Index: src/XMPPConnection.h
==================================================================
--- src/XMPPConnection.h
+++ src/XMPPConnection.h
@@ -22,10 +22,11 @@
  */
 
 #import <ObjFW/ObjFW.h>
 
 #import "XMPPCallback.h"
+#import "XMPPStorage.h"
 
 @class XMPPConnection;
 @class XMPPJID;
 @class XMPPIQ;
 @class XMPPMessage;
@@ -154,19 +155,21 @@
 	XMPPAuthenticator *authModule;
 	BOOL streamOpen;
 	BOOL needsSession;
 	BOOL encryptionRequired, encrypted;
 	unsigned int lastID;
+	id <XMPPStorage> dataStorage;
 /// \endcond
 }
 
 #ifdef OF_HAVE_PROPERTIES
 /// \brief The username to use for authentication
 @property (copy) OFString *username;
 /// \brief The password to use for authentication
 @property (copy) OFString *password;
-/** \brief The server to use for the connection
+/**
+ * \brief The server to use for the connection
  *
  * This is useful if the address of the server is different from the domain.
  */
 @property (copy) OFString *server;
 /// \brief The domain to connect to
@@ -187,10 +190,12 @@
 @property (readonly, retain, getter=socket) OFTCPSocket *sock;
 /// \brief Whether encryption is required
 @property BOOL encryptionRequired;
 /// \brief Whether the connection is encrypted
 @property (readonly) BOOL encrypted;
+/// \brief An object for data storage, conforming to the XMPPStorage protocol
+@property (assign) id <XMPPStorage> dataStorage;
 #endif
 
 /**
  * \brief Creates a new autoreleased XMPPConnection.
  *
@@ -324,10 +329,12 @@
 - (void)setResource: (OFString*)resource;
 - (OFString*)resource;
 - (XMPPJID*)JID;
 - (void)setPort: (uint16_t)port;
 - (uint16_t)port;
+- (void)setDataStorage: (id <XMPPStorage>)dataStorage;
+- (id <XMPPStorage>)dataStorage;
 - (void)setLanguage: (OFString*)language;
 - (OFString*)language;
 
 /// \cond internal
 - (void)XMPP_startStream;

Index: src/XMPPConnection.m
==================================================================
--- src/XMPPConnection.m
+++ src/XMPPConnection.m
@@ -34,10 +34,12 @@
 
 #import <ObjOpenSSL/SSLSocket.h>
 #import <ObjOpenSSL/SSLInvalidCertificateException.h>
 #import <ObjOpenSSL/X509Certificate.h>
 
+#import <ObjFW/OFInvalidArgumentException.h>
+
 #import "XMPPConnection.h"
 #import "XMPPCallback.h"
 #import "XMPPSRVLookup.h"
 #import "XMPPEXTERNALAuth.h"
 #import "XMPPSCRAMAuth.h"
@@ -1053,10 +1055,23 @@
 
 - (uint16_t)port
 {
 	return port;
 }
+
+- (void)setDataStorage: (id <XMPPStorage>)dataStorage_
+{
+	if (streamOpen)
+		@throw [OFInvalidArgumentException exceptionWithClass: isa];
+
+	dataStorage = dataStorage_;
+}
+
+- (id <XMPPStorage>)dataStorage
+{
+	return dataStorage;
+}
 
 - (void)setLanguage: (OFString*)language_
 {
 	OF_SETTER(language, language_, YES, YES)
 }

Index: src/XMPPRoster.h
==================================================================
--- src/XMPPRoster.h
+++ src/XMPPRoster.h
@@ -22,10 +22,11 @@
  */
 
 #import <ObjFW/ObjFW.h>
 
 #import "XMPPConnection.h"
+#import "XMPPStorage.h"
 
 @class XMPPRosterItem;
 @class XMPPIQ;
 @class XMPPRoster;
 @class XMPPMulticastDelegate;
@@ -69,12 +70,22 @@
 {
 /// \cond internal
 	XMPPConnection *connection;
 	OFMutableDictionary *rosterItems;
 	XMPPMulticastDelegate *delegates;
+	id <XMPPStorage> dataStorage;
 /// \endcond
 }
+
+#ifdef OF_HAVE_PROPERTIES
+/**
+ * \brief An object for data storage, conforming to the XMPPStorage protocol.
+ *
+ * Inherited from the connection if not overridden.
+ */
+@property (assign) id <XMPPStorage> dataStorage;
+#endif
 
 /**
  * \brief Initializes an already allocated XMPPRoster.
  *
  * \param connection The connection roster related stanzas
@@ -128,10 +139,13 @@
  * \brief Removes the specified delegate.
  *
  * \param delegate The delegate to remove
  */
 - (void)removeDelegate: (id <XMPPRosterDelegate>)delegate;
+
+- (void)setDataStorage: (id <XMPPStorage>)dataStorage;
+- (id <XMPPStorage>)dataStorage;
 
 /// \cond internal
 - (void)XMPP_addRosterItem: (XMPPRosterItem*)rosterItem;
 - (void)XMPP_updateRosterItem: (XMPPRosterItem*)rosterItem;
 - (void)XMPP_deleteRosterItem: (XMPPRosterItem*)rosterItem;

Index: src/XMPPRoster.m
==================================================================
--- src/XMPPRoster.m
+++ src/XMPPRoster.m
@@ -45,10 +45,11 @@
 	@try {
 		rosterItems = [[OFMutableDictionary alloc] init];
 		connection = connection_;
 		[connection addDelegate: self];
 		delegates = [[XMPPMulticastDelegate alloc] init];
+		dataStorage = [connection dataStorage];
 	} @catch (id e) {
 		[self release];
 		@throw e;
 	}
 
@@ -182,10 +183,21 @@
 
 - (void)removeDelegate: (id <XMPPRosterDelegate>)delegate
 {
 	[delegates removeDelegate: delegate];
 }
+
+- (void)setDataStorage: (id <XMPPStorage>)dataStorage_
+{
+	/* TODO: Prevent changing it after it has been used */
+	dataStorage = dataStorage_;
+}
+
+- (id <XMPPStorage>)dataStorage
+{
+	return dataStorage;
+}
 
 - (void)XMPP_addRosterItem: (XMPPRosterItem*)rosterItem
 {
 	return [self XMPP_updateRosterItem: rosterItem];
 }