Use the Splunk Python SDK command interface about jmespath

[lowell80]

Solved one of the 2 big hurdles.

The dynamic fields issue can be solved by using the following statement whenever the fields change from one event to the next:

self._record_writer.flush(finished=False)

Here's a silly example:

    def stream(self, records):
        i = 0
        last_v =0
        for record in records:
            i += 1
            v = i//3
            record["field_{}".format(v)] = "HI"
            yield record
            if v != last_v:
                self._record_writer.flush(finished=False)
                last_v = v

A record output example looks like this:

# gzcat MyCommand-1542855500.795022.getinfo.output.gz
chunked 1.0,50,0
{"required_fields":["f1","f2"],"type":"streaming"}
chunked 1.0,18,127
{"finished":false}f1,__mv_f1,f2,__mv_f2,_chunked_idx,__mv__chunked_idx,field_0,__mv_field_0
hi,,othe,,0,,HI,
hi,,othe,,1,,HI,
hi,,othe,,2,,,
chunked 1.0,18,127
{"finished":false}f1,__mv_f1,f2,__mv_f2,_chunked_idx,__mv__chunked_idx,field_1,__mv_field_1
hi,,othe,,3,,HI,
hi,,othe,,4,,HI,
hi,,othe,,5,,,
chunked 1.0,18,127
{"finished":false}f1,__mv_f1,f2,__mv_f2,_chunked_idx,__mv__chunked_idx,field_2,__mv_field_2
hi,,othe,,6,,HI,
hi,,othe,,7,,HI,
hi,,othe,,8,,,
chunked 1.0,17,93
{"finished":true}f1,__mv_f1,f2,__mv_f2,_chunked_idx,__mv__chunked_idx,field_3,__mv_field_3
hi,,othe,,9,,HI,

Splunk search looked like this: | makeresults count=10 | eval f1="hi", f2="othe", f3=if(random() % 3=0, "blah",null()) | mycmd record=t

Also, I think I've proven out that the fieldnames input can be any string can be anything as long as it's quoted, which is generally expected anyways.

[lowell80]

Hold up -- NEW PROBLEM

The use of the _chunked_idx column apparently doesn't work well if the output chunk is split into more pieces than the input. The output from the search command works okay, but any existing fields NOT passed into the streaming command are lost.

Emergency=done.
I just confirmed that dropping @Configuration(required_fields=["f1","f2"]) does keep this from happening, but this now requires that ALL fields are passed through the search command.

[lowell80]

Revised workaround version.

Returning too many new chunks causes issues. The exact number to chunks where this causes a problem is unknown. However, this logic attempts to minimize the number of chunks by making sure that all fields are accumulative (to handle the issue of sportatic fields). Need better visibility into how the chunking mechanism works under the covers before being able to solve this correctly. Is the issue the total number of chunks, or too many small chunks back-to-back, is there a timing thing involved (if chunks are produced more slowly does that make a difference.)

This probably needs to be taken to the next level and introduce some sort of buffer mechanism that processes hundreds or thousands of results, and then checks to reduce the total number of chunks returned.

The really simple approach would be to simply buffer the 50,000 results in memory all at once, which is what InterSplunk does, and to some degree what the SplunkSDK seems to do as well. (If all results are returned in one chunk (by default), then they are all being buffered in memory anyways. See use of the StringIO buffer.

    def prepare(self):
        #if self.fieldnames:
        #    self.configuration.required_fields = self.fieldnames
        pass

    def stream(self, records):
        known = None
        for record in self._stream(records):
            fields = set(record.keys())
            if known is None:
                known = fields
            elif fields.difference(known):
                # new fields found
                #self.logger.info("New fields found:  %s" % fields.difference(known))
                known.update(fields)
                #self.logger.info("Must missing fields  %s" % known.difference(fields))
                for f in known.difference(fields):
                    record[f] = ""
                self._record_writer.flush(finished=False)
            yield record

    def _stream(self, records):
        # Todo:  Add a check to see if any of the required variable names are missing from the Splunk fields.
        i = 0
        for record in records:
            i += 1
            try:
                record["field_{}".format(i % 10)] = "HI"
                yield record
            except:
                pass