From cbd43914a51f8b9c20133cf0b5f9204b7d6c8b7f Mon Sep 17 00:00:00 2001
From: Jordan Woyak <jordan.woyak@gmail.com>
Date: Fri, 13 Feb 2026 20:44:40 -0600
Subject: [PATCH] Network: Improve IPv4PortRange::ToString to support CIDR
 notation and only last octet difference.

---
 Source/Core/Common/Network.cpp             | 36 +++++++++++++++++-----
 Source/UnitTests/Common/StringUtilTest.cpp | 36 ++++++++++++++++++++++
 2 files changed, 65 insertions(+), 7 deletions(-)

diff --git a/Source/Core/Common/Network.cpp b/Source/Core/Common/Network.cpp
index 24289cc04d..d44d106da5 100644
--- a/Source/Core/Common/Network.cpp
+++ b/Source/Core/Common/Network.cpp
@@ -57,17 +57,39 @@ bool IPv4PortRange::IsMatch(IPv4Port subject) const
 
 std::string IPv4PortRange::ToString() const
 {
-  const std::string ip_range = first.ip_address == last.ip_address ?
-                                   Common::IPAddressToString(first.ip_address) :
-                                   fmt::format("{}-{}", Common::IPAddressToString(first.ip_address),
-                                               Common::IPAddressToString(last.ip_address));
+  const u32 first_ip_value = first.GetIPAddressValue();
+  const u32 last_ip_value = last.GetIPAddressValue();
+  const u32 different_bits = first_ip_value ^ last_ip_value;
+  const u32 common_high_bits = std::countl_zero(different_bits);
+
+  std::string ip_range = Common::IPAddressToString(first.ip_address);
+  if (common_high_bits == 32)
+  {
+    // Identical first and last IP.
+  }
+  else if ((last_ip_value - first_ip_value + 1) << common_high_bits == 0)
+  {
+    // An exact network range can use CIDR notation.
+    ip_range = fmt::format("{}/{}", ip_range, common_high_bits);
+  }
+  else if (common_high_bits >= 24)
+  {
+    // Only the last octet is different.
+    ip_range = fmt::format("{}-{}", ip_range, last.ip_address.back());
+  }
+  else
+  {
+    // Plainly specified range.
+    ip_range = fmt::format("{}-{}", ip_range, Common::IPAddressToString(last.ip_address));
+  }
 
   if (first.port == 0)
     return ip_range;
-  else if (first.port == last.port)
+
+  if (first.port == last.port)
     return fmt::format("{}:{}", ip_range, first.GetPortValue());
-  else
-    return fmt::format("{}:{}-{}", ip_range, first.GetPortValue(), last.GetPortValue());
+
+  return fmt::format("{}:{}-{}", ip_range, first.GetPortValue(), last.GetPortValue());
 }
 
 std::string IPAddressToString(IPAddress ip_address)
diff --git a/Source/UnitTests/Common/StringUtilTest.cpp b/Source/UnitTests/Common/StringUtilTest.cpp
index c8bd5f4deb..f7c3b9169b 100644
--- a/Source/UnitTests/Common/StringUtilTest.cpp
+++ b/Source/UnitTests/Common/StringUtilTest.cpp
@@ -373,6 +373,42 @@ TEST(StringUtil, StringToIPv4PortRange)
   EXPECT_TRUE(parse("192.168.0.13-14:80-81")->IsMatch(parse("192.168.0.14:81")->first));
 }
 
+TEST(StringUtil, IPv4PortRangeToString)
+{
+  Common::IPv4PortRange subject{
+      .first = {{10, 3, 0, 127}, 0},
+      .last = {{10, 3, 0, 127}, 0},
+  };
+
+  EXPECT_EQ(subject.ToString(), "10.3.0.127");
+
+  subject.last.port = Common::swap16(80);  // First port is still zero.
+  EXPECT_EQ(subject.ToString(), "10.3.0.127");
+
+  subject.first.port = Common::swap16(80);
+  EXPECT_EQ(subject.ToString(), "10.3.0.127:80");
+
+  subject.last.port = Common::swap16(88);
+  EXPECT_EQ(subject.ToString(), "10.3.0.127:80-88");
+
+  subject.last.ip_address = {10, 3, 0, 128};
+  EXPECT_EQ(subject.ToString(), "10.3.0.127-128:80-88");
+
+  subject.last.ip_address = {10, 3, 7, 35};
+  EXPECT_EQ(subject.ToString(), "10.3.0.127-10.3.7.35:80-88");
+
+  subject.first.ip_address = {192, 168, 0, 0};
+  subject.last.ip_address = {192, 168, 0, 255};
+  EXPECT_EQ(subject.ToString(), "192.168.0.0/24:80-88");
+
+  subject.last.ip_address = {192, 168, 3, 255};
+  EXPECT_EQ(subject.ToString(), "192.168.0.0/22:80-88");
+
+  subject.first.ip_address = {};
+  subject.last.ip_address = {255, 255, 255, 255};
+  EXPECT_EQ(subject.ToString(), "0.0.0.0/0:80-88");
+}
+
 TEST(StringUtil, CharacterEncodingConversion)
 {
   // wstring