Fix QStartNoAckMode handling

Author: MaxDesiatov

Sources/GDBRemoteProtocol/GDBHostCommandDecoder.swift

@@ -13,6 +13,7 @@ extension ByteBuffer {
 
 package struct GDBHostCommandDecoder: ByteToMessageDecoder {
     enum Error: Swift.Error {
+        case expectedAck
         case expectedCommandStart
         case unknownCommandKind(String)
         case expectedChecksum
@@ -35,25 +36,41 @@ package struct GDBHostCommandDecoder: ByteToMessageDecoder {
         UInt8(self.accummulatedSum % 256)
     }
 
+    private var isNoAckModeRequested = false
+    private var isNoAckModeActive = false
+
     mutating package func decode(buffer: inout ByteBuffer) throws -> GDBPacket<GDBHostCommand>? {
-        guard let firstStartDelimiter = self.accumulatedDelimiter ?? buffer.readInteger(as: UInt8.self) else {
+        guard var startDelimiter = self.accumulatedDelimiter ?? buffer.readInteger(as: UInt8.self) else {
             // Not enough data to parse.
             return nil
         }
-        guard let secondStartDelimiter = buffer.readInteger(as: UInt8.self) else {
-            // Preserve what we already read.
-            self.accumulatedDelimiter = firstStartDelimiter
 
-            // Not enough data to parse.
-            return nil
+        if !isNoAckModeActive {
+            let firstStartDelimiter = startDelimiter
+
+            guard firstStartDelimiter == UInt8(ascii: "+") else {
+                logger.error("unexpected ack character: \(Character(UnicodeScalar(startDelimiter)))")
+                throw Error.expectedAck
+            }
+
+            if isNoAckModeRequested {
+                self.isNoAckModeActive = true
+            }
+
+            guard let secondStartDelimiter = buffer.readInteger(as: UInt8.self) else {
+                // Preserve what we already read.
+                self.accumulatedDelimiter = firstStartDelimiter
+
+                // Not enough data to parse.
+                return nil
+            }
+
+            startDelimiter = secondStartDelimiter
         }
 
         // Command start delimiters.
-        guard
-            firstStartDelimiter == UInt8(ascii: "+")
-                && secondStartDelimiter == UInt8(ascii: "$")
-        else {
-            logger.error("unexpected delimiter: \(Character(UnicodeScalar(firstStartDelimiter)))\(Character(UnicodeScalar(secondStartDelimiter)))")
+        guard startDelimiter == UInt8(ascii: "$") else {
+            logger.error("unexpected delimiter: \(Character(UnicodeScalar(startDelimiter)))")
             throw Error.expectedCommandStart
         }
 
@@ -106,6 +123,10 @@ package struct GDBHostCommandDecoder: ByteToMessageDecoder {
                 throw Error.checksumIncorrect
             }
 
+            if commandKind == .startNoAckMode {
+                self.isNoAckModeRequested = true
+            }
+
             return .init(
                 payload: .init(
                     kind: commandKind,

Sources/GDBRemoteProtocol/GDBPacket.swift

@@ -1,6 +1,5 @@
 package struct GDBPacket<Payload: Sendable>: Sendable {
     package let payload: Payload
-
     package let checksum: UInt8
 
     package init(payload: Payload, checksum: UInt8) {

Sources/GDBRemoteProtocol/GDBTargetResponse.swift

@@ -18,10 +18,10 @@ package struct GDBTargetResponse {
     }
 
     package let kind: Kind
-    package let isNoAckModeActive: Bool
+    package let isNoAckModeActivated: Bool
 
-    package init(kind: Kind, isNoAckModeActive: Bool) {
+    package init(kind: Kind, isNoAckModeActivated: Bool) {
         self.kind = kind
-        self.isNoAckModeActive = isNoAckModeActive
+        self.isNoAckModeActivated = isNoAckModeActivated
     }
 }

Sources/GDBRemoteProtocol/GDBTargetResponseEncoder.swift

@@ -7,12 +7,17 @@ extension String {
     }
 }
 
-package struct GDBTargetResponseEncoder: MessageToByteEncoder {
+package class GDBTargetResponseEncoder: MessageToByteEncoder {
+    private var isNoAckModeActive = false
+
     package init() {}
     package func encode(data: GDBTargetResponse, out: inout ByteBuffer) throws {
-        if !data.isNoAckModeActive {
+        if !isNoAckModeActive {
             out.writeInteger(UInt8(ascii: "+"))
         }
+        if data.isNoAckModeActivated {
+            self.isNoAckModeActive = true
+        }
         out.writeInteger(UInt8(ascii: "$"))
 
         switch data.kind {

Sources/WasmKitGDBHandler/WasmKitDebugger.swift

@@ -1,12 +1,10 @@
 import GDBRemoteProtocol
 import Logging
+import Synchronization
 import SystemPackage
 import WasmKit
 
 package actor WasmKitDebugger {
-    /// Whether `QStartNoAckMode` command was previously sent.
-    private var isNoAckModeActive = false
-
     private let module: Module
     private let logger: Logger
 
@@ -19,9 +17,14 @@ package actor WasmKitDebugger {
         let responseKind: GDBTargetResponse.Kind
         logger.trace("handling GDB host command", metadata: ["GDBHostCommand": .string(command.kind.rawValue)])
 
+        var isNoAckModeActivated = false
         responseKind =
             switch command.kind {
-            case .startNoAckMode, .isThreadSuffixSupported, .listThreadsInStopReply:
+            case .startNoAckMode:
+                isNoAckModeActivated = true
+                fallthrough
+
+            case .isThreadSuffixSupported, .listThreadsInStopReply:
                 .ok
 
             case .hostInfo:
@@ -38,7 +41,7 @@ package actor WasmKitDebugger {
                 .raw(command.arguments)
 
             case .vContSupportedActions:
-                .vContSupportedActions([.continue, .step, .stop])
+                .vContSupportedActions([.continue, .step])
 
             case .isVAttachOrWaitSupported, .enableErrorStrings:
                 .empty
@@ -64,12 +67,9 @@ package actor WasmKitDebugger {
                 fatalError()
             }
 
-        defer {
-            if command.kind == .startNoAckMode {
-                self.isNoAckModeActive = true
-            }
-        }
-        return .init(kind: responseKind, isNoAckModeActive: self.isNoAckModeActive)
+        logger.trace("handler produced a response", metadata: ["GDBTargetResponse": .string("\(responseKind)")])
+
+        return .init(kind: responseKind, isNoAckModeActivated: isNoAckModeActivated)
     }
 
 }