nextcloud / server

apps/dav/lib/Connector/Sabre/Principal.php

Indentation +482 added lines, -482 removed lines

@@ -51,486 +51,486 @@
 
 class Principal implements BackendInterface {
 
-	/** @var IUserManager */
-	private $userManager;
-
-	/** @var IGroupManager */
-	private $groupManager;
-
-	/** @var IShareManager */
-	private $shareManager;
-
-	/** @var IUserSession */
-	private $userSession;
-
-	/** @var IAppManager */
-	private $appManager;
-
-	/** @var string */
-	private $principalPrefix;
-
-	/** @var bool */
-	private $hasGroups;
-
-	/** @var bool */
-	private $hasCircles;
-
-	/** @var ProxyMapper */
-	private $proxyMapper;
-
-	/** @var IConfig */
-	private $config;
-
-	/**
-	 * Principal constructor.
-	 *
-	 * @param IUserManager $userManager
-	 * @param IGroupManager $groupManager
-	 * @param IShareManager $shareManager
-	 * @param IUserSession $userSession
-	 * @param IAppManager $appManager
-	 * @param ProxyMapper $proxyMapper
-	 * @param IConfig $config
-	 * @param string $principalPrefix
-	 */
-	public function __construct(IUserManager $userManager,
-								IGroupManager $groupManager,
-								IShareManager $shareManager,
-								IUserSession $userSession,
-								IAppManager $appManager,
-								ProxyMapper $proxyMapper,
-								IConfig $config,
-								string $principalPrefix = 'principals/users/') {
-		$this->userManager = $userManager;
-		$this->groupManager = $groupManager;
-		$this->shareManager = $shareManager;
-		$this->userSession = $userSession;
-		$this->appManager = $appManager;
-		$this->principalPrefix = trim($principalPrefix, '/');
-		$this->hasGroups = $this->hasCircles = ($principalPrefix === 'principals/users/');
-		$this->proxyMapper = $proxyMapper;
-		$this->config = $config;
-	}
-
-	use PrincipalProxyTrait {
-		getGroupMembership as protected traitGetGroupMembership;
-	}
-
-	/**
-	 * Returns a list of principals based on a prefix.
-	 *
-	 * This prefix will often contain something like 'principals'. You are only
-	 * expected to return principals that are in this base path.
-	 *
-	 * You are expected to return at least a 'uri' for every user, you can
-	 * return any additional properties if you wish so. Common properties are:
-	 *   {DAV:}displayname
-	 *
-	 * @param string $prefixPath
-	 * @return string[]
-	 */
-	public function getPrincipalsByPrefix($prefixPath) {
-		$principals = [];
-
-		if ($prefixPath === $this->principalPrefix) {
-			foreach ($this->userManager->search('') as $user) {
-				$principals[] = $this->userToPrincipal($user);
-			}
-		}
-
-		return $principals;
-	}
-
-	/**
-	 * Returns a specific principal, specified by it's path.
-	 * The returned structure should be the exact same as from
-	 * getPrincipalsByPrefix.
-	 *
-	 * @param string $path
-	 * @return array
-	 */
-	public function getPrincipalByPath($path) {
-		list($prefix, $name) = \Sabre\Uri\split($path);
-
-		if ($name === 'calendar-proxy-write' || $name === 'calendar-proxy-read') {
-			list($prefix2, $name2) = \Sabre\Uri\split($prefix);
-
-			if ($prefix2 === $this->principalPrefix) {
-				$user = $this->userManager->get($name2);
-
-				if ($user !== null) {
-					return [
-						'uri' => 'principals/users/' . $user->getUID() . '/' . $name,
-					];
-				}
-				return null;
-			}
-		}
-
-		if ($prefix === $this->principalPrefix) {
-			// Depending on where it is called, it may happen that this function
-			// is called either with a urlencoded version of the name or with a non-urlencoded one.
-			// The urldecode function replaces %## and +, both of which are forbidden in usernames.
