Issue with Endpoint Handling in DiscoveryClient.getEndpoints()

[Pustj]

Hi,

I have encountered an issue with the way the library handles endpoint URLs when using DiscoveryClient.getEndpoints(). Specifically, even when I pass an endpoint URL in the following format:

opc.tcp://<srvname>.example.com:<port>/

The library retrieves endpoints with this structure instead:

opc.tcp://<srvname>:<port>/

As a result, if the server relies on fully qualified domain names (FQDNs), such as <srvname>.example.com, the mismatch causes a java.net.UnknownHostException. This happens because the library seems to drop the domain component (e.g., .example.com) from the provided endpoint URL.
This behavior introduces issues in environments where multiple servers or services with similar hostnames (but different domains) are used, and explicit domain resolution is required.
Steps to reproduce:

1. Provide an endpoint URL in the format opc.tcp://<srvname>.example.com:<port>/.
2. Call DiscoveryClient.getEndpoints(endpointUrl).
3. Observe that the returned endpoints are missing the domain, resulting in opc.tcp://<srvname>:<port>/.

Expected behavior: The discovered endpoints should retain the full structure of the provided endpointUrl, including the domain (e.g., .example.com), for accurate host resolution.

Temporary workaround: To mitigate the issue, I am manually replacing the endpoint URL in the returned EndpointDescription object, as follows:

// endpointUrl = opc.tcp://<srv name>.example.com:<port>/
List<EndpointDescription> endpoints =  DiscoveryClient.getEndpoints(endpointUrl).get();
EndpointDescription endpoint = endpoints.get(0);
EndpointDescription endpoint2 = new EndpointDescription(
        endpointUrl,                     // Updated endpoint URL
        endpoint.getServer(),
        endpoint.getServerCertificate(),
        endpoint.getSecurityMode(),
        endpoint.getSecurityPolicyUri(), 
        endpoint.getUserIdentityTokens(),
        endpoint.getTransportProfileUri(),
        endpoint.getSecurityLevel()
);

OpcUaClientConfig config = OpcUaClientConfig.builder()
        .setEndpoint(endpoint2)
        .build();

Consumer<OpcTcpClientTransportConfigBuilder> configureTransport = builder -> {
    ...
};

// Create and configure the OPC UA client
client = OpcUaClient.create(config, configureTransport);

While this workaround allows me to proceed, it is not ideal since it relies on manually constructing a new EndpointDescription object each time. This approach adds unnecessary complexity to the code and feels cumbersome for something that should be handled directly by the library.
I kindly ask for clarification about this behavior or guidance on any better way to ensure that the domain is preserved in the discovered endpoints.

Thank you in advance for your support!
Best regards

[kevinherron]

Take a look at a Wireshark capture and I think you’ll find that it’s the server returning these endpoint URLs in the EndpointDescriptions, not the client modifying them.

Modifying/replacing the EndpointDescription is the standard solution when a server has misconfigured endpoints or endpoint URLs with hostnames that otherwise don’t match the one your client is using. It’s what every OPC UA client out there does when it warns you about the hostname not matching the one you used for discovery (e.g. UaExpert).

You can make it a little less cumbersome by using one of the EndpointUtil.updateUrl methods:

milo/opc-ua-stack/stack-core/src/main/java/org/eclipse/milo/opcua/stack/core/util/EndpointUtil.java

Lines 97 to 114 in 241a35a

	/**
	* Replace the hostname in the endpoint URL field of {@code endpoint} with a new one.
	*
	* <p>All other fields of the original {@link EndpointDescription} remain equal.
	*
	* <p>If the endpoint URL does not match the expected format the original endpoint is returned.
	*
	* @param endpoint the {@link EndpointDescription} to modify.
	* @param hostname the new hostname to use. A null value will result in the original hostname
	* being used.
	* @return an updated {@link EndpointDescription} in which the hostname of the endpoint URL has
	* been replaced with {@code hostname}.
	*/
	public static EndpointDescription updateUrl(
	@NonNull EndpointDescription endpoint, @Nullable String hostname) {
	return updateUrl(endpoint, hostname, -1);
	}