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Californium (Cf) - Migration Hints

October, 2021

The version 2.x is now out for about more than a year and reached version 2.7.0. We have already started to work on a 3.0 on December 2020 starting with removing deprecates APIs.

To migrate to the 3.0 this gives some hints to do so. If you miss something, don't hesitate to create an issue.

Please, keep in mind, that the 3.0 API is under develop.

General

This document doesn't contain hints for migrating versions before 2.0. That excludes also hints to migrate any of the 2.0 MILESTONE releases.

If a 2.0.0 or newer is used, it's recommended to update first to 2.7.0 and cleanup all deprecation using the documentation on the deprecation.

The version 3.0.0-M4 is the last one with the old NetworkConfig and DtlsConnectorConfig.Builder. Depending on the usage of these classes, it may be easier to first migrate to that 3.0.0-M4 and then in a final step migrate to the 3.0 adapting for these changes in the configuration.

The file-format has also changed and old property files are not longer read!.

Old format:

ACK_TIMEOUT=2000
UDP_CONNECTOR_SEND_BUFFER=0
...
NETWORK_STAGE_RECEIVER_THREAD_COUNT=1

The order of the entries is random and the values don't provide some explanation.

# Initial CoAP acknowledge timeout.
# Default: 2[s]
COAP.ACK_TIMEOUT=2[s]
...
# Number of DTLS receiver threads.
# Default: 1
DTLS.RECEIVER_THREAD_COUNT=2
...
# DTLS send-buffer size.
DTLS.SEND_BUFFER_SIZE=
...
# Number of UDP receiver threads.
# Default: 1
UDP.RECEIVER_THREAD_COUNT=2
...
# UDP send-buffer size.
UDP.SEND_BUFFER_SIZE=

Grouped and alphabetic order of entries with some explanation.

It's recommended, that different values are checked and revalidated, if that difference still provides a benefit. If it still has a benefit for you, you may consider to add also a note into the resulting properties file. You may also consider to use an application specific defaults approach, see Configuration using a DefinitionsProvider.

First Experience

Migrating Eclipse/Hono and Eclipse/Leshan the major changes, which requires adaption, are the changes in the DTLS configuration and the related callbacks. Reading the section below should help all to overcome issues caused by these changes.

Noteworthy Behavior Changes

Experimental Bouncy Castle Support

In order to use newer crypto function with java 7 and java 8 (e.g. on Android) first experimental steps in supporting Bouncy Castle (1.69, jdk15on) has been made. That may change the behavior, if Bouncy Castle is already used, because some adaption are applied in order to make it more functional.

That uncovered a couple of differences just in order to make the unit test running. It is assumed, that more will be required. If you find some, don't hesitate to report issues, perhaps research and analysis, and fixes. On the other hand, the project Californium will for now not be able to provide support for Bouncy Castle questions with or without relation to Californium. You may create issues, but they may be not processed.

Please see Scandium - Support for Bouncy Castle for more details.

Element-Connector:

Bytes.equals(Object other):

Since 3.0 the sub-class may be ignored, depending on the provided value of the useClassInEquals parameter in Bytes(byte[], int, boolean, boolean). The default behavior is changed to ignore the sub-class.

StringUtil.getUriHostname(InetAddress address):

The IPv6-scope-separator "%" is replaced by the URL-encoded form "%25" (also fixed in 2.6.4).

DtlsEndpointContext.KEY_RESUMPTION_TIMEOUT is renamed into DtlsEndpointContext.KEY_AUTO_HANDSHAKE_TIMEOUT. The key's value is adjusted as well. The feature not only supports abbreviated handshakes, it also starts full handshakes, if the session is not able to be resumed.

Scandium:

Redesigned! May cause also unaware changes! If you detect one, please create an issue on Eclipse/Californium.

The Alert during the handshakes are adapted (more) towards the definitions in RFC 5246, Section 7.2, Alert Protocol.

During the CLIENT_HELLO / SERVER_HELLO cipher suite and parameter negotiation a HANDSHAKE_FAILURE is sent, if no common cipher suite or parameter are available. If in later messages unsupported parameters are used, a ILLEGAL_PARAMETER is sent. For unexpected certificate types a UNSUPPORTED_CERTIFICATE is sent. If certificate verification fails, a DECRYPT_ERROR is sent.

RFC 7627, Extended Master Secret TLS extension is introduced and enabled by default. If this extension is not used, the session is not resumable (until the configuration is adapted to none or optional).

The encoding of the SessionTicket has changed.

