Using fetch in @ethersproject/web's module breaks bundling for AWS Lambda

[Yoctoboy]

Ethers Version

5.6.9

Search Terms

module fetch

Describe the Problem

Hey man,

We've been trying to use ethers in a LambdaFunction to make a simple API call to alchemy in order to retrieve the latest block number on the blockchain:

import { ethers } from 'ethers';
[...]
const provider = new ethers.providers.AlchemyProvider(ETH_CHAIN_NAME, apiKey);
const latestBlockNumber = await provider.getBlockNumber();
console.log(latestBlockNumber);

We use esbuild to bundle our apps with mainFields: ['module', 'main'] so we check for ESM first and then fallback to CJS. We had to create a polyfill containing node-fetch to avoid a ReferenceError: fetch is not defined, but even then, when the lambda containing this snippet is triggered, the following error appears in the logs:

{
    "errorType": "Error",
    "errorMessage": "missing response (requestBody=\"{\\\"method\\\":\\\"eth_blockNumber\\\",\\\"params\\\":[],\\\"id\\\":42,\\\"jsonrpc\\\":\\\"2.0\\\"}\", requestMethod=\"POST\", serverError={\"input\":\"client\",\"code\":\"ERR_INVALID_URL\"}, url=\"https://eth-goerli.alchemyapi.io/v2/<API_KEY>\", code=SERVER_ERROR, version=web/5.6.1)",
    "code": "SERVER_ERROR",
    "reason": "missing response",
    "requestBody": "{\"method\":\"eth_blockNumber\",\"params\":[],\"id\":42,\"jsonrpc\":\"2.0\"}",
    [...]
}

We have found two solutions to solve this problem:

• Having the parameter mainFields: ['main', 'module'] in order to prioritize CJS, which makes our bundle un-treeshakable (which is bad for us)
• OR Patching ethers by removing line 35 ("module": "./lib.esm/index.js,") from the file @ethersproject/web/package.json.

The reason we think the problem is happening is the use of browser's fetch (and maybe other browser native functions) in @ethersproject/web's module. From reading other issues such as #3165 and #3158, I would guess that a fix is planned for v6 of ethers, but I'm still opening this issue in case there is a cleaner workaround. Tell me what you think about it 🙂

Code Snippet

No response

Contract ABI

No response

Errors

No response

Environment

node.js (v12 or newer)

Environment (Other)

No response

[ricmoo]

It should work fine if you use the skipFetchSetup flag in your connection: https://github.com/ethers-io/ethers.js/blob/master/packages/web/src.ts/types.ts#L15

[Yoctoboy]

Thanks for reading and for the answer 🙂 I still feel like this is weird as we need to polyfill node-fetch to make it work

[ricmoo]

It doesn’t have access to the http library? The node-fetch polyfill should support the properties passed in by ethers, so you shouldn’t need skipFetchSetup.

[Eikix]

It's not so clear where one can use skipFetchSetup, I've had a similar bug using only providers and contract instances, meaning I don't explicitly call @ethersproject/web but rather it is imported as a dependency by provider or contract.