The EtherscanProvider fails requests because of URL length

[DeltaBalances]

Issue

Some eth_call requests will always fail for the EtherscanProvider but they succeed with the Infura, Alchemy, Cloudflare and JsonRPC providers.

Looking at the requests, etherscan is the only provider using GET requests.
The appended data field can result in the URL reaching extreme lengths, over 6000 characters in the example below.

(Issue found in Chrome & Firefox browsers, might also be a browser enforced limitation)

Solution

The Etherscan API accepts POST requests, and these do succeed in many cases where GET calls fail.
A change to POST for certain request types will make the EtherscanProvider more reliable and increase compatibility with the other providers.

Examples

I tested these in the latest version of Chrome & Firefox.

The following examples call this function:
function tokenBalances(address user, address[] calldata tokens) external view returns (uint[] memory balances)
The EtherscanProvider starts to fail once the token array reaches a length of about 75-100.
Other providers can easily cope with much larger arrays.

The API key has been redacted, you probably have to add one to check these.

Case 1: array length 1
GET succeeds

https://api.etherscan.io/api?module=proxy&action=eth_call&to=0xbf320b8336b131e0270295c15478d91741f9fc11&data=0x3ad206cc000000000000000000000000f6e914d07d12636759868a61e52973d17ed7111b000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000000&apikey=YourApiKeyToken

POST succeeds

$.ajax({
    type: "POST",
    url: "https://api.etherscan.io/api",
    data: { apikey: "YourApiKeyToken", module:"proxy", action: "eth_call", to: "0xbf320b8336b131e0270295c15478d91741f9fc11", data:"0x3ad206cc000000000000000000000000f6e914d07d12636759868a61e52973d17ed7111b000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000000" }
})

Case 2: Array length 100
GET fails

https://api.etherscan.io/api?module=proxy&action=eth_call&to=0xbf320b8336b131e0270295c15478d91741f9fc11&data=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POST succeeds

$.ajax({
    type: "POST",
    url: "https://api.etherscan.io/api",
    data: { apikey: "YourApiKeyToken", module:"proxy", action: "eth_call", to: "0xbf320b8336b131e0270295c15478d91741f9fc11", data:"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}
})

[ricmoo]

I've verified this is an issue in Chrome. It works fine in node, but I will switch all proxy calls to use the POST method anyways because it's just better. :)

[DeltaBalances]

Looking good on my end, thanks for the fix.

[ricmoo]

Awesome! It's now been released in 5.0.19. Please re-open if you have any problems with it.

Thanks! :)