The SessionCache and resumption handshake behavior is changed. SessionCache is renamed to SessionStore and intended to return on calls "immediately". If the SessionStore is not used, the InMemoryConnectionStore limits the number of connection per session to one. That results in cleanup additionally connection earlier than with an SessionStore. That behavior without SessionStore is very close to that of the 2.6., except, that failing handshakes using the same ip-address/port as the current connection will not remove this current connection. Using the SessionStore changes the behavior of 2.6 more. Some connections may be cleaned up later by eviction of the least recently used connection. And the SessionStore is assumed to be weakly consistent, without it's strictly consistent.

Please Note: the new SessionStore feature is not well tested! If used and causing trouble, don't hesitate to create an issue.

The DTLSSession is split into DTLSContext (connection/association specific data) and DTLSSession (session only data).

The ApplicationLevelInfoSupplier.getInfo() supports now to return null in order to not alter the additional information.

The ResumingServerHandshaker supports now a none-blocking ResumptionVerifier and a fallback to a full handshake.

The CertificateProvider introduces the possibility to use multiple certificates.

The SignatureAndHashAlgorithm supports now isRecommended to address the upcoming draft-ietf-tls-md5-sha1-deprecate.

The lifetime of cookies, used during initial stateless phase of a handshake, is reduced from 5 minutes to 1 minute. With the already available support for the past cookie, a HELLO_VERIFY_REQUEST is valid from 1 minute up to 2 minutes. The CLIENT_HELLO deduplication filter is extended from 1 minute to 2m15s. The intention is a slightly improvement of protection against spoofed CLIENT_HELLOs.

The implementation of draft-ietf-tls-dtls-connection has been updated to use the new IANA assigned code point 54 for the extension and the new MAC definition introduced with version 09 of that draft. The old code point 53 and the old MAC definition maybe still used, if configured using DtlsConfig.DTLS_USE_DEPRECATED_CID and DtlsConfig.DTLS_SUPPORT_DEPRECATED_CID.

Note: mbedtls up to version 2.27 still uses a undefined code-point (254) and the deprecated MAC definition before version 09. To use mbedtls, please adjust the extension code point MBEDTLS_TLS_EXT_CID to 53 and configure Californium accordingly to DtlsConfig.DTLS_USE_DEPRECATED_CID or DtlsConfig.DTLS_SUPPORT_DEPRECATED_CID.

ECDHE - XECDHECryptography: to use X25519/X448 with bouncy-castle as JCE provider, the XDHPublicKeyApi has been introduced. A java 11 implementation may also be used by applications in order to omit the usage of the reflection based implementation. The encoding/decoding of the related public key is now based on the x509/ASN.1 encoding of it. That is more generic and doesn't depend on the details of the internal structure of the public keys.

The maximum message size calculations from Record Size Limit and Maximum Fragment Length is more precise and the resulting maximum message size is reported as KEY_MESSAGE_SIZE_LIMIT in the endpoint context.

Using X509 to authenticate the server now includes to match the destination with the server certificate's subject. This is enabled per default, as requested by RFC7252 - 9.1.3.3. X.509 Certificates. It could be disabled using DTLS.VERIFY_SERVER_CERTIFICATES_SUBJECT.

Introducing support for multiple x509 certificates (see KeyManagerCertificateProvider) and RSA, also in combination with CLIENT_ONLY and support the asymmetric certificate based handshakes (means: a peer may send credentials with algorithms, the peer itself doesn't support), makes the "auto-configuration" feature very hard. Please report, if you consider that the auto-configuration has issues. That may help to either improve it, or at least to improve the documentation.

The Connection provided in the callback of ConnectionListener.onConnectionRemoved(Connection connection) is now always "cleaned up" before. That results in a null peer address, ongoing handshake, and dtls context. Please consider to use a SessionListener instead. With Californium 3.2.0 this is included in the DtlsConnectorConfig (see issue #1868, PR #1869).

Element-Connector-TCP-Netty:

Using X509 to authenticate the server now includes to match the destination with the server certificate's subject. This is enabled per default, as requested by RFC7925 - 4.4.1. Certificates Used by Servers. It could be disabled using TCP.VERIFY_SERVER_CERTIFICATES_SUBJECT.

Californium-Core:

MessageObserver.onAcknowledgement():

Since 3.0 this is only called for separate ACKs, not longer for piggy-backed responses.

The local address of the receiving endpoint is now a separate field, the usage of the destination context for incoming messages is replaced by that. Affects CoapUriTranslator.getExposedInterface(Request). This Message.localAddress also supports UDPCOnnector with MulticastReceivers.

