Do not use jq when working with large number

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Do not use jq when working with large number

2021-09-07

We use etcd to store application configuration. On production, config is loaded from json file by using Python.

I’m wondering if we can use jq to do that. So, I tried something like this:

1host=${ETCD_HOST:-127.0.0.1}
2port=${ETCD_PORT:-2379}
3for key in $(jq -r 'keys[]' "$1"); do
4  value=$(jq -r ".$key" -c "$1")
5  ETCDCTL_API=3 etcdctl --endpoints="$host:$port" put "$key" "$value"
6done

Config is loaded into etcd but some values are not the same as in the JSON file. What is going on?

Looking more closely I found out that jq is rounding large number:

1$ echo 947295729583939162 | jq '.'
2947295729583939200

The reason is jq converts the JSON numbers to IEEE 754 64-bit values and the largest number is 2^53 (9,007,199,254,740,992), same as JavaScript:

1$ node -e "console.log(Number.MAX_SAFE_INTEGER);"
29007199254740991

Please take a look at FAQ for more details.

Tags: jq json javascript bigint

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