solana: Add check for no registered transceivers

Add guard on transfer instructions to prevent a transfer from being
processed when no transceivers are registered. This is done by checking
the `next_transceiver_id` field in the Config. This field
auto-increments when a transceiver is added. If this value is 0, then
the program is in a state where no transceivers have been registered.

Author: johnsaigle

solana/programs/example-native-token-transfers/src/bitmap.rs

@@ -49,6 +49,14 @@ impl Bitmap {
             .try_into()
             .expect("Bitmap length must not exceed the bounds of u8")
     }
+
+    pub fn len(self) -> usize {
+        BM::<128>::from_value(self.map).len()
+    }
+
+    pub fn is_empty(self) -> bool {
+        BM::<128>::from_value(self.map).is_empty()
+    }
 }
 
 #[cfg(test)]

solana/programs/example-native-token-transfers/src/error.rs

@@ -51,6 +51,8 @@ pub enum NTTError {
     OverflowScaledAmount,
     #[msg("BitmapIndexOutOfBounds")]
     BitmapIndexOutOfBounds,
+    #[msg("NoRegisteredTransceivers")]
+    NoRegisteredTransceivers,
 }
 
 impl From<ScalingError> for NTTError {

solana/programs/example-native-token-transfers/src/instructions/redeem.rs

@@ -24,6 +24,8 @@ pub struct Redeem<'info> {
     // NOTE: this works when the contract is paused
     #[account(
         constraint = config.threshold > 0 @ NTTError::ZeroThreshold,
+        constraint = config.next_transceiver_id != 0 @ NTTError::NoRegisteredTransceivers,
+        constraint = !config.enabled_transceivers.is_empty() @ NTTError::NoRegisteredTransceivers,
     )]
     pub config: Account<'info, Config>,
 

solana/programs/example-native-token-transfers/src/instructions/transfer.rs

@@ -22,6 +22,11 @@ pub struct Transfer<'info> {
     #[account(mut)]
     pub payer: Signer<'info>,
 
+    // Ensure that there exists at least one enabled transceiver
+    #[account(
+        constraint = config.next_transceiver_id != 0 @ NTTError::NoRegisteredTransceivers,
+        constraint = !config.enabled_transceivers.is_empty() @ NTTError::NoRegisteredTransceivers,
+    )]
     pub config: NotPausedConfig<'info>,
 
     #[account(
@@ -120,6 +125,7 @@ pub fn transfer_burn(ctx: Context<TransferBurn>, args: TransferArgs) -> Result<(
     );
 
     let accs = ctx.accounts;
+
     let TransferArgs {
         mut amount,
         recipient_chain,
@@ -223,6 +229,7 @@ pub fn transfer_lock(ctx: Context<TransferLock>, args: TransferArgs) -> Result<(
     );
 
     let accs = ctx.accounts;
+
     let TransferArgs {
         mut amount,
         recipient_chain,

solana/tests/example-native-token-transfer.ts

@@ -95,27 +95,40 @@ describe("example-native-token-transfers", () => {
         mode: "locking",
       });
 
-      await ntt.registerTransceiver({
+      const transceiver = await ntt.registerTransceiver({
         payer,
         owner: payer,
         transceiver: ntt.program.programId,
       });
 
-      await ntt.setWormholeTransceiverPeer({
+      if (transceiver === null) {
+        throw new Error('did not register transceiver')
+      }
+
+      const transceiverPeer = await ntt.setWormholeTransceiverPeer({
         payer,
         owner: payer,
         chain: "ethereum",
         address: Buffer.from("transceiver".padStart(32, "\0")),
       });
 
-      await ntt.setPeer({
+      if (transceiverPeer === null) {
+        throw new Error('did not set transceiver peer')
+      }
+
+      const peer = await ntt.setPeer({
         payer,
         owner: payer,
         chain: "ethereum",
         address: Buffer.from("nttManager".padStart(32, "\0")),
         limit: new BN(1000000),
         tokenDecimals: 18,
       });
+
+      if (peer === null) {
+        throw new Error('did not set peer')
+      }
+
     });
 
     it("Can send tokens", async () => {