panic: json: How to unmarshall nested json array in Golang

I'm having trouble unmarshalling a nested json array. Sample below:

{
"Subnets": [
{
"AvailabilityZone": "xx",
"AvailabilityZoneId": "xx",
"AvailableIpAddressCount": 173,
"CidrBlock": "xx",
"DefaultForAz": "xx",
"MapPublicIpOnLaunch": "xx",
"MapCustomerOwnedIpOnLaunch": "xx",
"State": "xx",
"SubnetId": "xx",
"VpcId": "xx",
"OwnerId": "xx",
"AssignIpv6AddressOnCreation": "xx",
"Ipv6CidrBlockAssociationSet": [],
"Tags": [
{
"Key": "Name",
"Value": "xx"
},
{
"Key": "workload",
"Value": "xx"
},
{
"Key": "xx",
"Value": "xx"
},
{
"Key": "aws:cloudformation:stack-name",
"Value": "xx"
},
{
"Key": "host_support_group",
"Value": "xx"
},
{
"Key": "environment",
"Value": "xx"
},
{
"Key": "client",
"Value": "xx"
},
{
"Key": "aws:cloudformation:stack-id",
"Value": "xx"
},
{
"Key": "application",
"Value": "Subnet"
},
{
"Key": "xx",
"Value": "xx"
},
{
"Key": "xx",
"Value": "xx"
},
{
"Key": "xx",
"Value": "xx"
},
{
"Key": "regions",
"Value": "ca-central-1"
}
],
"SubnetArn": "xx"
}]
,
"ResponseMetadata": {
"RequestId": "xx",
"HTTPStatusCode": 200,
"HTTPHeaders": {
"x-amzn-requestid": "xx",
"cache-control": "no-cache, no-store",
"strict-transport-security": "max-age=31536000; includeSubDomains",
"content-type": "text/xml;charset=UTF-8",
"content-length": "3176",
"vary": "accept-encoding",
"date": "xx",
"server": "AmazonEC2"
},
"RetryAttempts": 0
}
}

The only value I want is "AvailableIpAddressCount", I tried using interface{} but I'm not able to get the necessary value. Here's the Golang playground link - playground

Error-
I'm getting this error using interface{}

Is there any other way to extract just the "AvailableIpAddressCount" value from the json object?

Any help or references are appreciated.

You can create a struct with the desired field and unmarshal the JSON bytes using that struct which will populate fields mentioned in your struct.

type Something struct {
AvailableIpAddressCount int `json:"AvailableIpAddressCount"`
}
var data Something
if err := json.unmarshal(byt, &data); err != nil {
panic(err)
}
AvailableIpAddressCount = data.AvailableIpAddressCount

Go uses static structs to decode json, so you probably need to create a struct that contains at least what you are looking for. If you have your struct, you can access AvailableIPAddressCount like this:

tmp.Subnets[0].AvailableIPAddressCount

Here is the playground https://play.golang.org/p/FsjeOubov1Q.

To create json structs from example json you can use tools like this.

And if you need to loop through all subnets:

for _, subnet := range tmp.Subnets {
fmt.Println(subnet.AvailableIPAddressCount)
}

If you want to use json dynamically you can also use https://github.com/spf13/viper. But it's probably slower than statically decoding.