chore: add psalm

16 files changed, 782 insertions, 33 deletions

diff --git a/.github/workflows/static.yml b/.github/workflows/static.yml
new file mode 100644
index 0000000..901fea1
--- /dev/null
+++ b/.github/workflows/static.yml
@@ -0,0 +1,24 @@
+name: Static analysis
+on: [push]
+
+jobs:
+  static-psalm-analysis:
+    runs-on: ubuntu-latest
+    strategy:
+        matrix:
+            ocp-version: [ 'dev-stable21', 'dev-stable20' ]
+    name: Nextcloud ${{ matrix.ocp-version }}
+    steps:
+        - name: Checkout
+          uses: actions/checkout@master
+        - name: Set up php
+          uses: shivammathur/setup-php@master
+          with:
+            php-version: 7.4
+            coverage: none
+        - name: Install dependencies
+          run: composer i
+        - name: Install dependencies
+          run: composer require --dev christophwurst/nextcloud:${{ matrix.ocp-version }}
+        - name: Run coding standards check
+          run: composer run psalm
diff --git a/composer.json b/composer.json
index 108c50c..543e412 100644
--- a/composer.json
+++ b/composer.json
@@ -5,12 +5,18 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^8.5 || ^9.3",
-        "friendsofphp/php-cs-fixer": "^2.14"
+        "friendsofphp/php-cs-fixer": "^2.14",
+        "christophwurst/nextcloud": "dev-stable20 || dev-stable21",
+        "vimeo/psalm": "^4.5"
     },
     "scripts": {
         "test": "phpunit --configuration phpunit.xml",
         "cs:check": "php-cs-fixer fix --dry-run --diff",
         "cs:fix": "php-cs-fixer fix",
-        "lint": "find . -name \\*.php -not -path './vendor/*' -exec php -l \"{}\" \\;"
+        "lint": "find . -name \\*.php -not -path './vendor/*' -exec php -l \"{}\" \\;",
+        "psalm": "psalm --threads=1",
+        "psalm:clear": "psalm --clear-cache && psalm --clear-global-cache",
+        "psalm:fix": "psalm --alter --issues=InvalidReturnType,InvalidNullableReturnType,MissingParamType,InvalidFalsableReturnType",
+        "psalm:update": "psalm --set-baseline=tests/psalm-baseline.xml && psalm --update-baseline"
     }
 }
diff --git a/composer.lock b/composer.lock
index 3030ef6..024b87f 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "2c91c5530223b5de2568a7656ef0cb68",
+    "content-hash": "0034a93f7304f72dce2c31b68cb1b29d",
     "packages": [
         {
             "name": "sabre/uri",
@@ -133,6 +133,287 @@
     ],
     "packages-dev": [
         {
+            "name": "amphp/amp",
+            "version": "v2.5.2",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/amphp/amp.git",
+                "reference": "efca2b32a7580087adb8aabbff6be1dc1bb924a9"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/amphp/amp/zipball/efca2b32a7580087adb8aabbff6be1dc1bb924a9",
+                "reference": "efca2b32a7580087adb8aabbff6be1dc1bb924a9",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=7"
+            },
+            "require-dev": {
+                "amphp/php-cs-fixer-config": "dev-master",
+                "amphp/phpunit-util": "^1",
+                "ext-json": "*",
+                "jetbrains/phpstorm-stubs": "^2019.3",
+                "phpunit/phpunit": "^6.0.9 | ^7",
+                "psalm/phar": "^3.11@dev",
+                "react/promise": "^2"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "2.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Amp\\": "lib"
+                },
+                "files": [
+                    "lib/functions.php",
+                    "lib/Internal/functions.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Daniel Lowrey",
+                    "email": "rdlowrey@php.net"
+                },
+                {
+                    "name": "Aaron Piotrowski",
+                    "email": "aaron@trowski.com"
+                },
+                {
+                    "name": "Bob Weinand",
+                    "email": "bobwei9@hotmail.com"
+                },
+                {
+                    "name": "Niklas Keller",
+                    "email": "me@kelunik.com"
+                }
+            ],
+            "description": "A non-blocking concurrency framework for PHP applications.",
+            "homepage": "http://amphp.org/amp",
+            "keywords": [
+                "async",
+                "asynchronous",
+                "awaitable",
+                "concurrency",
+                "event",
+                "event-loop",
+                "future",
+                "non-blocking",
+                "promise"
+            ],
+            "support": {
+                "irc": "irc://irc.freenode.org/amphp",
+                "issues": "https://github.com/amphp/amp/issues",
+                "source": "https://github.com/amphp/amp/tree/v2.5.2"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/amphp",
+                    "type": "github"
+                }
+            ],
+            "time": "2021-01-10T17:06:37+00:00"
+        },
+        {
+            "name": "amphp/byte-stream",
+            "version": "v1.8.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/amphp/byte-stream.git",
