CDN detection for IP using PTR DNS records as fallback.

[brenocss]

CDN detection for IP using PTR DNS records as fallback.

I believe this feature can work, but I think it's worth a more in-depth analysis.

$ host -t ptr 104.87.29.118

118.29.87.104.in-addr.arpa domain name pointer a104-87-29-118.deploy.static.akamaitechnologies.com.
ns7.reverse.deploy.akamaitechnologies.com has address 184.26.161.32
ns5.reverse.deploy.akamaitechnologies.com has address 95.100.173.32
ns1.reverse.deploy.akamaitechnologies.com has address 96.7.50.32
ns3.reverse.deploy.akamaitechnologies.com has address 23.74.25.32
ns8.reverse.deploy.akamaitechnologies.com has address 2.22.230.32
ns6.reverse.deploy.akamaitechnologies.com has address 23.61.199.32
ns2.reverse.deploy.akamaitechnologies.com has address 2.16.40.32
ns4.reverse.deploy.akamaitechnologies.com has address 95.100.168.32

to add this feature we can add

cdncheck/cdncheck.go

Line 118 in 0006a77

func (c *Client) CheckDNSResponse(dnsResponse *retryabledns.DNSData) (matched bool, value string, itemType string, err error) {

	if dnsResponse.PTR != nil {
		matched, discovered, itemType, err := c.CheckSuffix(dnsResponse.PTR...)