-			// Hence there can be no ambiguity here and it is safe to call urldecode on all usernames
-			$user = $this->userManager->get(urldecode($name));
-
-			if ($user !== null) {
-				return $this->userToPrincipal($user);
-			}
-		} elseif ($prefix === 'principals/circles') {
-			try {
-				return $this->circleToPrincipal($name);
-			} catch (QueryException $e) {
-				return null;
-			}
-		}
-		return null;
-	}
-
-	/**
-	 * Returns the list of groups a principal is a member of
-	 *
-	 * @param string $principal
-	 * @param bool $needGroups
-	 * @return array
-	 * @throws Exception
-	 */
-	public function getGroupMembership($principal, $needGroups = false) {
-		list($prefix, $name) = \Sabre\Uri\split($principal);
-
-		if ($prefix !== $this->principalPrefix) {
-			return [];
-		}
-
-		$user = $this->userManager->get($name);
-		if (!$user) {
-			throw new Exception('Principal not found');
-		}
-
-		$groups = [];
-
-		if ($this->hasGroups || $needGroups) {
-			$userGroups = $this->groupManager->getUserGroups($user);
-			foreach ($userGroups as $userGroup) {
-				$groups[] = 'principals/groups/' . urlencode($userGroup->getGID());
-			}
-		}
-
-		$groups = array_unique(array_merge(
-			$groups,
-			$this->traitGetGroupMembership($principal, $needGroups)
-		));
-
-		return $groups;
-	}
-
-	/**
-	 * @param string $path
-	 * @param PropPatch $propPatch
-	 * @return int
-	 */
-	public function updatePrincipal($path, PropPatch $propPatch) {
-		return 0;
-	}
-
-	/**
-	 * Search user principals
-	 *
-	 * @param array $searchProperties
-	 * @param string $test
-	 * @return array
-	 */
-	protected function searchUserPrincipals(array $searchProperties, $test = 'allof') {
-		$results = [];
-
-		// If sharing is disabled, return the empty array
-		$shareAPIEnabled = $this->shareManager->shareApiEnabled();
-		if (!$shareAPIEnabled) {
-			return [];
-		}
-
-		$allowEnumeration = $this->shareManager->allowEnumeration();
-		$limitEnumeration = $this->shareManager->limitEnumerationToGroups();
-
-		// If sharing is restricted to group members only,
-		// return only members that have groups in common
-		$restrictGroups = false;
-		if ($this->shareManager->shareWithGroupMembersOnly()) {
-			$user = $this->userSession->getUser();
-			if (!$user) {
-				return [];
-			}
-
-			$restrictGroups = $this->groupManager->getUserGroupIds($user);
-		}
-
-		$currentUserGroups = [];
-		if ($limitEnumeration) {
-			$currentUser = $this->userSession->getUser();
-			if ($currentUser) {
-				$currentUserGroups = $this->groupManager->getUserGroupIds($currentUser);
-			}
-		}
-
-		foreach ($searchProperties as $prop => $value) {
-			switch ($prop) {
-				case '{http://sabredav.org/ns}email-address':
-					$users = $this->userManager->getByEmail($value);
-
-					if (!$allowEnumeration) {
-						$users = \array_filter($users, static function (IUser $user) use ($value) {
-							return $user->getEMailAddress() === $value;
-						});
-					}
-
-					if ($limitEnumeration) {
-						$users = \array_filter($users, function (IUser $user) use ($currentUserGroups, $value) {
-							return !empty(array_intersect(
-									$this->groupManager->getUserGroupIds($user),
-									$currentUserGroups
-								)) || $user->getEMailAddress() === $value;
-						});
-					}
-
-					$results[] = array_reduce($users, function (array $carry, IUser $user) use ($restrictGroups) {
-						// is sharing restricted to groups only?
-						if ($restrictGroups !== false) {
-							$userGroups = $this->groupManager->getUserGroupIds($user);
-							if (count(array_intersect($userGroups, $restrictGroups)) === 0) {
-								return $carry;
-							}
-						}
-
-						$carry[] = $this->principalPrefix . '/' . $user->getUID();
-						return $carry;
-					}, []);
-					break;
-
-				case '{DAV:}displayname':
-					$users = $this->userManager->searchDisplayName($value);
-
-					if (!$allowEnumeration) {
-						$users = \array_filter($users, static function (IUser $user) use ($value) {
-							return $user->getDisplayName() === $value;
-						});
-					}
-
-					if ($limitEnumeration) {
-						$users = \array_filter($users, function (IUser $user) use ($currentUserGroups, $value) {
-							return !empty(array_intersect(
-									$this->groupManager->getUserGroupIds($user),
-									$currentUserGroups
-								)) || $user->getDisplayName() === $value;
-						});
-					}
-
-					$results[] = array_reduce($users, function (array $carry, IUser $user) use ($restrictGroups) {
-						// is sharing restricted to groups only?
