FallbackProvider ignores blocktags

[0xngmi]

FallbackProvider doesn't work handle blocktags correctly

Reproduce

const provider = new ethers.providers.FallbackProvider(
    [
      {
       provider: new ethers.providers.StaticJsonRpcProvider(
        "URL",
         {
           name: "ethereum",
           chainId: 1,
         }
       ),
       priority: 1
     }],
     1
   )
 const b = await provider.call({
       to: '0xeefba1e63905ef1d7acba5a8513c70307c1ce441',
       data: '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'
     }, 1);
  console.log(b)

ignores the blocktag and instead returns the result as if blockTag was "latest". This should clearly break otherwise, we are trying to query a contract that didn't exist at block 1

[ricmoo]

I agree with you, but unfortunately this is how the nodes work and their provided API. I’ve spoken up at the JSON-RPC API meetings about this, but there is currently no way to distinguish if the results took a provided blockTag into account or not.

If you need blockTag-based responses, you will have to make sure all your backends are full archive mode (or partial archive mode and ensure your block ranges are within their safe range).

[0xngmi]

This is an issue with ethersjs not with RPC, the problem is that:

• If I use StaticJsonRpcProvider it works
• If I use StaticJsonRpcProvider wrapped on FallbackProvider it doesn't work

So:

const provider =new ethers.providers.StaticJsonRpcProvider(
        "URL",
         {
           name: "ethereum",
           chainId: 1,
         }
       )
 const b = await provider.call({
       to: '0xeefba1e63905ef1d7acba5a8513c70307c1ce441',
       data: '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'
     }, 1);
  console.log(b)

works properly but when I add the fallback provider wrapping it breaks

[0xngmi]

@ricmoo do you want me to provide more examples?

[area]

I'm encountering this too - I want a FallbackProvider consisting of archive nodes, but the provider silently strips the blockTag. Using the StaticJsonRpcProvider, it works.

At a glance, this looks suspicious - I would have expected blockTag to be passed in as well, but I'm very unfamiliar with the code base in general.

[ricmoo]

Thanks! I realize now what you meant, and this has been fixed in ab43e7d and will be released in v5.7.