scaffold basics of tcp and http sockets, connections, receiving data, sending data

2026-09-20 11:11:09 -07:00
commit 9bea995bf7
2 changed files with 116 additions and 0 deletions
@@ -0,0 +1,115 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <unistd.h>
+#include <string.h>
+
+int main(int argc, char **argv) {
+  printf("hello world\n");
+
+  // http is built on top of tcp
+  // http/1.0 creates a new tcp connection every request
+  
+  // for an http server implmentation, we listen for packets in a loop, and group request packets
+  // then we respond with a response broken down into separate packets (headers, body, etc)
+  int fd = socket(AF_INET, SOCK_STREAM, 0);
+  // ?? connect or bind the socket to the address?
+  struct sockaddr_in addr = {
+    .sin_family = AF_INET,
+    .sin_port = htons(8080),
+    .sin_addr = INADDR_ANY,
+  };
+
+  int yes = 1;
+  setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));
+
+  int r = bind(fd, (struct sockaddr *) &addr, sizeof(addr));
+  if (r == -1) {
+    printf("ERROR: unable to bind to address\n");
+    return r;
+  }
+
+  // go ahead and listen for incoming connections
+  r = listen(fd, 3);
+  if (r == -1) {
+    printf("ERROR: unable to use socket to listen for incoming connections\n");
+    return r;
+  }
+
+  printf("Listening on port 8080\n");
+  fflush(stdout);
+
+  // we loop and do blocking accept calls for incoming connections
+  while (true) {
+    // we pass in a sockaddr which is filled with the incoming client's information
+    struct sockaddr client_addr;
+    int addr_len = sizeof(client_addr);
+    int client_fd = accept(fd, &client_addr, (socklen_t *) &addr_len);
+    if (client_fd == -1) {
+      printf("ERROR: unable to accept incoming client connection\n");
+      return -1;
+    }
+
+    // new socket is created for the one client connection
+    // we can recv from this socket
+    size_t size = 1000;
+    char *buf = malloc(size);
+    // TCP is a byte stream so we need to keep calling recv until an end condition (\r\n). HTTP is the protocol which specifies this, not TCP streams
+
+    ssize_t received_bytes = recv(client_fd, buf, size, 0);
+    if (received_bytes > 0) {
+      printf("received bytes: %d\n", (int) received_bytes);
+      printf("%.*s\n", received_bytes, buf);
+    }
+
+    // parse the request
+    char current_line[1000];
+    int current_line_char = 0;
+    for (int i = 0; i < received_bytes; i++) {
+      printf("%c", buf[i]);
+      current_line[current_line_char] = buf[i];
+      current_line_char++;
+
+      if (buf[i] == '\n') {
+        printf("line complete: %.*s\n", current_line_char, current_line);
+        current_line_char = 0;
+      }
+
+      // TODO: find the path from the first header `GET /bootstrap HTTP/1.1`
+      // decode the request further
+    }
+    fflush(stdout);
+
+    free(buf);
+
+    const char *response =
+      "HTTP/1.1 200 OK\r\n"
+      "Content-Length: 5\r\n"
+      "Content-Type: text/plain\r\n"
+      "Connection: close\r\n"
+      "\r\n"
+      "hello";
+    r = send(client_fd, response, strlen(response), 0);
+    if (r == -1) {
+      printf("ERROR: in sending response");
+      fflush(stdout);
+    }
+    printf("sent %zd of %zu bytes\n", r, strlen(response));
+    fflush(stdout);
+
+    close(client_fd);
+  }
+  
+
+  // TODO: scaffolding
+  // keep track of multiple requests, examine the request data
+  // decode the request data
+  // then respond with particular html page
+
+  // close socket
+  close(fd);
+
+  // for an http client library, we need to create a tcp connection, send headers, and then body and other parts of the request in a structure that follows the protocol RFC
+}
+