-						if ($restrictGroups !== false) {
-							$userGroups = $this->groupManager->getUserGroupIds($user);
-							if (count(array_intersect($userGroups, $restrictGroups)) === 0) {
-								return $carry;
-							}
-						}
-
-						$carry[] = $this->principalPrefix . '/' . $user->getUID();
-						return $carry;
-					}, []);
-					break;
-
-				case '{urn:ietf:params:xml:ns:caldav}calendar-user-address-set':
-					// If you add support for more search properties that qualify as a user-address,
-					// please also add them to the array below
-					$results[] = $this->searchUserPrincipals([
-						// In theory this should also search for principal:principals/users/...
-						// but that's used internally only anyway and i don't know of any client querying that
-						'{http://sabredav.org/ns}email-address' => $value,
-					], 'anyof');
-					break;
-
-				default:
-					$results[] = [];
-					break;
-			}
-		}
-
-		// results is an array of arrays, so this is not the first search result
-		// but the results of the first searchProperty
-		if (count($results) === 1) {
-			return $results[0];
-		}
-
-		switch ($test) {
-			case 'anyof':
-				return array_values(array_unique(array_merge(...$results)));
-
-			case 'allof':
-			default:
-				return array_values(array_intersect(...$results));
-		}
-	}
-
-	/**
-	 * @param string $prefixPath
-	 * @param array $searchProperties
-	 * @param string $test
-	 * @return array
-	 */
-	public function searchPrincipals($prefixPath, array $searchProperties, $test = 'allof') {
-		if (count($searchProperties) === 0) {
-			return [];
-		}
-
-		switch ($prefixPath) {
-			case 'principals/users':
-				return $this->searchUserPrincipals($searchProperties, $test);
-
-			default:
-				return [];
-		}
-	}
-
-	/**
-	 * @param string $uri
-	 * @param string $principalPrefix
-	 * @return string
-	 */
-	public function findByUri($uri, $principalPrefix) {
-		// If sharing is disabled, return the empty array
-		$shareAPIEnabled = $this->shareManager->shareApiEnabled();
-		if (!$shareAPIEnabled) {
-			return null;
-		}
-
-		// If sharing is restricted to group members only,
-		// return only members that have groups in common
-		$restrictGroups = false;
-		if ($this->shareManager->shareWithGroupMembersOnly()) {
-			$user = $this->userSession->getUser();
-			if (!$user) {
-				return null;
-			}
-
-			$restrictGroups = $this->groupManager->getUserGroupIds($user);
-		}
-
-		if (strpos($uri, 'mailto:') === 0) {
-			if ($principalPrefix === 'principals/users') {
-				$users = $this->userManager->getByEmail(substr($uri, 7));
-				if (count($users) !== 1) {
-					return null;
-				}
-				$user = $users[0];
-
-				if ($restrictGroups !== false) {
-					$userGroups = $this->groupManager->getUserGroupIds($user);
-					if (count(array_intersect($userGroups, $restrictGroups)) === 0) {
-						return null;
-					}
-				}
-
-				return $this->principalPrefix . '/' . $user->getUID();
-			}
-		}
-		if (substr($uri, 0, 10) === 'principal:') {
-			$principal = substr($uri, 10);
-			$principal = $this->getPrincipalByPath($principal);
-			if ($principal !== null) {
-				return $principal['uri'];
-			}
-		}
-
-		return null;
-	}
-
-	/**
-	 * @param IUser $user
-	 * @return array
-	 */
-	protected function userToPrincipal($user) {
-		$userId = $user->getUID();
-		$displayName = $user->getDisplayName();
-		$principal = [
-			'uri' => $this->principalPrefix . '/' . $userId,
-			'{DAV:}displayname' => is_null($displayName) ? $userId : $displayName,
-			'{urn:ietf:params:xml:ns:caldav}calendar-user-type' => 'INDIVIDUAL',
-		];
-
-		$email = $user->getEMailAddress();
-		if (!empty($email)) {
-			$principal['{http://sabredav.org/ns}email-address'] = $email;
-		}
-
-		return $principal;
-	}
-
-	public function getPrincipalPrefix() {
-		return $this->principalPrefix;
-	}
