Use saturating_sub instead of overflowing sub (#54)

* Use saturating_sub instead of overflowing sub

Also adds tests

Author: ali-behjati

.github/workflows/pyth-sdk-solana.yml

@@ -18,7 +18,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Install dependencies
-      run: sudo apt-get install libudev-dev
+      run: sudo apt-get update && sudo apt-get install libudev-dev
     - name: Build
       run: cargo build --verbose
     - name: Run tests
@@ -31,7 +31,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Install dependencies
-      run: sudo apt-get install libudev-dev
+      run: sudo apt-get update && sudo apt-get install libudev-dev
     - name: Install Solana Binaries
       run: |
         sh -c "$(curl -sSfL https://release.solana.com/v1.8.14/install)"

.github/workflows/pyth-sdk-terra.yml

@@ -18,7 +18,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Install dependencies
-      run: sudo apt-get install libudev-dev
+      run: sudo apt-get update && sudo apt-get install libudev-dev
     - name: Build
       run: cargo build --verbose
     - name: Run tests

.github/workflows/pyth-sdk.yml

@@ -20,7 +20,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Install dependencies
-      run: sudo apt-get install libudev-dev
+      run: sudo apt-get update && sudo apt-get install libudev-dev
     - name: Build
       run: cargo build --verbose
     - name: Run tests

pyth-sdk-solana/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "pyth-sdk-solana"
-version = "0.4.0"
+version = "0.4.1"
 authors = ["Pyth Data Foundation"]
 edition = "2018"
 license = "Apache-2.0"

pyth-sdk-solana/src/state.rs

@@ -350,7 +350,7 @@ impl PriceAccount {
 
         #[cfg(target_arch = "bpf")]
         if matches!(status, PriceStatus::Trading)
-            && Clock::get().unwrap().slot - self.agg.pub_slot > VALID_SLOT_PERIOD
+            && Clock::get().unwrap().slot.saturating_sub(self.agg.pub_slot) > VALID_SLOT_PERIOD
         {
             status = PriceStatus::Unknown;
         }

pyth-sdk-solana/test-contract/tests/common.rs

@@ -7,11 +7,17 @@ use test_contract::processor::process_instruction;
 
 // Panics if running instruction fails
 pub async fn test_instr_exec_ok(instr: Instruction) {
-    let (mut banks_client, payer, recent_blockhash) =
-        ProgramTest::new("test_contract", id(), processor!(process_instruction))
-            .start()
-            .await;
-    let mut transaction = Transaction::new_with_payer(&[instr], Some(&payer.pubkey()));
-    transaction.sign(&[&payer], recent_blockhash);
-    banks_client.process_transaction(transaction).await.unwrap()
+    let mut context = ProgramTest::new("test_contract", id(), processor!(process_instruction))
+        .start_with_context()
+        .await;
+
+    context.warp_to_slot(1000).unwrap();
+
+    let mut transaction = Transaction::new_with_payer(&[instr], Some(&context.payer.pubkey()));
+    transaction.sign(&[&context.payer], context.last_blockhash);
+    context
+        .banks_client
+        .process_transaction(transaction)
+        .await
+        .unwrap()
 }

pyth-sdk-solana/test-contract/tests/stale_price.rs

@@ -5,6 +5,7 @@ use pyth_sdk_solana::state::{
     MAGIC,
     VERSION_2,
 };
+use pyth_sdk_solana::VALID_SLOT_PERIOD;
 use solana_program_test::*;
 use test_contract::instruction;
 
@@ -25,6 +26,20 @@ fn price_account_all_zero() -> PriceAccount {
 #[tokio::test]
 async fn test_price_not_stale() {
     let mut price = price_account_all_zero();
+    price.agg.pub_slot = 1000 - 10;
+    price.agg.status = PriceStatus::Trading;
+    test_instr_exec_ok(instruction::price_status_check(
+        &price,
+        PriceStatus::Trading,
+    ))
+    .await;
+}
+
+
+#[tokio::test]
+async fn test_price_not_stale_future() {
+    let mut price = price_account_all_zero();
+    price.agg.pub_slot = 1000 + 10;
     price.agg.status = PriceStatus::Trading;
     test_instr_exec_ok(instruction::price_status_check(
         &price,
@@ -38,10 +53,7 @@ async fn test_price_not_stale() {
 async fn test_price_stale() {
     let mut price = price_account_all_zero();
     price.agg.status = PriceStatus::Trading;
-    // Value 100 will cause an overflow because this is bigger than Solana slot in the test suite
-    // (its ~1-5). As the check will be 5u - 100u ~= 1e18 > MAX_SLOT_DIFFERENCE. It can only
-    // break when Solana slot in the test suite becomes between 100 and 100+MAX_SLOT_DIFFERENCE.
-    price.agg.pub_slot = 100;
+    price.agg.pub_slot = 1000 - VALID_SLOT_PERIOD - 1;
 
     #[cfg(feature = "test-bpf")] // Only in BPF the clock check is performed
     let expected_status = PriceStatus::Unknown;