chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/pmtud/icmp/check.go

@@ -2,24 +2,17 @@ package icmp
 
 import (
 	"bytes"
-	"errors"
 	"fmt"
 
 	"golang.org/x/net/icmp"
 )
 
-var (
-	ErrNextHopMTUTooLow  = errors.New("ICMP Next Hop MTU is too low")
-	ErrNextHopMTUTooHigh = errors.New("ICMP Next Hop MTU is too high")
-)
-
 func checkMTU(mtu, minMTU, physicalLinkMTU uint32) (err error) {
 	switch {
 	case mtu < minMTU:
-		return fmt.Errorf("%w: %d", ErrNextHopMTUTooLow, mtu)
+		return fmt.Errorf("ICMP Next Hop MTU is too low: %d", mtu)
 	case mtu > physicalLinkMTU:
-		return fmt.Errorf("%w: %d is larger than physical link MTU %d",
-			ErrNextHopMTUTooHigh, mtu, physicalLinkMTU)
+		return fmt.Errorf("ICMP Next Hop MTU is too high: %d is larger than physical link MTU %d", mtu, physicalLinkMTU)
 	default:
 		return nil
 	}
@@ -34,14 +27,12 @@ func checkInvokingReplyIDMatch(icmpProtocol int, received []byte,
 	}
 	inboundBody, ok := inboundMessage.Body.(*icmp.Echo)
 	if !ok {
-		return false, fmt.Errorf("%w: %T", ErrBodyUnsupported, inboundMessage.Body)
+		return false, fmt.Errorf("ICMP body type is not supported: %T", inboundMessage.Body)
 	}
 	outboundBody := outboundMessage.Body.(*icmp.Echo) //nolint:forcetypeassert
 	return inboundBody.ID == outboundBody.ID, nil
 }
 
-var ErrIDMismatch = errors.New("ICMP id mismatch")
-
 func checkEchoReply(icmpProtocol int, received []byte,
 	outboundMessage *icmp.Message, truncatedBody bool,
 ) (err error) {
@@ -51,12 +42,12 @@ func checkEchoReply(icmpProtocol int, received []byte,
 	}
 	inboundBody, ok := inboundMessage.Body.(*icmp.Echo)
 	if !ok {
-		return fmt.Errorf("%w: %T", ErrBodyUnsupported, inboundMessage.Body)
+		return fmt.Errorf("ICMP body type is not supported: %T", inboundMessage.Body)
 	}
 	outboundBody := outboundMessage.Body.(*icmp.Echo) //nolint:forcetypeassert
 	if inboundBody.ID != outboundBody.ID {
-		return fmt.Errorf("%w: sent id %d and received id %d",
-			ErrIDMismatch, outboundBody.ID, inboundBody.ID)
+		return fmt.Errorf("ICMP id mismatch: sent id %d and received id %d",
+			outboundBody.ID, inboundBody.ID)
 	}
 	err = checkEchoBodies(outboundBody.Data, inboundBody.Data, truncatedBody)
 	if err != nil {
@@ -65,19 +56,17 @@ func checkEchoReply(icmpProtocol int, received []byte,
 	return nil
 }
 
-var ErrEchoDataMismatch = errors.New("ICMP data mismatch")
-
 func checkEchoBodies(sent, received []byte, receivedTruncated bool) (err error) {
 	if len(received) > len(sent) {
-		return fmt.Errorf("%w: sent %d bytes and received %d bytes",
-			ErrEchoDataMismatch, len(sent), len(received))
+		return fmt.Errorf("ICMP data mismatch: sent %d bytes and received %d bytes",
+			len(sent), len(received))
 	}
 	if receivedTruncated {
 		sent = sent[:len(received)]
 	}
 	if !bytes.Equal(received, sent) {
-		return fmt.Errorf("%w: sent %x and received %x",
-			ErrEchoDataMismatch, sent, received)
+		return fmt.Errorf("ICMP data mismatch: sent %x and received %x",
+			sent, received)
 	}
 	return nil
 }

internal/pmtud/icmp/errors.go

@@ -10,9 +10,7 @@ import (
 
 var (
 	ErrNotPermitted                            = errors.New("ICMP not permitted")
-	ErrDestinationUnreachable                  = errors.New("ICMP destination unreachable")
-	ErrCommunicationAdministrativelyProhibited = errors.New("communication administratively prohibited")
-	ErrBodyUnsupported                         = errors.New("ICMP body type is not supported")
+	errCommunicationAdministrativelyProhibited = errors.New("communication administratively prohibited")
 	ErrMTUNotFound                             = errors.New("MTU not found")
 	errTimeout                                 = errors.New("operation timed out")
 )