-
-	/**
-	 * @param string $circleUniqueId
-	 * @return array|null
-	 * @throws \OCP\AppFramework\QueryException
-	 * @suppress PhanUndeclaredClassMethod
-	 * @suppress PhanUndeclaredClassCatch
-	 */
-	protected function circleToPrincipal($circleUniqueId) {
-		if (!$this->appManager->isEnabledForUser('circles') || !class_exists('\OCA\Circles\Api\v1\Circles')) {
-			return null;
-		}
-
-		try {
-			$circle = \OCA\Circles\Api\v1\Circles::detailsCircle($circleUniqueId, true);
-		} catch (QueryException $ex) {
-			return null;
-		} catch (CircleDoesNotExistException $ex) {
-			return null;
-		}
-
-		if (!$circle) {
-			return null;
-		}
-
-		$principal = [
-			'uri' => 'principals/circles/' . $circleUniqueId,
-			'{DAV:}displayname' => $circle->getName(),
-		];
-
-		return $principal;
-	}
-
-	/**
-	 * Returns the list of circles a principal is a member of
-	 *
-	 * @param string $principal
-	 * @return array
-	 * @throws Exception
-	 * @throws \OCP\AppFramework\QueryException
-	 * @suppress PhanUndeclaredClassMethod
-	 */
-	public function getCircleMembership($principal):array {
-		if (!$this->appManager->isEnabledForUser('circles') || !class_exists('\OCA\Circles\Api\v1\Circles')) {
-			return [];
-		}
-
-		list($prefix, $name) = \Sabre\Uri\split($principal);
-		if ($this->hasCircles && $prefix === $this->principalPrefix) {
-			$user = $this->userManager->get($name);
-			if (!$user) {
-				throw new Exception('Principal not found');
-			}
-
-			$circles = \OCA\Circles\Api\v1\Circles::joinedCircles($name, true);
-
-			$circles = array_map(function ($circle) {
-				/** @var \OCA\Circles\Model\Circle $circle */
-				return 'principals/circles/' . urlencode($circle->getUniqueId());
-			}, $circles);
-
-			return $circles;
-		}
-
-		return [];
-	}
+    /** @var IUserManager */
+    private $userManager;
+
+    /** @var IGroupManager */
+    private $groupManager;
+
+    /** @var IShareManager */
+    private $shareManager;
+
+    /** @var IUserSession */
+    private $userSession;
+
+    /** @var IAppManager */
+    private $appManager;
+
+    /** @var string */
+    private $principalPrefix;
+
+    /** @var bool */
+    private $hasGroups;
+
+    /** @var bool */
+    private $hasCircles;
+
+    /** @var ProxyMapper */
+    private $proxyMapper;
+
+    /** @var IConfig */
+    private $config;
+
+    /**
+     * Principal constructor.
+     *
+     * @param IUserManager $userManager
+     * @param IGroupManager $groupManager
+     * @param IShareManager $shareManager
+     * @param IUserSession $userSession
+     * @param IAppManager $appManager
+     * @param ProxyMapper $proxyMapper
+     * @param IConfig $config
+     * @param string $principalPrefix
+     */
+    public function __construct(IUserManager $userManager,
+                                IGroupManager $groupManager,
+                                IShareManager $shareManager,
+                                IUserSession $userSession,
+                                IAppManager $appManager,
+                                ProxyMapper $proxyMapper,
+                                IConfig $config,
+                                string $principalPrefix = 'principals/users/') {
+        $this->userManager = $userManager;
+        $this->groupManager = $groupManager;
+        $this->shareManager = $shareManager;
+        $this->userSession = $userSession;
+        $this->appManager = $appManager;
+        $this->principalPrefix = trim($principalPrefix, '/');
+        $this->hasGroups = $this->hasCircles = ($principalPrefix === 'principals/users/');
+        $this->proxyMapper = $proxyMapper;
+        $this->config = $config;
+    }
+
+    use PrincipalProxyTrait {
+        getGroupMembership as protected traitGetGroupMembership;
+    }
+
+    /**
+     * Returns a list of principals based on a prefix.