+                "reference": "acbd8002b3536485c997c4e019206b3f10ca15bd"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/amphp/byte-stream/zipball/acbd8002b3536485c997c4e019206b3f10ca15bd",
+                "reference": "acbd8002b3536485c997c4e019206b3f10ca15bd",
+                "shasum": ""
+            },
+            "require": {
+                "amphp/amp": "^2",
+                "php": ">=7.1"
+            },
+            "require-dev": {
+                "amphp/php-cs-fixer-config": "dev-master",
+                "amphp/phpunit-util": "^1.4",
+                "friendsofphp/php-cs-fixer": "^2.3",
+                "jetbrains/phpstorm-stubs": "^2019.3",
+                "phpunit/phpunit": "^6 || ^7 || ^8",
+                "psalm/phar": "^3.11.4"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Amp\\ByteStream\\": "lib"
+                },
+                "files": [
+                    "lib/functions.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Aaron Piotrowski",
+                    "email": "aaron@trowski.com"
+                },
+                {
+                    "name": "Niklas Keller",
+                    "email": "me@kelunik.com"
+                }
+            ],
+            "description": "A stream abstraction to make working with non-blocking I/O simple.",
+            "homepage": "http://amphp.org/byte-stream",
+            "keywords": [
+                "amp",
+                "amphp",
+                "async",
+                "io",
+                "non-blocking",
+                "stream"
+            ],
+            "support": {
+                "irc": "irc://irc.freenode.org/amphp",
+                "issues": "https://github.com/amphp/byte-stream/issues",
+                "source": "https://github.com/amphp/byte-stream/tree/v1.8.1"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/amphp",
+                    "type": "github"
+                }
+            ],
+            "time": "2021-03-30T17:13:30+00:00"
+        },
+        {
+            "name": "christophwurst/nextcloud",
+            "version": "dev-stable21",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/ChristophWurst/nextcloud_composer.git",
+                "reference": "be42b39d878f042fca36ffb7f71b09f8de8cd9d1"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/ChristophWurst/nextcloud_composer/zipball/be42b39d878f042fca36ffb7f71b09f8de8cd9d1",
+                "reference": "be42b39d878f042fca36ffb7f71b09f8de8cd9d1",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.3 || ~8.0.0",
+                "psr/container": "^1.0",
+                "psr/log": "^1.1"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "21.0.0-dev"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "AGPL-3.0-or-later"
+            ],
+            "authors": [
+                {
+                    "name": "Christoph Wurst",
+                    "email": "christoph@winzerhof-wurst.at"
+                }
+            ],
+            "description": "Composer package containing Nextcloud's public API (classes, interfaces)",
+            "support": {
+                "issues": "https://github.com/ChristophWurst/nextcloud_composer/issues",
+                "source": "https://github.com/ChristophWurst/nextcloud_composer/tree/stable21"
+            },
+            "time": "2021-03-26T07:42:50+00:00"
+        },
+        {
+            "name": "composer/package-versions-deprecated",
+            "version": "1.11.99.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/composer/package-versions-deprecated.git",
+                "reference": "7413f0b55a051e89485c5cb9f765fe24bb02a7b6"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/composer/package-versions-deprecated/zipball/7413f0b55a051e89485c5cb9f765fe24bb02a7b6",
+                "reference": "7413f0b55a051e89485c5cb9f765fe24bb02a7b6",
+                "shasum": ""
+            },
+            "require": {
+                "composer-plugin-api": "^1.1.0 || ^2.0",
+                "php": "^7 || ^8"
+            },
+            "replace": {
+                "ocramius/package-versions": "1.11.99"
+            },
+            "require-dev": {
+                "composer/composer": "^1.9.3 || ^2.0@dev",
+                "ext-zip": "^1.13",
+                "phpunit/phpunit": "^6.5 || ^7"
+            },
+            "type": "composer-plugin",
+            "extra": {
+                "class": "PackageVersions\\Installer",
+                "branch-alias": {
+                    "dev-master": "1.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "PackageVersions\\": "src/PackageVersions"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Marco Pivetta",
+                    "email": "ocramius@gmail.com"
+                },
+                {
+                    "name": "Jordi Boggiano",
+                    "email": "j.boggiano@seld.be"
+                }
+            ],
+            "description": "Composer plugin that provides efficient querying for installed package versions (no runtime IO)",
+            "support": {
