ws_receive/3 with format(json) sometimes does not yield JSON #84
Description
To reproduce with SWI-Prolog 7.5.1, please run the following query:
?- use_module(library(http/websocket)). true.
Followed by:
?- http_open_websocket('wss://ws.blockchain.info/inv', WS, []),
ws_send(WS, json(_{op: "unconfirmed_sub"})),
length(_, L),
portray_clause(L),
ws_receive(WS, Msg, [format(json)]),
\+ is_dict(Msg.data).
The output from this may vary between runs, but inevitably starts and ends like this:
0.
1.
2.
3.
4.
5.
...
53.
54.
WS = (0x7f801a8270d0,0x7f801a825620),
L = 54,
Msg = websocket{data:"{\n \"op\" : \"utx\",\n \"x\" : {\n \"lock_time\" : 0,\n \"ver\" : 1,\n \"size\" : 226,\n \"inputs\" : [ {\n \"sequence\" : 4294967295,\n \"prev_out\" : {\n \"spent\" : true,\n \"tx_index\" : 234701988,\n \"type\" : 0,\n \"addr\" : \"14Wa44aAqRGpcgv1dgCU1fRHvrqW9eMZ4m\",\n \"value\" : 25000000,\n \"n\" : 0,\n \"script\" : \"76a914268008048d14e5e40f1cd819a3c11add1e6c408588ac\"\n },\n \"script\" : \"483045022100d48db67257037add65f06729de36e15e79994d69e2376b8cb1e1ae378fc67dde0220094681ac5415d359e87b8bdbd2ea188dd508a6c76553420d7f11601a9d3861e701210255b7e52913a13df6cdbe16ba8e3ed88a90511c25ac98a84ebdca00d11ab6c41a\"\n } ],\n \"time\" : 1490116499,\n \"tx_index\" : 234709729,\n \"vin_sz\" : 1,\n \"hash\" : \"8576815930dcea2c67c8b1e8bdc0fab59f947605ffe6bc9163c35d699b3ede2a\",\n \"vout_sz\" : 2,\n \"relayed_by\" : \"217.111.66.79\",\n \"out\" : [ {\n \"spent\" : false,\n \"tx_index\" : 234709729,\n \"type\" : 0,\n \"addr\" : \"12BLZjSiPxNcU6dfJNjrvT3YyJcRBBJL76\",\n \"value\" : 12000000,\n \"n\" : 0,\n \"script\" : \"76a9140cec9dec93f2faa73fe1ed83329a1c5d080c5f9c88ac\"\n }, {\n \"spent\" : false,\n \"tx_index\" : 234709729,\n \"type\" : 0,\n \"addr\" : \"15n13xT3vobHAWkm8hVuJrRby6qqqjRSK6\",\n \"value\" : 12950300,\n \"n\" : 1,\n \"script\" : \"76a91434634392de4cbee99ff98d641ef8fcbfb721a57a88ac\"\n } ]\n }\n}", format:string, opcode:text}
This shows that ws_receive/3 sometimes does not yield a JSON dict, even if format(json) is specified.