From 7597fb3adf34e12400441be7b67538d00c3a7443 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sven=20G=C3=B6thel?= <sven.gothel@collabora.com>
Date: Tue, 29 Oct 2024 09:17:28 +0100
Subject: [PATCH] net::Defaults.maxTCPConnections: Use system's maximum
 concurrent TCP connections, disable if undefined
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Used system value on a Linux kernel are
- /proc/sys/net/ipv4/tcp_max_orphans
  See https://www.kernel.org/doc/html/latest/networking/ip-sysctl.html
- /proc/sys/net/nf_conntrack_max
  See https://www.kernel.org/doc/html/latest/networking/nf_conntrack-sysctl.html

Signed-off-by: Sven Göthel <sven.gothel@collabora.com>
Change-Id: Iad74f253bdac5636757b130b299b5deacda658db
---
 common/Util-desktop.cpp | 16 ++++++++++++++++
 common/Util-mobile.cpp  |  1 +
 common/Util.hpp         |  3 +++
 net/Socket.cpp          |  2 +-
 wsd/COOLWSD.cpp         |  3 +++
 5 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/common/Util-desktop.cpp b/common/Util-desktop.cpp
index bec440cf85f57..c37965ca01840 100644
--- a/common/Util-desktop.cpp
+++ b/common/Util-desktop.cpp
@@ -11,6 +11,7 @@
 #include <config.h>
 
 #include "Util.hpp"
+#include "FileUtil.hpp"
 
 #ifdef __linux__
 #include <sys/time.h>
@@ -160,6 +161,21 @@ std::size_t getTotalSystemMemoryKb()
     return totalMemKb;
 }
 
+std::size_t getMaxConcurrentTCPConnections()
+{
+#ifdef __linux__
+    char line[1024+1]; // includes EOS
+    const ssize_t tcp_max_orphans = FileUtil::readDecimal("/proc/sys/net/ipv4/tcp_max_orphans", line, sizeof(line)-1, 0);
+    const ssize_t nf_conntrack_max = FileUtil::readDecimal("/proc/sys/net/nf_conntrack_max", line, sizeof(line)-1, 0);
+    LOG_DBG("MaxConcurrentTCPConnections: min(orphans " << tcp_max_orphans
+            << ", conntrack " << nf_conntrack_max << ") = "
+            << std::min(tcp_max_orphans, nf_conntrack_max));
+    return std::min(tcp_max_orphans, nf_conntrack_max);
+#else
+    return 0;
+#endif
+}
+
 std::size_t getFromCGroup(const std::string& group, const std::string& key)
 {
     std::size_t num = 0;
diff --git a/common/Util-mobile.cpp b/common/Util-mobile.cpp
index 5271422398e2c..a8f9ac4cfcdea 100644
--- a/common/Util-mobile.cpp
+++ b/common/Util-mobile.cpp
@@ -21,6 +21,7 @@ int spawnProcess(const std::string& cmd, const StringVector& args) { return 0; }
 
 std::string getHumanizedBytes(unsigned long nBytes) { return std::string(); }
 size_t getTotalSystemMemoryKb() { return 0; }
+std::size_t getMaxConcurrentTCPConnections() { return 0; }
 std::size_t getFromFile(const char* path) { return 0; }
 std::size_t getCGroupMemLimit() { return 0; }
 std::size_t getCGroupMemSoftLimit() { return 0; }
diff --git a/common/Util.hpp b/common/Util.hpp
index eadbea1e8137e..a7197de67cf0c 100644
--- a/common/Util.hpp
+++ b/common/Util.hpp
@@ -353,6 +353,9 @@ namespace Util
     /// Returns the total physical memory (in kB) available in the system
     size_t getTotalSystemMemoryKb();
 
+    /// Returns the maximum number of concurrent TCP connections, zero if undefined.
+    std::size_t getMaxConcurrentTCPConnections();
+
     /// Returns the numerical content of a file at @path
     std::size_t getFromFile(const char *path);
 
diff --git a/net/Socket.cpp b/net/Socket.cpp
index eaf2aaeedf388..02e21bbce863b 100644
--- a/net/Socket.cpp
+++ b/net/Socket.cpp
@@ -68,7 +68,7 @@ std::unique_ptr<Watchdog> SocketPoll::PollWatchdog;
 std::atomic<size_t> StreamSocket::ExternalConnectionCount = 0;
 
 net::DefaultValues net::Defaults = { .inactivityTimeout = std::chrono::seconds(3600),
-                                     .maxExtConnections = 200000 /* arbitrary value to be resolved */ };
+                                     .maxExtConnections = 0 /* unlimited default */};
 
 #define SOCKET_ABSTRACT_UNIX_NAME "0coolwsd-"
 
diff --git a/wsd/COOLWSD.cpp b/wsd/COOLWSD.cpp
index ae00f311893f2..0c996c2debddc 100644
--- a/wsd/COOLWSD.cpp
+++ b/wsd/COOLWSD.cpp
@@ -2334,6 +2334,9 @@ void COOLWSD::innerInitialize(Poco::Util::Application& self)
     }
     UnitWSD::get().setWSD(this);
 
+    // net::Defaults: Determine maxExtConnections field
+    net::Defaults.maxExtConnections = std::max(Util::getMaxConcurrentTCPConnections(), std::max<size_t>(3, MAX_CONNECTIONS));
+
     // Allow UT to manipulate before using configuration values.
     UnitWSD::get().configure(conf);