From 439350753ed2e27b0aa4fa1cfdf3ea80ea344644 Mon Sep 17 00:00:00 2001
From: networkException <git@nwex.de>
Date: Wed, 13 Dec 2023 02:51:17 +0100
Subject: [PATCH 1/2] nixos/sysctl: use highest value on conflict for
 net.core.wmem_max

we previously defined a custom type for `boot.kernel.sysctl."net.core.rmem_max"`
to resolve to the highest value set. this patch adds the same behavior to
`"net.core.wmem_max"`.

as this changes the type from a string to an integer, which is a breaking
change this patch also includes a release note and updates the transmission
module to use a number for `wmem_max`.
---
 .../manual/release-notes/rl-2405.section.md   |  2 ++
 nixos/modules/config/sysctl.nix               | 24 ++++++++++++-------
 .../modules/services/torrent/transmission.nix |  2 +-
 3 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/nixos/doc/manual/release-notes/rl-2405.section.md b/nixos/doc/manual/release-notes/rl-2405.section.md
index 2e9cd781ffb1..6e9c741e8347 100644
--- a/nixos/doc/manual/release-notes/rl-2405.section.md
+++ b/nixos/doc/manual/release-notes/rl-2405.section.md
@@ -67,6 +67,8 @@ The pre-existing [services.ankisyncd](#opt-services.ankisyncd.enable) has been m
   `globalRedirect` can now have redirect codes other than 301 through
   `redirectCode`.
 
+- [](#opt-boot.kernel.sysctl._net.core.wmem_max_) changed from a string to an integer because of the addition of a custom merge option (taking the highest value defined to avoid conflicts between 2 services trying to set that value), just as [](#opt-boot.kernel.sysctl._net.core.rmem_max_) since 22.11.
+
 - Gitea 1.21 upgrade has several breaking changes, including:
   - Custom themes and other assets that were previously stored in `custom/public/*` now belong in `custom/public/assets/*`
   - New instances of Gitea using MySQL now ignore the `[database].CHARSET` config option and always use the `utf8mb4` charset, existing instances should migrate via the `gitea doctor convert` CLI command.
diff --git a/nixos/modules/config/sysctl.nix b/nixos/modules/config/sysctl.nix
index 452c050b6dda..b779f12aca30 100644
--- a/nixos/modules/config/sysctl.nix
+++ b/nixos/modules/config/sysctl.nix
@@ -21,19 +21,27 @@ in
   options = {
 
     boot.kernel.sysctl = mkOption {
-      type = types.submodule {
+      type = let
+        highestValueType = types.ints.unsigned // {
+          merge = loc: defs:
+            foldl
+              (a: b: if b.value == null then null else lib.max a b.value)
+              0
+              (filterOverrides defs);
+        };
+      in types.submodule {
         freeformType = types.attrsOf sysctlOption;
         options."net.core.rmem_max" = mkOption {
-          type = types.nullOr types.ints.unsigned // {
-            merge = loc: defs:
-              foldl
-                (a: b: if b.value == null then null else lib.max a b.value)
-                0
-                (filterOverrides defs);
-          };
+          type = types.nullOr highestValueType;
           default = null;
           description = lib.mdDoc "The maximum socket receive buffer size. In case of conflicting values, the highest will be used.";
         };
+
+        options."net.core.wmem_max" = mkOption {
+          type = types.nullOr highestValueType;
+          default = null;
+          description = lib.mdDoc "The maximum socket send buffer size. In case of conflicting values, the highest will be used.";
+        };
       };
       default = {};
       example = literalExpression ''
diff --git a/nixos/modules/services/torrent/transmission.nix b/nixos/modules/services/torrent/transmission.nix
index 88537f8c4f7b..7fb7847ce935 100644
--- a/nixos/modules/services/torrent/transmission.nix
+++ b/nixos/modules/services/torrent/transmission.nix
@@ -434,7 +434,7 @@ in
       # at least up to the values hardcoded here:
       (mkIf cfg.settings.utp-enabled {
         "net.core.rmem_max" = mkDefault 4194304; # 4MB
-        "net.core.wmem_max" = mkDefault "1048576"; # 1MB
+        "net.core.wmem_max" = mkDefault 1048576; # 1MB
       })
       (mkIf cfg.performanceNetParameters {
         # Increase the number of available source (local) TCP and UDP ports to 49151.

From 968905ab76aba874bc4818eb3a491b94241aca25 Mon Sep 17 00:00:00 2001
From: networkException <git@nwex.de>
Date: Wed, 13 Dec 2023 02:55:50 +0100
Subject: [PATCH 2/2] nixos/caddy: also increase socket send buffer size as
 recommended by upstream

this patch adjusts the `boot.kernel.sysctl."net.core.wmem_max"` to match the
value suggested in the quic-go wiki, just as `"net.core.wmem_max"`.

see fdfdc5df21d3df985b751bc61929e2305882dd48
see https://github.com/quic-go/quic-go/issues/3923
---
 nixos/modules/services/web-servers/caddy/default.nix | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/services/web-servers/caddy/default.nix b/nixos/modules/services/web-servers/caddy/default.nix
index 9a544e98cfc4..95dc219d108c 100644
--- a/nixos/modules/services/web-servers/caddy/default.nix
+++ b/nixos/modules/services/web-servers/caddy/default.nix
@@ -342,8 +342,9 @@ in
       }
     '';
 
-    # https://github.com/lucas-clemente/quic-go/wiki/UDP-Receive-Buffer-Size
+    # https://github.com/quic-go/quic-go/wiki/UDP-Buffer-Sizes
     boot.kernel.sysctl."net.core.rmem_max" = mkDefault 2500000;
+    boot.kernel.sysctl."net.core.wmem_max" = mkDefault 2500000;
 
     systemd.packages = [ cfg.package ];
     systemd.services.caddy = {