How to write a REGEXP_EXTRACT expression in Google Cloud Logging config json?

I am trying to extract the value at the end of this log:

Chat request completed in 3.818780105999849

This is a log saved in Google Cloud Logging and the message is written in the textPayload field. I am trying to create a log-based metric using the gcloud logging metrics create command (docs found here). Since I am trying to create a distribution metric, I am required to create a config file for the metric.

This is what I have for the config json:

{
    "name": "end-to-end-response-time-shell",
    "description": "Time duration of a chat request (in seconds).",
    "filter": "resource.type=\"cloud_run_revision\" AND logName=\"log_name\" AND severity=\"INFO\" AND textPayload=~\"Chat request completed in\"",
    "metricDescriptor": {
        "name": "cloud_run_revision",
        "type": "logging.googleapis.com/user/end-to-end-response-time-shell",
        "metricKind": "CUMULATIVE",
        "valueType": "DISTRIBUTION",
        "unit": "s",
        "description": "Time duration of a chat request (in seconds).",
        "displayName": "end-to-end-response-time-shell (sec)"
    },
    "valueExtractor": "REGEXP_EXTRACT(textPayload, \"\\s(\\d+\\.*\\d*)\\s\")"
}

The command is erroring at the valueExtractor field with this error message:

ERROR: (gcloud.logging.metrics.create) INVALID_ARGUMENT: Failed to parse extractor expression: syntax error at line 1, column 29, token '"\s(\d+\.*\d*)\s"'

How should I write the regex expression for this task?

I think you'll need to double-escape (yeah!) the RegEx.

In the documentation for REGEXP_EXTRACT, the RegEx value is escaped in the string.

You'll want to re-escape it for your escaped string in JSON ..... e.g. \\\\s and \\\\d etc.