+                "issues": "https://github.com/composer/package-versions-deprecated/issues",
+                "source": "https://github.com/composer/package-versions-deprecated/tree/1.11.99.1"
+            },
+            "funding": [
+                {
+                    "url": "https://packagist.com",
+                    "type": "custom"
+                },
+                {
+                    "url": "https://github.com/composer",
+                    "type": "github"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/composer/composer",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2020-11-11T10:22:58+00:00"
+        },
+        {
             "name": "composer/semver",
             "version": "3.2.4",
             "source": {
@@ -278,6 +559,43 @@
             "time": "2021-05-05T19:37:51+00:00"
         },
         {
+            "name": "dnoegel/php-xdg-base-dir",
+            "version": "v0.1.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/dnoegel/php-xdg-base-dir.git",
+                "reference": "8f8a6e48c5ecb0f991c2fdcf5f154a47d85f9ffd"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/dnoegel/php-xdg-base-dir/zipball/8f8a6e48c5ecb0f991c2fdcf5f154a47d85f9ffd",
+                "reference": "8f8a6e48c5ecb0f991c2fdcf5f154a47d85f9ffd",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.2"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "~7.0|~6.0|~5.0|~4.8.35"
+            },
+            "type": "library",
+            "autoload": {
+                "psr-4": {
+                    "XdgBaseDir\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "description": "implementation of xdg base directory specification for php",
+            "support": {
+                "issues": "https://github.com/dnoegel/php-xdg-base-dir/issues",
+                "source": "https://github.com/dnoegel/php-xdg-base-dir/tree/v0.1.1"
+            },
+            "time": "2019-12-04T15:06:13+00:00"
+        },
+        {
             "name": "doctrine/annotations",
             "version": "1.13.0",
             "source": {
@@ -499,6 +817,107 @@
             "time": "2020-05-25T17:44:05+00:00"
         },
         {
+            "name": "felixfbecker/advanced-json-rpc",
+            "version": "v3.2.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/felixfbecker/php-advanced-json-rpc.git",
+                "reference": "06f0b06043c7438959dbdeed8bb3f699a19be22e"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/felixfbecker/php-advanced-json-rpc/zipball/06f0b06043c7438959dbdeed8bb3f699a19be22e",
+                "reference": "06f0b06043c7438959dbdeed8bb3f699a19be22e",
+                "shasum": ""
+            },
+            "require": {
+                "netresearch/jsonmapper": "^1.0 || ^2.0",
+                "php": "^7.1 || ^8.0",
+                "phpdocumentor/reflection-docblock": "^4.3.4 || ^5.0.0"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^7.0 || ^8.0"
+            },
+            "type": "library",
+            "autoload": {
+                "psr-4": {
+                    "AdvancedJsonRpc\\": "lib/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "ISC"
+            ],
+            "authors": [
+                {
+                    "name": "Felix Becker",
+                    "email": "felix.b@outlook.com"
+                }
+            ],
+            "description": "A more advanced JSONRPC implementation",
+            "support": {
+                "issues": "https://github.com/felixfbecker/php-advanced-json-rpc/issues",
+                "source": "https://github.com/felixfbecker/php-advanced-json-rpc/tree/v3.2.0"
+            },
+            "time": "2021-01-10T17:48:47+00:00"
+        },
+        {
+            "name": "felixfbecker/language-server-protocol",
+            "version": "1.5.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/felixfbecker/php-language-server-protocol.git",
+                "reference": "9d846d1f5cf101deee7a61c8ba7caa0a975cd730"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/felixfbecker/php-language-server-protocol/zipball/9d846d1f5cf101deee7a61c8ba7caa0a975cd730",
+                "reference": "9d846d1f5cf101deee7a61c8ba7caa0a975cd730",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=7.1"
+            },
+            "require-dev": {
+                "phpstan/phpstan": "*",
+                "squizlabs/php_codesniffer": "^3.1",
+                "vimeo/psalm": "^4.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "LanguageServerProtocol\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "ISC"
+            ],
+            "authors": [
+                {
+                    "name": "Felix Becker",
+                    "email": "felix.b@outlook.com"
+                }
+            ],
+            "description": "PHP classes for the Language Server Protocol",
+            "keywords": [
+                "language",
+                "microsoft",
+                "php",
+                "server"
+            ],
+            "support": {
+                "issues": "https://github.com/felixfbecker/php-language-server-protocol/issues",
