Re: [tarantool-patches] [PATCH 4/8] netbox: extend codec with 'decode' methods

[Konstantin Osipov <kostja@tarantool.org>]

* Vladislav Shpilevoy <v.shpilevoy@tarantool.org> [18/04/16 21:44]:
> Netbox has a table 'method_codec' that is used to encode a
> request by a method name. But a response is decoded out of codec.
> It leads to
> 1) decoding into Lua tables before decoding into tuples where
> needed - it is double decoding and produces a lot of garbage;
> 2) each method contains hacks like one_tuple(), or single tuple
> check.
> 
> These things can not be fixed with no real codec instead of
> encoder only.
> 
> Also global table with decoders is needed for #3107, where
> a request could be sent async with no fiber blocking. An async
> response when received already does not have a call context - it
> has only method name.
> 
> Needed for #3107
> ---
>  src/box/lua/net_box.lua | 116 +++++++++++++++++++++++++++++-------------------
>  test/box/net.box.result |  14 ++++++
>  test/box/sql.result     |   2 +
>  3 files changed, 87 insertions(+), 45 deletions(-)
> 
> diff --git a/src/box/lua/net_box.lua b/src/box/lua/net_box.lua
> index 4ed2b375d..3868cdf1c 100644
> --- a/src/box/lua/net_box.lua
> +++ b/src/box/lua/net_box.lua
> @@ -50,7 +50,34 @@ local E_PROC_LUA             = box.error.PROC_LUA
>  
>  -- utility tables
>  local is_final_state         = {closed = 1, error = 1}
> -local method_codec           = {
> +
> +local function decode_nil(...) end
> +local function decode_nothing(...) return ... end

decode_nothing -> decode_nop

> +local function decode_one_tuple(response)
> +    if response[1] then
> +        return box.tuple.new(response[1])
> +    end
> +end

decode_one_tuple -> decode_tuple

Why do you need the if () guard?

> +local function decode_single_tuple(response)
> +    if response[2] then
> +        return nil, box.error.MORE_THAN_ONE_TUPLE
> +    end
> +    if response[1] then
> +        return box.tuple.new(response[1])
> +    end
> +end

decode_single_tuple -> decode_get()

> +local function decode_select(response)
> +    setmetatable(response, sequence_mt)
> +    for i, v in pairs(response) do
> +        response[i] = box.tuple.new(v)
> +    end
> +    return response
> +end

Why are you using pairs() rather than ipairs()?

How does this avoid double decode as you claim in changeset
comment?

> +local function decode_count(response)
> +    return response[1]
> +end
> +
> @@ -336,7 +385,10 @@ local function create_transport(host, port, user, password, callback,
>          -- Decode xrow.body[DATA] to Lua objects
>          body, body_end_check = decode(body_rpos)
>          assert(body_end == body_end_check, "invalid xrow length")
> -            return res -- the length of xrow.body
> -        elseif not err then
> -            setmetatable(res, sequence_mt)
> -            local postproc = method ~= 'eval' and method ~= 'call_17'
> -            if postproc then
> -                local tnew = box.tuple.new

You removed this local variable from the decoder - it was here
for a reason. Please put it back in your implementation of decoder.

> diff --git a/test/box/net.box.result b/test/box/net.box.result
> index cf7b27f0b..6a3713fc0 100644
> --- a/test/box/net.box.result
> +++ b/test/box/net.box.result
> @@ -416,9 +416,11 @@ cn.space.net_box_test_space:select({234}, { iterator = 'LT' })
>  ...
>  cn.space.net_box_test_space:update({1}, { { '+', 2, 2 } })
>  ---
> +- null

net.box calling convention should be the same as local box, if a
tuple is not found, it should return nothing, not null.


-- 
Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
http://tarantool.io - www.twitter.com/kostja_osipov