C bindings: Implement _DeepCopy() & some unittests.

mojo/public/c/bindings/lib/struct.c

Index: mojo/public/c/bindings/lib/struct.c
diff --git a/mojo/public/c/bindings/lib/struct.c b/mojo/public/c/bindings/lib/struct.c
index 93a552c5c7f75de34f677275f37cc544b31e105b..a0581fada54adc45b2dc5ac5a797e870db4bfe10 100644
--- a/mojo/public/c/bindings/lib/struct.c
+++ b/mojo/public/c/bindings/lib/struct.c
@@ -5,6 +5,7 @@
 #include "mojo/public/c/bindings/struct.h"
 
 #include <assert.h>
+#include <string.h>
 
 #include "mojo/public/c/bindings/lib/type_descriptor.h"
 #include "mojo/public/c/bindings/union.h"
@@ -163,3 +164,37 @@ MojomValidationResult MojomStruct_Validate(
 
   return MOJOM_VALIDATION_ERROR_NONE;
 }
+
+struct MojomStructHeader* MojomStruct_DeepCopy(
+    struct MojomBuffer* buffer,
+    const struct MojomTypeDescriptorStruct* in_type_desc,
+    struct MojomStructHeader* in_struct) {
+  assert(in_type_desc);
+  assert(in_struct);
+  assert(buffer->buf_size - buffer->num_bytes_used >= in_struct->num_bytes);
+
+  struct MojomStructHeader* out_struct =
+      MojomBuffer_Allocate(buffer, in_struct->num_bytes);
+  memcpy(out_struct, in_struct, in_struct->num_bytes);
+
+  for (size_t i = 0; i < in_type_desc->num_entries; i++) {
+    const struct MojomTypeDescriptorStructEntry* entry =
+        &(in_type_desc->entries[i]);
+
+    if (in_struct->version < entry->min_version)
+        continue;
+
+    void* in_elem_data =
+        ((char*)in_struct + sizeof(struct MojomStructHeader) + entry->offset);
+    void* out_elem_data = ((char*)out_struct +
+                           sizeof(struct MojomStructHeader) + entry->offset);
+    MojomType_DispatchDeepCopy(
+        buffer,
+        entry->elem_type,
+        entry->elem_descriptor,
+        in_elem_data,
+        out_elem_data);
+  }
+
+  return out_struct;
+}