Add helpers for accessing data in libuv handles

Libuv handles have a single generic pointer for storing user data, this adds
some functions for adding/retrieving pointers to "slots" in the new `HandleData`
structure, which increase flexibility when using shared handles(job streams for
example)

src/os/uv_helpers.c

@@ -0,0 +1,70 @@
+#include <uv.h>
+
+#include "os/uv_helpers.h"
+#include "vim.h"
+#include "memory.h"
+
+/// Common structure that will always be assigned to the `data` field of
+/// libuv handles. It has fields for many types of pointers, and allow a single
+/// handle to contain data from many sources
+typedef struct {
+  WStream *wstream;
+  RStream *rstream;
+  Job *job;
+} HandleData;
+
+static HandleData *init(uv_handle_t *handle);
+
+RStream *handle_get_rstream(uv_handle_t *handle)
+{
+  RStream *rv = init(handle)->rstream;
+  assert(rv != NULL);
+  return rv;
+}
+
+void handle_set_rstream(uv_handle_t *handle, RStream *rstream)
+{
+  init(handle)->rstream = rstream;
+}
+
+WStream *handle_get_wstream(uv_handle_t *handle)
+{
+  WStream *rv = init(handle)->wstream;
+  assert(rv != NULL);
+  return rv;
+}
+
+void handle_set_wstream(uv_handle_t *handle, WStream *wstream)
+{
+  HandleData *data = init(handle);
+  data->wstream = wstream;
+}
+
+Job *handle_get_job(uv_handle_t *handle)
+{
+  Job *rv = init(handle)->job;
+  assert(rv != NULL);
+  return rv;
+}
+
+void handle_set_job(uv_handle_t *handle, Job *job)
+{
+  init(handle)->job = job;
+}
+
+static HandleData *init(uv_handle_t *handle)
+{
+  HandleData *rv;
+
+  if (handle->data == NULL) {
+    rv = xmalloc(sizeof(HandleData));
+    rv->rstream = NULL;
+    rv->wstream = NULL;
+    rv->job = NULL;
+    handle->data = rv;
+  } else {
+    rv = handle->data;
+  }
+
+  return rv;
+}

src/os/uv_helpers.h

@@ -0,0 +1,47 @@
+#ifndef NEOVIM_OS_UV_HELPERS_H
+#define NEOVIM_OS_UV_HELPERS_H
+
+#include <uv.h>
+
+#include "os/wstream_defs.h"
+#include "os/rstream_defs.h"
+#include "os/job_defs.h"
+
+/// Gets the RStream instance associated with a libuv handle
+///
+/// @param handle libuv handle
+/// @return the RStream pointer
+RStream *handle_get_rstream(uv_handle_t *handle);
+
+/// Associates a RStream instance with a libuv handle
+///
+/// @param handle libuv handle
+/// @param rstream the RStream pointer
+void handle_set_rstream(uv_handle_t *handle, RStream *rstream);
+
+/// Gets the WStream instance associated with a libuv handle
+///
+/// @param handle libuv handle
+/// @return the WStream pointer
+WStream *handle_get_wstream(uv_handle_t *handle);
+
+/// Associates a WStream instance with a libuv handle
+///
+/// @param handle libuv handle
+/// @param wstream the WStream pointer
+void handle_set_wstream(uv_handle_t *handle, WStream *wstream);
+
+/// Gets the Job instance associated with a libuv handle
+///
+/// @param handle libuv handle
+/// @return the Job pointer
+Job *handle_get_job(uv_handle_t *handle);
+
+/// Associates a Job instance with a libuv handle
+///
+/// @param handle libuv handle
+/// @param job the Job pointer
+void handle_set_job(uv_handle_t *handle, Job *job);
+
+#endif  // NEOVIM_OS_UV_HELPERS_H
+