+     *
+     * This prefix will often contain something like 'principals'. You are only
+     * expected to return principals that are in this base path.
+     *
+     * You are expected to return at least a 'uri' for every user, you can
+     * return any additional properties if you wish so. Common properties are:
+     *   {DAV:}displayname
+     *
+     * @param string $prefixPath
+     * @return string[]
+     */
+    public function getPrincipalsByPrefix($prefixPath) {
+        $principals = [];
+
+        if ($prefixPath === $this->principalPrefix) {
+            foreach ($this->userManager->search('') as $user) {
+                $principals[] = $this->userToPrincipal($user);
+            }
+        }
+
+        return $principals;
+    }
+
+    /**
+     * Returns a specific principal, specified by it's path.
+     * The returned structure should be the exact same as from
+     * getPrincipalsByPrefix.
+     *
+     * @param string $path
+     * @return array
+     */
+    public function getPrincipalByPath($path) {
+        list($prefix, $name) = \Sabre\Uri\split($path);
+
+        if ($name === 'calendar-proxy-write' || $name === 'calendar-proxy-read') {
+            list($prefix2, $name2) = \Sabre\Uri\split($prefix);
+
+            if ($prefix2 === $this->principalPrefix) {
+                $user = $this->userManager->get($name2);
+
+                if ($user !== null) {
+                    return [
+                        'uri' => 'principals/users/' . $user->getUID() . '/' . $name,
+                    ];
+                }
+                return null;
+            }
+        }
+
+        if ($prefix === $this->principalPrefix) {
+            // Depending on where it is called, it may happen that this function
+            // is called either with a urlencoded version of the name or with a non-urlencoded one.
+            // The urldecode function replaces %## and +, both of which are forbidden in usernames.
+            // Hence there can be no ambiguity here and it is safe to call urldecode on all usernames
+            $user = $this->userManager->get(urldecode($name));
+
+            if ($user !== null) {
+                return $this->userToPrincipal($user);
+            }
+        } elseif ($prefix === 'principals/circles') {
+            try {
+                return $this->circleToPrincipal($name);
+            } catch (QueryException $e) {
+                return null;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Returns the list of groups a principal is a member of
+     *
+     * @param string $principal
+     * @param bool $needGroups
+     * @return array
+     * @throws Exception
+     */
+    public function getGroupMembership($principal, $needGroups = false) {
+        list($prefix, $name) = \Sabre\Uri\split($principal);
+
+        if ($prefix !== $this->principalPrefix) {
+            return [];
+        }
+
+        $user = $this->userManager->get($name);
+        if (!$user) {
+            throw new Exception('Principal not found');
+        }
+
+        $groups = [];
+
+        if ($this->hasGroups || $needGroups) {
+            $userGroups = $this->groupManager->getUserGroups($user);
+            foreach ($userGroups as $userGroup) {
+                $groups[] = 'principals/groups/' . urlencode($userGroup->getGID());
+            }
+        }
+
+        $groups = array_unique(array_merge(
+            $groups,
+            $this->traitGetGroupMembership($principal, $needGroups)
+        ));
+
+        return $groups;
+    }
+
+    /**
+     * @param string $path
+     * @param PropPatch $propPatch
+     * @return int
+     */
+    public function updatePrincipal($path, PropPatch $propPatch) {
+        return 0;
+    }
+
+    /**
+     * Search user principals
+     *
+     * @param array $searchProperties
+     * @param string $test
+     * @return array
+     */
+    protected function searchUserPrincipals(array $searchProperties, $test = 'allof') {
+        $results = [];
+
+        // If sharing is disabled, return the empty array
+        $shareAPIEnabled = $this->shareManager->shareApiEnabled();
+        if (!$shareAPIEnabled) {
+            return [];
+        }
+
+        $allowEnumeration = $this->shareManager->allowEnumeration();
+        $limitEnumeration = $this->shareManager->limitEnumerationToGroups();
+
+        // If sharing is restricted to group members only,
+        // return only members that have groups in common
+        $restrictGroups = false;
+        if ($this->shareManager->shareWithGroupMembersOnly()) {
+            $user = $this->userSession->getUser();
+            if (!$user) {
+                return [];
+            }
+
+            $restrictGroups = $this->groupManager->getUserGroupIds($user);
+        }
+
+        $currentUserGroups = [];
+        if ($limitEnumeration) {
+            $currentUser = $this->userSession->getUser();
+            if ($currentUser) {
+                $currentUserGroups = $this->groupManager->getUserGroupIds($currentUser);
+            }
+        }
+
+        foreach ($searchProperties as $prop => $value) {
+            switch ($prop) {
+                case '{http://sabredav.org/ns}email-address':
+                    $users = $this->userManager->getByEmail($value);
+
+                    if (!$allowEnumeration) {
+                        $users = \array_filter($users, static function (IUser $user) use ($value) {
+                            return $user->getEMailAddress() === $value;
+                        });
+                    }
+
+                    if ($limitEnumeration) {
+                        $users = \array_filter($users, function (IUser $user) use ($currentUserGroups, $value) {
+                            return !empty(array_intersect(
+                                    $this->groupManager->getUserGroupIds($user),
+                                    $currentUserGroups
+                                )) || $user->getEMailAddress() === $value;
+                        });
+                    }
+
+                    $results[] = array_reduce($users, function (array $carry, IUser $user) use ($restrictGroups) {
+                        // is sharing restricted to groups only?
