Expose block number in seal_random (#8329)

* Allow contract callable functions to specify the module

* Add new version of `seal_random`

* Fix overlong lines

* Fix benchmarking code

* Update README.md

* Replace Module by Pallet

substrate/frame/contracts/src/wasm/mod.rs

@@ -192,8 +192,8 @@ where
 
 		let mut imports = sp_sandbox::EnvironmentDefinitionBuilder::new();
 		imports.add_memory(self::prepare::IMPORT_MODULE_MEMORY, "memory", memory.clone());
-		runtime::Env::impls(&mut |name, func_ptr| {
-			imports.add_host_func(self::prepare::IMPORT_MODULE_FN, name, func_ptr);
+		runtime::Env::impls(&mut |module, name, func_ptr| {
+			imports.add_host_func(module, name, func_ptr);
 		});
 
 		let mut runtime = Runtime::new(
@@ -246,7 +246,7 @@ mod tests {
 	use super::*;
 	use crate::{
 		CodeHash, BalanceOf, Error, Pallet as Contracts,
-		exec::{Ext, StorageKey, AccountIdOf, Executable, RentParams},
+		exec::{Ext, StorageKey, AccountIdOf, Executable, SeedOf, BlockNumberOf, RentParams},
 		gas::GasMeter,
 		tests::{Test, Call, ALICE, BOB},
 	};
@@ -414,8 +414,8 @@ mod tests {
 		fn tombstone_deposit(&self) -> u64 {
 			16
 		}
-		fn random(&self, subject: &[u8]) -> H256 {
-			H256::from_slice(subject)
+		fn random(&self, subject: &[u8]) -> (SeedOf<Self::T>, BlockNumberOf<Self::T>) {
+			(H256::from_slice(subject), 42)
 		}
 		fn deposit_event(&mut self, topics: Vec<H256>, data: Vec<u8>) {
 			self.events.push((topics, data))
@@ -515,7 +515,7 @@ mod tests {
 		fn tombstone_deposit(&self) -> u64 {
 			(**self).tombstone_deposit()
 		}
-		fn random(&self, subject: &[u8]) -> H256 {
+		fn random(&self, subject: &[u8]) -> (SeedOf<Self::T>, BlockNumberOf<Self::T>) {
 			(**self).random(subject)
 		}
 		fn deposit_event(&mut self, topics: Vec<H256>, data: Vec<u8>) {
@@ -1531,6 +1531,85 @@ mod tests {
 		);
 	}
 
+	const CODE_RANDOM_V1: &str = r#"
+(module
+	(import "seal1" "seal_random" (func $seal_random (param i32 i32 i32 i32)))
+	(import "seal0" "seal_return" (func $seal_return (param i32 i32 i32)))
+	(import "env" "memory" (memory 1 1))
+
+	;; [0,128) is reserved for the result of PRNG.
+
+	;; the subject used for the PRNG. [128,160)
+	(data (i32.const 128)
+		"\00\01\02\03\04\05\06\07\08\09\0A\0B\0C\0D\0E\0F"
+		"\00\01\02\03\04\05\06\07\08\09\0A\0B\0C\0D\0E\0F"
+	)
+
+	;; size of our buffer is 128 bytes
+	(data (i32.const 160) "\80")
+
+	(func $assert (param i32)
+		(block $ok
+			(br_if $ok
+				(get_local 0)
+			)
+			(unreachable)
+		)
+	)
+
+	(func (export "call")
+		;; This stores the block random seed in the buffer
+		(call $seal_random
+			(i32.const 128) ;; Pointer in memory to the start of the subject buffer
+			(i32.const 32) ;; The subject buffer's length
+			(i32.const 0) ;; Pointer to the output buffer
+			(i32.const 160) ;; Pointer to the output buffer length
+		)
+
+		;; assert len == 32
+		(call $assert
+			(i32.eq
+				(i32.load (i32.const 160))
+				(i32.const 40)
+			)
+		)
+
+		;; return the random data
+		(call $seal_return
+			(i32.const 0)
+			(i32.const 0)
+			(i32.const 40)
+		)
+	)
+	(func (export "deploy"))
+)
+"#;
+
+	#[test]
+	fn random_v1() {
+		let mut gas_meter = GasMeter::new(GAS_LIMIT);
+
+		let output = execute(
+			CODE_RANDOM_V1,
+			vec![],
+			MockExt::default(),
+			&mut gas_meter,
+		).unwrap();
+
+		// The mock ext just returns the same data that was passed as the subject.
+		assert_eq!(
+			output,
+			ExecReturnValue {
+				flags: ReturnFlags::empty(),
+				data: (
+						hex!("000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F"),
+						42u64,
+					).encode(),
+			},
+		);
+	}
+
+
 	const CODE_DEPOSIT_EVENT: &str = r#"
 (module
 	(import "seal0" "seal_deposit_event" (func $seal_deposit_event (param i32 i32 i32 i32)))