+                "source": "https://github.com/felixfbecker/php-language-server-protocol/tree/1.5.1"
+            },
+            "time": "2021-02-22T14:02:09+00:00"
+        },
+        {
             "name": "friendsofphp/php-cs-fixer",
             "version": "v2.19.0",
             "source": {
@@ -666,6 +1085,57 @@
             "time": "2020-11-13T09:40:50+00:00"
         },
         {
+            "name": "netresearch/jsonmapper",
+            "version": "v2.1.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/cweiske/jsonmapper.git",
+                "reference": "e0f1e33a71587aca81be5cffbb9746510e1fe04e"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/cweiske/jsonmapper/zipball/e0f1e33a71587aca81be5cffbb9746510e1fe04e",
+                "reference": "e0f1e33a71587aca81be5cffbb9746510e1fe04e",
+                "shasum": ""
+            },
+            "require": {
+                "ext-json": "*",
+                "ext-pcre": "*",
+                "ext-reflection": "*",
+                "ext-spl": "*",
+                "php": ">=5.6"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "~4.8.35 || ~5.7 || ~6.4 || ~7.0",
+                "squizlabs/php_codesniffer": "~3.5"
+            },
+            "type": "library",
+            "autoload": {
+                "psr-0": {
+                    "JsonMapper": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "OSL-3.0"
+            ],
+            "authors": [
+                {
+                    "name": "Christian Weiske",
+                    "email": "cweiske@cweiske.de",
+                    "homepage": "http://github.com/cweiske/jsonmapper/",
+                    "role": "Developer"
+                }
+            ],
+            "description": "Map nested JSON structures onto PHP classes",
+            "support": {
+                "email": "cweiske@cweiske.de",
+                "issues": "https://github.com/cweiske/jsonmapper/issues",
+                "source": "https://github.com/cweiske/jsonmapper/tree/master"
+            },
+            "time": "2020-04-16T18:48:43+00:00"
+        },
+        {
             "name": "nikic/php-parser",
             "version": "v4.10.5",
             "source": {
@@ -722,6 +1192,59 @@
             "time": "2021-05-03T19:11:20+00:00"
         },
         {
+            "name": "openlss/lib-array2xml",
+            "version": "1.0.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/nullivex/lib-array2xml.git",
+                "reference": "a91f18a8dfc69ffabe5f9b068bc39bb202c81d90"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/nullivex/lib-array2xml/zipball/a91f18a8dfc69ffabe5f9b068bc39bb202c81d90",
+                "reference": "a91f18a8dfc69ffabe5f9b068bc39bb202c81d90",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.2"
+            },
+            "type": "library",
+            "autoload": {
+                "psr-0": {
+                    "LSS": ""
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "Apache-2.0"
+            ],
+            "authors": [
+                {
+                    "name": "Bryan Tong",
+                    "email": "bryan@nullivex.com",
+                    "homepage": "https://www.nullivex.com"
+                },
+                {
+                    "name": "Tony Butler",
+                    "email": "spudz76@gmail.com",
+                    "homepage": "https://www.nullivex.com"
+                }
+            ],
+            "description": "Array2XML conversion library credit to lalit.org",
+            "homepage": "https://www.nullivex.com",
+            "keywords": [
+                "array",
+                "array conversion",
+                "xml",
+                "xml conversion"
+            ],
+            "support": {
+                "issues": "https://github.com/nullivex/lib-array2xml/issues",
+                "source": "https://github.com/nullivex/lib-array2xml/tree/master"
+            },
+            "time": "2019-03-29T20:06:56+00:00"
+        },
+        {
             "name": "phar-io/manifest",
             "version": "2.0.1",
             "source": {
@@ -4181,6 +4704,111 @@
             "time": "2020-07-12T23:59:07+00:00"
         },
         {
+            "name": "vimeo/psalm",
+            "version": "4.7.2",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/vimeo/psalm.git",
+                "reference": "83a0325c0a95c0ab531d6b90c877068b464377b5"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/vimeo/psalm/zipball/83a0325c0a95c0ab531d6b90c877068b464377b5",
+                "reference": "83a0325c0a95c0ab531d6b90c877068b464377b5",
+                "shasum": ""
+            },
+            "require": {
+                "amphp/amp": "^2.4.2",
+                "amphp/byte-stream": "^1.5",
+                "composer/package-versions-deprecated": "^1.8.0",
+                "composer/semver": "^1.4 || ^2.0 || ^3.0",
+                "composer/xdebug-handler": "^1.1 || ^2.0",
+                "dnoegel/php-xdg-base-dir": "^0.1.1",
+                "ext-dom": "*",
+                "ext-json": "*",
