1 files changed, 66 insertions, 0 deletions
diff --git a/seqnum_server.c b/seqnum_server.c
new file mode 100644
index 0000000..aa6ab42
--- /dev/null
+++ b/seqnum_server.c
@@ -0,0 +1,66 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include "icmp_server.h"
+#include "util.h"
+
+
+static const uint8_t* detect_payload(const uint8_t *data, size_t length) {
+	// Detects the 16-byte "padding" payload one can send using the ping(1) utility.
+	// This payload starts at byte 16 and repeats thereafter.
+	if (length < 32) return NULL;
+
+	// For each byte in the padding
+	for (size_t i = 0; i < 16; i++) {
+		// For each repetition
+		for (size_t j = 1; 16 + 16 * j + i < length; j++) {
+			// Assert that the padding indeed repeats
+			if (data[16 + i] != data[16 + 16 * j + i]) return NULL;
+		}
+	}
+
+	return data + 16;
+}
+
+int main() {
+	int sock = icmp_server_open_socket();
+	if (sock < 0) {
+		perror("socket (icmp_server_open_socket)");
+		return 1;
+	}
+
+	while (true) {
+		struct icmp_incoming pkt = icmp_server_receive(sock);
+		if (pkt.data == NULL) {
+			perror("recvmsg (icmp_server_receive)");
+			usleep(500000);
+			continue;
+		}
+		// xxd(stderr, pkt.data, pkt.length);
+
+		const uint8_t *payload = detect_payload(pkt.data, pkt.length);
+
+		if (payload != NULL) {
+			printf("payl");
+			fwrite(&pkt.source_addr, 1, 4, stdout);
+			fwrite(payload, 1, 16, stdout);
+			fflush(stdout);
+			uint16_t new_seqnum;
+			if (readall(STDIN_FILENO, &new_seqnum, 2) < 0) {
+				perror("read");
+				new_seqnum = pkt.seqnum;
+			}
+			pkt.seqnum = new_seqnum;
+		} else {
+			fprintf(stderr, "Echoing packet due to invalid payload\n");
+		}
+
+		int ret = icmp_server_send_reply(sock, pkt.source_addr, pkt.id, pkt.seqnum, pkt.data, pkt.length);
+		if (ret < 0) {
+			perror("sendto (icmp_server_send_reply)");
+			usleep(500000);
+			continue;
+		}
+	}
+}