Move ICMP packet creation and parsing out of Pinger implementation

ios/MullvadVPN.xcodeproj/project.pbxproj

@@ -39,6 +39,7 @@
 		06799AFC28F98EE300ACD94E /* AddressCache.swift in Sources */ = {isa = PBXBuildFile; fileRef = 06AC114128F8413A0037AF9A /* AddressCache.swift */; };
 		0697D6E728F01513007A9E99 /* TransportMonitor.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0697D6E628F01513007A9E99 /* TransportMonitor.swift */; };
 		06AC116228F94C450037AF9A /* ApplicationConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58BFA5CB22A7CE1F00A6173D /* ApplicationConfiguration.swift */; };
+		449275422C3570CA000526DE /* ICMP.swift in Sources */ = {isa = PBXBuildFile; fileRef = 449275412C3570CA000526DE /* ICMP.swift */; };
 		449872E12B7BBC5400094DDC /* TunnelSettingsUpdate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 449872E02B7BBC5400094DDC /* TunnelSettingsUpdate.swift */; };
 		449872E42B7CB96300094DDC /* TunnelSettingsUpdateTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 449872E32B7CB96300094DDC /* TunnelSettingsUpdateTests.swift */; };
 		449EBA262B975B9700DFA4EB /* PostQuantumKeyReceiving.swift in Sources */ = {isa = PBXBuildFile; fileRef = 449EBA252B975B9700DFA4EB /* PostQuantumKeyReceiving.swift */; };
@@ -1451,6 +1452,7 @@
 		06FAE67A28F83CA50033DD93 /* RESTDevicesProxy.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = RESTDevicesProxy.swift; sourceTree = "<group>"; };
 		06FAE67B28F83CA50033DD93 /* REST.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = REST.swift; sourceTree = "<group>"; };
 		06FAE67D28F83CA50033DD93 /* RESTTransport.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = RESTTransport.swift; sourceTree = "<group>"; };
+		449275412C3570CA000526DE /* ICMP.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ICMP.swift; sourceTree = "<group>"; };
 		449872E02B7BBC5400094DDC /* TunnelSettingsUpdate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TunnelSettingsUpdate.swift; sourceTree = "<group>"; };
 		449872E32B7CB96300094DDC /* TunnelSettingsUpdateTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TunnelSettingsUpdateTests.swift; sourceTree = "<group>"; };
 		449EB9FC2B95F8AD00DFA4EB /* DeviceMock.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = DeviceMock.swift; sourceTree = "<group>"; };
@@ -3419,6 +3421,7 @@
 				58218E1428B65058000C624F /* IPv4Header.h */,
 				5838318A27C40A3900000571 /* Pinger.swift */,
 				58799A352A84FC9F007BE51F /* PingerProtocol.swift */,
+				449275412C3570CA000526DE /* ICMP.swift */,
 			);
 			path = Pinger;
 			sourceTree = "<group>";
@@ -5615,6 +5618,7 @@
 				58C7A4512A863FB50060C66F /* PingerProtocol.swift in Sources */,
 				583832292AC3DF1300EA2071 /* PacketTunnelActorCommand.swift in Sources */,
 				58CF95A22AD6F35800B59F5D /* ObservedState.swift in Sources */,
+				449275422C3570CA000526DE /* ICMP.swift in Sources */,
 				583832232AC3181400EA2071 /* PacketTunnelActor+ErrorState.swift in Sources */,
 				58C7AF112ABD8480007EDD7A /* TunnelProviderMessage.swift in Sources */,
 				58C7AF162ABD84A8007EDD7A /* URLRequestProxy.swift in Sources */,

