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JSONRPC Handler with JSONCPP+Code Generator

JSONRPC Specification : http://www.jsonrpc.org/specification

  • Start with JSONRPC V2.0 and made some adjustment for my need.
  • Focus on Web Application rather than typical Clinet/Server Applicaiton.
  • Auto-Generated Code as much as possible. More can be done.

ThingsBoard IoT Platform - RPC Capabilities

DISCLAIMER :

(6/11/2018) Found ThingsBoard.io while I was reviewing IoT platforms. Personally no association with ThingsBoard.io.

ThingsBoard GPIO RPC example

set-gpio-request.json

{
  "method": "setGpio",
  "params": {
    "pin": "23",
    "value": 1
  }
}

set-gpio-request.sh

curl -v -X POST -d @set-gpio-request.json http://localhost:8080/api/plugins/rpc/twoway/$DEVICE_ID \
--header "Content-Type:application/json" \
--header "X-Authorization: $JWT_TOKEN"

Implementation

For a simplicity reason, I use Microsoft Excel to put all examples in a single file.

  • math.xlsx becomes Math class. Each tab becomes method definition.
  • user-defined-types.xlsx has a simple struct definition.

Limitations : No type checking. Support int and simple struct with 3 fields.

Read .xls and generate codes as much as possible. - generator.py

The following packages are used :

  • jsoncpp (MIT License)
  • AppWeb 2 EgiHandler (Commercial or GPL)
  • python

Generated Code sonrpc_handler.switch.include will be called from EgiForm::run().

 /* ...omitted for brevity... */
 	case MATH_SUBTRACT_1 : { 
		Math math_instance;   // Math Class
		math_subtract_1_in_t math_subtract_1_input;    
		math_subtract_1_out_t math_subtract_1_output;
		Json::Value JRes;  // A temporary place for JSON response
		int index = 0;
		math_subtract_1_input.first = JsonReq["params"]["first"].asInt();
		math_subtract_1_input.second = JsonReq["params"]["second"].asInt();
		// method call
		jsonError = math_instance.subtract_1(math_subtract_1_input , math_subtract_1_output);  
		JRes["result"] = math_subtract_1_output.result;
		JsonRes["result"] = JRes["result"];  // The final place
	}
/* ...omitted for brevity... */

test/unittest_jsonrpc.py is a test script for all examples.

RPC Error Detection

  • Parsing Error (JSON Format Error) -32700

run::req[{ 'jsonrpc': '2.0', 'build' : '10101', 'method': '407', 'params': '[ a,b,c,d,'' , 'id': '7'}] size : 93

run::res[{"error":{"code":-32700,"message":"Parse error"},"id":0,"jsonrpc":"2.0","session":""}] size : 86

  • Unknown "method" -32601

run::req[{"id": 7, "params": {"second": {"p2": 75, "p3": 20, "p1": 33}, "first": {"p2": 5, "p3": 110, "p1": 44}}, "jsonrpc": "2.0", "build": 10101, "method": 600}] size : 153

run::res[{"error":{"code":-32601,"message":"Method not found"},"id":7,"jsonrpc":"2.0","session":"wsxaljren"}] size : 100

Supported JSONRPC formats

run::req --> data sent to Server

run::res <-- data sent to Client

1. RPC with named parameters

math_subtract_1.csv
INPUT TYPE OUTPUT TYPE
first int result int
second int
INPUT VALUE OUTPUT VALUE
first 4 result 3
second 1

run::req[{"id": 1, "params": {"second": 13, "first": 18}, "jsonrpc": "2.0", "build": 10101, "method": 401}] size : 97

run::res[{"id":1,"jsonrpc":"2.0","result":5,"session":"wsxaljren"}] size : 58

math_subtract_2.csv
INPUT TYPE OUTPUT TYPE
first int first int
second int second int
third int
INPUT VALUE OUTPUT VALUE
first 7 first 6
second 8 second 7
third 9

run::req[{"id": 2, "params": {"second": 9, "first": 7}, "jsonrpc": "2.0", "build": 10101, "method": 402}] size : 95

