Witness account data in Budget (#4650)

* Add support for contracts based on account data to Budget

* Add program_id to account constraints

* No longer require a signature for the account data witness

* Rename bank::store to store_account

* fmt

* Add a doc

* clippy

programs/budget_api/src/budget_expr.rs

@@ -5,6 +5,7 @@
 
 use chrono::prelude::*;
 use serde_derive::{Deserialize, Serialize};
+use solana_sdk::hash::Hash;
 use solana_sdk::pubkey::Pubkey;
 use std::mem;
 
@@ -16,6 +17,9 @@ pub enum Witness {
 
     /// A signature from Pubkey.
     Signature,
+
+    /// Account snapshot.
+    AccountData(Hash, Pubkey),
 }
 
 /// Some amount of lamports that should be sent to the `to` `Pubkey`.
@@ -28,6 +32,23 @@ pub struct Payment {
     pub to: Pubkey,
 }
 
+/// The account constraints a Condition would wait on.
+/// Note: ideally this would be function that accepts an Account and returns
+/// a bool, but we don't have a way to pass functions over the wire. To simulate
+/// higher order programming, create your own program that includes an instruction
+/// that sets account data to a boolean. Pass that account key and program_id here.
+#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
+pub struct AccountConstraints {
+    /// The account holder.
+    pub key: Pubkey,
+
+    /// The program id that must own the account at `key`.
+    pub program_id: Pubkey,
+
+    /// The hash of the data in the account at `key`.
+    pub data_hash: Hash,
+}
+
 /// A data type representing a `Witness` that the payment plan is waiting on.
 #[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
 pub enum Condition {
@@ -36,6 +57,9 @@ pub enum Condition {
 
     /// Wait for a `Signature` `Witness` from `Pubkey`.
     Signature(Pubkey),
+
+    /// Wait for the account with the given constraints.
+    AccountData(AccountConstraints),
 }
 
 impl Condition {
@@ -46,6 +70,14 @@ impl Condition {
             (Condition::Timestamp(dt, pubkey), Witness::Timestamp(last_time)) => {
                 pubkey == from && dt <= last_time
             }
+            (
+                Condition::AccountData(constraints),
+                Witness::AccountData(actual_hash, program_id),
+            ) => {
+                constraints.program_id == *program_id
+                    && constraints.key == *from
+                    && constraints.data_hash == *actual_hash
+            }
             _ => false,
         }
     }
@@ -83,6 +115,24 @@ impl BudgetExpr {
         )
     }
 
+    /// Create a budget that pays `lamports` to `to` after witnessing account data in `account_pubkey` with the given hash.
+    pub fn new_payment_when_account_data(
+        account_pubkey: &Pubkey,
+        account_program_id: &Pubkey,
+        account_hash: Hash,
+        lamports: u64,
+        to: &Pubkey,
+    ) -> Self {
+        BudgetExpr::After(
+            Condition::AccountData(AccountConstraints {
+                key: *account_pubkey,
+                program_id: *account_program_id,
+                data_hash: account_hash,
+            }),
+            Box::new(Self::new_payment(lamports, to)),
+        )
+    }
+
     /// Create a budget that pays `lamports` to `to` after being witnessed by `witness` unless
     /// canceled with a signature from `from`.
     pub fn new_cancelable_authorized_payment(