Convert verification of options structs to use the new user pointer handling (see r285350).

mojo/system/options_validation.h

Index: mojo/system/options_validation.h
diff --git a/mojo/system/options_validation.h b/mojo/system/options_validation.h
index 04514adf752e1274d015623495393162b5675f4b..90c15685b971e78eff4afb5cf1dbf5c7f4df69c8 100644
--- a/mojo/system/options_validation.h
+++ b/mojo/system/options_validation.h
@@ -14,108 +14,88 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <algorithm>
+
+#include "base/logging.h"
 #include "base/macros.h"
 #include "mojo/public/c/system/types.h"
+#include "mojo/system/constants.h"
 #include "mojo/system/memory.h"
 #include "mojo/system/system_impl_export.h"
 
 namespace mojo {
 namespace system {
 
-// Checks that |buffer| appears to contain a valid Options struct, namely
-// properly aligned and with a |struct_size| field (which must the first field
-// of the struct and be a |uint32_t|) containing a plausible size.
-template <class Options>
-bool IsOptionsStructPointerAndSizeValid(const void* buffer) {
-  COMPILE_ASSERT(offsetof(Options, struct_size) == 0,
-                 Options_struct_size_not_first_member);
-  // TODO(vtl): With C++11, use |sizeof(Options::struct_size)| instead.
-  COMPILE_ASSERT(sizeof(static_cast<const Options*>(buffer)->struct_size) ==
-                     sizeof(uint32_t),
-                 Options_struct_size_not_32_bits);
-
-  // Note: Use |MOJO_ALIGNOF()| here to match the exact macro used in the
-  // declaration of Options structs.
-  if (!internal::VerifyUserPointerHelper<sizeof(uint32_t),
-                                         MOJO_ALIGNOF(Options)>(buffer))
-    return false;
-
-  return static_cast<const Options*>(buffer)->struct_size >= sizeof(uint32_t);
-}
-
-// Checks that the Options struct in |buffer| has a member with the given offset
-// and size. This may be called only if |IsOptionsStructPointerAndSizeValid()|
-// returned true.
-//
-// You may want to use the macro |HAS_OPTIONS_STRUCT_MEMBER()| instead.
-template <class Options, size_t offset, size_t size>
-bool HasOptionsStructMember(const void* buffer) {
-  // We assume that |offset| and |size| are reasonable, since they should come
-  // from |offsetof(Options, some_member)| and |sizeof(Options::some_member)|,
-  // respectively.
-  return static_cast<const Options*>(buffer)->struct_size >=
-      offset + size;
-}
-
-// Macro to invoke |HasOptionsStructMember()| parametrized by member name
-// instead of offset and size.
-//
-// (We can't just give |HasOptionsStructMember()| a member pointer template
-// argument instead, since there's no good/strictly-correct way to get an offset
-// from that.)
-//
-// TODO(vtl): With C++11, use |sizeof(Options::member)| instead.
-#define HAS_OPTIONS_STRUCT_MEMBER(Options, member, buffer) \
-    (HasOptionsStructMember< \
-        Options, \
-        offsetof(Options, member), \
-        sizeof(static_cast<const Options*>(buffer)->member)>(buffer))
-
-// Checks that the (standard) |flags| member consists of only known flags. This
-// should only be called if |HAS_OPTIONS_STRUCT_MEMBER()| returned true for the
-// |flags| field.
-//
-// The rationale for *not* ignoring these flags is that the caller should have a
-// way of specifying that certain options not be ignored. E.g., one may have a
-// |MOJO_..._OPTIONS_FLAG_DONT_IGNORE_FOO| flag and a |foo| member; if the flag
-// is set, it will guarantee that the version of the system knows about the
-// |foo| member (and won't ignore it).
-template <class Options>
-bool AreOptionsFlagsAllKnown(const void* buffer, uint32_t known_flags) {
-  return (static_cast<const Options*>(buffer)->flags & ~known_flags) == 0;
-}
-
-// Does basic cursory checks on |in_options| (|struct_size| and |flags|; |flags|
-// must immediately follow |struct_size|); |in_options| must be non-null. The
-// following should be done before calling this:
-//   - Set |out_options| to the default options.
-//   - If |in_options| is null, don't continue (success).
-// This function then:
-//   - Checks if (according to |IsOptionsStructPointerAndSizeValid()|),
-//     |struct_size| is valid; if not returns |MOJO_RESULT_INVALID_ARGUMENT|.
-//   - If |in_options| has a |flags| field, checks that it only has
-//     |known_flags| set; if so copies it to |out_options->flags|, and if not
-//     returns |MOJO_RESULT_UNIMPLEMENTED|.
-//   - At this point, returns |MOJO_RESULT_OK|.
 template <class Options>
-MojoResult ValidateOptionsStructPointerSizeAndFlags(
-    const Options* in_options,
-    uint32_t known_flags,
-    Options* out_options) {
-  COMPILE_ASSERT(offsetof(Options, flags) == sizeof(uint32_t),
-                 Options_flags_doesnt_immediately_follow_struct_size);
-
-  if (!IsOptionsStructPointerAndSizeValid<Options>(in_options))
-    return MOJO_RESULT_INVALID_ARGUMENT;
-
-  if (HAS_OPTIONS_STRUCT_MEMBER(Options, flags, in_options)) {
-    if (!AreOptionsFlagsAllKnown<Options>(in_options, known_flags))
-      return MOJO_RESULT_UNIMPLEMENTED;
-    out_options->flags = in_options->flags;
+class UserOptionsReader {
+ public:
+  // Constructor from a |UserPointer<const Options>| (which it checks -- this
+  // constructor has side effects!).
+  // Note: We initialize |options_reader_| without checking, since we do a check
+  // in |GetSizeForReader()|.
+  explicit UserOptionsReader(UserPointer<const Options> options)
+      : options_reader_(UserPointer<const char>::Reader::NoCheck(),
+                        options.template ReinterpretCast<const char>(),
+                        GetSizeForReader(options)) {
+    COMPILE_ASSERT(offsetof(Options, struct_size) == 0,
+                   Options_struct_size_not_first_member);
+    // TODO(vtl): With C++11, compile-assert that |sizeof(Options::struct_size)
+    // == sizeof(uint32_t)| somewhere.
   }
 
