Enable nosprintfhostport linter

... and fix lints on the way.

Inline the IsIPV6String function, as it had only one use left, which was
inlined as a one-liner.

Signed-off-by: Tom Wieczorek <[email protected]>

.golangci.yml

@@ -10,16 +10,17 @@ run:
 
 linters:
   enable:
-    - copyloopvar # Detects unnecessary copies of loop variables for Go >= 1.22
-    - depguard    # Checks if package imports are in a list of acceptable packages
-    - dupword     # Finds word repetitions
-    - errorlint   # Find code that will cause problems with Go's error wrapping scheme
-    - gofmt       # Checks whether code was gofmt-ed
-    - goheader    # Checks is file headers matche a given pattern
-    - intrange    # Checking for loops that could use an integer range
-    - revive      # Stricter drop-in replacement for golint
-    - testifylint # Checks usage of github.com/stretchr/testify
-    - unconvert   # Checks for unnecessary type conversions
+    - copyloopvar       # Detects unnecessary copies of loop variables for Go >= 1.22
+    - depguard          # Checks if package imports are in a list of acceptable packages
+    - dupword           # Finds word repetitions
+    - errorlint         # Find code that will cause problems with Go's error wrapping scheme
+    - gofmt             # Checks whether code was gofmt-ed
+    - goheader          # Checks is file headers matche a given pattern
+    - intrange          # Checking for loops that could use an integer range
+    - nosprintfhostport # Detects misuses of Sprintf to construct hosts with ports in a URL
+    - revive            # Stricter drop-in replacement for golint
+    - testifylint       # Checks usage of github.com/stretchr/testify
+    - unconvert         # Checks for unnecessary type conversions
 
 linters-settings:
   depguard:

inttest/customports/customports_test.go

@@ -18,9 +18,11 @@ package customports
 
 import (
 	"bytes"
-	"fmt"
 	"html/template"
+	"net"
+	"net/url"
 	"os"
+	"strconv"
 	"testing"
 
 	"github.com/k0sproject/k0s/inttest/common"
@@ -138,12 +140,13 @@ func (s *customPortsSuite) TestControllerJoinsWithCustomPort() {
 
 	// https://github.com/k0sproject/k0s/issues/1202
 	s.Run("kubeconfigIncludesExternalAddress", func() {
+		expectedURL := url.URL{Scheme: "https", Host: net.JoinHostPort(ipAddress, strconv.Itoa(kubeAPIPort))}
 		ssh, err := s.SSH(s.Context(), s.ControllerNode(0))
 		s.Require().NoError(err)
 		defer ssh.Disconnect()
 
 		out, err := ssh.ExecWithOutput(s.Context(), "/usr/local/bin/k0s kubeconfig create user | awk '$1 == \"server:\" {print $2}'")
 		s.Require().NoError(err)
-		s.Require().Equal(fmt.Sprintf("https://%s:%d", ipAddress, kubeAPIPort), out)
+		s.Require().Equal(expectedURL.String(), out)
 	})
 }

pkg/apis/k0s/v1beta1/api.go

@@ -18,8 +18,9 @@ package v1beta1
 
 import (
 	"encoding/json"
-	"fmt"
 	"net"
+	"net/url"
+	"strconv"
 
 	"github.com/k0sproject/k0s/internal/pkg/iface"
 	"github.com/k0sproject/k0s/internal/pkg/stringslice"
@@ -84,12 +85,6 @@ func (a *APISpec) APIAddressURL() string {
 	return a.getExternalURIForPort(a.Port)
 }
 
-// IsIPv6String returns if ip is IPv6.
-func IsIPv6String(ip string) bool {
-	netIP := net.ParseIP(ip)
-	return netIP != nil && netIP.To4() == nil
-}
-
 // K0sControlPlaneAPIAddress returns the controller join APIs address
 func (a *APISpec) K0sControlPlaneAPIAddress() string {
 	return a.getExternalURIForPort(a.K0sAPIPort)
@@ -100,10 +95,7 @@ func (a *APISpec) getExternalURIForPort(port int) string {
 	if a.ExternalAddress != "" {
 		addr = a.ExternalAddress
 	}
-	if IsIPv6String(addr) {
-		return fmt.Sprintf("https://[%s]:%d", addr, port)
-	}
-	return fmt.Sprintf("https://%s:%d", addr, port)
+	return (&url.URL{Scheme: "https", Host: net.JoinHostPort(addr, strconv.Itoa(port))}).String()
 }
 
 // Sans return the given SANS plus all local addresses and externalAddress if given

pkg/apis/k0s/v1beta1/network.go

@@ -136,7 +136,7 @@ func (n *Network) DNSAddress() (string, error) {
 	}
 
 	address := ipnet.IP.To4()
-	if IsIPv6String(ipnet.IP.String()) {
+	if address == nil {
 		address = ipnet.IP.To16()
 	}
 
@@ -209,11 +209,10 @@ func (n *Network) BuildServiceCIDR(addr string) string {
 	if !n.DualStack.Enabled {
 		return n.ServiceCIDR
 	}
-	// because in the dual-stack mode k8s
-	// relies on the ordering of the given CIDRs
-	// we need to first give family on which
-	// api server listens
-	if IsIPv6String(addr) {
+	// Because Kubernetes relies on the order of the given CIDRs in dual-stack
+	// mode, the CIDR whose version matches the version of the IP address the
+	// API server is listening on must be specified first.
+	if ip := net.ParseIP(addr); ip != nil && ip.To4() == nil {
 		return n.DualStack.IPv6ServiceCIDR + "," + n.ServiceCIDR
 	}
 	return n.ServiceCIDR + "," + n.DualStack.IPv6ServiceCIDR