Add functions to look up req and handle sizes

Useful for FFI bindings. Closes #370.

include/uv.h

@@ -382,6 +382,18 @@ struct uv_handle_s {
   UV_HANDLE_FIELDS
 };
 
+/*
+ * Returns size of various handle types, useful for FFI
+ * bindings to allocate correct memory without copying struct
+ * definitions
+ */
+UV_EXTERN size_t uv_handle_size(uv_handle_type type);
+
+/*
+ * Returns size of request types, useful for dynamic lookup with FFI
+ */
+UV_EXTERN size_t uv_req_size(uv_req_type type);
+
 /*
  * Returns 1 if the prepare/check/idle/timer handle has been started, 0
  * otherwise. For other handle types this always returns 1.

src/uv-common.c

@@ -32,6 +32,25 @@
 #include "ares/inet_net_pton.h"
 #include "ares/inet_ntop.h"
 
+#define XX(uc, lc) case UV_##uc: return sizeof(uv_##lc##_t);
+
+size_t uv_handle_size(uv_handle_type type) {
+  switch (type) {
+    UV_HANDLE_TYPE_MAP(XX)
+    default:
+      return -1;
+  }
+}
+
+size_t uv_req_size(uv_req_type type) {
+  switch(type) {
+    UV_REQ_TYPE_MAP(XX)
+    default:
+      return -1;
+  }
+}
+
+#undef XX
 
 size_t uv_strlcpy(char* dst, const char* src, size_t size) {
   size_t n;