How to query the max extrinsic weight over rpc?

Question

How do i query over rpc the maximum weight for normal extrinsics as defined in frame_system here:

https://github.com/paritytech/substrate/blob/master/frame/system/src/limits.rs#L99-L122

Answer 1

1. use state_getMetadata

curl -X POST -H 'Content-Type:application/json' https://rpc.polkadot.io -d '{"id":0,"jsonrpc":"2.0","method":"state_getMetadata","params":[]}'

2. find the frame system constants part

constants: [
  {
      name: BlockWeights
      type: 161
      value: 0x5872d25c0100000000204aa9d1010000603b14050000000001a094cb9158010000010098f73e5d010000010000000000000000603b14050000000001a01c1efccc0100000100204aa9d1010000010088526a74000000603b140500000000000000
      docs: [
          Block & extrinsics weights: base values and limits.
      ]
  }
]

3. decode the value

parity_scale_codec::Decode::decode::<FrameSystemLimitsBlockWeights>(&mut &*array_bytes::hex2bytes_unchecked(value)).unwrap();

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That's how PolkadotApps do.