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/provider/airvpn/updater/api.go

@@ -6,8 +6,6 @@ import (
 	"fmt"
 	"net/http"
 	"net/netip"
-
-	"github.com/qdm12/gluetun/internal/provider/common"
 )
 
 type apiData struct {
@@ -48,8 +46,8 @@ func fetchAPI(ctx context.Context, client *http.Client) (
 
 	if response.StatusCode != http.StatusOK {
 		_ = response.Body.Close()
-		return data, fmt.Errorf("%w: %d %s",
-			common.ErrHTTPStatusCodeNotOK, response.StatusCode, response.Status)
+		return data, fmt.Errorf("HTTP status code not OK: %d %s",
+			response.StatusCode, response.Status)
 	}
 
 	decoder := json.NewDecoder(response.Body)

internal/provider/common/portforward.go

@@ -1,5 +0,0 @@
-package common
-
-import "errors"
-
-var ErrPortForwardNotSupported = errors.New("port forwarding not supported")

internal/provider/common/updater.go

@@ -10,10 +10,8 @@ import (
 )
 
 var (
-	ErrNotEnoughServers     = errors.New("not enough servers found")
-	ErrHTTPStatusCodeNotOK  = errors.New("HTTP status code not OK")
-	ErrIPFetcherUnsupported = errors.New("IP fetcher not supported")
-	ErrCredentialsMissing   = errors.New("credentials missing")
+	ErrNotEnoughServers   = errors.New("not enough servers found")
+	ErrCredentialsMissing = errors.New("credentials are missing")
 )
 
 type Fetcher interface {

internal/provider/custom/connection.go

@@ -1,7 +1,6 @@
 package custom
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/qdm12/gluetun/internal/configuration/settings"
@@ -10,8 +9,6 @@ import (
 	"github.com/qdm12/gluetun/internal/models"
 )
 
-var ErrVPNTypeNotSupported = errors.New("VPN type not supported for custom provider")
-
 // GetConnection gets the connection from the OpenVPN configuration file.
 func (p *Provider) GetConnection(selection settings.ServerSelection, _ bool) (
 	connection models.Connection, err error,
@@ -22,7 +19,7 @@ func (p *Provider) GetConnection(selection settings.ServerSelection, _ bool) (
 	case vpn.Wireguard, vpn.AmneziaWg:
 		return getWireguardConnection(selection), nil
 	default:
-		return connection, fmt.Errorf("%w: %s", ErrVPNTypeNotSupported, selection.VPN)
+		return connection, fmt.Errorf("VPN type not supported for custom provider: %s", selection.VPN)
 	}
 }
 

internal/provider/custom/openvpnconf.go

@@ -1,7 +1,6 @@
 package custom
 
 import (
-	"errors"
 	"fmt"
 	"strconv"
 	"strings"
@@ -12,8 +11,6 @@ import (
 	"github.com/qdm12/gluetun/internal/provider/utils"
 )
 
-var ErrExtractData = errors.New("failed extracting information from custom configuration file")
-
 func (p *Provider) OpenVPNConfig(connection models.Connection,
 	settings settings.OpenVPN, ipv6Supported bool,
 ) (lines []string) {

internal/provider/example/updater/api.go

@@ -3,13 +3,10 @@ package updater
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"net/http"
 )
 
-var errHTTPStatusCodeNotOK = errors.New("HTTP status code not OK")
-
 type apiData struct {
 	Servers []apiServer `json:"servers"`
 }
@@ -42,8 +39,8 @@ func fetchAPI(ctx context.Context, client *http.Client) (
 
 	if response.StatusCode != http.StatusOK {
 		_ = response.Body.Close()
-		return data, fmt.Errorf("%w: %d %s",
-			errHTTPStatusCodeNotOK, response.StatusCode, response.Status)
+		return data, fmt.Errorf("HTTP status code not OK: %d %s",
+			response.StatusCode, response.Status)
 	}
 
