Add port scanner example

examples/portscan.c

@@ -0,0 +1,48 @@
+// Port scanning
+//
+// Thanks to @sigidagi for recommending this example.
+// See https://github.com/tidwall/neco/issues/14
+
+#include <stdio.h>
+#include <unistd.h>
+#include "../neco.h"
+
+void co_dial_port(int argc, void** argv) {
+    const char *host = argv[0];    // host
+    int port = *(int*)argv[1];     // port
+    neco_waitgroup *wg = argv[2];  // waitgroup
+
+    // Dial the port with a one second deadline
+    char addr[256];
+    snprintf(addr, sizeof(addr), "%s:%d", host, port);
+    int fd = neco_dial_dl("tcp", addr, neco_now() + NECO_SECOND);
+    if (fd < 0) {
+        printf("%-5d FAIL\t%s\n", port, neco_strerror(neco_lasterr()));
+    } else {
+        printf("%-5d OK\n", port);
+        close(fd);
+    }
+    // Notify the waitgroup that we are done.
+    neco_waitgroup_done(wg);
+}
+
+int neco_main(int argc, char** argv) {
+    const char *host = "scanme.nmap.org";
+    int ports[] = { 22, 80, 8080, 443 };
+
+
+    // Use a waitgroup to synchronize the coroutines
+    neco_waitgroup wg;
+    neco_waitgroup_init(&wg);
+
+    // Dial all the ports
+    printf("%s\n", host);
+    for (int i = 0; i < sizeof(ports)/sizeof(int); i++) {
+        neco_waitgroup_add(&wg, 1);
+        neco_start(co_dial_port, 3, host, &ports[i], &wg);
+    } 
+
+    // Wait for all coroutines to finish
+    neco_waitgroup_wait(&wg);
+    return 0;
+}