Detect EOF when reading stdio from terminal on Mac OS

runtime/bin/socket.cc

Index: runtime/bin/socket.cc
diff --git a/runtime/bin/socket.cc b/runtime/bin/socket.cc
index a5e64dd2095f712c06bc49b5ae86eb603353494e..0d07897ea18d62d852d5c62757dd76c2f11c1296 100644
--- a/runtime/bin/socket.cc
+++ b/runtime/bin/socket.cc
@@ -149,12 +149,19 @@ void FUNCTION_NAME(Socket_Read)(Dart_NativeArguments args) {
       intptr_t bytes_read = Socket::Read(socket, buffer, length);
       if (bytes_read == length) {
         Dart_SetReturnValue(args, result);
-      } else if (bytes_read == 0) {
-        // On MacOS when reading from a tty Ctrl-D will result in one
-        // byte reported as available. Attempting to read it out will
-        // result in zero bytes read. When that happens there is no
-        // data which is indicated by a null return value.
-        Dart_SetReturnValue(args, Dart_Null());
+      } else if (bytes_read < length) {
+        // On MacOS when reading from a tty Ctrl-D will result in reading one
+        // less byte then reported as available.
+        if (bytes_read == 0) {
+          Dart_SetReturnValue(args, Dart_Null());
+        } else {
+          uint8_t* new_buffer = NULL;
+          Dart_Handle new_result = IOBuffer::Allocate(bytes_read, &new_buffer);
+          if (Dart_IsError(new_result)) Dart_PropagateError(new_result);
+          ASSERT(new_buffer != NULL);
+          memmove(new_buffer, buffer, bytes_read);
+          Dart_SetReturnValue(args, new_result);
+        }
       } else {
         ASSERT(bytes_read == -1);
         Dart_SetReturnValue(args, DartUtils::NewDartOSError());