From a93e53aa54cd1c66b326ee58138184abf02d3aec Mon Sep 17 00:00:00 2001
From: Lev Gromov <gromovl3a@gmail.com>
Date: Wed, 16 Oct 2024 18:40:05 +0200
Subject: [PATCH] Fix checking if port is free

---
 hpc/Makefile             |  5 ++++-
 hpc/hq_scripts/job.sh    |  2 +-
 hpc/is_port_free.cpp     | 43 ++++++++++++++++++++++++++++++++++++++++
 hpc/slurm_scripts/job.sh |  2 +-
 4 files changed, 49 insertions(+), 3 deletions(-)
 create mode 100644 hpc/is_port_free.cpp

diff --git a/hpc/Makefile b/hpc/Makefile
index 5757bea..3a420d4 100644
--- a/hpc/Makefile
+++ b/hpc/Makefile
@@ -1,7 +1,10 @@
-all: build-load-balancer build-testmodel
+all: build-load-balancer build-is-port-free build-testmodel
 
 build-load-balancer:
 	- g++ -O3 -Wno-unused-result -std=c++17 -I../lib/ LoadBalancer.cpp -o load-balancer -pthread
 
+build-is-port-free:
+	- g++ -O3 -std=c++17 is_port_free.cpp -o is_port_free
+
 build-testmodel:
 	- g++ -O3 -Wno-unused-result -std=c++17 -I../lib/ ../models/testmodel/minimal-server.cpp -o testmodel -pthread
diff --git a/hpc/hq_scripts/job.sh b/hpc/hq_scripts/job.sh
index fcbb91a..8c4a38f 100755
--- a/hpc/hq_scripts/job.sh
+++ b/hpc/hq_scripts/job.sh
@@ -18,7 +18,7 @@ function get_available_port {
     port=$(shuf -i $MIN_PORT-$MAX_PORT -n 1)
 
     # Check if the port is in use
-    while lsof -Pi :$port -sTCP:LISTEN -t >/dev/null; do
+    until ./is_port_free $port; do
         # If the port is in use, generate a new random port number
         port=$(shuf -i $MIN_PORT-$MAX_PORT -n 1)
     done
diff --git a/hpc/is_port_free.cpp b/hpc/is_port_free.cpp
new file mode 100644
index 0000000..2ac6c48
--- /dev/null
+++ b/hpc/is_port_free.cpp
@@ -0,0 +1,43 @@
+#include "../lib/httplib.h"
+
+#include <iostream>
+
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+// Takes one integer argument - a port.
+// If the port is free, returns EXIT_SUCCESS; otherwise returns EXIT_FAILURE.
+// Note: Uses the Linux IPv4 protocol implementation!
+int main(int argc, char* argv[])
+{
+    // Get port to check from command line args
+    if (argc < 2) {
+        std::cerr << "Missing required positional argument: port" << std::endl;
+        return EXIT_FAILURE;
+    }
+    int port = std::atoi(argv[1]);
+
+    // Create socket
+    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
+    if (sockfd == -1) {
+        std::cerr << "Failed to create socket: " << std::strerror(errno) << std::endl;
+        return EXIT_FAILURE;
+    }
+
+    // Set address to 0.0.0.0:port
+    struct sockaddr_in addr;
+    memset(&addr, 0, sizeof(addr));
+    addr.sin_family = AF_INET;
+    addr.sin_port = htons(port);
+    addr.sin_addr.s_addr = htonl(INADDR_ANY);
+
+    // Attempt to assign address to socket
+    int success = bind(sockfd, (struct sockaddr*) &addr, sizeof(addr));
+
+    if (success == -1) {
+        return EXIT_FAILURE;
+    } else {
+        return EXIT_SUCCESS;
+    }
+}
\ No newline at end of file
diff --git a/hpc/slurm_scripts/job.sh b/hpc/slurm_scripts/job.sh
index a843db5..23a5719 100755
--- a/hpc/slurm_scripts/job.sh
+++ b/hpc/slurm_scripts/job.sh
@@ -16,7 +16,7 @@ function get_available_port {
     port=$(shuf -i $MIN_PORT-$MAX_PORT -n 1)
 
     # Check if the port is in use
-    while lsof -Pi :$port -sTCP:LISTEN -t >/dev/null; do
+    until ./is_port_free $port; do
         # If the port is in use, generate a new random port number
         port=$(shuf -i $MIN_PORT-$MAX_PORT -n 1)
     done