Always require funder auth

README.md

@@ -56,7 +56,7 @@ stateDiagram-v2
 
 | Function | Description |
 |---|---|
-| `__constructor` | Open a channel with an initial deposit. Callable by the funder, or anyone if amount is zero. |
+| `__constructor` | Open a channel with an initial deposit. Callable by the deployer, authorized by the funder. |
 | `top_up` | Deposit additional tokens into the channel. |
 | `settle` | Withdraw funds using a signed commitment without closing the channel. |
 | `close` | Close the channel using a signed commitment, withdrawing funds to the recipient. Automatically attempts to refund the funder. |

contracts/channel-factory/src/lib.rs

@@ -80,16 +80,14 @@ impl FactoryContract {
 
     /// Deploy a new channel.
     ///
-    /// Callable by anyone.
+    /// Callable by anyone, authorized by the funder (from).
     ///
     /// # Auth
-    /// - `from`: required if amount > 0.
+    /// - `from`: required.
     pub fn open(env: &Env, salt: BytesN<32>, token: Address, from: Address, commitment_key: BytesN<32>, to: Address, amount: i128, refund_waiting_period: u32) -> Address {
-        if amount > 0 {
-            // Authorize the funder at the factory level so that the channel
-            // constructor's top_up does not require non-root authorization.
-            from.require_auth();
-        }
+        // Authorize the funder at the factory level so that the channel
+        // constructor's top_up does not require non-root authorization.
+        from.require_auth();
 
         // Deploy the channel contract using the stored wasm hash.
         let wasm_hash = Self::wasm_hash(env);

contracts/channel-factory/src/test.rs

@@ -2,10 +2,10 @@
 
 use ed25519_dalek::SigningKey;
 use soroban_sdk::{
-    testutils::Address as _,
+    testutils::{Address as _, AuthorizedFunction, AuthorizedInvocation},
     token::{StellarAssetClient, TokenClient},
     xdr::ToXdr,
-    Address, BytesN, Env,
+    Address, BytesN, Env, IntoVal, Symbol,
 };
 
 use crate::{DeploymentSaltPreimage, FactoryContract, FactoryContractClient};
@@ -59,3 +59,55 @@ fn test_open() {
     assert_eq!(token.balance(&channel_id), 500);
     assert_eq!(token.balance(&funder), 500);
 }
+
+/// Opening a channel with amount 0 still requires the funder's auth.
+#[test]
+fn test_open_zero_amount() {
+    let env = Env::default();
+    env.mock_all_auths();
+
+    let admin = Address::generate(&env);
+    let wasm_hash = env.deployer().upload_contract_wasm(channel_contract::WASM);
+
+    // Deploy the factory.
+    let factory_id = env.register(FactoryContract, (&admin, &wasm_hash));
+    let factory_client = FactoryContractClient::new(&env, &factory_id);
+
+    // Set up a channel.
+    let auth_key = SigningKey::from_bytes(&[2u8; 32]);
+    let auth_pubkey = BytesN::from_array(&env, &auth_key.verifying_key().to_bytes());
+    let funder = Address::generate(&env);
+    let to = Address::generate(&env);
+
+    let (token_addr, token, asset_admin) = create_token(&env);
+    asset_admin.mint(&funder, &1000);
+
+    // Deploy a channel via the factory with no initial deposit.
+    let salt = BytesN::from_array(&env, &[0u8; 32]);
+    let channel_id = factory_client.open(&salt, &token_addr, &funder, &auth_pubkey, &to, &0i128, &100u32);
+
+    assert_eq!(
+        env.auths(),
+        [(
+            funder.clone(),
+            AuthorizedInvocation {
+                function: AuthorizedFunction::Contract((
+                    factory_id.clone(),
+                    Symbol::new(&env, "open"),
+                    (salt.clone(), token_addr.clone(), funder.clone(), auth_pubkey.clone(), to.clone(), 0i128, 100u32).into_val(&env),
+                )),
+                sub_invocations: [AuthorizedInvocation {
+                    function: AuthorizedFunction::Contract((
+                        channel_id.clone(),
+                        Symbol::new(&env, "__constructor"),
+                        (token_addr.clone(), funder.clone(), auth_pubkey.clone(), to.clone(), 0i128, 100u32).into_val(&env),
+                    )),
+                    sub_invocations: [].into(),
+                }]
+                .into(),
+            }
+        )]
+    );
+    assert_eq!(token.balance(&channel_id), 0);
+    assert_eq!(token.balance(&funder), 1000);
+}