token-swap: Assess swap fee on input token (#562)

* token-swap: Assess swap fee on input token

* Update token-swap/program/src/curve.rs

Co-authored-by: Tyera Eulberg <[email protected]>

* Update token-swap/program/src/curve.rs

Co-authored-by: Tyera Eulberg <[email protected]>

* Fix new var name everywhere

Co-authored-by: Tyera Eulberg <[email protected]>

Author: joncinque

bpf-sdk-install.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -e
 
-channel=${1:-v1.3.13}
+channel=${1:-v1.3.14}
 installDir="$(dirname "$0")"/bin
 cacheDir=~/.cache/solana-bpf-sdk/"$channel"
 

memo/program/Cargo.toml

@@ -17,7 +17,7 @@ program = ["solana-sdk/program"]
 default = ["solana-sdk/default"]
 
 [dependencies]
-solana-sdk = { version = "1.3.12", default-features = false, optional = true }
+solana-sdk = { version = "1.3.14", default-features = false, optional = true }
 
 [lib]
 name = "spl_memo"

token-swap/js/cli/token-swap-test.js

@@ -39,7 +39,7 @@ let tokenAccountB: PublicKey;
 const BASE_AMOUNT = 1000;
 // Amount passed to swap instruction
 const SWAP_AMOUNT_IN = 100;
-const SWAP_AMOUNT_OUT = 69;
+const SWAP_AMOUNT_OUT = 70;
 // Pool token amount minted on init
 const DEFAULT_POOL_TOKEN_AMOUNT = 1000000000;
 // Pool token amount to withdraw / deposit

token-swap/program/Cargo.toml

@@ -22,7 +22,7 @@ arrayref = "0.3.6"
 num-derive = "0.3"
 num-traits = "0.2"
 remove_dir_all = "=0.5.0"
-solana-sdk = { version = "1.3.12", default-features = false, optional = true }
+solana-sdk = { version = "1.3.14", default-features = false, optional = true }
 spl-token = { path = "../../token/program", default-features = false, optional = true }
 thiserror = "1.0"
 

token-swap/program/src/curve.rs

@@ -27,14 +27,19 @@ impl SwapResult {
         fee_denominator: u64,
     ) -> Option<SwapResult> {
         let invariant = swap_source_amount.checked_mul(swap_destination_amount)?;
-        let new_source_amount = swap_source_amount.checked_add(source_amount)?;
-        let new_destination_amount = invariant.checked_div(new_source_amount)?;
-        let remove = swap_destination_amount.checked_sub(new_destination_amount)?;
-        let fee = remove
+
+        // debit the fee to calculate the amount swapped
+        let fee = source_amount
             .checked_mul(fee_numerator)?
             .checked_div(fee_denominator)?;
-        let new_destination_amount = new_destination_amount.checked_add(fee)?;
-        let amount_swapped = remove.checked_sub(fee)?;
+        let new_source_amount_less_fee = swap_source_amount
+            .checked_add(source_amount)?
+            .checked_sub(fee)?;
+        let new_destination_amount = invariant.checked_div(new_source_amount_less_fee)?;
+        let amount_swapped = swap_destination_amount.checked_sub(new_destination_amount)?;
+
+        // actually add the whole amount coming in
+        let new_source_amount = swap_source_amount.checked_add(source_amount)?;
         Some(SwapResult {
             new_source_amount,
             new_destination_amount,
@@ -162,4 +167,25 @@ mod tests {
         check_pool_token_a_rate(5, u64::MAX, 5, 10, Some(2));
         check_pool_token_a_rate(u64::MAX, u64::MAX, 5, 10, None);
     }
+
+    #[test]
+    fn swap_calculation() {
+        // calculation on https://github.com/solana-labs/solana-program-library/issues/341
+        let swap_source_amount: u64 = 1000;
+        let swap_destination_amount: u64 = 50000;
+        let fee_numerator: u64 = 1;
+        let fee_denominator: u64 = 100;
+        let source_amount: u64 = 100;
+        let result = SwapResult::swap_to(
+            source_amount,
+            swap_source_amount,
+            swap_destination_amount,
+            fee_numerator,
+            fee_denominator,
+        )
+        .unwrap();
+        assert_eq!(result.new_source_amount, 1100);
+        assert_eq!(result.amount_swapped, 4505);
+        assert_eq!(result.new_destination_amount, 45495);
+    }
 }

token/js/package.json

@@ -22,7 +22,7 @@
     "/lib",
     "/module.flow.js"
   ],
-  "testnetDefaultChannel": "v1.3.13",
+  "testnetDefaultChannel": "v1.3.14",
   "scripts": {
     "build": "rollup -c",
     "start": "babel-node cli/main.js",

token/program-v3/Cargo.toml

@@ -21,7 +21,7 @@ default = ["solana-sdk/default"]
 num-derive = "0.3"
 num-traits = "0.2"
 remove_dir_all = "=0.5.0"
-solana-sdk = { version = "1.3.12", default-features = false, optional = true }
+solana-sdk = { version = "1.3.14", default-features = false, optional = true }
 thiserror = "1.0"
 arrayref = "0.3.6"
 num_enum = "0.5.1"