Blockwise Implementation RFC 7959:

Since 3.0 the blockwise implementation has been redesigned. That includes the blockwise request/response matching, which is not longer based on the block's num in the Block Option RFC 7959 - 2.2. Structure of a Block Option. It's now based on the calculated block's offset num * size IETF core-mailing list. Using the "transparent blockwise mode" (MAX_RESOURCE_BODY_SIZE larger than 0) in mix with application block options seems to be not completely defined. There are currently two use-cases, block2 early negotiation, and "random block access". But it seems to be hard, to document and test, what is exactly the API for such a mixed usage. Please consider to disable the "transparent blockwise mode" (MAX_RESOURCE_BODY_SIZE with 0), if application block options are required. Maybe these mixed (corner) cases gets discussed in a future version of Californium. (See also below, EndpointIdentityResolver is now used for blockwise as well.)

Message.getPayload():

Since 3.0 null is replaced by Bytes.EMPTY. The method will now always return an byte array, which may be empty.

Request.setOnResponseError(Throwable error) is not longer accompanied by Request.setCanceled(boolean canceled).

Option(int number):

Since 3.0, the value is not initialized and must be provided with a separate setter call or using a other Option constructor. Though the 3.0 will now validate the option value, using Bytes.EMPTY as default would fail in too many cases.

The OptionSet and the Options are now strictly validated. If that cause trouble, please check, if the value is valid according RFC 7252, 5.10. Option Definitions or the other specific RFCs.

RFC 7967, Option for No Server Response is introduced.

Changing network configuration values during runtime is not supported by Californium's components. Therefore the NetworkConfigObserver is now removed.

In order to support peers with dynamically assigned ip-addresses, Californium introduced the EndpointIdentityResolver for tokens and MIDs with 2.0. The returned identity depends then on the implementation. Using the provided ones, the PrincipalEndpointContextMatcher enables to use the Principal instead of the InetSocketAddress. That is configured using the CoapConfig.RESPONSE_MATCHING. The feature is mainly useful for the side, which initially accepts traffic (usually a server) and may cause errors on the side, which initiates the traffic. A work-around for that is added only to a ping-exchange, which enables clients to use the Principal, if a ping is the first exchange. The plugtest clients has been adapted to demonstrate that. With 3.0 this will now be extended for blockwise transfers. If used on the server-side, that enables a client-side to PUT/POST payload, even if a quiet phase causes an address change.

Ensure, that onResponse(Response response) and onResponse(CoapResponse response) are only called with nonNull. Some code smells seems to assume, it could be null, even if I can't see, that this would have been actually happen. Only user code may have cause this and will now cause a NullPointerException.

Responses for multicast requests are randomly postponed up to CoapConfig.LEISURE, as specified in RFC7252, 8.2, .

Californium-Proxy2:

The apache http-components have been updated to http-client 5.0.3 and http-core 5.0.2. That requires to update all custom cross-proxy implementations as well. Please consider the migration information on the apache http-components web-page

The updated proxy2 now processes more coap-options and http-headers.

Noteworthy API Changes

Element-Connector:

  1. The ExtendedConnector interface is integrated in Connector.

  2. The EndpointContext supports now String, Long, Integer, Bytes, Boolean, and InetSocketAddress.

  3. The MulticastReceivers interface (californium-core) is integrated in UDPConnector.

  4. The UdpMulticastConnector must be build using UdpMulticastConnector.Builder.setMulticastReceiver(true) in order to be added and used as mutlicast receiver to a UDPConnector.

  5. The SslContextUtil.configure(String, String) is removed, use SslContextUtil.configure(String, KeyStoreType) instead. KeyStoreType requires now either a type for the java KeyStore implementation, or a SimpleKeyStore custom reader.

  6. The NetworkConfig is replaced by Configuration with the SystemConfig, UdpConfig, TcpConfig, DtlsConfig, CoapConfig, and Proxy2Config.

  7. Some function from Asn1DerDecoder have been moved to JceProviderUtil, though they are related to the JCE and not to ASN.1.

Scandium:

  1. PskStore, StaticPskStore, StringPskStore and InMemoryPskStore

are removed and must be replaced by

AdvancedPskStore, AdvancedSinglePskStore and AdvancedMultiPskStore.

  1. TrustedRpkStore, TrustAllRpks, InMemoryRpkTrustStore, CertificateVerifier, and AdvancedCertificateVerifier

are removed and must be replaced by

NewAdvancedCertificateVerifier, and StaticNewAdvancedCertificateVerifier.

  1. The DTLSession in NewAdvancedCertificateVerifier.verifyCertificate is removed. Therefore the InetSocketAddress of the remote peer has been added. The parameter Boolean clientUsage is replaced by boolean clientUsage. With that, the key-usage extension is always checked, if provided.