+                "ext-libxml": "*",
+                "ext-mbstring": "*",
+                "ext-simplexml": "*",
+                "ext-tokenizer": "*",
+                "felixfbecker/advanced-json-rpc": "^3.0.3",
+                "felixfbecker/language-server-protocol": "^1.5",
+                "netresearch/jsonmapper": "^1.0 || ^2.0 || ^3.0 || ^4.0",
+                "nikic/php-parser": "^4.10.1",
+                "openlss/lib-array2xml": "^1.0",
+                "php": "^7.1|^8",
+                "sebastian/diff": "^3.0 || ^4.0",
+                "symfony/console": "^3.4.17 || ^4.1.6 || ^5.0",
+                "webmozart/path-util": "^2.3"
+            },
+            "provide": {
+                "psalm/psalm": "self.version"
+            },
+            "require-dev": {
+                "bamarni/composer-bin-plugin": "^1.2",
+                "brianium/paratest": "^4.0||^6.0",
+                "ext-curl": "*",
+                "php-parallel-lint/php-parallel-lint": "^1.2",
+                "phpdocumentor/reflection-docblock": "^5",
+                "phpmyadmin/sql-parser": "5.1.0||dev-master",
+                "phpspec/prophecy": ">=1.9.0",
+                "phpunit/phpunit": "^9.0",
+                "psalm/plugin-phpunit": "^0.13",
+                "slevomat/coding-standard": "^6.3.11",
+                "squizlabs/php_codesniffer": "^3.5",
+                "symfony/process": "^4.3",
+                "weirdan/phpunit-appveyor-reporter": "^1.0.0",
+                "weirdan/prophecy-shim": "^1.0 || ^2.0"
+            },
+            "suggest": {
+                "ext-igbinary": "^2.0.5"
+            },
+            "bin": [
+                "psalm",
+                "psalm-language-server",
+                "psalm-plugin",
+                "psalm-refactor",
+                "psalter"
+            ],
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "4.x-dev",
+                    "dev-3.x": "3.x-dev",
+                    "dev-2.x": "2.x-dev",
+                    "dev-1.x": "1.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Psalm\\": "src/Psalm/"
+                },
+                "files": [
+                    "src/functions.php",
+                    "src/spl_object_id.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Matthew Brown"
+                }
+            ],
+            "description": "A static analysis tool for finding errors in PHP applications",
+            "keywords": [
+                "code",
+                "inspection",
+                "php"
+            ],
+            "support": {
+                "issues": "https://github.com/vimeo/psalm/issues",
+                "source": "https://github.com/vimeo/psalm/tree/4.7.2"
+            },
+            "time": "2021-05-01T20:56:25+00:00"
+        },
+        {
             "name": "webmozart/assert",
             "version": "1.10.0",
             "source": {
@@ -4237,11 +4865,63 @@
                 "source": "https://github.com/webmozarts/assert/tree/1.10.0"
             },
             "time": "2021-03-09T10:59:23+00:00"
+        },
+        {
+            "name": "webmozart/path-util",
+            "version": "2.3.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/webmozart/path-util.git",
+                "reference": "d939f7edc24c9a1bb9c0dee5cb05d8e859490725"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/webmozart/path-util/zipball/d939f7edc24c9a1bb9c0dee5cb05d8e859490725",
+                "reference": "d939f7edc24c9a1bb9c0dee5cb05d8e859490725",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.3",
+                "webmozart/assert": "~1.0"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^4.6",
+                "sebastian/version": "^1.0.1"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "2.3-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Webmozart\\PathUtil\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Bernhard Schussek",
+                    "email": "bschussek@gmail.com"
+                }
+            ],
+            "description": "A robust cross-platform utility for normalizing, comparing and modifying file paths.",
+            "support": {
+                "issues": "https://github.com/webmozart/path-util/issues",
+                "source": "https://github.com/webmozart/path-util/tree/2.3.0"
+            },
+            "time": "2015-12-17T08:42:14+00:00"
         }
     ],
     "aliases": [],
     "minimum-stability": "stable",
-    "stability-flags": [],
+    "stability-flags": {
+        "christophwurst/nextcloud": 20
+    },
     "prefer-stable": false,
     "prefer-lowest": false,
     "platform": [],
diff --git a/lib/AppInfo/Application.php b/lib/AppInfo/Application.php
index 02700aa..417ea17 100644
--- a/lib/AppInfo/Application.php
+++ b/lib/AppInfo/Application.php
@@ -30,11 +30,11 @@ use OCA\OJSXC\Hooks;
 use OCA\OJSXC\UserManagerUserProvider;
 use OCA\OJSXC\ContactsStoreUserProvider;
 use OCA\OJSXC\Config;
-use OCP\AppFramework\App;
 use OCP\IContainer;
 use OCP\IRequest;
 use OCP\IUserBackend;
 use OCA\OJSXC\Migration\MigrateConfig;
+use OCP\AppFramework\App;
 
