nginx: support dynamic modules

A module opts in with `dynamic = true` The build writes a `load_module`
line for every .so it installed to $out/etc/nginx/dynamic-modules.conf,
and the NixOS module includes that file.

Closes: #258260

Assisted-by: Claude:claude-fable-5-1

nixos/modules/services/web-servers/nginx/default.nix

@@ -195,6 +195,11 @@ let
         error_log ${cfg.logError};
         daemon off;
 
+        # load_module is a main-context directive that must precede events{}/http{}.
+        ${optionalString (
+          (cfg.package.dynamicModules or [ ]) != [ ]
+        ) "include ${cfg.package}/etc/nginx/dynamic-modules.conf;"}
+
         ${optionalString cfg.enableQuicBPF ''
           quic_bpf on;
         ''}

nixos/tests/all-tests.nix

@@ -1199,6 +1199,7 @@ in
   nginx = runTest ./nginx.nix;
   nginx-auth = runTest ./nginx-auth.nix;
   nginx-compression = runTest ./nginx-compression.nix;
+  nginx-dynamic-modules = runTest ./nginx-dynamic-modules.nix;
   nginx-etag = runTest ./nginx-etag.nix;
   nginx-etag-compression = runTest ./nginx-etag-compression.nix;
   nginx-globalredirect = runTest ./nginx-globalredirect.nix;

nixos/tests/nginx-dynamic-modules.nix

@@ -0,0 +1,32 @@
+{
+  name = "nginx-dynamic-modules";
+
+  nodes.machine =
+    { pkgs, ... }:
+    {
+      services.nginx = {
+        enable = true;
+        additionalModules = [ (pkgs.nginxModules.echo // { dynamic = true; }) ];
+        virtualHosts."localhost".locations."/".extraConfig = ''
+          echo "dynamic-module-ok";
+        '';
+      };
+    };
+
+  testScript =
+    { nodes, ... }:
+    let
+      cfg = nodes.machine.services.nginx;
+    in
+    ''
+      machine.wait_for_unit("nginx")
+      machine.wait_for_open_port(80)
+
+      machine.succeed("ls ${cfg.package}/modules/*.so")
+      machine.succeed("grep -F load_module ${cfg.package}/etc/nginx/dynamic-modules.conf")
+
+      # The echo directive only exists once nginx has dlopen'd the .so.
+      response = machine.wait_until_succeeds("curl -fsS http://127.0.0.1/")
+      assert "dynamic-module-ok" in response, response
+    '';
+}

pkgs/servers/http/nginx/generic.nix

@@ -53,6 +53,8 @@ let
 
   moduleNames = map (mod: mod.pname) modules;
 
+  dynamicModules = lib.filter (mod: mod.dynamic or false) modules;
+
   mapModules =
     attrPath:
     lib.flip lib.concatMap modules (
@@ -169,6 +171,7 @@ stdenv.mkDerivation {
   ++ lib.optional (
     stdenv.buildPlatform != stdenv.hostPlatform
   ) "--crossbuild=${stdenv.hostPlatform.uname.system}::${stdenv.hostPlatform.uname.processor}"
+  ++ lib.optional (dynamicModules != [ ]) "--modules-path=${placeholder "out"}/modules"
   ++ configureFlags;
 
   env = {
@@ -212,13 +215,18 @@ stdenv.mkDerivation {
   ''
   # Make all modules source trees writable
   + ''
-    for module in ${toString modules}; do
-      dst="$NIX_BUILD_TOP/$(basename "$module")"
-      cp --recursive "$module" "$dst"
+    addModule() {
+      local dst="$NIX_BUILD_TOP/$(basename "$2")"
+      cp --recursive "$2" "$dst"
       chmod --recursive +w "$dst"
-      appendToVar configureFlags "--add-module=$dst"
-    done
+      appendToVar configureFlags "$1=$dst"
+    }
   ''
+  + lib.concatLines (
+    map (
+      mod: "addModule ${if mod.dynamic or false then "--add-dynamic-module" else "--add-module"} ${mod}"
+    ) modules
+  )
   + preConfigure
   + lib.concatMapStringsSep "\n" (mod: mod.preConfigure or "") modules;
 
@@ -275,21 +283,39 @@ stdenv.mkDerivation {
 
   disallowedReferences = map (m: m.src) modules;
 
+  stripDebugList = [
+    "bin"
+    "sbin"
+    "lib"
+    "modules"
+  ];
+
   postInstall =
     let
       noSourceRefs = lib.concatMapStrings (
         m: "remove-references-to -t ${m.src} $(readlink -fn $out/bin/nginx)\n"
       ) modules;
+      dynamicPost = lib.optionalString (dynamicModules != [ ]) ''
+        shopt -s nullglob
+        sofiles=("$out"/modules/*.so)
+        if (( ''${#sofiles[@]} == 0 )); then
+          echo "nginx: dynamic modules were requested but no .so was produced in $out/modules" >&2
+          exit 1
+        fi
+        mkdir -p "$out/etc/nginx"
+        printf 'load_module %s;\n' "''${sofiles[@]}" > "$out/etc/nginx/dynamic-modules.conf"
+      '';
     in
-    postInstall + noSourceRefs;
+    postInstall + noSourceRefs + dynamicPost;
 
   passthru = {
-    inherit modules;
+    inherit modules dynamicModules;
     tests =
       passthru.tests or {
         inherit (nixosTests)
           nginx
           nginx-auth
+          nginx-dynamic-modules
           nginx-etag
           nginx-etag-compression
           nginx-globalredirect