 	decoder := json.NewDecoder(response.Body)

internal/provider/expressvpn/connection_test.go

@@ -21,21 +21,17 @@ func Test_Provider_GetConnection(t *testing.T) {
 
 	const provider = providers.Expressvpn
 
-	errTest := errors.New("test error")
-
 	testCases := map[string]struct {
 		filteredServers []models.Server
 		storageErr      error
 		selection       settings.ServerSelection
 		ipv6Supported   bool
 		connection      models.Connection
-		errWrapped      error
 		errMessage      string
 		panicMessage    string
 	}{
 		"error": {
-			storageErr: errTest,
-			errWrapped: errTest,
+			storageErr: errors.New("test error"),
 			errMessage: "filtering servers: test error",
 		},
 		"default OpenVPN TCP port": {
@@ -100,9 +96,10 @@ func Test_Provider_GetConnection(t *testing.T) {
 
 			connection, err := provider.GetConnection(testCase.selection, testCase.ipv6Supported)
 
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 
 			assert.Equal(t, testCase.connection, connection)

internal/provider/fastestvpn/updater/api.go

@@ -3,14 +3,11 @@ package updater
 import (
 	"bytes"
 	"context"
-	"errors"
 	"fmt"
 	"io"
 	"net/http"
 	"net/url"
 	"strings"
-
-	"github.com/qdm12/gluetun/internal/provider/common"
 )
 
 type apiServer struct {
@@ -19,8 +16,6 @@ type apiServer struct {
 	hostname string
 }
 
-var ErrDataMalformed = errors.New("data is malformed")
-
 const apiURL = "https://support.fastestvpn.com/wp-admin/admin-ajax.php"
 
 // The API URL and requests are shamelessly taken from network operations
@@ -49,7 +44,7 @@ func fetchAPIServers(ctx context.Context, client *http.Client, protocol string)
 
 	if response.StatusCode != http.StatusOK {
 		_ = response.Body.Close()
-		return nil, fmt.Errorf("%w: %d", common.ErrHTTPStatusCodeNotOK, response.StatusCode)
+		return nil, fmt.Errorf("HTTP status code not OK: %d", response.StatusCode)
 	}
 
 	data, err := io.ReadAll(response.Body)
@@ -79,8 +74,8 @@ func fetchAPIServers(ctx context.Context, client *http.Client, protocol string)
 		for i := range numberOfTDBlocks {
 			tdBlock := getNextTDBlock(trBlock)
 			if tdBlock == nil {
-				return nil, fmt.Errorf("%w: expected 3 <td> blocks in <tr> block %q",
-					ErrDataMalformed, string(trBlock))
+				return nil, fmt.Errorf("data is malformed: expected 3 <td> blocks in <tr> block %q",
+					string(trBlock))
 			}
 			trBlock = trBlock[len(tdBlock):]
 

internal/provider/fastestvpn/updater/api_test.go

@@ -8,7 +8,6 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/qdm12/gluetun/internal/provider/common"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -21,8 +20,6 @@ func (f roundTripFunc) RoundTrip(r *http.Request) (*http.Response, error) {
 func Test_fechAPIServers(t *testing.T) {
 	t.Parallel()
 
-	errTest := errors.New("test error")
-
 	testCases := map[string]struct {
 		ctx            context.Context
 		protocol       string
@@ -31,7 +28,6 @@ func Test_fechAPIServers(t *testing.T) {
 		responseBody   io.ReadCloser
 		transportErr   error
 		servers        []apiServer
-		errWrapped     error
 		errMessage     string
 	}{
 		"transport_error": {
@@ -39,8 +35,7 @@ func Test_fechAPIServers(t *testing.T) {
 			protocol:       "tcp",
 			requestBody:    "action=vpn_servers&protocol=tcp",
 			responseStatus: http.StatusOK,
-			transportErr:   errTest,
-			errWrapped:     errTest,
+			transportErr:   errors.New("test error"),
 			errMessage: `sending request: Post ` +
 				`"https://support.fastestvpn.com/wp-admin/admin-ajax.php": ` +
 				`test error`,
@@ -50,7 +45,6 @@ func Test_fechAPIServers(t *testing.T) {
 			protocol:       "tcp",
 			requestBody:    "action=vpn_servers&protocol=tcp",
 			responseStatus: http.StatusNotFound,
-			errWrapped:     common.ErrHTTPStatusCodeNotOK,
 			errMessage:     "HTTP status code not OK: 404",
 		},
 		"empty_data": {
@@ -110,9 +104,10 @@ func Test_fechAPIServers(t *testing.T) {
 
