p2p/dnsdisc: add implementation of EIP-1459 (#20094)

This adds an implementation of node discovery via DNS TXT records to the
go-ethereum library. The implementation doesn't match EIP-1459 exactly,
the main difference being that this implementation uses separate merkle
trees for tree links and ENRs. The EIP will be updated to match p2p/dnsdisc.

To maintain DNS trees, cmd/devp2p provides a frontend for the p2p/dnsdisc
library. The new 'dns' subcommands can be used to create, sign and deploy DNS
discovery trees.

vendor/github.com/cloudflare/cloudflare-go/ips.go

@@ -0,0 +1,44 @@
+package cloudflare
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/pkg/errors"
+)
+
+// IPRanges contains lists of IPv4 and IPv6 CIDRs.
+type IPRanges struct {
+	IPv4CIDRs []string `json:"ipv4_cidrs"`
+	IPv6CIDRs []string `json:"ipv6_cidrs"`
+}
+
+// IPsResponse is the API response containing a list of IPs.
+type IPsResponse struct {
+	Response
+	Result IPRanges `json:"result"`
+}
+
+// IPs gets a list of Cloudflare's IP ranges.
+//
+// This does not require logging in to the API.
+//
+// API reference: https://api.cloudflare.com/#cloudflare-ips
+func IPs() (IPRanges, error) {
+	resp, err := http.Get(apiURL + "/ips")
+	if err != nil {
+		return IPRanges{}, errors.Wrap(err, "HTTP request failed")
+	}
+	defer resp.Body.Close()
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return IPRanges{}, errors.Wrap(err, "Response body could not be read")
+	}
+	var r IPsResponse
+	err = json.Unmarshal(body, &r)
+	if err != nil {
+		return IPRanges{}, errors.Wrap(err, errUnmarshalError)
+	}
+	return r.Result, nil
+}