nextcloud: add `nextcloud.nginx.enableFastcgiRequestBuffering` option

Enabling this option fixes (works around) Nextcloud's notorious "0 byte file"
issue. See these upstream issues:

- https://github.com/nextcloud/documentation/issues/9574
- https://github.com/nextcloud/server/issues/7995

This fixes https://github.com/NixOS/nixpkgs/issues/252980

Co-authored-by: Maximilian Bosch <[e-mail]>

nixos/modules/services/web-apps/nextcloud.md

···
     services.nextcloud.phpOptions."realpath_cache_size" = "0";
     ```
 
+  - **Empty Files on chunked uploads**
+
+    Due to a limitation of PHP-FPM, Nextcloud is unable to handle chunked
+    uploads. See upstream issue
+    [nextcloud/server#7995](https://github.com/nextcloud/server/issues/7995)
+    for details.
+
+    A workaround is to disable chunked uploads with
+    {option}`nextcloud.nginx.enableFastcgiRequestBuffering`.
+
 ## Using an alternative webserver as reverse-proxy (e.g. `httpd`) {#module-services-nextcloud-httpd}
 
 By default, `nginx` is used as reverse-proxy for `nextcloud`.

nixos/modules/services/web-apps/nextcloud.nix

···
           directive and header.
         '';
       };
+      enableFastcgiRequestBuffering = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Whether to buffer requests against fastcgi requests. This is a workaround
+          for `PUT` requests with the `Transfer-Encoding: chunked` header set and
+          an unspecified `Content-Length`. Without request buffering for these requests,
+          Nextcloud will create files with zero bytes length as described in
+          [nextcloud/server#7995](https://github.com/nextcloud/server/issues/7995).
+
+          ::: {.note}
+          Please keep in mind that upstream suggests to not enable this as it might
+          lead to timeouts on large files being uploaded as described in the
+          [administrator manual](https://docs.nextcloud.com/server/latest/admin_manual/configuration_files/big_file_upload_configuration.html#nginx).
+          :::
+        '';
+      };
     };
 
     cli.memoryLimit = mkOption {
···
               fastcgi_param front_controller_active true;
               fastcgi_pass unix:${fpm.socket};
               fastcgi_intercept_errors on;
-              fastcgi_request_buffering off;
+              fastcgi_request_buffering ${if cfg.nginx.enableFastcgiRequestBuffering then "on" else "off"};
               fastcgi_read_timeout ${builtins.toString cfg.fastcgiTimeout}s;
             '';
           };

nixos/tests/nextcloud/basic.nix

···
               startAt = "20:00";
             };
             phpExtraExtensions = all: [ all.bz2 ];
+            nginx.enableFastcgiRequestBuffering = true;
           };
 
           specialisation.withoutMagick.configuration = {
···
         nexcloudWithImagick = findInClosure "imagick" nodes.nextcloud.system.build.vm;
         nextcloudWithoutImagick = findInClosure "imagick" nodes.nextcloud.specialisation.withoutMagick.configuration.system.build.vm;
       in
+      # python
       ''
         with subtest("File is in proper nextcloud home"):
             nextcloud.succeed("test -f ${nodes.nextcloud.services.nextcloud.datadir}/data/root/files/test-shared-file")
···
 
         with subtest("Ensure SSE is disabled by default"):
             nextcloud.succeed("grep -vE '^HBEGIN:oc_encryption_module' /var/lib/nextcloud-data/data/root/files/test-shared-file")
+
+        with subtest("Create non-empty files with Transfer-Encoding: chunked"):
+            client.succeed(
+              'dd if=/dev/urandom of=testfile.bin bs=1M count=10',
+              'curl --fail -v -X PUT --header "Transfer-Encoding: chunked" --data-binary @testfile.bin "http://nextcloud/remote.php/webdav/testfile.bin" -u ${config.adminuser}:${config.adminpass}',
+            )
+
+            # Verify the local and remote copies of the file are identical.
+            client_hash = client.succeed("nix-hash testfile.bin").strip()
+            nextcloud_hash = nextcloud.succeed("nix-hash /var/lib/nextcloud-data/data/root/files/testfile.bin").strip()
+            t.assertEqual(client_hash, nextcloud_hash)
       '';
   }
 )