Calling JSON-RPC APIs with C: A Guide
JSON-RPC (JavaScript Object Notation Remote Procedure Call) is a lightweight, open standard for remote procedure calls that allows developers to interact with servers over HTTP. Although the JSON-RPC protocol has become increasingly popular in recent years, it is still possible to call these APIs from languages other than JavaScript, including C.
In this article, we’ll walk through how to make RPC calls from C, focusing on calling a JSON-RPC API using the command-line tool “curl” and its Windows equivalent: “cURL”.
Why use C for RPC calls?
Although it is possible to call JSON-RPC APIs in other languages such as Python or Ruby, C offers several advantages:
- Performance: C is a low-level language that allows direct access to hardware resources, resulting in faster execution times.
- Memory management: C has manual memory management that can be more efficient than garbage collection mechanisms in other languages.
- Portability: C code can run on any platform that supports the standard library and
cURL/curl, making it a great choice for cross-platform development.
Step 1: Set up your JSON-RPC API
First, you need to set up your JSON-RPC API. This usually involves creating a server-side application using languages such as Node.js, Python, or Ruby that provides an interface with specific methods and parameters.
For this example, we’ll use the curl command line tool to interact with our JSON-RPC API.
Step 2: Write C code for the API
Here’s an example of how you might write a simple JSON-RPC API using C:
“`c
#include
#include
// Define the API structure
typedef struct {
char* method;
void (func)(void);
} rpc_api;
// Function to handle incoming RPC requests
rpc_api handle_rpc_request(rpc_api api, const char* method) {
// Check if the request is valid
if (strcmp(method, “example_method”) != 0) {
printf(“Invalid request: %s\n”, method);
return NULL;
}
// Call the function with a placeholder argument value
char* arg = “Hello world!”;
api->func(arg);
return api;
}
// Function for processing incoming RPC responses
void handle_rpc_response(void response, int status_code) {
switch (status_code) {
case 200:
// Return response as JSON string
fprintf(stderr, “Response: %s\n”, response);
break;
default:
fprintf(stderr, “Error: %d\n”, status_code);
return NULL;
}
}
// Main function for processing incoming RPC requests
int main() {
rpc_api api;
// Initialize API with a placeholder function
api.method = “example_method”;
api.func = handle_rpc_request;
//Set up an HTTP server listener
int server_fd, new_socket;
struct sockaddr_in address;
socketn_t addrlen = sizeof(address);
// Bind port 8080 to the socket
if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
perror(“socket”);
exit(1);
}
address.sin_family = AF_INET;
address.sin_port = htons(8080);
inet_pton(AF_INET, “127.0.0.1”, &address.sin_addr);
// Wait for incoming connections
if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) == -1) {
perror(“bind”);
exit(1);
}
// Accept incoming connections
if ((new_socket = accept(server_fd, (struct sockaddr *)&address, &addrlen)) < 0) {
perror(“accept”);
exit(1);
}
printf(“Server is listening on port 8080…