+                        if ($restrictGroups !== false) {
+                            $userGroups = $this->groupManager->getUserGroupIds($user);
+                            if (count(array_intersect($userGroups, $restrictGroups)) === 0) {
+                                return $carry;
+                            }
+                        }
+
+                        $carry[] = $this->principalPrefix . '/' . $user->getUID();
+                        return $carry;
+                    }, []);
+                    break;
+
+                case '{DAV:}displayname':
+                    $users = $this->userManager->searchDisplayName($value);
+
+                    if (!$allowEnumeration) {
+                        $users = \array_filter($users, static function (IUser $user) use ($value) {
+                            return $user->getDisplayName() === $value;
+                        });
+                    }
+
+                    if ($limitEnumeration) {
+                        $users = \array_filter($users, function (IUser $user) use ($currentUserGroups, $value) {
+                            return !empty(array_intersect(
+                                    $this->groupManager->getUserGroupIds($user),
+                                    $currentUserGroups
+                                )) || $user->getDisplayName() === $value;
+                        });
+                    }
+
+                    $results[] = array_reduce($users, function (array $carry, IUser $user) use ($restrictGroups) {
+                        // is sharing restricted to groups only?
+                        if ($restrictGroups !== false) {
+                            $userGroups = $this->groupManager->getUserGroupIds($user);
+                            if (count(array_intersect($userGroups, $restrictGroups)) === 0) {
+                                return $carry;
+                            }
+                        }
+
+                        $carry[] = $this->principalPrefix . '/' . $user->getUID();
+                        return $carry;
+                    }, []);
+                    break;
+
+                case '{urn:ietf:params:xml:ns:caldav}calendar-user-address-set':
+                    // If you add support for more search properties that qualify as a user-address,
+                    // please also add them to the array below
+                    $results[] = $this->searchUserPrincipals([
+                        // In theory this should also search for principal:principals/users/...
