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oscoin / oscoin-parity-wasm-prototype

Prototype implemenation of Oscoin ledger on Parity Ethereum Wasm
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serde + pwasm-abi-derive + no_std #37

Closed geigerzaehler closed 5 years ago

geigerzaehler commented 5 years ago

I started using serde for #25 and discovered that the combination of serde, pwasm-abi-derive and no_std does not work. serde can be compiled with no_std support but pwasm-abi-derive uses serde with std. Altough pwasm-abi-derive is a proc macro it uses the same serde configuration as the library, i.e. the no_std configuration. This results in an error when compiling pwasm-abi-derive. (This issue is a known cargo bug.)

To solve this issue we can drop either of the three.

Dropping serde

As outlined in #25 we need a serialization mechanism to store structured data in the key value store that the protocol (currently parity ethereum) provides. I’m not aware of any alternative to serde that has a comparable feature set and no_std support.

Dropping pwasm-abi-derive

The pwasm-abi-derive crate provides a macro to create Ethereum ABI compatible glue code from a Rust trait. This eliminates the need to write this glue code or similar dispatching logic ourselves and provides interoperability with the Web3 client.

If we drop pwasm-abi-derive we need to implement this glue code for the the ledger as well as the client.

Dropping no_std

Compiling the ledger without no_std to the wasm32 target works in theory as long as we don’t use OS features.

However a trial revealed that the size of the generated Wasm deployment code exceeded the initial memory of 2 pages. This results in a failure when the contract is deployed. To address this issue we need to patch wasm-utils so that pack_instance makes sure that enough memory is provided.

Another problem is that serde withtout no_std generates code that involves floating point computations. These are rejected by Parity Ethereum when inject_gas_counter is called. (This is not intuitive and results in a “bytecode invalid” error.) This can be changed by removing .with_forbidden_floats() from the rule set

geigerzaehler commented 5 years ago

Updated the description of the no_std case

geigerzaehler commented 5 years ago

Fixed in #47. We dropped pwasm-abi-derive and used serde with no_std.