C bindings: Implement _Validate(), and some pre-requisites

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 d5d54683e0f27a1f16789b222dad2dc86a0298f4..93a552c5c7f75de34f677275f37cc544b31e105b 100644
--- a/mojo/public/c/bindings/lib/struct.c
+++ b/mojo/public/c/bindings/lib/struct.c
@@ -7,7 +7,6 @@
 #include <assert.h>
 
 #include "mojo/public/c/bindings/lib/type_descriptor.h"
-#include "mojo/public/c/bindings/lib/util.h"
 #include "mojo/public/c/bindings/union.h"
 
 size_t MojomStruct_ComputeSerializedSize(
@@ -96,3 +95,71 @@ void MojomStruct_DecodePointersAndHandles(
         in_num_handles);
   }
 }
+
+static bool is_valid_size_for_version(
+    const struct MojomStructHeader* in_struct,
+    const struct MojomTypeDescriptorStructVersion versions[],
+    uint32_t num_versions) {
+  // Scan for a version size in reverse order (assuming structs are often newer
+  // versions than old). Seek to the most recent version that |in_struct| is
+  // compatible with.
+  uint32_t i = num_versions - 1;
+  for (; i > 0 && versions[i].version > in_struct->version; i--);
+
+  if (in_struct->version == versions[i].version) {
+    return in_struct->num_bytes == versions[i].num_bytes;
+  } else {
+    return in_struct->num_bytes >= versions[i].num_bytes;
+  }
+}
+
+MojomValidationResult MojomStruct_Validate(
+    const struct MojomTypeDescriptorStruct* in_type_desc,
+    const struct MojomStructHeader* in_struct,
+    uint32_t in_struct_size,
+    uint32_t in_num_handles,
+    struct MojomValidationContext* inout_context) {
+  assert(in_type_desc);
+  assert(in_struct);
+
+  // Struct header validation.
+  if (in_struct_size < sizeof(struct MojomStructHeader))
+    return MOJOM_VALIDATION_ILLEGAL_MEMORY_RANGE;
+
+  if (in_struct->num_bytes > in_struct_size)
+    return MOJOM_VALIDATION_ILLEGAL_MEMORY_RANGE;
+
+  if (!is_valid_size_for_version(in_struct, in_type_desc->versions,
+                                 in_type_desc->num_versions)) {
+    return MOJOM_VALIDATION_UNEXPECTED_STRUCT_HEADER;
+  }
+
+  if ((in_struct->num_bytes & 7) != 0)
+    return MOJOM_VALIDATION_MISALIGNED_OBJECT;
+
+  // From here on out, all pointers need to point past the end of this struct.
+  inout_context->next_pointer = (char*)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* elem_data = ((char*)in_struct + sizeof(struct MojomStructHeader) +
+                       entry->offset);
+    MojomValidationResult result = MojomType_DispatchValidate(
+        entry->elem_type,
+        entry->elem_descriptor,
+        entry->nullable,
+        elem_data,
+        in_struct_size - ((char*)elem_data - (char*)in_struct),
+        in_num_handles,
+        inout_context);
+    if (result != MOJOM_VALIDATION_ERROR_NONE)
+      return result;
+  }
+
+  return MOJOM_VALIDATION_ERROR_NONE;
+}