Re: Java PVA client: connect directly to known IOC endpoint without any search (no UDP multicast/unicast, no TCP directed search)

[Abdalla Ahmad via Tech-talk <tech-talk at aps.anl.gov>]

Hi

Is it possible to do the same in channel access? i.e. Avoid UDP and TCP search and going directly to TCP connect?

Best Regards,

Abdalla

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of White, Greg R. via Tech-talk <tech-talk at aps.anl.gov>
Sent: Tuesday, August 4, 2026 7:19 PM
To: Usharani Kandula <ukandula at fnal.gov>
Cc: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: Java PVA client: connect directly to known IOC endpoint without any search (no UDP multicast/unicast, no TCP directed search)

Hi Usharani, the first implementations of pvaccess for Java, pvAccessJava and pvDataJava did exactly what you want- as I understand it to be. I think there is an example in the Normative Types document for the type NTURI. Maybe that functionality has made it into more recent implementations. I hope so. 

Cheers 

Greg

On Aug 4, 2026, at 9:00 AM, Usharani Kandula via Tech-talk <tech-talk at aps.anl.gov> wrote:



Hello Team,

I’m looking for guidance on a Java PVA client use case where I already know the IOC endpoint for a PV (resolved via an internal lookup/database), and I want to connect directly to that IOC and read the PV without performing any PVA search.

Goal / Requirement

Given:

- PV name (example: `ABC:TEMP`)

- Known IOC endpoint (example: `127.0.0.1:5075`)

I want:

- No UDP multicast search

- No UDP unicast search

- No TCP directed search (i.e., avoid the `EPICS_PVA_NAME_SERVERS` search step)

- Instead: direct TCP connect + CreateChannel + read

In other words, since my internal lookup already tells me where the PV lives, I want to avoid asking the IOC again “do you have this PV?”

What I tried

1) Standard configuration to disable multicast/broadcast

I can disable multicast/broadcast discovery via:

```

EPICS_PVA_AUTO_ADDR_LIST=NO

EPICS_PVA_ADDR_LIST=

```

But the remaining supported approach is to use `EPICS_PVA_NAME_SERVERS=host:port`, which performs a directed TCP search. That still sends a search request to the IOC.

2) core-pva (Phoebus) low-level POC that skips search entirely

I built a proof-of-concept using `org.phoebus:core-pva:5.0.5` that successfully reads a PV from a known endpoint without any search.

High-level summary of the POC:

- Creates a `PVAClient`

- Creates a `PVAChannel`

- Unregisters it from search

- Creates a direct TCP handler to the known IOC endpoint

- Manually sets channel state to FOUND

- Registers the channel with the TCP handler (sends CreateChannelRequest)

- Connects and reads

This works (tested against a Python fake IOC), but it relies on package-private/internal APIs such as:

- `ClientTCPHandler`

- `ClientChannelState`

- `PVAChannel.setState()`

- `PVAChannel.registerWithServer()`

- `client.search.unregister()`

To access these, the POC code is placed in the same Java package as the library (`org.epics.pva.client`), which is not ideal for production.

Questions

1. Is there a supported/public Java API (in core-pva or elsewhere) to do a true direct connect to a known IOC endpoint without any search?

2. If not, would the community consider a change to core-pva to add a public API such as:

```java

PVAChannel connectDirect(String pvName, InetSocketAddress iocAddress)

```

that encapsulates the internal wiring currently required?

3. Are there protocol-level concerns with skipping search entirely (e.g., server GUID handling, channel lifecycle expectations) that would make this approach problematic?

Additional details

- Library: `org.phoebus:core-pva:5.0.5`

- Java: 21

- Current POC output shows successful connect/read and prints the returned `PVAStructure`.

Thanks in advance for any guidance.

Best regards,  

Usharani

Fermi National Accelerator Laboratory