 class Application extends App
 {
diff --git a/lib/command/refreshroster.php b/lib/Command/RefreshRoster.php
index 331810b..b7eb769 100644
--- a/lib/command/refreshroster.php
+++ b/lib/Command/RefreshRoster.php
@@ -50,5 +50,7 @@ class RefreshRoster extends Command
 		$stats = $this->rosterPush->refreshRoster();
 		$output->writeln("Updated " . $stats["updated"] . " roster items");
 		$output->writeln("Removed " . $stats["removed"] . " roster items");
+
+		return 0;
 	}
 }
diff --git a/lib/command/serversharing.php b/lib/Command/ServerSharing.php
index eb6189b..c290581 100644
--- a/lib/command/serversharing.php
+++ b/lib/Command/ServerSharing.php
@@ -8,7 +8,7 @@ use Symfony\Component\Console\Command\Command;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 
-class serversharing extends Command
+class ServerSharing extends Command
 {
 
 	/**
@@ -33,14 +33,9 @@ class serversharing extends Command
 
 	protected function execute(InputInterface $input, OutputInterface $output)
 	{
-		if (\OCP\Util::getVersion()[0] < 13) {
-			$output->write('This feature is only supported in Nextcloud 13 or later.', true);
-			return;
-		}
-
 		if (Application::getServerType() !== 'internal') {
 			$output->write('This feature is only supported using the internal backend.', true);
-			return;
+			return 0;
 		}
 
 		$enable = $input->getOption('enable');
@@ -53,13 +48,13 @@ class serversharing extends Command
 				$state = 'disabled';
 			}
 			$output->write('This feature is currently ' . $state, true);
-			return;
+			return 0;
 		}
 
 		if ($enable === $disable) {
 			// if both enable and disable passed or none option
 			$output->write('Please provide only --enable or --disable', true);
-			return;
+			return 1;
 		}
 
