[tarantool-patches] Re: [PATCH] box: add tuple:size function
- From: Vladislav Shpilevoy <v.shpilevoy@xxxxxxxxxxxxx>
- To: tarantool-patches@xxxxxxxxxxxxx, Konstantin Osipov <kostja@xxxxxxxxxxxxx>, Alexander Turenko <alexander.turenko@xxxxxxxxxxxxx>
- Date: Wed, 17 Oct 2018 21:06:37 +0300
On 17/10/2018 18:29, Konstantin Osipov wrote:
* Alexander Turenko <alexander.turenko@xxxxxxxxxxxxx> [18/10/17 10:45]:
Are tuple.bsize and box_tuple_bsize() subjects to change or it is only
about the Lua part?
tuple.bsize is used internally, so I don't think you should change
it. But it's better to rename it to msgpack_size or something like
that to avoid ambiguity.
box_tuple_bsize() should be ok to change.
box_tuple_bsize() is already documented in module.h as
returning only tuple data.
Also, some people can use it right now to allocate a
buffer of a correct size before calling box_tuple_to_buf.
I understand, that box_tuple_to_buf(tuple, NULL, 0) returns
bsize as well, but some people could miss it, or just use
box_tuple_bsize because it looks better when you write like
this:
size = box_tuple_bsize(tuple)
buf = alloc(size)
box_tuple_to_buf(tuple, buf, size)
than like this:
size = box_tuple_to_buf(tuple, NULL, 0) // <- difference
buf = alloc(size)
box_tuple_to_buf(tuple, buf, size)
Even if we close eyes on the fact, that a user of
the first way will allocate more data than needed,
imagine, that then he does something like this:
send(sockfd, buf, size)
Now, he send some garbage uninitialized data of 14
bytes at the end of buf.
I understand, that you likely not believe me that
the first way looks more intuitive, but look at
our own code: box_tuple_bsize() is used now in
*box/lua/tuple.c in tuple_to_mpstream();
* box/lua/tuple.lua via FFI;
to allocate a buffer before copying tuple data
directly or via tuple_to_buf. We can fix our code,
but can not fix user's one.
So here we can either
* fix documentation of the site without breaking anything
* or break behavior of public API destroying an ability to
learn tuple data size in a natural way;
* add new method and again fix the site documentation.
I described it just for the record that you have chosen
the second, most destructive way.
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