Example 04: TCP HTTP Client

Utilizing lwIP to establish an outbound TCP connection.

--- This advanced example demonstrates the steps required to use the raw network system calls to establish a connection with an external HTTP server and dump the response over the terminal. ## 📝 Concepts Introduced * Verifying the network state (`sys_network_is_initialized`, `sys_network_has_ip`). * Performing DNS lookups manually via `sys_dns_lookup`. * Managing strict TCP flow logic (`sys_tcp_connect`, send, block for receive). * Using the terminal `SYS_WRITE` output for debugging. * Declaring app metadata via source annotations. --- ## The Code (`src/userland/cli/http_get.c`) ```c // BOREDOS_APP_DESC: HTTP GET client — fetches a webpage over TCP. // BOREDOS_APP_ICONS: /Library/images/icons/colloid/network-wired.png #include #include #include int main(void) { if (!sys_network_is_initialized() || !sys_network_has_ip()) { printf("Network is unreachable! Make sure you inited the network first!\n"); return 1; } // 1. Resolve host name to IP const char *target_host = "boreddev.nl"; net_ipv4_address_t server_ip; printf("Resolving %s...\n", target_host); if (sys_dns_lookup(target_host, &server_ip) < 0) { printf("DNS Lookup failed.\n"); return 1; } printf("Resolved to: %d.%d.%d.%d\n", server_ip.bytes[0], server_ip.bytes[1], server_ip.bytes[2], server_ip.bytes[3]); // 2. Establish a TCP connection on port 80 (HTTP) printf("Connecting...\n"); if (sys_tcp_connect(&server_ip, 80) < 0) { printf("Connection failed.\n"); return 1; } printf("Connected! Sending GET request...\n"); // 3. Format and send the raw HTTP Request char request[256]; strcpy(request, "GET / HTTP/1.1\r\nHost: "); strcat(request, target_host); strcat(request, "\r\nConnection: close\r\n\r\n"); if (sys_tcp_send(request, strlen(request)) < 0) { printf("Failed to send data.\n"); sys_tcp_close(); return 1; } // 4. Block and wait for response data char recv_buf[512]; int bytes_received; printf("\n--- RESPONSE ---\n"); while ((bytes_received = sys_tcp_recv(recv_buf, sizeof(recv_buf) - 1)) > 0) { recv_buf[bytes_received] = '\0'; // Null-terminate the chunk printf("%s", recv_buf); // Print the chunk to stdout } // 5. Cleanup printf("\n--- END RESPONSE ---\n"); sys_tcp_close(); printf("Connection closed.\n"); return 0; } ``` ## How it Works 1. **Network Setup**: First, we must ensure the host machine or QEMU environment gave BoredOS a valid IP address via DHCP. The `sys_network_has_ip()` check prevents our app from hanging trying to route data to nowhere. 2. **DNS (`sys_dns_lookup`)**: Since we want to connect to a domain name, not a raw IP, we query the DNS server configured by the OS (which it received via DHCP). 3. **Connection (`sys_tcp_connect`)**: We block the application thread while the OS performs the 3-way TCP handshake over port 80. 4. **Payload (`sys_tcp_send`)**: We format a compliant HTTP/1.1 payload representing a simple GET request for the root directory `/`. 5. **Chunked Receiving (`sys_tcp_recv`)**: The server's response might be larger than our `recv_buf` (512 bytes). Therefore, we loop. `sys_tcp_recv` blocks execution until data arrives. If it returns `0`, the remote server cleanly closed the connection (which happens automatically because we specified `Connection: close` in our request payload!). 6. **`BOREDOS_APP_DESC` / `BOREDOS_APP_ICONS`**: Embedded into the compiled `.elf` as a BoredOS NOTE section. The Desktop and File Explorer read this to display the app's icon. See [`elf_metadata.md`](../elf_metadata.md) for full details. ## Running It Make sure QEMU is running with networking enabled. Launch the terminal and type `http_get`. You will see the raw headers and HTML source of the target webpage scroll down the CLI interface!