node:string_decoder

The node:string_decoder module in Azion Runtime: how StringDecoder turns Buffer data into strings, and a sample that decodes a multi-byte character.

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The node:string_decoder module decodes Buffer objects into strings, as the Node.js string_decoder documentation describes. Use it when binary data arrives in pieces, such as a chunked request or response body, and a multi-byte character can be split between two pieces. In Azion Runtime, import string_decoder from "node:string_decoder" builds, and StringDecoder returns the same values in a deployed function and under azion dev.

A StringDecoder created with utf8 keeps an incomplete character between write() calls. Written the bytes 0xe2 0x82, it returns an empty string; written the next byte, 0xac, it returns €; and end() then returns an empty string. For a decoder created with base64, write() of ab followed by end() of c returns YWJj across the two calls. Buffer is a global, so a function can call Buffer.from() without importing node:buffer.

Example

The function below decodes the two bytes of the ¢ character, logs the result, and returns it in the response body:

JavaScript
01/**
02 * An example of using the Node.js StringDecoder API in an Azion Function.
03 * @example
04 * // Build and run locally with the Azion CLI:
05 * azion build
06 * azion dev
07 */
08import string_decoder from "node:string_decoder";
09
10/**
11 * An example of using the Node.js StringDecoder API in an Azion Function.
12 * @param {*} event
13 * @returns {Promise<Response>}
14 */
15const main = async (event) => {
16 const decoder = new string_decoder.StringDecoder("utf8");
17 const buffer = Buffer.from([0xc2, 0xa2]);
18 const decoded = decoder.write(buffer);
19 console.log(decoded);
20 // ¢
21
22 return new Response(decoded, { status: 200 });
23};
24
25export default main;

The function logs ¢ and responds with status 200 and this body:

¢
Node.js APIs

Every Node.js module Azion Runtime resolves, and how each one behaves.

node:buffer

The Buffer class whose objects a StringDecoder reads.

Use Node.js APIs through polyfills

How the build resolves Node.js APIs through polyfills, shown in a JavaScript project.

Handlers

The recommended handler shape, and the notice azion build prints for the export default main shape this sample uses.