How to return the table with tuples of the SELECT()?

It tarantool-cartridge. Caller function:

local function http_redirections(req)
    log.info("-- redirections started")

    local b_id = tostring(req)
    local bucket_id = vshard.router.bucket_id_mpcrc32(b_id)
    log.info("-- bucket_id: %s", bucket_id)
    local answer, error = err_vshard_router:pcall(
        vshard.router.call,
        bucket_id,
        'read',
        'redirections'
    )

    for k, v in pairs(answer) do log.info(" http: key: %s value: %s", k, v) end
end

Handler:

local function redirections(req)
    log.info("-- redirections handler started")
    local response = {}
    local answer = {}
    response = box.space.space_name:select()
    for k, v in pairs(response) do answer[k] = v end
    for k, v in pairs(answer) do log.info("key: %s value: %s", k, v) end
    log.info("-- response size: %d", #answer)
    return answer
end

Result in the calling function: http: key: 1 value: table: 0x418e3d10 http: key: 2 value Result in handler OK: key = value from select(). Why does a table from a table return to the calling function ?

Solution

In short, you don't have any legal ways to return tuples from netbox/vshard call.

How does it work:

-- You have a tuple
tuple = box.tuple.new({1, 2, 3})
tarantool> box.tuple.is(tuple) -- It's tuple, cdata object
---
- true
...
-- In order to transfer your tuple via network you need convert
-- them to binary form
msgpack = require('msgpack')
tarantool> msgpack.encode(tuple)
---
- !!binary kwECAw==
...
-- But you don't know after that it was a tuple or simple lua table
tarantool> msgpack.encode({1, 2, 3}) -- The same, but input is a lua table
---
- !!binary kwECAw==
...
-- After receive you need to decode you tuple/table back to lua object
tarantool> msgpack.decode(msgpack.encode({1, 2, 3}))
---
- [1, 2, 3]
- 5
...

tarantool> msgpack.decode(msgpack.encode(tuple))
---
- [1, 2, 3]
- 5
...
tarantool> box.tuple.is(msgpack.decode(msgpack.encode(tuple)))
---
- false
...

But if you use connection you could directly call "select/insert/..." functions directly. Since Tarantool 2.2 such tuples even have a format. For details see issue.

box.cfg{listen = 3302}
box.schema.user.grant('guest','read, write, execute', 'space')
box.schema.user.grant('guest', 'create', 'space')

box.schema.create_space("named", {format = {{name = "id"}}})
box.space.named:create_index('id', {parts = {{1, 'unsigned'}}})
box.space.named:insert({1})
require('net.box').connect('localhost', 3302).space.named:get(1).id

Result:

tarantool> require('net.box').connect('localhost', 3302).space.named:get(1).id
---
- 1
...

If you need to convert lua tables to tuples you could use box.tuple.new() function. But it will be tuples without format.

tarantool> tbl = {1, 2, 3}
---
...

tarantool> box.tuple.is(tbl)
---
- false
...

tarantool> tuple = box.tuple.new(tbl)
---
...

tarantool> box.tuple.is(tuple)
---
- true
...

And here I should finish my answer. But you have illegal way to return formatted tuples from netbox call.

netbox = require('net.box')
netboxlib = require('net.box.lib')
buffer = require('buffer')
msgpackffi = require('msgpackffi')
msgpack = require('msgpack')
ffi = require('ffi')

box.cfg{listen = 3301}
box.schema.user.passwd('admin', 'test')

s = box.schema.space.create('test')
s:format({{name = 'id', type = 'string'}, {name = 'value', type = 'string'}})
s:create_index('pk')
s:replace({'key', 'value'})
c = netbox.connect('admin:test@localhost:3301')
function get()
    return s:select()
end

call_buffer = buffer.ibuf()
c:call('get', {}, {buffer = call_buffer, skip_header = true})
len, call_buffer.rpos = msgpack.decode_array_header(call_buffer.rpos, call_buffer:size())
buf = buffer.ibuf()
encode_fix = msgpackffi.internal.encode_fix
encode_r = msgpackffi.internal.encode_r
encode_fix(buf, 0x80, 1)
encode_r(buf, 0x30, 1)
wpos = buf:alloc(call_buffer:size())
ffi.copy(wpos, call_buffer.rpos, call_buffer:size())

tarantool> netboxlib.decode_select(buf.rpos, nil, c.space.test._format_cdata)
---
- - ['key', 'value']
- 'cdata<char *>: 0x010586803e'
...
tarantool> tuples = netboxlib.decode_select(buf.rpos, nil, c.space.test._format_cdata)
---
...

tarantool> tuples 
---
- - ['key', 'value']
...

tarantool> tuples[1]
---
- ['key', 'value']
...

tarantool> tuples[1]:tomap()
---
- 1: key
  2: value
  value: value
  id: key
...

This code works since Tarantool 2.2 and easily could be broken in future as it uses some internal Tarantool functions. I don't recommend you to use them. I hope it will be changed after this issue will be resolved.