  2. MtuUtil is removed and must be replaced by NetworkInterfacesUtil.

  3. The ConnectionExecutionListener interface is integrated in ConnectionListener.

  4. The DTLSSession is split into DTLSSession and DTLSContext.

  5. The SessionListener interface is adapted, sessionEstablished is now contextEstablished.

  6. useKeyUsageVerification is removed from configuration. The key-usage extension is always checked, if provided.

  7. useHandshakeStateValidation is removed from configuration. The handshake-state machine is now always.

  8. The ClientSessionCache is removed and replaced by the DTLSSession serialization. The extended ConnectionListener and the DTLSConnector.restoreConnection(Connection connection) are for saving and restoring Connections.

  9. The SessionCache is renamed into SessionStore. It's now part of the DtlsConnectorConfig and not longer a parameter of the constructor for the DTLSConnector. SessionStore.get(SessionId) returns now a DTLSSession instead of the now obsolete and removed SessionTicket.

  10. The ResumptionSupportingConnectionStore.remove(Connection) is removed, use ResumptionSupportingConnectionStore.remove(Connection, boolean) and provided explicit, if the session is to be removed from the session store as well.

  11. The ResumptionSupportingConnectionStore.find(SessionId) returns now a new DTLSSession instead of a connection.

  12. Change useNoServerSessionId into useServerSessionId with inverse logic.

  13. To support RFC 7627, Extended Master Secret, a parameter useExtendedMasterSecret is added to AdvancedPskStore.requestPskSecretResult.

  14. Change DtlsConnectorConfig.getPrivateKey, getPublicKey, and getCertificateChain are replaced by the introduced CertificateProvider. DtlsConnectorConfig.getCertificateIdentityProvider is added to access the CertificateProvider. The SingleCertificateProvider is provided, if only a single certificate based identity is required. The related setters in the DtlsConnectorConfig.Builder are replaced also by setCertificateIdentityProvider.

  15. Many parameters are moved from DtlsConnectorConfig.Builder to DtlsConfig and Configuration.

Californium-Core:

  1. The MessageObserver2 interface is integrated in MessageObserver.

  2. The InternalMessageObserver interface is integrated in MessageObserver.

  3. The InternalMessageObserverAdapter is integrated in MessageObserverAdapter.

  4. The InternalMessageObserverAdapter interface is integrated in MessageObserverAdapter.

  5. CoapEndpointHealth and CoapEndpointHealthLogger

are removed and must be replaced by

HealthStatisticLogger

  1. The MessagePostProcessInterceptors interface is integrated in Endpoint.

  2. The MulticastReceivers interface is moved into UDPConnector.

  3. Renamed Message.onComplete() to onTransferComplete(), including MessageObserver.onComplete().

  4. Changed Exchange.getRetransmissionHandle() to isTransmissionPending().

  5. Add DelivererException to ServerMessageDeliverer.findResource(Exchange exchange) and ServerMessageDeliverer.findResource(List<String> list)

  6. Change the return type of MediaTypeRegistry.parseWildcard(String wildcard) from Integer[] to int[].

  7. Removed Resource.getSecondaryExecutor() and change the return type of Resource.getExecutor() from ExecutorService to the simpler Executor. Specific Resource implementation may maintain the executors as required by them.

  8. Removed CoapResource.createClient(???). Though Resource.getExecutor() may return null, it depends on the implementation of the Resource not to return null, but that changes other executions. Therefore implement createClient(???) for the specific Resources and provide the executors there.

  9. Removed CoapEndpoint.Builder.setConnectorWithAutoConfiguration(UDPConnector). Configuration must now be provided to the Connector's constructors.

  10. The NetworkConfig is replaced by SystemConfig, UdpConfig, TcpConfig, CoapConfig and Configuration.

  11. The Request.setResponse(Response response) will now throw a NullPointerException, if called with null.

  12. The class methods ResponseCode.is???(ResponseCode code) are converted into instance methods ResponseCode.is???().

Californium-Proxy2:

  1. Update to http-client 5.0.3 and http-core 5.0.2. The apache http-components are not encapsulated. Therefore this update causes several API changes, where these classes are used. Please consider the migration information on the apache http-components web-page

  2. Add package org.eclipse.californium.proxy2.http and moved all http-translation relevant classes into that. Rename HttpTranslator into CrossProtocolTranslator

  3. Add package org.eclipse.californium.proxy2.http.server and moved the http-server specific classes into that.

  4. Add Proxy2Config.