getChanInfo() / getGroupInfo() return nullptr in CENTRAL_COMPAT CLIENT mode

[SamJBoyer]

Description:

When Central is running, SdkSession::create() correctly detects Central's shared memory and connects in CLIENT mode with ShmemLayout::CENTRAL_COMPAT. However, several SdkSession public getters fail silently in this mode because they call ShmemSession::getNativeConfigBuffer(), which explicitly returns nullptr when the layout is CENTRAL_COMPAT (not NATIVE).

Affected methods:

SdkSession::getChanInfo() (sdk_session.cpp:1066) -- returns nullptr for all channels
SdkSession::getGroupInfo() (sdk_session.cpp:1077) -- returns nullptr for all groups
SdkSession::Impl::getChanInfoPtr() (sdk_session.cpp:1179) -- returns nullptr, breaking all bulk getters (getChannelLabels, getChannelField, getMatchingChannelIds, getChannelPositions)
SdkSession::getProtocolVersion() (sdk_session.cpp:1111) -- hardcoded return 0 for CLIENT mode
SdkSession::getProcIdent() (sdk_session.cpp:1117) -- returns empty string for CLIENT mode
Root cause:

ShmemSession::getNativeConfigBuffer() (shmem_session.cpp:1064) guards with m_impl->layout != ShmemLayout::NATIVE and returns nullptr for CENTRAL_COMPAT. But the data IS available -- ShmemSession::getChanInfo(uint32_t) (shmem_session.cpp:917) correctly handles both layouts by falling back to legacyCfg()->chaninfo[channel].

Suggested fix:

In each affected SdkSession method, after the getNativeConfigBuffer() check fails, fall back to getLegacyConfigBuffer(). For example in getChanInfo():

const auto* legacy = m_impl->shmem_session->getLegacyConfigBuffer();
if (legacy)
return &legacy->chaninfo[chan_id - 1];
For getGroupInfo(), the legacy layout uses a 2D array groupinfo[proc][group], so the instrument index from getCentralInstrumentIndex(config.device_type) is needed.

Note that setChannelSampleGroup() in CLIENT mode (sdk_session.cpp:1284) correctly uses shmem_session->getChanInfo() and works fine -- only the read-side getters are broken.

[cboulay]

Thanks for the report!

I won't have access to a Windows machine (and therefore Central) for a few days. If you want to do a preliminary fix and PR then I'll take a look at it and might be able to merge it if it looks good.