Set base prng to zero in preflight and invoke

cmd/crates/soroban-test/tests/fixtures/test-wasms/hello_world/src/lib.rs

@@ -42,6 +42,10 @@ impl Contract {
         count
     }
 
+    pub fn prng_u64_in_range(env: Env, low: u64, high: u64) -> u64 {
+        env.prng().u64_in_range(low..=high)
+    }
+
     #[allow(unused_variables)]
     pub fn multi_word_cmd(env: Env, contract_owner: String) {}
     /// Logs a string with `hello ` in front.

cmd/crates/soroban-test/tests/it/contract_sandbox.rs

@@ -465,3 +465,29 @@ fn build() {
         .assert()
         .success();
 }
+
+#[test]
+fn invoke_prng_u64_in_range_test() {
+    let sandbox = TestEnv::default();
+    let res = sandbox
+        .new_assert_cmd("contract")
+        .arg("deploy")
+        .arg("--wasm")
+        .arg(HELLO_WORLD.path())
+        .assert()
+        .success();
+    let stdout = String::from_utf8(res.get_output().stdout.clone()).unwrap();
+    let id = stdout.trim_end();
+    println!("{id}");
+    sandbox
+        .new_assert_cmd("contract")
+        .arg("invoke")
+        .arg("--id")
+        .arg(id)
+        .arg("--")
+        .arg("prng_u64_in_range")
+        .arg("--low=0")
+        .arg("--high=100")
+        .assert()
+        .success();
+}

cmd/soroban-cli/src/commands/contract/invoke.rs

@@ -382,6 +382,7 @@ impl Cmd {
         let h = Host::with_storage_and_budget(storage, budget);
         h.switch_to_recording_auth(true)?;
         h.set_source_account(source_account)?;
+        h.set_base_prng_seed(rand::Rng::gen(&mut rand::thread_rng()))?;
 
         let mut ledger_info = state.ledger_info();
         ledger_info.sequence_number += 1;

cmd/soroban-rpc/internal/test/simulate_transaction_test.go

@@ -904,3 +904,114 @@ func waitForLedgerEntryToExpire(t *testing.T, client *jrpc2.Client, expirationKe
 	}
 	require.True(t, expired)
 }
+
+func TestSimulateInvokePrng_u64_in_range(t *testing.T) {
+	test := NewTest(t)
+
+	ch := jhttp.NewChannel(test.sorobanRPCURL(), nil)
+	client := jrpc2.NewClient(ch, nil)
+
+	sourceAccount := keypair.Root(StandaloneNetworkPassphrase)
+	address := sourceAccount.Address()
+	account := txnbuild.NewSimpleAccount(address, 0)
+
+	helloWorldContract := getHelloWorldContract(t)
+
+	params := preflightTransactionParams(t, client, txnbuild.TransactionParams{
+		SourceAccount:        &account,
+		IncrementSequenceNum: true,
+		Operations: []txnbuild.Operation{
+			createInstallContractCodeOperation(account.AccountID, helloWorldContract),
+		},
+		BaseFee: txnbuild.MinBaseFee,
+		Preconditions: txnbuild.Preconditions{
+			TimeBounds: txnbuild.NewInfiniteTimeout(),
+		},
+	})
+
+	tx, err := txnbuild.NewTransaction(params)
+	require.NoError(t, err)
+	sendSuccessfulTransaction(t, client, sourceAccount, tx)
+
+	params = preflightTransactionParams(t, client, txnbuild.TransactionParams{
+		SourceAccount:        &account,
+		IncrementSequenceNum: true,
+		Operations: []txnbuild.Operation{
+			createCreateContractOperation(address, helloWorldContract),
+		},
+		BaseFee: txnbuild.MinBaseFee,
+		Preconditions: txnbuild.Preconditions{
+			TimeBounds: txnbuild.NewInfiniteTimeout(),
+		},
+	})
+
+	tx, err = txnbuild.NewTransaction(params)
+	require.NoError(t, err)
+	sendSuccessfulTransaction(t, client, sourceAccount, tx)
+
+	contractID := getContractID(t, address, testSalt, StandaloneNetworkPassphrase)
+	authAddrArg := "GBRPYHIL2CI3FNQ4BXLFMNDLFJUNPU2HY3ZMFSHONUCEOASW7QC7OX2H"
+	tx, err = txnbuild.NewTransaction(txnbuild.TransactionParams{
+		SourceAccount:        &account,
+		IncrementSequenceNum: true,
+		Operations: []txnbuild.Operation{
+			&txnbuild.CreateAccount{
+				Destination:   authAddrArg,
+				Amount:        "100000",
+				SourceAccount: address,
+			},
+		},
+		BaseFee: txnbuild.MinBaseFee,
+		Preconditions: txnbuild.Preconditions{
+			TimeBounds: txnbuild.NewInfiniteTimeout(),
+		},
+	})
+	require.NoError(t, err)
+	sendSuccessfulTransaction(t, client, sourceAccount, tx)
+	low := xdr.Uint64(1500)
+	high := xdr.Uint64(10000)
+	params = txnbuild.TransactionParams{
+		SourceAccount:        &account,
+		IncrementSequenceNum: false,
+		Operations: []txnbuild.Operation{
+			createInvokeHostOperation(
+				address,
+				contractID,
+				"prng_u64_in_range",
+				xdr.ScVal{
+					Type: xdr.ScValTypeScvU64,
+					U64:  &low,
+				},
+				xdr.ScVal{
+					Type: xdr.ScValTypeScvU64,
+					U64:  &high,
+				},
+			),
+		},
+		BaseFee: txnbuild.MinBaseFee,
+		Preconditions: txnbuild.Preconditions{
+			TimeBounds: txnbuild.NewInfiniteTimeout(),
+		},
+	}
+	tx, err = txnbuild.NewTransaction(params)
+
+	require.NoError(t, err)
+
+	txB64, err := tx.Base64()
+	require.NoError(t, err)
+
+	request := methods.SimulateTransactionRequest{Transaction: txB64}
+	var response methods.SimulateTransactionResponse
+	err = client.CallResult(context.Background(), "simulateTransaction", request, &response)
+	require.NoError(t, err)
+	require.Empty(t, response.Error)
+
+	// check the result
+	require.Len(t, response.Results, 1)
+	var obtainedResult xdr.ScVal
+	err = xdr.SafeUnmarshalBase64(response.Results[0].XDR, &obtainedResult)
+	require.NoError(t, err)
+	require.Equal(t, xdr.ScValTypeScvU64, obtainedResult.Type)
+	require.LessOrEqual(t, uint64(*obtainedResult.U64), uint64(high))
+	require.GreaterOrEqual(t, uint64(*obtainedResult.U64), uint64(low))
+}

cmd/soroban-rpc/lib/preflight/Cargo.toml

@@ -13,4 +13,4 @@ thiserror = { workspace = true }
 libc = "0.2.147"
 sha2 = { workspace = true }
 soroban-env-host = { workspace = true }
-
+rand = "0.8.5"

cmd/soroban-rpc/lib/preflight/src/preflight.rs

@@ -52,6 +52,8 @@ pub(crate) fn preflight_invoke_hf_op(
         .context("cannot set debug diagnostic level")?;
     host.set_ledger_info(ledger_info.clone())
         .context("cannot set ledger info")?;
+    host.set_base_prng_seed(rand::Rng::gen(&mut rand::thread_rng()))
+        .context("cannot set base prng seed")?;
 
     // We make an assumption here:
     // - if a transaction doesn't include any soroban authorization entries the client either