08 Feb Ethereum: How to call JSON RPC API from C?
Calling JSON-RPC APIs with C: A Guide
JSON-RPC (JavaScript Object Notation Remote Procedure Call) is a lightweight, open standard for remote procedure call that allows developers to interact with servers over HTTP. While the JSON-RPC protocol has become increasingly popular in recent years, it’s 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 curl command-line tool and its equivalent for Windows: cURL.
Why use C for RPC calls?
While it’s possible to call JSON-RPC APIs in other languages, such as Python or Ruby, C provides 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, which can be more efficient than garbage collection mechanisms found 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’ll need to set up your JSON-RPC API. This typically involves creating a server-side application using languages like Node.js, Python, or Ruby that expose 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 could 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 to handle incoming RPC responses
void handle_rpc_response(void response, int status_code) {
switch (status_code) {
case 200:
// Return the response as a JSON string
fprintf(stderr, “Response: %s\n”, response);
break;
default:
fprintf(stderr, “Error: %d\n”, status_code);
return NULL;
}
}
// Main function to handle incoming RPC requests
int main() {
rpc_api api;
// Initialize the 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;
socklen_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);
// Listen 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 listening on port 8080…
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