Config program - useful for storing/updating simple config items on chain

programs/config_api/Cargo.toml

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+[package]
+name = "solana-config-api"
+version = "0.13.0"
+description = "config program API"
+authors = ["Solana Maintainers <maintainers@solana.com>"]
+repository = "https://github.com/solana-labs/solana"
+license = "Apache-2.0"
+homepage = "https://solana.com/"
+edition = "2018"
+
+[dependencies]
+bincode = "1.1.2"
+log = "0.4.2"
+serde = "1.0.89"
+serde_derive = "1.0.89"
+solana-sdk = { path = "../../sdk", version = "0.13.0" }
+
+[lib]
+name = "solana_config_api"
+crate-type = ["lib"]
+

programs/config_api/src/config_instruction.rs

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+use crate::id;
+use crate::ConfigState;
+use solana_sdk::pubkey::Pubkey;
+use solana_sdk::system_instruction::SystemInstruction;
+use solana_sdk::transaction::Instruction;
+
+pub struct ConfigInstruction {}
+
+impl ConfigInstruction {
+    /// Create a new, empty configuration account
+    pub fn new_account<T: ConfigState>(
+        from_account_pubkey: &Pubkey,
+        config_account_pubkey: &Pubkey,
+        lamports: u64,
+    ) -> Instruction {
+        SystemInstruction::new_program_account(
+            from_account_pubkey,
+            config_account_pubkey,
+            lamports,
+            T::max_space(),
+            &id(),
+        )
+    }
+
+    /// Store new data in a configuration account
+    pub fn new_store<T: ConfigState>(config_account_pubkey: &Pubkey, data: &T) -> Instruction {
+        Instruction::new(id(), data, vec![(*config_account_pubkey, true)])
+    }
+}

programs/config_api/src/config_transaction.rs

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+use crate::config_instruction::ConfigInstruction;
+use crate::ConfigState;
+use solana_sdk::hash::Hash;
+use solana_sdk::pubkey::Pubkey;
+use solana_sdk::signature::{Keypair, KeypairUtil};
+use solana_sdk::transaction::Transaction;
+
+pub struct ConfigTransaction {}
+
+impl ConfigTransaction {
+    /// Create a new, empty configuration account
+    pub fn new_account<T: ConfigState>(
+        from_keypair: &Keypair,
+        config_account_pubkey: &Pubkey,
+        recent_blockhash: Hash,
+        lamports: u64,
+        fee: u64,
+    ) -> Transaction {
+        let mut transaction = Transaction::new(vec![ConfigInstruction::new_account::<T>(
+            &from_keypair.pubkey(),
+            config_account_pubkey,
+            lamports,
+        )]);
+        transaction.fee = fee;
+
+        transaction.sign(&[from_keypair], recent_blockhash);
+        transaction
+    }
+
+    /// Store new state in a configuration account
+    pub fn new_store<T: ConfigState>(
+        config_account_keypair: &Keypair,
+        data: &T,
+        recent_blockhash: Hash,
+        fee: u64,
+    ) -> Transaction {
+        let mut transaction = Transaction::new(vec![ConfigInstruction::new_store(
+            &config_account_keypair.pubkey(),
+            data,
+        )]);
+        transaction.fee = fee;
+        transaction.sign(&[config_account_keypair], recent_blockhash);
+        transaction
+    }
+}

programs/config_api/src/lib.rs

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+use serde::Serialize;
+use solana_sdk::pubkey::Pubkey;
+
+mod config_instruction;
+mod config_transaction;
+
+pub use config_instruction::ConfigInstruction;
+pub use config_transaction::ConfigTransaction;
+
+const CONFIG_PROGRAM_ID: [u8; 32] = [
+    133, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,
+];
+
+pub fn check_id(program_id: &Pubkey) -> bool {
+    program_id.as_ref() == CONFIG_PROGRAM_ID
+}
+
+pub fn id() -> Pubkey {
+    Pubkey::new(&CONFIG_PROGRAM_ID)
+}
+
+pub trait ConfigState: Serialize {
+    /// Maximum space that the serialized representation will require
+    fn max_space() -> u64;
+}