Using regular expressions in payloads

In some operations (both in NGSIv1 and NGSIv2) regular expressions can be used, as shown below.

NGSIv1 example:

POST /v1/queryContext

{
  "entities": [
    {
      "type": "Sensor",
      "isPattern": "true",
      "id": ".*"
    }
  ]
}

NGSIv2 example:

POST /v2/op/query

{
  "entities": [
    {
      "idPattern": ".*",
      "type": "Sensor"
    }
  ]
}

The regular expression language allows the usage of backslash (\). For example, SENSOR\d{2} matches strings containing SENSOR followed by two digits. However, note that \ is a special character in JSON, which, according to the JSON specification, needs to be encoded as \\.

POST /v1/queryContext

{
  "entities": [
    {
      "type": "Sensor",
      "isPattern": "true",
      "id": "SENSOR\\d{2}"
    }
  ]
}

NGSIv2 example:

POST /v2/op/query

{
  "entities": [
    {
      "idPattern": "SENSOR\\d{2}",
      "type": "Sensor"
    }
  ]
}

The issue could be even funnier if you use the shell to send the request. For example, if you use multi-line curl you need to escape \ at shell level. Eg:

curl localhost:1026/v2/op/query -s -S --header 'Content-Type: application/json' --header 'Accept: application/json' -d @- | python -mjson.tool) <<EOF
{
  "entities": [
    {
      "idPattern": "SENSOR\\\\d{2}",
      "type": "Sensor"
    }
  ]
}
EOF

In other words, the SENSOR\\\\d{2} string at shell level is transformed to SENSOR\\d{2} at payload level (i.e. the actual HTTP request that is sent over the wire) which, in sequence, corresponds to the SENSOR\d{2} regular expression after JSON parsing stage at Orion. However, note that if you use a file for your payload, the shell escaping isn't needed, i.e.:

curl localhost:1026/v2/op/query -s -S --header 'Content-Type: application/json' --header 'Accept: application/json' -d @payload.json

would use the following payload.json file:

{
  "entities": [
    {
      "idPattern": "SENSOR\\d{2}",
      "type": "Sensor"
    }
  ]
}

More details on this can be found in the following issue comment at github.