* gnatcol json vs network read
@ 2018-12-14 17:50 Stephen Leake
2018-12-14 18:53 ` Olivier Henley
` (2 more replies)
0 siblings, 3 replies; 5+ messages in thread
From: Stephen Leake @ 2018-12-14 17:50 UTC (permalink / raw)
I'm reading json over a network, with code like:
function Check_Ack (DB : not null access Database) return
GNATCOLL.JSON.JSON_Value
is
use GNATCOLL.JSON;
Msg : constant String := String (Network_String'Input (DB.Stream));
begin
if DB.Verbosity > 1 then
Ada.Text_IO.Put_Line ("Remote: " & Msg);
end if;
declare
Response : constant JSON_Value := Read (Msg);
begin
if Response.Get ("Status") /= Ack_Nack'Image (Ack) then
raise SAL.Invalid_Operation with Response.Get ("Message");
end if;
return Response.Get ("Data");
end;
end Check_Ack;
Occasionally, this will throw INVALID_JSON_STREAM <data>:1:155: empty stream
Apparently this is because the network is sending a data packet with less then a whole JSON object; in the case I'm currently debugging, it's missing two closing }.
So I need to check Msg for complete syntax before calling Read. However, GNATCOLL.JSON does not provide a function for that, and event the lower level Read in gnatcol-json.adb raises the exception.
So I guess I'll write a {} counter, and wait for more data from the network if the first object is not complete.
Has anyone else dealt with this problem?
-- Stephe
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: gnatcol json vs network read
2018-12-14 17:50 gnatcol json vs network read Stephen Leake
@ 2018-12-14 18:53 ` Olivier Henley
2018-12-14 19:00 ` Stephen Leake
2018-12-14 21:58 ` Per Sandberg
2 siblings, 0 replies; 5+ messages in thread
From: Olivier Henley @ 2018-12-14 18:53 UTC (permalink / raw)
> Occasionally, this will throw INVALID_JSON_STREAM <data>:1:155: empty stream
side note:
make sure the source of your json stream does not contain capital letters for keys. If you have such anomalies, perform a to_lower() before trying to parse/extract the json. It happened to me before and the error message was not helping... the kind you got.
olivier
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: gnatcol json vs network read
2018-12-14 17:50 gnatcol json vs network read Stephen Leake
2018-12-14 18:53 ` Olivier Henley
@ 2018-12-14 19:00 ` Stephen Leake
2018-12-14 21:58 ` Per Sandberg
2 siblings, 0 replies; 5+ messages in thread
From: Stephen Leake @ 2018-12-14 19:00 UTC (permalink / raw)
On Friday, December 14, 2018 at 9:50:10 AM UTC-8, Stephen Leake wrote:
>
> So I guess I'll write a {} counter, and wait for more data from the network if the first object is not complete.
Arg. The problem turned out to be the client (an Android app) is sending ' as UTF-8 16#e28099# instead of ASCII ', throwing off the byte count. sigh.
There should still be an incomplete object problem, but apparently I haven't actually seen it yet.
-- Stephe
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: gnatcol json vs network read
2018-12-14 17:50 gnatcol json vs network read Stephen Leake
2018-12-14 18:53 ` Olivier Henley
2018-12-14 19:00 ` Stephen Leake
@ 2018-12-14 21:58 ` Per Sandberg
2018-12-15 9:41 ` Stephen Leake
2 siblings, 1 reply; 5+ messages in thread
From: Per Sandberg @ 2018-12-14 21:58 UTC (permalink / raw)
Well this all depends on the definition of Network_String'Input and
Network_String'Output.
Will Network_String'Output always send the whole string in such a format
that Network_String'Input is able to reconstruct it regardless of
fragmentation on the transport.
/P
On 12/14/18 6:50 PM, Stephen Leake wrote:
> I'm reading json over a network, with code like:
>
> function Check_Ack (DB : not null access Database) return
> GNATCOLL.JSON.JSON_Value
> is
> use GNATCOLL.JSON;
> Msg : constant String := String (Network_String'Input (DB.Stream));
> begin
> if DB.Verbosity > 1 then
> Ada.Text_IO.Put_Line ("Remote: " & Msg);
> end if;
>
> declare
> Response : constant JSON_Value := Read (Msg);
> begin
> if Response.Get ("Status") /= Ack_Nack'Image (Ack) then
> raise SAL.Invalid_Operation with Response.Get ("Message");
> end if;
> return Response.Get ("Data");
> end;
> end Check_Ack;
>
> Occasionally, this will throw INVALID_JSON_STREAM <data>:1:155: empty stream
>
> Apparently this is because the network is sending a data packet with less then a whole JSON object; in the case I'm currently debugging, it's missing two closing }.
>
> So I need to check Msg for complete syntax before calling Read. However, GNATCOLL.JSON does not provide a function for that, and event the lower level Read in gnatcol-json.adb raises the exception.
>
> So I guess I'll write a {} counter, and wait for more data from the network if the first object is not complete.
>
> Has anyone else dealt with this problem?
>
> -- Stephe
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: gnatcol json vs network read
2018-12-14 21:58 ` Per Sandberg
@ 2018-12-15 9:41 ` Stephen Leake
0 siblings, 0 replies; 5+ messages in thread
From: Stephen Leake @ 2018-12-15 9:41 UTC (permalink / raw)
On Friday, December 14, 2018 at 1:58:05 PM UTC-8, Per Sandberg wrote:
> Well this all depends on the definition of Network_String'Input and
> Network_String'Output.
>
> Will Network_String'Output always send the whole string in such a format
> that Network_String'Input is able to reconstruct it regardless of
> fragmentation on the transport.
Sigh, you are right. I use this for 'Input:
Str : Stream_Element_Array (1 .. 8);
Str_Last : Stream_Element_Offset;
begin
Read (Stream.all, Str, Str_Last);
if Str_Last < Str'Last then
raise Ada.IO_Exceptions.End_Error;
end if;
So 'Input either returns all the bytes sent, or raises End_Error.
Thanks for the nudge :).
-- Stephe
^ permalink raw reply [flat|nested] 5+ messages in thread
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2018-12-14 17:50 gnatcol json vs network read Stephen Leake
2018-12-14 18:53 ` Olivier Henley
2018-12-14 19:00 ` Stephen Leake
2018-12-14 21:58 ` Per Sandberg
2018-12-15 9:41 ` Stephen Leake
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