Implement Delete Operation Support (#24)

* init delete support

* delete signature refactor

* NF error added

Author: dkz2

Sources/SwiftMemcache/Extensions/UInt8+Characters.swift

@@ -19,6 +19,7 @@ extension UInt8 {
     static var m: UInt8 = .init(ascii: "m")
     static var s: UInt8 = .init(ascii: "s")
     static var g: UInt8 = .init(ascii: "g")
+    static var d: UInt8 = .init(ascii: "d")
     static var v: UInt8 = .init(ascii: "v")
     static var T: UInt8 = .init(ascii: "T")
     static var zero: UInt8 = .init(ascii: "0")

Sources/SwiftMemcache/MemcachedConnection.swift

@@ -59,6 +59,8 @@ public actor MemcachedConnection {
         case connectionShutdown
         /// Indicates that a nil response was received from the server.
         case unexpectedNilResponse
+        /// Indicates that the key was not found.
+        case keyNotFound
     }
 
     private var state: State
@@ -247,4 +249,35 @@ public actor MemcachedConnection {
             throw MemcachedConnectionError.connectionShutdown
         }
     }
+
+    // MARK: - Deleting a Value
+
+    /// Delete the value for a key from the Memcache server.
+    ///
+    /// - Parameter key: The key of the item to be deleted.
+    /// - Throws: A `MemcachedConnectionError.connectionShutdown` error if the connection to the Memcache server is shut down.
+    /// - Throws: A `MemcachedConnectionError.unexpectedNilResponse` error if the key was not found or if an unexpected response code was returned.
+    public func delete(_ key: String) async throws {
+        switch self.state {
+        case .initial(_, _, _, _),
+             .running:
+
+            let command = MemcachedRequest.DeleteCommand(key: key)
+            let request = MemcachedRequest.delete(command)
+
+            let response = try await sendRequest(request)
+
+            switch response.returnCode {
+            case .HD:
+                return
+            case .NF:
+                throw MemcachedConnectionError.keyNotFound
+            default:
+                throw MemcachedConnectionError.unexpectedNilResponse
+            }
+
+        case .finished:
+            throw MemcachedConnectionError.connectionShutdown
+        }
+    }
 }

Sources/SwiftMemcache/MemcachedRequest.swift

@@ -25,6 +25,11 @@ enum MemcachedRequest {
         var flags: MemcachedFlags
     }
 
+    struct DeleteCommand {
+        let key: String
+    }
+
     case set(SetCommand)
     case get(GetCommand)
+    case delete(DeleteCommand)
 }

Sources/SwiftMemcache/MemcachedRequestEncoder.swift

@@ -60,6 +60,19 @@ struct MemcachedRequestEncoder: MessageToByteEncoder {
             // write flags if there are any
             out.writeMemcachedFlags(flags: command.flags)
 
+            // write separator
+            out.writeInteger(UInt8.carriageReturn)
+            out.writeInteger(UInt8.newline)
+
+        case .delete(let command):
+            precondition(!command.key.isEmpty, "Key must not be empty")
+
+            // write command and key
+            out.writeInteger(UInt8.m)
+            out.writeInteger(UInt8.d)
+            out.writeInteger(UInt8.whitespace)
+            out.writeBytes(command.key.utf8)
+
             // write separator
             out.writeInteger(UInt8.carriageReturn)
             out.writeInteger(UInt8.newline)

Tests/SwiftMemcacheTests/IntegrationTest/MemcachedIntegrationTests.swift

@@ -230,6 +230,30 @@ final class MemcachedIntegrationTest: XCTestCase {
         }
     }
 
+    func testDeleteValue() async throws {
+        let group = MultiThreadedEventLoopGroup(numberOfThreads: 1)
+        defer {
+            XCTAssertNoThrow(try! group.syncShutdownGracefully())
+        }
+        let memcachedConnection = MemcachedConnection(host: "memcached", port: 11211, eventLoopGroup: group)
+
+        try await withThrowingTaskGroup(of: Void.self) { group in
+            group.addTask { try await memcachedConnection.run() }
+
+            // Set key and value
+            let setValue = "foo"
+            try await memcachedConnection.set("bar", value: setValue)
+
+            // Delete the key
+            do {
+                try await memcachedConnection.delete("bar")
+            } catch {
+                XCTFail("Deletion attempt should be successful, but threw: \(error)")
+            }
+            group.cancelAll()
+        }
+    }
+
     func testMemcachedConnectionWithUInt() async throws {
         let group = MultiThreadedEventLoopGroup(numberOfThreads: 1)
         defer {

Tests/SwiftMemcacheTests/UnitTest/MemcachedRequestEncoderTests.swift

@@ -139,4 +139,21 @@ final class MemcachedRequestEncoderTests: XCTestCase {
         let expectedEncodedData = "mg foo v\r\n"
         XCTAssertEqual(outBuffer.getString(at: 0, length: outBuffer.readableBytes), expectedEncodedData)
     }
+
+    func testEncodeDeleteRequest() {
+        // Prepare a MemcachedRequest
+        let command = MemcachedRequest.DeleteCommand(key: "foo")
+        let request = MemcachedRequest.delete(command)
+
+        // Pass our request through the encoder
+        var outBuffer = ByteBufferAllocator().buffer(capacity: 0)
+        do {
+            try self.encoder.encode(data: request, out: &outBuffer)
+        } catch {
+            XCTFail("Encoding failed with error: \(error)")
+        }
+
+        let expectedEncodedData = "md foo\r\n"
+        XCTAssertEqual(outBuffer.getString(at: 0, length: outBuffer.readableBytes), expectedEncodedData)
+    }
 }