LDM 6.11.7 Released

Version 6.11.7 of the LDM has been released. It fixes a bug that caused the NOAAPORT ingest component to crash.

Here's the story:

The NOAAPORT Satellite Broadcast System contains a lot of GRIB-2 messages. Such messages require external tables in order to be interpreted. The NOAAPORT ingest component of the LDM uses the tables that come with GEMPAK to interpret GRIB-2 messages in order to generate meaningful LDM product-identifiers. Unfortunately, not all tables are complete and creators of GRIB-2 messages are free to add data for which no corresponding table-entry exists.

The LDM adds a diagnostic log message to the GEMPAK function that interprets level or layer data to report when a table entry is missing. In such a case, it logs the table lookup information and the last entry in the table (for reference purposes). Unfortunately, the code made the assumption that a table would always have some entries in it.

This turns out not to be the case.

On February 25th, 2014, a GRIB-2 message was broadcast that resulted in a completely empty table being given to the level/layer interpretation function. The subsequent attempt to log the diagnostic message resulted in the NOAAPORT ingestion process receiving a segmentation violation signal (i.e., SIGSEGV). The rest of the LDM system then did what it's supposed to when a child-process terminates abnormally: it shut down.

The fix was easy once the cause was determined. A diagnostic message will still be logged, but no SIGSEGV will occur.

Those of you who use the LDM to ingest NOAAPORT should upgrade to this new version before another such GRIB-2 message is broadcast. As always, the relevant URL is https://www.unidata.ucar.edu/software/ldm/.

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