Unknown key for a START_OBJECT in [layers]

When trying to send my json formatted tcpdump to elasticsearch, I get the following error:

curl -X PUT --data-binary @myjson 'localhost:9200/_bulk?pretty'
{
  "error" : {
    "root_cause" : [
      {
        "type" : "parsing_exception",
        "reason" : "Unknown key for a START_OBJECT in [layers].",
        "line" : 1,
        "col" : 95
      }
    ],
    "type" : "parsing_exception",
    "reason" : "Unknown key for a START_OBJECT in [layers].",
    "line" : 1,
    "col" : 95
  },
  "status" : 400
}

The json file was obtained using tshark with the "-T json" option. The json file was modified using jq with the filter "{index: .[]}" and the option -c since elasticsearch requires an entry to fit in a single line. I am using elasticsearch 5.5.1 with the standard configuration. jsonformatter marks the json object as valid.

A json object that produces the error looks as follows:

{"index":{"_index":"packets-2017-08-04","_type":"pcap_file","_score":null,"_source":{"layers":{"frame":{"frame.encap_type":"25","frame.time":"Aug  5, 2001 13:10:06.559762000 CEST","frame.offset_shift":"0.000000000","frame.time_epoch":"1501773006.559765000","frame.time_delta":"0.000000000","frame.time_delta_displayed":"0.000000000","frame.time_relative":"0.000000000","frame.number":"1","frame.len":"200","frame.cap_len":"200","frame.marked":"0","frame.ignored":"0","frame.protocols":"sll:ethertype:ip:tcp:data"},"sll":{"sll.pkttype":"4","sll.hatype":"65135","sll.halen":"0","sll.etype":"0x00000800"},"ip":{"ip.version":"4","ip.hdr_len":"20","ip.dsfield":"0x00000010","ip.dsfield_tree":{"ip.dsfield.dscp":"4","ip.dsfield.ecn":"0"},"ip.len":"184","ip.id":"0x000093f2","ip.flags":"0x00000002","ip.flags_tree":{"ip.flags.rb":"0","ip.flags.df":"1","ip.flags.mf":"0"},"ip.frag_offset":"0","ip.ttl":"64","ip.proto":"6","ip.checksum":"0x0000ef4b","ip.checksum.status":"2","ip.src":"0.0.00","ip.addr":"0.0.0.0","ip.src_host":"0.0.0.0","ip.host":"0.0.0.0","ip.dst":"0.0.0.0","ip.dst_host":"0.0.0.0","Source GeoIP: Germany":{"ip.geoip.src_country":"Germany","ip.geoip.country":"Germany","ip.geoip.src_city":"Frankfurt, 1","ip.geoip.city":"Berlin, 1","ip.geoip.src_asnum":"123","ip.geoip.asnum":"123","ip.geoip.src_lat":"701","ip.geoip.lat":"523,01","ip.geoip.src_lon":"2313,4","ip.geoip.lon":"12,13"},"Destination GeoIP: Germany":{"ip.geoip.dst_country":"Germany","ip.geoip.country":"Germany","ip.geoip.dst_asnum":"123","ip.geoip.asnum":"123","ip.geoip.dst_lat":"3321","ip.geoip.lat":"41","ip.geoip.dst_lon":"1","ip.geoip.lon":"2"}},"tcp":{"tcp.srcport":"41","tcp.dstport":"124","tcp.port":"234","tcp.stream":"3","tcp.len":"134","tcp.seq":"1","tcp.nxtseq":"133","tcp.ack":"4","tcp.hdr_len":"32","tcp.flags":"0x00000018","tcp.flags_tree":{"tcp.flags.res":"0","tcp.flags.ns":"0","tcp.flags.cwr":"0","tcp.flags.ecn":"0","tcp.flags.urg":"0","tcp.flags.ack":"1","tcp.flags.push":"1","tcp.flags.reset":"0","tcp.flags.syn":"0","tcp.flags.fin":"0","tcp.flags.str":"·······AP···"},"tcp.window_size_value":"223","tcp.window_size":"31","tcp.window_size_scalefactor":"-1","tcp.checksum":"0x0000b79c","tcp.checksum.status":"1","tcp.urgent_pointer":"0","tcp.options":"123","tcp.options_tree":{"No-Operation (NOP)":{"tcp.options.type":"1","tcp.options.type_tree":{"tcp.options.type.copy":"0","tcp.options.type.class":"0","tcp.options.type.number":"1"}},"Timestamps: TSval 1875055084, TSecr 5726840":{"tcp.option_kind":"8","tcp.option_len":"10","tcp.options.timestamp.tsval":"185084","tcp.options.timestamp.tsecr":"1116840"}},"tcp.analysis":{"tcp.analysis.bytes_in_flight":"123","tcp.analysis.push_bytes_sent":"133"}},"data":{"data.data":"01:01:02","data.len":"265"}}}}}

My question is: What is wrong with this json, so that elasticsearch rejects it?

This is not really a jq problem - Unknown key for a START_OBJECT is an elasticsearch error. The [layers] is a hint that the problem is in the object there which unfortunately was elided in the problem description so there's really not much to go on here.

Since the jq filter you specified is just {index:.[]}, jq is doing nothing to the part of the json elasticsearch is complaining about. If your workflow is expecting jq to correct that portion somehow you'll need to investigate the data closer and use a more sophisticated filter.

For reference, the elasticsearch test suite contains an example of this particular error:

---
"junk in source fails":
  - do:
      catch: /Unknown key for a START_OBJECT in \[junk\]./
      reindex:
        body:
          source:
            junk: {}

Hope this helps.