examples/: Add webserver.cpp

rt/examples/webserver.cpp

+#include <typon/typon.hpp>
+
+#include <cerrno>
+#include <cstdio>
+#include <cstring>
+#include <exception>
+#include <string>
+#include <string_view>
+#include <system_error>
+
+#include <netdb.h>
+#include <netinet/in.h>
+
+#include <fmt/format.h>
+
+
+constexpr int BACKLOG = 1024;
+constexpr int PORT = 8000;
+
+
+using namespace typon;
+
+
+#define system_error(err, message) \
+  do { puts(message); throw fmt::system_error(err, message); } while(0)
+
+
+constexpr const char * response_fmt = \
+  "HTTP/1.0 200 OK\r\n"
+  "Content-type: text/plain\r\n"
+  "Content-length: {}\r\n"
+  "\r\n"
+  "{}";
+
+
+Task<int> create_listening_socket(int port) {
+  // asynchronous socket() system call with io_uring
+  // is only supported starting with kernel version 5.19
+  int sockfd = socket(PF_INET6, SOCK_STREAM, 0);
+  if (sockfd < 0) {
+    system_error(errno, "socket()");
+  }
+
+  int yes = 1;
+  if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) < 0) {
+    co_await io::close(sockfd);
+    system_error(errno, "setsockopt(SO_REUSEADDR)");
+  }
+
+  sockaddr_in6 addr;
+  std::memset(&addr, 0, sizeof(addr));
+  addr.sin6_family = AF_INET6;
+  addr.sin6_port = htons(port);
+  addr.sin6_addr = in6addr_any;
+
+  if (bind(sockfd, (const sockaddr *) &addr, sizeof(addr)) < 0) {
+    co_await io::close(sockfd);
+    system_error(errno, "bind()");
+  }
+
+  if (listen(sockfd, BACKLOG) < 0) {
+    co_await io::close(sockfd);
+    system_error(errno, "listen()");
+  }
+
+  co_return sockfd;
+}
+
+
+Task<std::string> read_file(const char * path) {
+  struct statx statxbuf;
+  if (int err = co_await io::statx(AT_FDCWD, path, 0, STATX_SIZE, &statxbuf)) {
+    system_error(-err, "statx()");
+  }
+
+  int fd = co_await io::openat(AT_FDCWD, path, O_RDONLY, 0);
+  if (fd < 0) {
+    system_error(-fd, "openat()");
+  }
+
+  auto size = statxbuf.stx_size;
+  std::string buf(size, '\0');
+  int nbytes = co_await io::read(fd, buf.data(), size);
+
+  co_await io::close(fd);
+
+  if (nbytes < 0) {
+    system_error(-nbytes, "read()");
+  }
+
+  co_return std::move(buf);
+}
+
+
+Task<void> handle_connection(int connfd, const char * filepath) {
+  std::string buf(1024, '\0');
+  int nbytes = co_await io::recv(connfd, buf.data(), buf.size(), 0);
+  auto length = buf.find("\r\n\r\n");
+  if (length == std::string::npos) {
+    length = nbytes;
+  }
+  std::string_view message(buf.data(), length);
+
+  std::string content;
+  try {
+    content = co_await read_file(filepath);
+  } catch(std::exception &) {
+    co_await io::close(connfd);
+    throw;
+  }
+
+  std::string response = fmt::format(response_fmt, content.size(), content);
+
+  int sbytes = co_await io::send(connfd, response, 0);
+  if (sbytes < 0) {
+    co_await io::close(connfd);
+    system_error(-sbytes, "send()");
+  }
+
+  co_await io::close(connfd);
+}
+
+
+Join<void> server_loop(int sockfd, const char * filepath) {
+  for(;;) {
+    int connfd = co_await io::accept(sockfd, NULL, NULL);
+    if (connfd < 0) {
+      system_error(-connfd, "accept()");
+    }
+
+    co_await fork(handle_connection(connfd, filepath));
+  }
+}
+
+
+Join<void> server_loops(int sockfd, const char * filepath) {
+  for (int i = 0; i < 20; i++) {
+    co_await fork(server_loop(sockfd, filepath));
+  }
+}
+
+
+Root root(int argc, char * argv[]) {
+  if (argc > 2)
+  {
+    co_await io::write(1, "Usage: webserver [ filepath ]\n");
+    co_return;
+  }
+
+  const char * filepath = argc == 2 ? argv[1] : "webserver.cpp";
+
+  int sockfd = co_await create_listening_socket(PORT);
+
+  try {
+    co_await server_loops(sockfd, filepath);
+  } catch(std::exception & e) {
+    puts(e.what());
+  }
+
+  co_await io::close(sockfd);
+}
+
+
+int main(int argc, char * argv[]) {
+  root(argc, argv).call();
+}