OLMKit: Add wrappers for export/import of inbound group sessions

xcode/OLMKit/OLMInboundGroupSession.h

@@ -22,9 +22,17 @@
 
 - (instancetype)initInboundGroupSessionWithSessionKey:(NSString*)sessionKey error:(NSError**)error;
 
+- (instancetype)initInboundGroupSessionWithImportedSession:(NSString*)sessionKey error:(NSError**)error;
+
 - (NSString*)sessionIdentifier;
 
 /** base64 ciphertext -> UTF-8 plaintext */
 - (NSString*)decryptMessage:(NSString*)message messageIndex:(NSUInteger*)messageIndex error:(NSError**)error;
 
+- (NSUInteger)firstKnownIndex;
+
+- (BOOL)isVerified;
+
+- (NSString*)exportSessionAtMessageIndex:(NSUInteger*)messageIndex error:(NSError**)error;
+
 @end

xcode/OLMKit/OLMInboundGroupSession.m

@@ -76,6 +76,33 @@
     return self;
 }
 
+- (instancetype)initInboundGroupSessionWithImportedSession:(NSString *)sessionKey error:(NSError *__autoreleasing *)error
+{
+    self = [self init];
+    if (self) {
+        NSData *sessionKeyData = [sessionKey dataUsingEncoding:NSUTF8StringEncoding];
+        size_t result = olm_import_inbound_group_session(session, sessionKeyData.bytes, sessionKeyData.length);
+        if (result == olm_error())   {
+            const char *olm_error = olm_inbound_group_session_last_error(session);
+
+            NSString *errorString = [NSString stringWithUTF8String:olm_error];
+            NSLog(@"olm_import_inbound_group_session error: %@", errorString);
+
+            if (error && olm_error && errorString) {
+                *error = [NSError errorWithDomain:OLMErrorDomain
+                                             code:0
+                                         userInfo:@{
+                                                    NSLocalizedDescriptionKey: errorString,
+                                                    NSLocalizedFailureReasonErrorKey: [NSString stringWithFormat:@"olm_import_inbound_group_session error: %@", errorString]
+                                                    }];
+            }
+
+            return nil;
+        }
+    }
+    return self;
+}
+
 - (NSString *)sessionIdentifier {
     size_t length = olm_inbound_group_session_id_length(session);
     NSMutableData *idData = [NSMutableData dataWithLength:length];
@@ -153,6 +180,33 @@
     return plaintext;
 }
 
+- (NSUInteger)firstKnownIndex
+{
+    return olm_inbound_group_session_first_known_index(session);
+}
+
+- (BOOL)isVerified
+{
+    return (0 != olm_inbound_group_session_is_verified(session));
+}
+
+- (NSString*)exportSessionAtMessageIndex:(NSUInteger*)messageIndex error:(NSError**)error;
+{
+    size_t length = olm_export_inbound_group_session_length(session);
+    NSMutableData *key = [NSMutableData dataWithLength:length];
+    size_t result = olm_export_inbound_group_session(session, key.mutableBytes, key.length, messageIndex);
+    if (result == olm_error()) {
+        const char *olm_error = olm_inbound_group_session_last_error(session);
+        NSString *errorString = [NSString stringWithUTF8String:olm_error];
+        if (error && errorString) {
+            *error = [NSError errorWithDomain:OLMErrorDomain code:0 userInfo:@{NSLocalizedDescriptionKey: errorString}];
+        }
+        return nil;
+    }
+    NSString *keyString = [[NSString alloc] initWithData:key encoding:NSUTF8StringEncoding];
+    return keyString;
+}
+
 
 #pragma mark OLMSerializable
 

xcode/OLMKitTests/OLMKitGroupTests.m

@@ -91,4 +91,56 @@
     XCTAssertEqualObjects(bobSession2.sessionIdentifier, aliceSession.sessionIdentifier);
 }
 
+- (void)testInboundGroupSessionImportExport {
+
+    NSError *error;
+
+    NSString *sessionKey = @"AgAAAAAwMTIzNDU2Nzg5QUJERUYwMTIzNDU2Nzg5QUJDREVGMDEyMzQ1Njc4OUFCREVGM" \
+                            "DEyMzQ1Njc4OUFCQ0RFRjAxMjM0NTY3ODlBQkRFRjAxMjM0NTY3ODlBQkNERUYwMTIzND" \
+                            "U2Nzg5QUJERUYwMTIzNDU2Nzg5QUJDREVGMDEyMw0bdg1BDq4Px/slBow06q8n/B9WBfw" \
+                            "WYyNOB8DlUmXGGwrFmaSb9bR/eY8xgERrxmP07hFmD9uqA2p8PMHdnV5ysmgufE6oLZ5+" \
+                            "8/mWQOW3VVTnDIlnwd8oHUYRuk8TCQ";
+
+    NSString *message = @"AwgAEhAcbh6UpbByoyZxufQ+h2B+8XHMjhR69G8F4+qjMaFlnIXusJZX3r8LnRORG9T3D" \
+                        "XFdbVuvIWrLyRfm4i8QRbe8VPwGRFG57B1CtmxanuP8bHtnnYqlwPsD";
+
+    // init first inbound group session, and decrypt */
+    OLMInboundGroupSession *session1 = [[OLMInboundGroupSession alloc] initInboundGroupSessionWithSessionKey:sessionKey error:&error];
+
+    XCTAssertNil(error);
+    XCTAssertTrue(session1.isVerified);
+
+    // decrypt the message
+    NSUInteger messageIndex;
+    NSString *plaintext = [session1 decryptMessage:message messageIndex:&messageIndex error:&error];
+
+    XCTAssertNil(error);
+    XCTAssertEqualObjects(plaintext, @"Message");
+    XCTAssertEqual(messageIndex, 0);
+
+    // export the keys
+    NSString *export = [session1 exportSessionAtMessageIndex:0 error:&error];
+
+    XCTAssertNil(error);
+    XCTAssertGreaterThan(export.length, 0);
+
+    // free the old session to check there is no shared data
+    session1 = nil;
+
+    // import the keys into another inbound group session
+    OLMInboundGroupSession *session2 = [[OLMInboundGroupSession alloc] initInboundGroupSessionWithImportedSession:export error:&error];
+
+    XCTAssertNil(error);
+    XCTAssert(session2);
+    XCTAssertFalse(session2.isVerified);
+
+    // decrypt the message with the new session
+    NSString *plaintext2 = [session2 decryptMessage:message messageIndex:&messageIndex error:&error];
+
+    XCTAssertNil(error);
+    XCTAssertEqualObjects(plaintext2, @"Message");
+    XCTAssertEqual(messageIndex, 0);
+    XCTAssertTrue(session2.isVerified);
+}
+
 @end