Documentation Center

This topic provides answers to some commonly asked questions about the Fetch API supported by EdgeRoutine (ER).

Does Fetch support decompression?

By default, automatic decompression is enabled for Fetch. Fetch supports the following decompression methods:

decompress: the default method. This method reads the content-encoding header in the response and uses the decompression algorithm specified by the rightmost value, excluding Identity. For example, in content-encoding: gzip, identity, gzip is the decompression algorithm. If you delete this value from the response header, the following scenarios occur:
- content-encoding: identity, gzip is the fetched response header. content-encoding: identity is the response header after gzip is deleted.
- content-encoding: gzip is the fetched response header. content-encoding is the response header after gzip is deleted.
Note
After the decompression algorithm is deleted from the response header, the data becomes visible. The same scenario occurs when the origin server returns the data without using Gzip to compress the data. If ER cannot recognize the algorithm, ER throws an exception. ER supports only Gzip. Brotli may be supported in later versions.
fallbackIdentity: similar to the decompress method. ER does not throw exceptions when data fails to be decompressed. Instead, ER treats the algorithm value as the identity. In this case, no exception is thrown because the fetched data is decompressed. You cannot read the data without decompression.
manual: does not decompress data.

You can use the following methods to manually configure a decompression policy for Fetch:

fetch(url, {decompress: "manual"})
fetch(url, {decompress: "fallbackIdentity"})

What is the maximum number of subrequests supported by Fetch?

The maximum number of subrequests supported by Fetch is 32. This includes all contexts, which are equal to contexts of all requests captured on points of presence (POPs). The maximum number of subrequests for 3xx redirects or Cache API calls is also 32. To request a quota increase, submit a ticket.

Can ER recognize invalid URLs?

ER cannot recognize invalid URLs. If a URL contains invalid characters, ER prompts that the data is incorrectly encoded. Make sure that your URL is valid.

What is the maximum number of connections supported by a connection pool?

ER provides a connection pool for Fetch in case all connections are consumed by TCP or SSL handshakes. By default, a connection pool supports up to 128 connections. When the number of connections reaches 128, the connection pool stops caching connections. If you want to create additional connections, you can request a quota increase.

A connection pool is created for each user instead of each request. If no connection is established in the connection pool, ER attempts to create connections. ER caches a connection only after the entire response body is retrieved.

The following code ensures that the entire response body is retrieved after it is fetched:

async function fetchAndIgnore(url, options) {
  let response = await fetch(url, options);
  // This method forces ER to ignore the response body and ensures that the entire response body is retrieved. 
  await response.ignore();
}