ios/PacketTunnelCore/Pinger/ICMP.swift

@@ -0,0 +1,119 @@
+//
+//  ICMP.swift
+//  PacketTunnelCore
+//
+//  Created by Andrew Bulhak on 2024-07-03.
+//  Copyright © 2024 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+struct ICMP {
+    public enum Error: LocalizedError {
+        case malformedResponse(MalformedResponseReason)
+
+        public var errorDescription: String? {
+            switch self {
+            case let .malformedResponse(reason):
+                return "Malformed response: \(reason)."
+            }
+        }
+    }
+
+    public enum MalformedResponseReason {
+        case ipv4PacketTooSmall
+        case icmpHeaderTooSmall
+        case invalidIPVersion
+        case checksumMismatch(UInt16, UInt16)
+    }
+
+    private static func in_chksum(_ data: some Sequence<UInt8>) -> UInt16 {
+        var iterator = data.makeIterator()
+        var words = [UInt16]()
+
+        while let byte = iterator.next() {
+            let nextByte = iterator.next() ?? 0
+            let word = UInt16(byte) << 8 | UInt16(nextByte)
+
+            words.append(word)
+        }
+
+        let sum = words.reduce(0, &+)
+
+        return ~sum
+    }
+
+    static func createICMPPacket(identifier: UInt16, sequenceNumber: UInt16) -> Data {
+        var header = ICMPHeader(
+            type: UInt8(ICMP_ECHO),
+            code: 0,
+            checksum: 0,
+            identifier: identifier.bigEndian,
+            sequenceNumber: sequenceNumber.bigEndian
+        )
+        header.checksum = withUnsafeBytes(of: &header) { in_chksum($0).bigEndian }
+
+        return withUnsafeBytes(of: &header) { Data($0) }
+    }
+
+    static func parseICMPResponse(buffer: inout [UInt8], length: Int) throws -> ICMPHeader {
+        try buffer.withUnsafeMutableBytes { bufferPointer in
+            // Check IP packet size.
+            guard length >= MemoryLayout<IPv4Header>.size else {
+                throw Error.malformedResponse(.ipv4PacketTooSmall)
+            }
+
+            // Verify IPv4 header.
+            let ipv4Header = bufferPointer.load(as: IPv4Header.self)
+            let payloadLength = length - ipv4Header.headerLength
+
+            guard payloadLength >= MemoryLayout<ICMPHeader>.size else {
+                throw Error.malformedResponse(.icmpHeaderTooSmall)
+            }
+
+            guard ipv4Header.isIPv4Version else {
+                throw Error.malformedResponse(.invalidIPVersion)
+            }
+
+            // Parse ICMP header.
+            let icmpHeaderPointer = bufferPointer.baseAddress!
+                .advanced(by: ipv4Header.headerLength)
+                .assumingMemoryBound(to: ICMPHeader.self)
+
+            // Copy server checksum.
+            let serverChecksum = icmpHeaderPointer.pointee.checksum.bigEndian
+
+            // Reset checksum field before calculating checksum.
+            icmpHeaderPointer.pointee.checksum = 0
+
+            // Verify ICMP checksum.
+            let payloadPointer = UnsafeRawBufferPointer(
+                start: icmpHeaderPointer,
+                count: payloadLength
+            )
+            let clientChecksum = ICMP.in_chksum(payloadPointer)
+            if clientChecksum != serverChecksum {
+                throw Error.malformedResponse(.checksumMismatch(clientChecksum, serverChecksum))
+            }
+
+            // Ensure endianness before returning ICMP packet to delegate.
+            var icmpHeader = icmpHeaderPointer.pointee
+            icmpHeader.identifier = icmpHeader.identifier.bigEndian
+            icmpHeader.sequenceNumber = icmpHeader.sequenceNumber.bigEndian
+            icmpHeader.checksum = serverChecksum
+            return icmpHeader
+        }
+    }
+}
+
+private extension IPv4Header {
+    /// Returns IPv4 header length.
+    var headerLength: Int {
+        Int(versionAndHeaderLength & 0x0F) * MemoryLayout<UInt32>.size
+    }
+
+    /// Returns `true` if version header indicates IPv4.
+    var isIPv4Version: Bool {
+        (versionAndHeaderLength & 0xF0) == 0x40
+    }
+}

ios/PacketTunnelCore/Pinger/Pinger.swift

@@ -125,7 +125,7 @@ public final class Pinger: PingerProtocol {
         }
 
         let sequenceNumber = nextSequenceNumber()
-        let packetData = Self.createICMPPacket(
+        let packetData = ICMP.createICMPPacket(
             identifier: identifier,
             sequenceNumber: sequenceNumber
         )
@@ -177,7 +177,13 @@ public final class Pinger: PingerProtocol {
         do {
             guard bytesRead > 0 else { throw Error.receivePacket(errno) }
 
-            let icmpHeader = try parseICMPResponse(buffer: &readBuffer, length: bytesRead)
+            let icmpHeader = try ICMP.parseICMPResponse(buffer: &readBuffer, length: bytesRead)
+            guard icmpHeader.identifier == identifier else {
+                throw Error.clientIdentifierMismatch
+            }
+            guard icmpHeader.type == ICMP_ECHOREPLY else {
+                throw Error.invalidICMPType(icmpHeader.type)
+            }
             guard let sender = Self.makeIPAddress(from: address) else { throw Error.parseIPAddress }
 
             replyQueue.async {
@@ -192,65 +198,6 @@ public final class Pinger: PingerProtocol {
         }
     }
 
