How can I read JSON files in substrate

Question

I am trying to modify the kitties pallet(https://docs.substrate.io/tutorials/v3/kitties/pt1/) in order to read some json data from an already existing file. So, I need to read the contents of the file and parse json from it. For this I am following https://github.com/nightraiser/daily-code-rust/blob/master/json-reading/src/main.rs But this code is only compiling when I am running SKIP_WASM_BUILD=1 cargo build --release. On running cargo build --release I am getting the below error

I am a beginner in Rust. Can someone please guide me how can I make this run or is there any other package for this task that I can use?

Answer 1

You definitely should not do this.

1. You cannot use std inside the runtime. The Substrate runtime does not have access to the file system of the computer, so any kind of File::open stuff is definitely not allowed; and it does not make sense in the context of blockchains anyway. Do you expect that everyone on your whole network will have some specific file on their computer, or else, what will happen when that file doesn't exist with nodes on your network?

2. You should not be using JSON inside the runtime. The language of Substrate is SCALE. Whereas JSON wastes many bytes by being a self-descriptive format, on the blockchain we have no need for a format like this. Instead we should use well known type structures encoded by SCALE. Any front-end can take a JSON file, turn it into SCALE, and then submit those bytes to the chain. This will save the chain from bloat, which adds up over the history of a chain.