src: remove UncheckedMalloc(0) workaround

Assuming that UncheckedMalloc(0) returns a non-nullptr is non-standard
and we use other allocators as well (e.g., OPENSSL_malloc) that do not
guarantee this behavior. It is the caller's responsibility to check that
size != 0 implies UncheckedMalloc(size) != nullptr, and that's exactly
what the checked variants (Malloc etc.) already do.

The current behavior is also inconsistent with UncheckedRealloc(), which
always returns a nullptr when the size is 0, and with the documentation
in src/README.md as well as with multiple comments in the source code.

This changes UncheckedMalloc(), UncheckedCalloc(), and
UncheckedRealloc() to always return a nullptr when the size is 0 instead
of doing fake allocations in UncheckedMalloc() and UncheckedCalloc()
while returning a nullptr from UncheckedRealloc(). This is consistent
with existing documentation and comments.

Refs: nodejs#8571
Refs: nodejs#8572

src/string_bytes.cc

@@ -704,20 +704,21 @@ MaybeLocal<Value> StringBytes::Encode(Isolate* isolate,
     }
 
     case UCS2: {
+      size_t str_len = buflen / 2;
       if (IsBigEndian()) {
-        uint16_t* dst = node::UncheckedMalloc<uint16_t>(buflen / 2);
-        if (dst == nullptr) {
+        uint16_t* dst = node::UncheckedMalloc<uint16_t>(str_len);
+        if (str_len != 0 && dst == nullptr) {
           *error = node::ERR_MEMORY_ALLOCATION_FAILED(isolate);
           return MaybeLocal<Value>();
         }
-        for (size_t i = 0, k = 0; k < buflen / 2; i += 2, k += 1) {
+        for (size_t i = 0, k = 0; k < str_len; i += 2, k += 1) {
           // The input is in *little endian*, because that's what Node.js
           // expects, so the high byte comes after the low byte.
           const uint8_t hi = static_cast<uint8_t>(buf[i + 1]);
           const uint8_t lo = static_cast<uint8_t>(buf[i + 0]);
           dst[k] = static_cast<uint16_t>(hi) << 8 | lo;
         }
-        return ExternTwoByteString::New(isolate, dst, buflen / 2, error);
+        return ExternTwoByteString::New(isolate, dst, str_len, error);
       }
       if (reinterpret_cast<uintptr_t>(buf) % 2 != 0) {
         // Unaligned data still means we can't directly pass it to V8.
@@ -728,10 +729,10 @@ MaybeLocal<Value> StringBytes::Encode(Isolate* isolate,
         }
         memcpy(dst, buf, buflen);
         return ExternTwoByteString::New(
-            isolate, reinterpret_cast<uint16_t*>(dst), buflen / 2, error);
+            isolate, reinterpret_cast<uint16_t*>(dst), str_len, error);
       }
       return ExternTwoByteString::NewFromCopy(
-          isolate, reinterpret_cast<const uint16_t*>(buf), buflen / 2, error);
+          isolate, reinterpret_cast<const uint16_t*>(buf), str_len, error);
     }
 
     default:
@@ -747,6 +748,7 @@ MaybeLocal<Value> StringBytes::Encode(Isolate* isolate,
                                       const uint16_t* buf,
                                       size_t buflen,
                                       Local<Value>* error) {
+  if (buflen == 0) return String::Empty(isolate);
   CHECK_BUFLEN_IN_RANGE(buflen);
 
   // Node's "ucs2" encoding expects LE character data inside a

src/util-inl.h

@@ -361,14 +361,12 @@ T* UncheckedRealloc(T* pointer, size_t n) {
 // As per spec realloc behaves like malloc if passed nullptr.
 template <typename T>
 inline T* UncheckedMalloc(size_t n) {
-  if (n == 0) n = 1;
   return UncheckedRealloc<T>(nullptr, n);
 }
 
 template <typename T>
 inline T* UncheckedCalloc(size_t n) {
-  if (n == 0) n = 1;
-  MultiplyWithOverflowCheck(sizeof(T), n);
+  if (MultiplyWithOverflowCheck(sizeof(T), n) == 0) return nullptr;
   return static_cast<T*>(calloc(n, sizeof(T)));
 }
 

test/cctest/test_util.cc

@@ -97,39 +97,39 @@ TEST(UtilTest, ToLower) {
   EXPECT_EQ('a', ToLower('A'));
 }
 
-#define TEST_AND_FREE(expression)                                             \
-  do {                                                                        \
-    auto pointer = expression;                                                \
-    EXPECT_NE(nullptr, pointer);                                              \
-    free(pointer);                                                            \
+#define TEST_AND_FREE(expression, size)                                        \
+  do {                                                                         \
+    auto pointer = expression(size);                                           \
+    EXPECT_EQ(pointer == nullptr, size == 0);                                  \
+    free(pointer);                                                             \
   } while (0)
 
 TEST(UtilTest, Malloc) {
-  TEST_AND_FREE(Malloc<char>(0));
-  TEST_AND_FREE(Malloc<char>(1));
-  TEST_AND_FREE(Malloc(0));
-  TEST_AND_FREE(Malloc(1));
+  TEST_AND_FREE(Malloc<char>, 0);
+  TEST_AND_FREE(Malloc<char>, 1);
+  TEST_AND_FREE(Malloc, 0);
+  TEST_AND_FREE(Malloc, 1);
 }
 
 TEST(UtilTest, Calloc) {
-  TEST_AND_FREE(Calloc<char>(0));
-  TEST_AND_FREE(Calloc<char>(1));
-  TEST_AND_FREE(Calloc(0));
-  TEST_AND_FREE(Calloc(1));
+  TEST_AND_FREE(Calloc<char>, 0);
+  TEST_AND_FREE(Calloc<char>, 1);
+  TEST_AND_FREE(Calloc, 0);
+  TEST_AND_FREE(Calloc, 1);
 }
 
 TEST(UtilTest, UncheckedMalloc) {
-  TEST_AND_FREE(UncheckedMalloc<char>(0));
-  TEST_AND_FREE(UncheckedMalloc<char>(1));
-  TEST_AND_FREE(UncheckedMalloc(0));
-  TEST_AND_FREE(UncheckedMalloc(1));
+  TEST_AND_FREE(UncheckedMalloc<char>, 0);
+  TEST_AND_FREE(UncheckedMalloc<char>, 1);
+  TEST_AND_FREE(UncheckedMalloc, 0);
+  TEST_AND_FREE(UncheckedMalloc, 1);
 }
 
 TEST(UtilTest, UncheckedCalloc) {
-  TEST_AND_FREE(UncheckedCalloc<char>(0));
-  TEST_AND_FREE(UncheckedCalloc<char>(1));
-  TEST_AND_FREE(UncheckedCalloc(0));
-  TEST_AND_FREE(UncheckedCalloc(1));
+  TEST_AND_FREE(UncheckedCalloc<char>, 0);
+  TEST_AND_FREE(UncheckedCalloc<char>, 1);
+  TEST_AND_FREE(UncheckedCalloc, 0);
+  TEST_AND_FREE(UncheckedCalloc, 1);
 }
 
 template <typename T>