-    private func parseICMPResponse(buffer: inout [UInt8], length: Int) throws -> ICMPHeader {
-        try buffer.withUnsafeMutableBytes { bufferPointer in
-            // Check IP packet size.
-            guard length >= MemoryLayout<IPv4Header>.size else {
-                throw Error.malformedResponse(.ipv4PacketTooSmall)
-            }
-
-            // Verify IPv4 header.
-            let ipv4Header = bufferPointer.load(as: IPv4Header.self)
-            let payloadLength = length - ipv4Header.headerLength
-
-            guard payloadLength >= MemoryLayout<ICMPHeader>.size else {
-                throw Error.malformedResponse(.icmpHeaderTooSmall)
-            }
-
-            guard ipv4Header.isIPv4Version else {
-                throw Error.malformedResponse(.invalidIPVersion)
-            }
-
-            // Parse ICMP header.
-            let icmpHeaderPointer = bufferPointer.baseAddress!
-                .advanced(by: ipv4Header.headerLength)
-                .assumingMemoryBound(to: ICMPHeader.self)
-
-            // Check if ICMP response identifier matches the one from sender.
-            guard icmpHeaderPointer.pointee.identifier.bigEndian == identifier else {
-                throw Error.clientIdentifierMismatch
-            }
-
-            // Verify ICMP type.
-            guard icmpHeaderPointer.pointee.type == ICMP_ECHOREPLY else {
-                throw Error.malformedResponse(.invalidEchoReplyType)
-            }
-
-            // Copy server checksum.
-            let serverChecksum = icmpHeaderPointer.pointee.checksum.bigEndian
-
-            // Reset checksum field before calculating checksum.
-            icmpHeaderPointer.pointee.checksum = 0
-
-            // Verify ICMP checksum.
-            let payloadPointer = UnsafeRawBufferPointer(
-                start: icmpHeaderPointer,
-                count: payloadLength
-            )
-            let clientChecksum = in_chksum(payloadPointer)
-            if clientChecksum != serverChecksum {
-                throw Error.malformedResponse(.checksumMismatch(clientChecksum, serverChecksum))
-            }
-
-            // Ensure endianness before returning ICMP packet to delegate.
-            var icmpHeader = icmpHeaderPointer.pointee
-            icmpHeader.identifier = icmpHeader.identifier.bigEndian
-            icmpHeader.sequenceNumber = icmpHeader.sequenceNumber.bigEndian
-            icmpHeader.checksum = serverChecksum
-            return icmpHeader
-        }
-    }
-
     private func bindSocket(_ socket: CFSocket, to interfaceName: String) throws {
         var index = if_nametoindex(interfaceName)
         guard index > 0 else {
@@ -270,19 +217,6 @@ public final class Pinger: PingerProtocol {
         }
     }
 
-    private class func createICMPPacket(identifier: UInt16, sequenceNumber: UInt16) -> Data {
-        var header = ICMPHeader(
-            type: UInt8(ICMP_ECHO),
-            code: 0,
-            checksum: 0,
-            identifier: identifier.bigEndian,
-            sequenceNumber: sequenceNumber.bigEndian
-        )
-        header.checksum = withUnsafeBytes(of: &header) { in_chksum($0).bigEndian }
-
-        return withUnsafeBytes(of: &header) { Data($0) }
-    }
-
     private class func makeIPAddress(from sa: sockaddr) -> IPAddress? {
         if sa.sa_family == AF_INET {
             return withUnsafeBytes(of: sa) { buffer -> IPAddress? in
@@ -337,12 +271,12 @@ extension Pinger {
         /// Failure to receive packet. Contains the `errno`.
         case receivePacket(Int32)
 
+        /// Unexpected ICMP reply type
+        case invalidICMPType(UInt8)
+
         /// Response identifier does not match the sender identifier.
         case clientIdentifierMismatch
 
-        /// Malformed response.
-        case malformedResponse(MalformedResponseReason)
-
         /// Failure to parse IP address.
         case parseIPAddress
 
@@ -362,51 +296,13 @@ extension Pinger {
                 return "Failure to send packet (errno: \(code))."
             case let .receivePacket(code):
                 return "Failure to receive packet (errno: \(code))."
+            case let .invalidICMPType(type):
+                return "Unexpected ICMP reply type: \(type)"
             case .clientIdentifierMismatch:
                 return "Response identifier does not match the sender identifier."
-            case let .malformedResponse(reason):
-                return "Malformed response: \(reason)."
             case .parseIPAddress:
                 return "Failed to parse IP address."
             }
         }
     }
-
-    public enum MalformedResponseReason {
-        case ipv4PacketTooSmall
-        case icmpHeaderTooSmall
-        case invalidIPVersion
-        case invalidEchoReplyType
-        case checksumMismatch(UInt16, UInt16)
-    }
-}
-
-private func in_chksum(_ data: some Sequence<UInt8>) -> UInt16 {
-    var iterator = data.makeIterator()
-    var words = [UInt16]()
-
-    while let byte = iterator.next() {
-        let nextByte = iterator.next() ?? 0
-        let word = UInt16(byte) << 8 | UInt16(nextByte)
-
-        words.append(word)
-    }
-
-    let sum = words.reduce(0, &+)
-
-    return ~sum
-}
-
-private extension IPv4Header {
-    /// Returns IPv4 header length.
-    var headerLength: Int {
-        Int(versionAndHeaderLength & 0x0F) * MemoryLayout<UInt32>.size
-    }
-
-    /// Returns `true` if version header indicates IPv4.
-    var isIPv4Version: Bool {
-        (versionAndHeaderLength & 0xF0) == 0x40
-    }
-
-    // swiftlint:disable:next file_length
 }