+                        // but that's used internally only anyway and i don't know of any client querying that
+                        '{http://sabredav.org/ns}email-address' => $value,
+                    ], 'anyof');
+                    break;
+
+                default:
+                    $results[] = [];
+                    break;
+            }
+        }
+
+        // results is an array of arrays, so this is not the first search result
+        // but the results of the first searchProperty
+        if (count($results) === 1) {
+            return $results[0];
+        }
+
+        switch ($test) {
+            case 'anyof':
+                return array_values(array_unique(array_merge(...$results)));
+
+            case 'allof':
+            default:
+                return array_values(array_intersect(...$results));
+        }
+    }
+
+    /**
+     * @param string $prefixPath
+     * @param array $searchProperties
+     * @param string $test
+     * @return array
+     */
+    public function searchPrincipals($prefixPath, array $searchProperties, $test = 'allof') {
+        if (count($searchProperties) === 0) {
+            return [];
+        }
+
+        switch ($prefixPath) {
+            case 'principals/users':
+                return $this->searchUserPrincipals($searchProperties, $test);
+
+            default:
+                return [];
+        }
+    }
+
+    /**
+     * @param string $uri
+     * @param string $principalPrefix
+     * @return string
+     */
+    public function findByUri($uri, $principalPrefix) {
+        // If sharing is disabled, return the empty array
+        $shareAPIEnabled = $this->shareManager->shareApiEnabled();
+        if (!$shareAPIEnabled) {
+            return null;
+        }
+
+        // If sharing is restricted to group members only,
+        // return only members that have groups in common
+        $restrictGroups = false;
+        if ($this->shareManager->shareWithGroupMembersOnly()) {
+            $user = $this->userSession->getUser();
+            if (!$user) {
+                return null;
+            }
+
+            $restrictGroups = $this->groupManager->getUserGroupIds($user);
+        }
+
+        if (strpos($uri, 'mailto:') === 0) {
+            if ($principalPrefix === 'principals/users') {
+                $users = $this->userManager->getByEmail(substr($uri, 7));
+                if (count($users) !== 1) {
+                    return null;
+                }
+                $user = $users[0];
+
+                if ($restrictGroups !== false) {
+                    $userGroups = $this->groupManager->getUserGroupIds($user);
+                    if (count(array_intersect($userGroups, $restrictGroups)) === 0) {
+                        return null;
+                    }
+                }
+
+                return $this->principalPrefix . '/' . $user->getUID();
+            }
+        }
+        if (substr($uri, 0, 10) === 'principal:') {
+            $principal = substr($uri, 10);
+            $principal = $this->getPrincipalByPath($principal);
+            if ($principal !== null) {
+                return $principal['uri'];
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * @param IUser $user
+     * @return array
+     */
+    protected function userToPrincipal($user) {
+        $userId = $user->getUID();
+        $displayName = $user->getDisplayName();
+        $principal = [
+            'uri' => $this->principalPrefix . '/' . $userId,
+            '{DAV:}displayname' => is_null($displayName) ? $userId : $displayName,
+            '{urn:ietf:params:xml:ns:caldav}calendar-user-type' => 'INDIVIDUAL',
+        ];
+
+        $email = $user->getEMailAddress();
+        if (!empty($email)) {
+            $principal['{http://sabredav.org/ns}email-address'] = $email;
+        }
+
+        return $principal;
+    }
+
+    public function getPrincipalPrefix() {
+        return $this->principalPrefix;
+    }
+
+    /**
+     * @param string $circleUniqueId
+     * @return array|null
+     * @throws \OCP\AppFramework\QueryException
+     * @suppress PhanUndeclaredClassMethod
+     * @suppress PhanUndeclaredClassCatch
+     */
+    protected function circleToPrincipal($circleUniqueId) {
+        if (!$this->appManager->isEnabledForUser('circles') || !class_exists('\OCA\Circles\Api\v1\Circles')) {
+            return null;
+        }
+
+        try {
+            $circle = \OCA\Circles\Api\v1\Circles::detailsCircle($circleUniqueId, true);
+        } catch (QueryException $ex) {
+            return null;
+        } catch (CircleDoesNotExistException $ex) {
+            return null;
+        }
+
+        if (!$circle) {
+            return null;
+        }
+
+        $principal = [
+            'uri' => 'principals/circles/' . $circleUniqueId,
+            '{DAV:}displayname' => $circle->getName(),
+        ];
+
+        return $principal;
+    }
+
+    /**
+     * Returns the list of circles a principal is a member of
+     *
+     * @param string $principal
+     * @return array
+     * @throws Exception
+     * @throws \OCP\AppFramework\QueryException
+     * @suppress PhanUndeclaredClassMethod
+     */
+    public function getCircleMembership($principal):array {
+        if (!$this->appManager->isEnabledForUser('circles') || !class_exists('\OCA\Circles\Api\v1\Circles')) {
+            return [];
+        }
+
+        list($prefix, $name) = \Sabre\Uri\split($principal);
+        if ($this->hasCircles && $prefix === $this->principalPrefix) {
+            $user = $this->userManager->get($name);
+            if (!$user) {
+                throw new Exception('Principal not found');
+            }
+
+            $circles = \OCA\Circles\Api\v1\Circles::joinedCircles($name, true);
+
+            $circles = array_map(function ($circle) {
+                /** @var \OCA\Circles\Model\Circle $circle */
+                return 'principals/circles/' . urlencode($circle->getUniqueId());
+            }, $circles);
+
+            return $circles;
+        }
+
+        return [];
+    }
 }