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[NPC] Adding JSON RPC protocol for MPC endpoints
author June Park <parkjune1995@gmail.com>
date Fri, 23 Jan 2026 21:07:08 -0800
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180:3a4ebe4552bf 181:a2720eac50ce
1 #include "seobeo/seobeo.h"
2 #include <string.h>
3 #include <time.h>
4
5 static _Atomic uint32_t counter = 0;
6
7 static void build_response(char *out, size_t size, const char *id, const char *result) {
8 snprintf(out, size, "{\"jsonrpc\":\"2.0\",\"id\":%s,\"result\":%s}", id, result);
9 }
10
11 static void build_error(char *out, size_t size, const char *id, int code, const char *msg) {
12 snprintf(out, size,
13 "{\"jsonrpc\":\"2.0\",\"id\":%s,\"error\":{\"code\":%d,\"message\":\"%s\"}}",
14 id, code, msg);
15 }
16
17 static void handle_initialize(char *out, size_t size, const char *id) {
18 const char *result = "{"
19 "\"protocolVersion\":\"2024-11-05\","
20 "\"capabilities\":{\"tools\":{}},"
21 "\"serverInfo\":{\"name\":\"simple-mcp\",\"version\":\"1.0.0\"}"
22 "}";
23 build_response(out, size, id, result);
24 }
25
26 static void handle_tools_list(char *out, size_t size, const char *id) {
27 const char *result = "{"
28 "\"tools\":["
29 "{"
30 "\"name\":\"get_time\","
31 "\"description\":\"Get current Unix timestamp\","
32 "\"inputSchema\":{\"type\":\"object\",\"properties\":{}}"
33 "},"
34 "{"
35 "\"name\":\"get_counter\","
36 "\"description\":\"Get and increment a counter\","
37 "\"inputSchema\":{\"type\":\"object\",\"properties\":{}}"
38 "}"
39 "]"
40 "}";
41 build_response(out, size, id, result);
42 }
43
44 static void handle_tools_call(char *out, size_t size, const char *id, Dowa_JSON_Entry *json) {
45 Dowa_JSON_Value *params_val = Dowa_JSON_Get(json, "params");
46 if (!params_val || params_val->type != DOWA_JSON_OBJECT)
47 {
48 build_error(out, size, id, -32602, "Missing params");
49 return;
50 }
51
52 Dowa_JSON_Entry *params = (Dowa_JSON_Entry *)params_val->object_val;
53 char *tool_name = Dowa_JSON_Get_String(params, "name");
54
55 if (!tool_name) {
56 build_error(out, size, id, -32602, "Missing tool name");
57 return;
58 }
59
60 char result[256];
61 if (strcmp(tool_name, "get_time") == 0) {
62 time_t now = time(NULL);
63 snprintf(result, sizeof(result),
64 "{\"content\":[{\"type\":\"text\",\"text\":\"Current timestamp: %ld\"}]}",
65 (long)now);
66 } else if (strcmp(tool_name, "get_counter") == 0) {
67 uint32_t val = ++counter;
68 snprintf(result, sizeof(result),
69 "{\"content\":[{\"type\":\"text\",\"text\":\"Counter value: %u\"}]}",
70 val);
71 } else {
72 build_error(out, size, id, -32601, "Unknown tool");
73 return;
74 }
75
76 build_response(out, size, id, result);
77 }
78
79 Seobeo_Request_Entry* HandleMCP(Seobeo_Request_Entry *req, Dowa_Arena *arena)
80 {
81 Seobeo_Request_Entry *resp = NULL;
82
83 void *body_kv = Dowa_HashMap_Get_Ptr(req, "Body");
84 if (!body_kv)
85 {
86 char *err = "{\"jsonrpc\":\"2.0\",\"id\":null,\"error\":{\"code\":-32700,\"message\":\"No body\"}}";
87 Dowa_HashMap_Push_Arena(resp, "status", "400", arena);
88 Dowa_HashMap_Push_Arena(resp, "content-type", "application/json", arena);
89 Dowa_HashMap_Push_Arena(resp, "body", err, arena);
90 return resp;
91 }
92
93 const char *body = ((Seobeo_Request_Entry*)body_kv)->value;
94 int32 body_len = strlen(body);
95
96 Dowa_JSON_Value parsed = Dowa_JSON_Parse(body, body_len, arena);
97 if (parsed.type != DOWA_JSON_OBJECT || !parsed.object_val)
98 {
99 char *err = "{\"jsonrpc\":\"2.0\",\"id\":null,\"error\":{\"code\":-32700,\"message\":\"Parse error\"}}";
100 Dowa_HashMap_Push_Arena(resp, "status", "400", arena);
101 Dowa_HashMap_Push_Arena(resp, "content-type", "application/json", arena);
102 Dowa_HashMap_Push_Arena(resp, "body", err, arena);
103 return resp;
104 }
105
106 Dowa_JSON_Entry *json = (Dowa_JSON_Entry *)parsed.object_val;
107 char *method = Dowa_JSON_Get_String(json, "method");
108 Dowa_JSON_Value *id_val = Dowa_JSON_Get(json, "id");
109 char id_buf[32] = "null";
110 if (id_val)
111 {
112 if (id_val->type == DOWA_JSON_NUMBER)
113 snprintf(id_buf, sizeof(id_buf), "%.0f", id_val->num_val);
114 else if (id_val->type == DOWA_JSON_STRING)
115 snprintf(id_buf, sizeof(id_buf), "\"%s\"", id_val->str_val);
116 }
117
118 char *response = Dowa_Arena_Allocate(arena, 2048);
119
120 if (!method)
121 build_error(response, 2048, id_buf, -32600, "Missing method");
122 else if (strcmp(method, "initialize") == 0)
123 handle_initialize(response, 2048, id_buf);
124 else if (strcmp(method, "tools/list") == 0)
125 handle_tools_list(response, 2048, id_buf);
126 else if (strcmp(method, "tools/call") == 0)
127 handle_tools_call(response, 2048, id_buf, json);
128 else if (strcmp(method, "notifications/initialized") == 0)
129 snprintf(response, 2048, "{\"jsonrpc\":\"2.0\",\"id\":%s,\"result\":{}}", id_buf);
130 else
131 build_error(response, 2048, id_buf, -32601, "Method not found");
132
133 Dowa_HashMap_Push_Arena(resp, "status", "200", arena);
134 Dowa_HashMap_Push_Arena(resp, "content-type", "application/json", arena);
135 Dowa_HashMap_Push_Arena(resp, "body", response, arena);
136 return resp;
137 }
138
139 int main(void) {
140 Seobeo_Router_Init();
141 Seobeo_Router_Register("POST", "/mcp", HandleMCP);
142
143 Seobeo_Log(SEOBEO_INFO, "MCP server running on http://localhost:8080/mcp\n");
144 Seobeo_Web_Server_Start(NULL, "8080", SEOBEO_MODE_FORK, 0);
145 return 0;
146 }