From d179a5b469d609a7c7f15d841dfb95fe77b3125e Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Mon, 4 Nov 2019 12:24:08 +0100
Subject: Seqnum server

---
 .gitignore      |  3 +--
 Makefile        |  2 +-
 run_server.sh   | 19 ++++++++++++++++-
 seqnum_server.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 86 insertions(+), 4 deletions(-)
 create mode 100644 seqnum_server.c

diff --git a/.gitignore b/.gitignore
index 21c78dc..a781ccc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,7 +1,6 @@
 *.o
 client
 server
-clientd
-serverd
+seqnum_server
 
 bak/
diff --git a/Makefile b/Makefile
index 1e2834c..b63a27b 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@ CC = gcc
 CFLAGS = -Wall -Wextra -O2 -g -std=c11 -fwrapv -pthread
 LDFLAGS = -pthread
 
-TARGETS = server client
+TARGETS = server client seqnum_server
 
 SOURCES = $(filter-out $(patsubst %,%.c,$(TARGETS)),$(wildcard *.c))
 OBJECTS = $(patsubst %.c,%.o,$(SOURCES))
diff --git a/run_server.sh b/run_server.sh
index e6beee9..c3e9759 100755
--- a/run_server.sh
+++ b/run_server.sh
@@ -1,9 +1,26 @@
 #!/usr/bin/env bash
+set -euo pipefail
+
 if [[ "$(id -u)" -ne 0 ]]; then
 	echo >&2 "Run with sudo"
 	exit 1
 fi
 
+if [[ $# -eq 0 ]]; then
+	server_exec=./server
+elif [[ $# -eq 1 ]]; then
+	server_exec="$1"
+else
+	echo >&2 "Usage: $0 [server executable]"
+	echo >&2 "By default runs ./server"
+	exit 1
+fi
+
+if [[ ! -x "$server_exec" ]]; then
+	echo >&2 "Cannot execute server executable $server_exec"
+	exit 1
+fi
+
 echo 1 >/proc/sys/net/ipv4/icmp_echo_ignore_all
 trap "echo 0 >/proc/sys/net/ipv4/icmp_echo_ignore_all" EXIT
-./serverd
+"$server_exec"
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;
+		}
+	}
+}
-- 
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