This is a layer 3 TUN driver for Windows 7, 8, 8.1, and 10. Originally created for [WireGuard](https://www.wireguard.com/), it is intended to be useful to a wide variety of projects that require layer 3 tunneling devices with implementations primarily in userspace.
Wintun is deployed as a platform-specific `wintun.dll` file. Install the `wintun.dll` file side-by-side with your application. Download the dll from [wintun.net](https://www.wintun.net/), alongside the header file for your application described below.
Include the [`wintun.h` file](https://git.zx2c4.com/wintun/tree/api/wintun.h) in your project simply by copying it there and dynamically load the `wintun.dll` using [`LoadLibraryEx()`](https://docs.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-loadlibraryexa) and [`GetProcAddress()`](https://docs.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-getprocaddress) to resolve each function, using the typedefs provided in the header file. The [`InitializeWintun` function in the example.c code](https://git.zx2c4.com/wintun/tree/example/example.c) provides this in a function that you can simply copy and paste.
With the library setup, Wintun can then be used by first creating an adapter, and then starting a tunnel session on that adapter. Adapters have names (e.g. "OfficeNet"), and each one belongs to a _pool_ (e.g. "WireGuard"). So, for example, the WireGuard application app creates multiple tunnels all inside of its "WireGuard" _pool_:
Then, the `WintunAllocateSendPacket` and `WintunSendPacket` functions can be used for sending packets ([used by `SendPackets` in the example.c code](https://git.zx2c4.com/wintun/tree/example/example.c)):
And the `WintunReceivePacket` and `WintunReleaseReceivePacket` functions can be used for receiving packets ([used by `ReceivePackets` in the example.c code](https://git.zx2c4.com/wintun/tree/example/example.c)):
Some high performance use cases may want to spin on `WintunReceivePackets` for a number of cycles before falling back to waiting on the read-wait event.
You are **highly encouraged** to read the [**example.c short example**](https://git.zx2c4.com/wintun/tree/example/example.c) to see how to put together a simple userspace network tunnel.
- *Pool*: Name of the adapter pool. Zero-terminated string of up to WINTUN\_MAX\_POOL-1 characters.
- *Name*: The requested name of the adapter. Zero-terminated string of up to MAX\_ADAPTER\_NAME-1 characters.
- *RequestedGUID*: The GUID of the created network adapter, which then influences NLA generation deterministically. If it is set to NULL, the GUID is chosen by the system at random, and hence a new NLA entry is created for each new adapter. It is called "requested" GUID because the API it uses is completely undocumented, and so there could be minor interesting complications with its usage.
- *RebootRequired*: Optional pointer to a boolean flag to be set to TRUE in case SetupAPI suggests a reboot.
**Returns**
If the function succeeds, the return value is the adapter handle. Must be released with WintunFreeAdapter. If the function fails, the return value is NULL. To get extended error information, call GetLastError.
If the function succeeds, the return value is adapter handle. Must be released with WintunFreeAdapter. If the function fails, the return value is NULL. To get extended error information, call GetLastError. Possible errors include the following: ERROR\_FILE\_NOT\_FOUND if adapter with given name is not found; ERROR\_ALREADY\_EXISTS if adapter is found but not a Wintun-class or not a member of the pool
- *Adapter*: Adapter handle obtained with WintunOpenAdapter or WintunCreateAdapter.
- *ForceCloseSessions*: Force close adapter handles that may be in use by other processes. Only set this to TRUE with extreme care, as this is resource intensive and may put processes into an undefined or unpredictable state. Most users should set this to FALSE.
- *RebootRequired*: Optional pointer to a boolean flag to be set to TRUE in case SetupAPI suggests a reboot.
**Returns**
If the function succeeds, the return value is nonzero. If the function fails, the return value is zero. To get extended error information, call GetLastError.
#### WintunEnumAdapters()
`BOOL WintunEnumAdapters (const WCHAR * Pool, WINTUN_ENUM_CALLBACK Callback, LPARAM Param)`
Enumerates all Wintun adapters.
**Parameters**
- *Pool*: Name of the adapter pool. Zero-terminated string of up to WINTUN\_MAX\_POOL-1 characters.
- *Callback*: Callback function. To continue enumeration, the callback function must return TRUE; to stop enumeration, it must return FALSE.
- *Param*: An application-defined value to be passed to the callback function.
**Returns**
If the function succeeds, the return value is nonzero. If the function fails, the return value is zero. To get extended error information, call GetLastError.
