handle UTF-strings as pvnames - fixed UDP-datagram buffer sizes

[TBirkeHZB]

This fixes a bug in handling UTF-8/16 PVnames.

Querying for a PV with german umlauts (due to a typo), all IOCs issued error-messages like

unterminated PV name in UDP search request?

and older ca-gateways even hung consuming 100%CPU and stop doing any I/O.

Test with pv-name "Führungsgröße":

• name.length() says 13, but
• name.getBytes().length gives 16

13 bytes would have fit in the default UDP-datagram buffer for name-resolution requests (size = 16 bytes), but the 16 real bytes left no space for the terminating NULL-byte, which caused all kinds of errors.

With the proposed fix, JCA neither crashes any gateways nor produces any error messages on IOCs/Gateways. An existing PV named "Führungsgröße" now connects properly and returns values.

[ralphlange]

The alternative would be rejecting invalid PV names... What does the C library of Channel Access do in such cases?

[TBirkeHZB]

At least it doesn't miscalculate buffer sizes and hence crashes software ;-)

The C-version perfectly handles umlauts, since it doesn't know about UTF-whatever. It's just an array of bytes. Both creating PVs named "Käsebrötchen" and querying them works just fine.

Are UTF-8 characters forbidden? (can't find the proper source-code that quickly)

[ralphlange]

Tolerated by source code, not in the set of allowed characters by definition/documentation.

[ralphlange]

But your answer is fine. I would always argue in favor of making the two implementation act the same.

[TBirkeHZB]

Where is the definition of allowed characters in CA-PVnames? I just found the forbidden characters for EPICS-database-record-names.

[ralphlange]

Right, there is none. I rest my case.

[kasemir]

Looks like the issue only arises for longer names. This one where the string length of the PV name is 5, the byte length 7, runs without problems.

record(bi, "Größe")
{
  field(ZNAM, "mäßig")
  field(ONAM, "elefantös")
}

Works fine with 'caget' for both the basic PV name as well as enum labels:

$ caget -d CTRL_ENUM Größe
Größe
    Native data type: DBF_ENUM
    Request type:     DBR_CTRL_ENUM
    Element count:    1
    Value:            mäßig
..
    Enums:            ( 2)
                      [ 0] mäßig
                      [ 1] elefantös

.. as well as jca:

[TBirkeHZB]

It seems only to be a problem when

name.length() < N * 8

and

name.getBytes().length >= N * 8

(assumption: UDP-datagram buffers are allocated in sizes that are multiples of 8 bytes) In this case, the NULL-byte is getting lost.

I could have lived with error-messages, but the gateways (still V2.1.0.0 here - to be updated soon) getting unresponsive is a real showstopper...

[kasemir]

Fixing the same issue in the PVA client