-  return MOJO_RESULT_OK;
-}
+  bool is_valid() const {
+    return !!options_reader_.GetPointer();
+  }
+
+  const Options& options() const {
+    DCHECK(is_valid());
+    return *reinterpret_cast<const Options*>(options_reader_.GetPointer());
+  }
+
+  // Checks that the given (variable-size) |options| passed to the constructor
+  // (plausibly) has a member at the given offset with the given size. You
+  // probably want to use |OPTIONS_STRUCT_HAS_MEMBER()| instead.
+  bool HasMember(size_t offset, size_t size) const {
+    DCHECK(is_valid());
+    // We assume that |offset| and |size| are reasonable, since they should come
+    // from |offsetof(Options, some_member)| and |sizeof(Options::some_member)|,
+    // respectively.
+    return options().struct_size >= offset + size;
+  }
+
+ private:
+  static inline size_t GetSizeForReader(UserPointer<const Options> options) {
+    uint32_t struct_size =
+        options.template ReinterpretCast<const uint32_t>().Get();
+    if (struct_size < sizeof(uint32_t))
+      return 0;
+
+    // Check the full requested size.
+    // Note: Use |MOJO_ALIGNOF()| here to match the exact macro used in the
+    // declaration of Options structs.
+    internal::CheckUserPointerWithSize<MOJO_ALIGNOF(Options)>(options.pointer_,
+                                                              struct_size);
+    options.template ReinterpretCast<const char>().CheckArray(struct_size);
+    // But we'll never look at more than |sizeof(Options)| bytes.
+    return std::min(static_cast<size_t>(struct_size), sizeof(Options));
+  }
+
+  UserPointer<const char>::Reader options_reader_;
+
+  DISALLOW_COPY_AND_ASSIGN(UserOptionsReader);
+};
+
+// Macro to invoke |UserOptionsReader<Options>::HasMember()| parametrized by
+// member name instead of offset and size.
+//
+// (We can't just give |HasMember()| a member pointer template argument instead,
+// since there's no good/strictly-correct way to get an offset from that.)
+//
+// TODO(vtl): With C++11, use |sizeof(Options::member)| instead of (the
+// contortion below). We might also be able to pull out the type |Options| from
+// |reader| (using |decltype|) instead of requiring a parameter.
+#define OPTIONS_STRUCT_HAS_MEMBER(Options, member, reader) \
+    reader.HasMember(offsetof(Options, member), sizeof(reader.options().member))
 
 }  // namespace system
 }  // namespace mojo