wallet: fix sendall creates tx that fails tx-size check

The `sendall` RPC doesn't use `CreateTransactionInternal`as the rest of
the wallet RPCs and it never checks against the tx-size mempool limit.
Add a check for tx-size as well as test coverage for that case.

Author: kouloumos

src/wallet/rpc/spend.cpp

@@ -1414,6 +1414,11 @@ RPCHelpMan sendall()
                 }
             }
 
+            // If this transaction is too large, e.g. because the wallet has many UTXOs, it will be rejected by the node's mempool.
+            if (tx_size.weight > MAX_STANDARD_TX_WEIGHT) {
+                throw JSONRPCError(RPC_WALLET_ERROR, "Transaction too large.");
+            }
+
             CAmount output_amounts_claimed{0};
             for (const CTxOut& out : rawTx.vout) {
                 output_amounts_claimed += out.nValue;

test/functional/wallet_sendall.py

@@ -276,6 +276,20 @@ def sendall_fails_on_high_fee(self):
                 recipients=[self.remainder_target],
                 fee_rate=100000)
 
+    # This tests needs to be the last one otherwise @cleanup will fail with "Transaction too large" error
+    def sendall_fails_with_transaction_too_large(self):
+        self.log.info("Test that sendall fails if resulting transaction is too large")
+        # create many inputs
+        outputs = {self.wallet.getnewaddress(): 0.000025 for _ in range(1600)}
+        self.def_wallet.sendmany(amounts=outputs)
+        self.generate(self.nodes[0], 1)
+
+        assert_raises_rpc_error(
+                -4,
+                "Transaction too large.",
+                self.wallet.sendall,
+                recipients=[self.remainder_target])
+
     def run_test(self):
         self.nodes[0].createwallet("activewallet")
         self.wallet = self.nodes[0].get_wallet_rpc("activewallet")
@@ -327,5 +341,8 @@ def run_test(self):
         # Sendall fails when providing a fee that is too high
         self.sendall_fails_on_high_fee()
 
+        # Sendall fails when many inputs result to too large transaction
+        self.sendall_fails_with_transaction_too_large()
+
 if __name__ == '__main__':
     SendallTest().main()