internal/pmtud/icmp/icmp.go

@@ -25,7 +25,7 @@ func PathMTUDiscover(ctx context.Context, ip netip.Addr,
 		switch {
 		case err == nil:
 			return mtu, nil
-		case errors.Is(err, errTimeout) || errors.Is(err, ErrCommunicationAdministrativelyProhibited): // blackhole
+		case errors.Is(err, errTimeout) || errors.Is(err, errCommunicationAdministrativelyProhibited): // blackhole
 		default:
 			return 0, fmt.Errorf("finding IPv4 next hop MTU to %s: %w", ip, err)
 		}

internal/pmtud/icmp/ipv4.go

@@ -117,13 +117,10 @@ func findIPv4NextHopMTU(ctx context.Context, ip netip.Addr,
 			case portUnreachable: // triggered by TCP or UDP from applications
 				continue // ignore and wait for the next message
 			case communicationAdministrativelyProhibitedCode:
-				return 0, fmt.Errorf("%w: %w (code %d)",
-					ErrDestinationUnreachable,
-					ErrCommunicationAdministrativelyProhibited,
+				return 0, fmt.Errorf("ICMP destination unreachable: %w (code %d)", errCommunicationAdministrativelyProhibited,
 					inboundMessage.Code)
 			default:
-				return 0, fmt.Errorf("%w: code %d",
-					ErrDestinationUnreachable, inboundMessage.Code)
+				return 0, fmt.Errorf("ICMP destination unreachable: code %d", inboundMessage.Code)
 			}
 
 			// See https://datatracker.ietf.org/doc/html/rfc1191#section-4
@@ -158,7 +155,7 @@ func findIPv4NextHopMTU(ctx context.Context, ip netip.Addr,
 				inboundID, outboundID)
 			continue
 		default:
-			return 0, fmt.Errorf("%w: %T", ErrBodyUnsupported, typedBody)
+			return 0, fmt.Errorf("ICMP body type is not supported: %T", typedBody)
 		}
 	}
 }

internal/pmtud/icmp/ipv6.go

@@ -2,6 +2,7 @@ package icmp
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"net"
 	"net/netip"
@@ -115,7 +116,7 @@ func getIPv6PacketTooBig(ctx context.Context, ip netip.Addr,
 			if err != nil {
 				return 0, fmt.Errorf("checking invoking message id: %w", err)
 			} else if idMatch {
-				return 0, fmt.Errorf("%w", ErrDestinationUnreachable)
+				return 0, errors.New("ICMP destination unreachable")
 			}
 			logger.Debug("discarding received ICMP destination unreachable reply with an unknown id")
 			continue
@@ -128,7 +129,7 @@ func getIPv6PacketTooBig(ctx context.Context, ip netip.Addr,
 				inboundID, outboundID)
 			continue
 		default:
-			return 0, fmt.Errorf("%w: %T", ErrBodyUnsupported, typedBody)
+			return 0, fmt.Errorf("ICMP body type %T is not supported", typedBody)
 		}
 	}
 }

internal/pmtud/icmp/multi.go

@@ -71,7 +71,7 @@ func pmtudMultiSizes(ctx context.Context, ip netip.Addr,
 		_, err = conn.WriteTo(encodedMessage, &net.IPAddr{IP: ip.AsSlice()})
 		if err != nil {
 			if strings.HasSuffix(err.Error(), "sendto: operation not permitted") {
-				err = fmt.Errorf("%w", ErrNotPermitted)
+				err = ErrNotPermitted
 			}
 			return 0, fmt.Errorf("writing ICMP message: %w", err)
 		}
@@ -157,7 +157,7 @@ func collectReplies(conn net.PacketConn, ipVersion string,
 			logger.Debugf("ignoring ICMP message (type: %d, code: %d)", message.Type, message.Code)
 			continue
 		default:
-			return fmt.Errorf("%w: %T", ErrBodyUnsupported, message.Body)
+			return fmt.Errorf("ICMP body type is not supported: %T", message.Body)
 		}
 
 		echoBody, _ := message.Body.(*icmp.Echo)
@@ -183,8 +183,8 @@ func collectReplies(conn net.PacketConn, ipVersion string,
 			ipPacketLength == conservativeReplyLength
 		// Check the packet size is the same if the reply is not truncated
 		if !truncated && sentBytes != ipPacketLength {
-			return fmt.Errorf("%w: sent %dB and received %dB",
-				ErrEchoDataMismatch, sentBytes, ipPacketLength)
+			return fmt.Errorf("ICMP data mismatch: sent %dB and received %dB",
+				sentBytes, ipPacketLength)
 		}
 		// Truncated reply or matching reply size
 		tests[testIndex].ok = true