# `uv_req_t` — Base request

uv_req_t is the base type for all libuv request types.

Structures are aligned so that any libuv request can be cast to uv_req_t. All API functions defined here work with any request type.

## Data types

type uv_req_t

  The base libuv request structure.

type uv_any_req

  Union of all request types.

### Public members

void *uv_req_t.data

  Space for user-defined arbitrary data. libuv does not use this field.

uv_req_type uv_req_t.type

  Indicated the type of request. Readonly.

      typedef enum {
          UV_UNKNOWN_REQ = 0,
          UV_REQ,
          UV_CONNECT,
          UV_WRITE,
          UV_SHUTDOWN,
          UV_UDP_SEND,
          UV_FS,
          UV_WORK,
          UV_GETADDRINFO,
          UV_GETNAMEINFO,
          UV_REQ_TYPE_MAX,
      } uv_req_type;

## API

UV_REQ_TYPE_MAP(iter_macro)

  Macro that expands to a series of invocations of iter_macro for each of the request types. iter_macro is invoked with two arguments: the name of the uv_req_type element without the UV_ prefix, and the name of the corresponding structure type without the uv_ prefix and _t suffix.

int uv_cancel(uv_req_t *req)

  Cancel a pending request. Fails if the request is executing or has finished executing.

  Returns 0 on success, or an error code < 0 on failure.

  Only cancellation of `uv_fs_t`, `uv_getaddrinfo_t`, `uv_getnameinfo_t`, `uv_random_t` and `uv_work_t` requests is currently supported.

  Cancelled requests have their callbacks invoked some time in the future. It’s not safe to free the memory associated with the request until the callback is called.

  Here is how cancellation is reported to the callback:

  - A `uv_fs_t` request has its req->result field set to UV_ECANCELED.

  - A `uv_work_t`, `uv_getaddrinfo_t`, `uv_getnameinfo_t` or `uv_random_t` request has its callback invoked with status == UV_ECANCELED.

size_t uv_req_size(uv_req_type type)

  Returns the size of the given request type. Useful for FFI binding writers who don’t want to know the structure layout.

void *uv_req_get_data(const uv_req_t *req)

  Returns req->data.

  New in version 1.19.0.

void *uv_req_set_data(uv_req_t *req, void *data)

  Sets req->data to data.

  New in version 1.19.0.

uv_req_type uv_req_get_type(const uv_req_t *req)

  Returns req->type.

  New in version 1.19.0.

const char *uv_req_type_name(uv_req_type type)

  Returns the name for the equivalent struct for a given request type, e.g. “connect” (as in `uv_connect_t`) for UV_CONNECT.

  If no such request type exists, this returns NULL.

  New in version 1.19.0.