Add a test for poll_oneoff

Implementation for POSIX platforms of `poll_oneoff` syscall from WebAssembly System Interface standard should have corresponding tests in WasmKit. This change wires it up via `WASIBridgeToHost` for testability, which then allows exercising clock subscription events in a simple test. Hardcoded test constants for pointer offsets are also generalized to make the test more readable.

Author: MaxDesiatov

Sources/WASI/WASI.swift

@@ -2012,21 +2012,9 @@ public class WASIBridgeToHost: WASI {
         subscriptions: UnsafeGuestBufferPointer<WASIAbi.Subscription>,
         events: UnsafeGuestBufferPointer<WASIAbi.Event>
     ) throws -> WASIAbi.Size {
-        for subscription in subscriptions {
-            switch subscription.union {
-            case .clock:
-                throw WASIAbi.Errno.ENOTSUP
-
-            case .fdRead(let fd), .fdWrite(let fd):
-                guard case let .file(entry) = self.fdTable[fd] else {
-                    throw WASIAbi.Errno.EBADF
-
-                }
-                throw WASIAbi.Errno.ENOTSUP
-            }
-        }
-
-        return 0
+        guard !subscriptions.isEmpty else { throw WASIAbi.Errno.EINVAL }
+        try poll(subscriptions: subscriptions, self.fdTable)
+        return .init(subscriptions.count)
     }
 
     func random_get(buffer: UnsafeGuestPointer<UInt8>, length: WASIAbi.Size) {

Tests/WASITests/WASITests.swift

@@ -147,26 +147,35 @@ final class WASITests: XCTestCase {
         var pointer = start
         let read = WASIAbi.Subscription.Union.fdRead(.init(0))
         let write = WASIAbi.Subscription.Union.fdWrite(.init(0))
-        let clock = WASIAbi.Subscription.Union.clock(.init(id: .REALTIME, timeout: 42, precision: 0, flags: []))
+        let writeOffset = WASIAbi.Subscription.sizeInGuest
+        let timeout: WASIAbi.Timestamp = 100_000_000
+        let clock = WASIAbi.Subscription.Union.clock(.init(id: .REALTIME, timeout: timeout, precision: 0, flags: []))
+        let clockOffset = writeOffset + WASIAbi.Subscription.sizeInGuest
         let event = WASIAbi.Event(userData: 3, error: .EIO, eventType: .fdRead, fdReadWrite: .init(nBytes: 37, flags: [.hangup]))
+        let eventOffset = clockOffset + WASIAbi.Subscription.sizeInGuest
+        let finalOffset = eventOffset + WASIAbi.Event.sizeInGuest
         WASIAbi.Subscription.writeToGuest(at: &pointer, value: .init(userData: 1, union: read))
-        XCTAssertEqual(pointer.offset, 48)
+        XCTAssertEqual(pointer.offset, writeOffset)
         WASIAbi.Subscription.writeToGuest(at: &pointer, value: .init(userData: 2, union: write))
-        XCTAssertEqual(pointer.offset, 48 * 2)
+        XCTAssertEqual(pointer.offset, clockOffset)
         WASIAbi.Subscription.writeToGuest(at: &pointer, value: .init(userData: 3, union: clock))
-        XCTAssertEqual(pointer.offset, 48 * 3)
+        XCTAssertEqual(pointer.offset, eventOffset)
         WASIAbi.Event.writeToGuest(at: &pointer, value: event)
-        XCTAssertEqual(pointer.offset, 48 * 3 + 32)
+        XCTAssertEqual(pointer.offset, finalOffset)
 
         // Test that reading back yields same result
         pointer = start
         XCTAssertEqual(WASIAbi.Subscription.readFromGuest(&pointer), .init(userData: 1, union: read))
-        XCTAssertEqual(pointer.offset, 48)
+        XCTAssertEqual(pointer.offset, writeOffset)
         XCTAssertEqual(WASIAbi.Subscription.readFromGuest(&pointer), .init(userData: 2, union: write))
-        XCTAssertEqual(pointer.offset, 48 * 2)
+        XCTAssertEqual(pointer.offset, clockOffset)
         XCTAssertEqual(WASIAbi.Subscription.readFromGuest(&pointer), .init(userData: 3, union: clock))
-        XCTAssertEqual(pointer.offset, 48 * 3)
+        XCTAssertEqual(pointer.offset, eventOffset)
         XCTAssertEqual(WASIAbi.Event.readFromGuest(&pointer), event)
-        XCTAssertEqual(pointer.offset, 48 * 3 + 32)
+        XCTAssertEqual(pointer.offset, finalOffset)
+        XCTAssertTrue(try ContinuousClock().measure {
+            let clockPointer = UnsafeGuestBufferPointer<WASIAbi.Subscription>(baseAddress: .init(memorySpace: memory, offset: clockOffset), count: 1)
+            XCTAssertEqual(try WASIBridgeToHost().poll_oneoff(subscriptions: clockPointer, events: .init(baseAddress: .init(memorySpace: memory, offset: finalOffset), count: 1)), 1)
+        } > .nanoseconds(timeout))
     }
 }