Significant JSON::Stringify, Uint8Array, or ArrayBuffer changes between v5.4 to v6.0.186

[muscovy]

I have a custom buffer-like object whose contents are handed by an ArrayBuffer:

    Local<ArrayBuffer> buf = obj.As<Uint8Array>()->Buffer();

    *data = static_cast<char *>(buf->GetContents().Data());

I also have a js file that uses it, with lines like:

String(data.length)

JSON.stringify(data)

This is called over a few hundred objects.

After upgrading from v8 version 5.4ish to 6.0.186, it seems that for a handful of objects, obj.length is 1-2 smaller than before, and the output of JSON.stringify(obj) is also shorter by that amount (the missing bytes come from anywhere in the buffer). 

Based on what's happening, I think some change in Uint8Array, ArrayBuffer, or possibly JSON::Stringify could be related, but I haven't had any luck so far trying to figure it out. Anyone able to point me in the right direction? Thanks in advance!

[Zac Hansen]

can you provide some examples of outputs that have changed?

[muscovy]

In UTF-8, calling JSON.stringify() on the buffer contents:

Old version: \\�����u�\"~JM@\u0015'7�`��\u001a]G�MA�\u001fJ�.� 

New version: \\���u�\"~JM@\u0015'7�`��\u001a]G�MA�\u001fJ�.�

However, in both versions, calling String(x) on each array element produces the same output:

[0]:92

[1]:137

[2]:242

[3]:152

[4]:138

[5]:251

[6]:117

[7]:216

[8]:34

[9]:126

[10]:74

[11]:77

[12]:64

[13]:21

[14]:39

[15]:55

[16]:165

[17]:96

[18]:135

[19]:197

[20]:26

[21]:93

[22]:71

[23]:134

[24]:77

[25]:65

[26]:230

[27]:31

[28]:74

[29]:184

[30]:46

[31]:141

[Jakob Gruber]

Interesting. It'd be very helpful if you could open a bug at crbug.com/v8/new with a full code example (including build instructions if it includes C++) and instructions to reproduce the issue. Feel free to assign it to me (jgr...@chromium.org) and I'll have a look.

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[muscovy]

Thanks Jakob. Sorry, I'm not sure how to assign issues, but here's the link: https://bugs.chromium.org/p/v8/issues/detail?id=6533

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