run::res[{"id":2,"jsonrpc":"2.0","result":{"first":-2,"second":2,"third":4},"session":"wsxaljren"}] size : 90

math_subtract_3.csv
INPUT TYPE OUTPUT TYPE
first int first int
second int second int
third int
INPUT VALUE OUTPUT VALUE
first 7 first 6
second 8 second 7
third 9

run::req[{"id": 3, "params": {"second": 17, "third": 5, "first": 16}, "jsonrpc": "2.0", "build": 10101, "method": 403}] size : 109

run::res[{"id":3,"jsonrpc":"2.0","result":{"first":-1,"second":12},"session":"wsxaljren"}] size : 81

2. RPC with positioned parameters (Array)

math_subtract_4.csv
INPUT TYPE OUTPUT TYPE
first [3] first [3]
INPUT VALUE OUTPUT VALUE
first [7,9,10] first [6,8,9]

run::req[{"id": 4, "params": [20, 41, 63], "jsonrpc": "2.0", "build": 10101, "method": 404}] size : 82

run::res[{"id":4,"jsonrpc":"2.0","result":[19,40,62],"session":"wsxaljren"}] size : 67

math_subtract_5.csv
INPUT TYPE OUTPUT TYPE
first int[3] first int[3]
second int[5] second int[8]
INPUT VALUE OUTPUT VALUE
first [7,9,10] first [6,8,9]
second [7,9,10,...] second [6,8,9,...]

run::req[{"id": 5, "params": {"second": [11, 21, 31, 41, 51], "first": [20, 21, 23]}, "jsonrpc": "2.0", "build": 10101, "method": 405}] size : 125

run::res[{"id":5,"jsonrpc":"2.0","result":{"first":[19,20,22],"second":[9,19,29,1908443698,32506,0,0,0]},"session":"wsxaljren"}] size : 119

3. RPC with dictionary (struct)

math_subtract_6.csv

dict type is a similar to struct in C/C++.

INPUT TYPE OUTPUT TYPE
first simple_struct{} first simple_struct{}
INPUT VALUE OUTPUT VALUE
first { "p1" : 2 , "p2" : 4 , "p3" : 10} first { "p1" : 4 , "p2" : 5, "p3" : 6}

simple_struct for math_subtract_dict example.

PARAMETER TYPE
p1 int
p2 int
p3 int

run::req[{"id": 6, "params": {"first": {"p2": 5, "p3": 110, "p1": 44}}, "jsonrpc": "2.0", "build": 10101, "method": 406}] size : 111

run::res[{"id":6,"jsonrpc":"2.0","result":{"first":{"p1":40,"p2":1,"p3":106}},"session":"wsxaljren"}] size : 92

math_subtract_7.csv

dict type is a similar to struct in C/C++.

INPUT TYPE OUTPUT TYPE
first simple_struct{} first simple_struct{}
second simple_struct{} second simple_struct{}
INPUT VALUE OUTPUT VALUE
first { "p1" : 2 , "p2" : 4 , "p3" : 10} first { "p1" : 4 , "p2" : 5, "p3" : 6}
second { "p1" : 2 , "p2" : 4 , "p3" : 10} second { "p1" : 4 , "p2" : 5, "p3" : 6}

run::req[{"id": 7, "params": {"second": {"p2": 75, "p3": 20, "p1": 33}, "first": {"p2": 5, "p3": 110, "p1": 44}}, "jsonrpc": "2.0", "build": 10101, "method": 407}] size : 153

run::res[{"id":7,"jsonrpc":"2.0","result":{"first":{"p1":40,"p2":1,"p3":106},"second":{"p1":28,"p2":70,"p3":15}},"session":"wsxaljren"}] size : 127

Additioanl Parameters (Automatically Added)

INPUT TYPE OUTPUT TYPE
id int id int
session int session string
jsonrpc string jsonrpc string
build int

session is an unique ID allocated by the back-end.

build is the release number.

method is an enum value from code-generator. (V2.0 uses a string instead)

4. RPC Batch

TBD

Consideration

  • Use *.h (type definitions, function protoypes definitiosn, etc) instead.