 
@@ -72,5 +67,7 @@ class serversharing extends Command
 			$this->config->setAppValue('ojsxc', 'use_server_sharing_settings', 'no');
 			$output->write('Successfully disabled.', true);
 		}
+
+		return 0;
 	}
 }
diff --git a/lib/Controller/HttpBindController.php b/lib/Controller/HttpBindController.php
index 4f20762..84e5bb0 100644
--- a/lib/Controller/HttpBindController.php
+++ b/lib/Controller/HttpBindController.php
@@ -58,18 +58,16 @@ class HttpBindController extends Controller
 	 */
 	private $messageHandler;
 
-	/**
-	 * @var Body request body
-	 */
+	/** @var string */
 	private $body;
 
 	/**
-	 * @var SleepTime
+	 * @var int SleepTime
 	 */
 	private $sleepTime;
 
 	/**
-	 * @var SleepTime
+	 * @var int
 	 */
 	private $maxCicles;
 
@@ -245,7 +243,7 @@ class HttpBindController extends Controller
 
 	/**
 	 * @param $stanza
-	 * @return int
+	 * @return int|null
 	 * @codeCoverageIgnore
 	 */
 	private function getStanzaType($stanza)
diff --git a/lib/Controller/ManagedServerController.php b/lib/Controller/ManagedServerController.php
index 58cd0be..878fac6 100644
--- a/lib/Controller/ManagedServerController.php
+++ b/lib/Controller/ManagedServerController.php
@@ -23,8 +23,9 @@ class ManagedServerController extends Controller
 	private $userSession;
 	private $logger;
 	private $dataRetriever;
-	private $registrationUrl;
 	private $random;
+	private $appManager;
+	private $registrationUrl;
 
 	public function __construct(
 		$appName,
diff --git a/lib/Migration/MigrateConfig.php b/lib/Migration/MigrateConfig.php
index a4ab91f..b4c49c6 100644
--- a/lib/Migration/MigrateConfig.php
+++ b/lib/Migration/MigrateConfig.php
@@ -3,6 +3,7 @@
 namespace OCA\OJSXC\Migration;
 
 use OCA\OJSXC\Config;
+use OCP\ILogger;
 use OCP\Migration\IOutput;
 use OCP\Migration\IRepairStep;
 
@@ -14,7 +15,7 @@ class MigrateConfig implements IRepairStep
 	private $config;
 
 	/**
-	 * @param IConfig $config
+	 * @param Config $config
 	 * @param ILogger $logger
 	 */
 	public function __construct(Config $config)
diff --git a/lib/Migration/RefreshRoster.php b/lib/Migration/RefreshRoster.php
index f7023d5..b4779ac 100644
--- a/lib/Migration/RefreshRoster.php
+++ b/lib/Migration/RefreshRoster.php
@@ -64,7 +64,7 @@ class RefreshRoster implements IRepairStep
 		 * We want only to refresh the rosters if this app was installed before,
 		 * since only then the rosters can be outdated.
 		 */
-		if ($this->config->getAppValue('ojsxc', 'installed_version', null) !== null
+		if ($this->config->getAppValue('ojsxc', 'installed_version') !== ''
 			&& Application::getServerType() === Application::INTERNAL) {
 			$stats = $this->rosterPush->refreshRoster();
 			$output->info("Updated " . $stats["updated"] . " roster items");
diff --git a/lib/UserManagerUserProvider.php b/lib/UserManagerUserProvider.php
index 7685d64..bcc7ce0 100644
--- a/lib/UserManagerUserProvider.php
+++ b/lib/UserManagerUserProvider.php
@@ -68,13 +68,13 @@ class UserManagerUserProvider implements IUserProvider
 	public function hasUserForUser(User $user1, User $user2)
 	{
 		// since we don't have access to the ContactsStore, we don't apply the enhancement privacy rules.
-		$this->hasUser($user2);
+		return $this->hasUser($user2);
 	}
 
 	public function hasUserForUserByUID($uid1, $uid2)
 	{
 		// since we don't have access to the ContactsStore, we don't apply the enhancement privacy rules.
-		$this->hasUserByUID($uid2);
+		return $this->hasUserByUID($uid2);
 	}
 