Deletes all Wintun adapters in a pool and if there are no more adapters in any other pools, also removes Wintun from the driver store, usually called by uninstallers.
If the function succeeds, the return value is nonzero. If the function fails, the return value is zero. To get extended error information, call GetLastError.
If the function succeeds, the return value is adapter device object handle. Must be released with CloseHandle. If the function fails, the return value is INVALID\_HANDLE\_VALUE. To get extended error information, call GetLastError.
- *Name*: Pointer to a string to receive adapter name
**Returns**
If the function succeeds, the return value is nonzero. If the function fails, the return value is zero. To get extended error information, call GetLastError.
- *Name*: Adapter name. Zero-terminated string of up to MAX\_ADAPTER\_NAME-1 characters.
**Returns**
If the function succeeds, the return value is nonzero. If the function fails, the return value is zero. To get extended error information, call GetLastError.
#### WintunGetRunningDriverVersion()
`DWORD WintunGetRunningDriverVersion (void )`
Determines the version of the Wintun driver currently loaded.
**Returns**
If the function succeeds, the return value is the version number. If the function fails, the return value is zero. To get extended error information, call GetLastError. Possible errors include the following: ERROR\_FILE\_NOT\_FOUND Wintun not loaded
- *NewLogger*: Pointer to callback function to use as a new global logger. NewLogger may be called from various threads concurrently. Should the logging require serialization, you must handle serialization in NewLogger. Set to NULL to disable.
- *Capacity*: Rings capacity. Must be between WINTUN\_MIN\_RING\_CAPACITY and WINTUN\_MAX\_RING\_CAPACITY (incl.) Must be a power of two.
**Returns**
Wintun session handle. Must be released with WintunEndSession. If the function fails, the return value is NULL. To get extended error information, call GetLastError.
- *Session*: Wintun session handle obtained with WintunStartSession
**Returns**
Pointer to receive event handle to wait for available data when reading. Should WintunReceivePackets return ERROR\_NO\_MORE\_ITEMS (after spinning on it for a while under heavy load), wait for this event to become signaled before retrying WintunReceivePackets. Do not call CloseHandle on this event - it is managed by the session.
Retrieves one or packet. After the packet content is consumed, call WintunReleaseReceivePacket with Packet returned from this function to release internal buffer. This function is thread-safe.
- *Session*: Wintun session handle obtained with WintunStartSession
- *PacketSize*: Pointer to receive packet size.
**Returns**
Pointer to layer 3 IPv4 or IPv6 packet. Client may modify its content at will. If the function fails, the return value is NULL. To get extended error information, call GetLastError. Possible errors include the following: ERROR\_HANDLE\_EOF Wintun adapter is terminating; ERROR\_NO\_MORE\_ITEMS Wintun buffer is exhausted; ERROR\_INVALID\_DATA Wintun buffer is corrupt
Allocates memory for a packet to send. After the memory is filled with packet data, call WintunSendPacket to send and release internal buffer. WintunAllocateSendPacket is thread-safe and the WintunAllocateSendPacket order of calls define the packet sending order.
**Parameters**
- *Session*: Wintun session handle obtained with WintunStartSession
- *PacketSize*: Exact packet size. Must be less or equal to WINTUN\_MAX\_IP\_PACKET\_SIZE.
**Returns**
Returns pointer to memory where to prepare layer 3 IPv4 or IPv6 packet for sending. If the function fails, the return value is NULL. To get extended error information, call GetLastError. Possible errors include the following: ERROR\_HANDLE\_EOF Wintun adapter is terminating; ERROR\_BUFFER\_OVERFLOW Wintun buffer is full;
Sends the packet and releases internal buffer. WintunSendPacket is thread-safe, but the WintunAllocateSendPacket order of calls define the packet sending order. This means the packet is not guaranteed to be sent in the WintunSendPacket yet.
**Parameters**
- *Session*: Wintun session handle obtained with WintunStartSession
- *Packet*: Packet obtained with WintunAllocateSendPacket
**Do not distribute drivers or files named "Wintun", as they will most certainly clash with official deployments. Instead distribute [`wintun.dll` as downloaded from wintun.net](https://www.wintun.net).**
`wintun.sln` may be opened in Visual Studio for development and building. Be sure to run `bcdedit /set testsigning on` before to enable unsigned driver loading. The default run sequence (F5) in Visual Studio will build the example project.