 	public function isUserExcluded($userId)
diff --git a/lib/db/stanza.php b/lib/db/stanza.php
index 7db1b5b..a3e5145 100644
--- a/lib/db/stanza.php
+++ b/lib/db/stanza.php
@@ -64,10 +64,10 @@ class Stanza extends Entity implements XmlSerializable
 	 * Sets the to user as a `user`.
 	 *
 	 * @see setFullTo
-	 * @param $userId
-	 * @param null $host_and_or_resource
+	 * @param string $userId
+	 * @param string $host_and_or_resource
 	 */
-	public function setTo($userId, $host_and_or_resource = null)
+	public function setTo($userId, ?string $host_and_or_resource = null)
 	{
 		if (is_array($userId)) {
 			// support mapFromRow
@@ -87,9 +87,9 @@ class Stanza extends Entity implements XmlSerializable
 	 *
 	 * @see setFullFrom
 	 * @param $userId
-	 * @param null $host_and_or_resource
+	 * @param string $host_and_or_resource
 	 */
-	public function setFrom($userId, $host_and_or_resource = null)
+	public function setFrom($userId, ?string $host_and_or_resource = null)
 	{
 		if (is_array($userId)) {
 			// support mapFromRow
diff --git a/lib/dblock.php b/lib/dblock.php
index 31a5888..791c8ed 100644
--- a/lib/dblock.php
+++ b/lib/dblock.php
@@ -27,6 +27,9 @@ class DbLock implements ILock
 	 */
 	private $pollingId;
 
+	/** @var IDBConnection */
+	private $con;
+
 	/**
 	 * DbLock constructor.
 	 *
diff --git a/lib/memlock.php b/lib/memlock.php
index 64ddb0a..902bfdd 100644
--- a/lib/memlock.php
+++ b/lib/memlock.php
@@ -13,7 +13,7 @@ class MemLock implements ILock
 {
 
 	/**
-	 * @var \OCP\ICache $memcache
+	 * @var ICache $memcache
 	 */
 	private $memcache;
 
@@ -43,7 +43,7 @@ class MemLock implements ILock
 	public function setLock()
 	{
 		$this->memcache->remove('-' . $this->userId . '-ojxsc-lock');
-		$this->memcache->add('-' . $this->userId . '-ojxsc-lock', $this->pollingId);
+		$this->memcache->set('-' . $this->userId . '-ojxsc-lock', $this->pollingId);
 	}
 
 	/**
diff --git a/lib/stanzahandlers/iq.php b/lib/stanzahandlers/iq.php
index 8ccc5c0..dd4cd36 100644
--- a/lib/stanzahandlers/iq.php
+++ b/lib/stanzahandlers/iq.php
@@ -53,7 +53,7 @@ class IQ extends StanzaHandler
 
 	/**
 	 * @param array $stanza
-	 * @return Stanza
+	 * @return Stanza|null
 	 * @throws TerminateException
 	 */
 	public function handle(array $stanza)
diff --git a/psalm.xml b/psalm.xml
new file mode 100644
index 0000000..e7b226e
--- /dev/null
+++ b/psalm.xml
@@ -0,0 +1,37 @@
+<?xml version="1.0"?>
+<psalm
+    totallyTyped="true"
+    errorLevel="5"
+    resolveFromConfigFile="true"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="https://getpsalm.org/schema/config"
+    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
+>
+    <projectFiles>
+        <directory name="lib" />
+        <ignoreFiles>
+            <directory name="vendor" />
+        </ignoreFiles>
+    </projectFiles>
+    <extraFiles>
+        <directory name="vendor" />
+        <ignoreFiles>
+            <directory name="vendor/phpunit/php-code-coverage" />
+        </ignoreFiles>
+    </extraFiles>
+    <issueHandlers>
+        <UndefinedClass>
+            <errorLevel type="suppress">
+                <referencedClass name="OC" />
+            </errorLevel>
+        </UndefinedClass>
+        <UndefinedDocblockClass>
+            <errorLevel type="suppress">
+                <referencedClass name="Doctrine\DBAL\Schema\Schema" />
+                <referencedClass name="Doctrine\DBAL\Schema\SchemaException" />
+                <referencedClass name="Doctrine\DBAL\Driver\Statement" />
+                <referencedClass name="Doctrine\DBAL\Schema\Table" />
+            </errorLevel>
+        </UndefinedDocblockClass>
+    </issueHandlers>
+</psalm>