 			entries, err := fetchAPIServers(testCase.ctx, client, testCase.protocol)
 
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 			assert.Equal(t, testCase.servers, entries)
 		})

internal/provider/giganews/updater/filename.go

@@ -1,19 +1,16 @@
 package updater
 
 import (
-	"errors"
 	"fmt"
 	"strings"
 )
 
-var errNotOvpnExt = errors.New("filename does not have the openvpn file extension")
-
 func parseFilename(fileName string) (
 	region string, err error,
 ) {
 	const suffix = ".ovpn"
 	if !strings.HasSuffix(fileName, suffix) {
-		return "", fmt.Errorf("%w: %s", errNotOvpnExt, fileName)
+		return "", fmt.Errorf("filename does not have the openvpn file extension: %s", fileName)
 	}
 
 	region = strings.TrimSuffix(fileName, suffix)

internal/provider/ipvanish/updater/filename.go

@@ -1,7 +1,6 @@
 package updater
 
 import (
-	"errors"
 	"fmt"
 	"strings"
 
@@ -9,8 +8,6 @@ import (
 	"golang.org/x/text/cases"
 )
 
-var errCountryCodeUnknown = errors.New("country code is unknown")
-
 func parseFilename(fileName, hostname string, titleCaser cases.Caser) (
 	country, city string, err error,
 ) {
@@ -28,7 +25,7 @@ func parseFilename(fileName, hostname string, titleCaser cases.Caser) (
 	countryCode := strings.ToLower(parts[0])
 	country, ok := countryCodes[countryCode]
 	if !ok {
-		return "", "", fmt.Errorf("%w: %s", errCountryCodeUnknown, countryCode)
+		return "", "", fmt.Errorf("country code is unknown: %s", countryCode)
 	}
 	country = titleCaser.String(country)
 

internal/provider/ivpn/connection_test.go

@@ -22,20 +22,16 @@ func Test_Provider_GetConnection(t *testing.T) {
 
 	const provider = providers.Ivpn
 
-	errTest := errors.New("test error")
-
 	testCases := map[string]struct {
 		filteredServers []models.Server
 		storageErr      error
 		selection       settings.ServerSelection
 		ipv6Supported   bool
 		connection      models.Connection
-		errWrapped      error
 		errMessage      string
 	}{
 		"error": {
-			storageErr: errTest,
-			errWrapped: errTest,
+			storageErr: errors.New("test error"),
 			errMessage: "filtering servers: test error",
 		},
 		"default OpenVPN TCP port": {
@@ -104,9 +100,10 @@ func Test_Provider_GetConnection(t *testing.T) {
 
 			connection, err := provider.GetConnection(testCase.selection, testCase.ipv6Supported)
 
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 
 			assert.Equal(t, testCase.connection, connection)

internal/provider/ivpn/updater/api.go

@@ -3,13 +3,10 @@ package updater
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"net/http"
 )
 
-var errHTTPStatusCodeNotOK = errors.New("HTTP status code not OK")
-
 type apiData struct {
 	Servers []apiServer `json:"servers"`
 }
@@ -45,8 +42,8 @@ func fetchAPI(ctx context.Context, client *http.Client) (
 
 	if response.StatusCode != http.StatusOK {
 		_ = response.Body.Close()
-		return data, fmt.Errorf("%w: %d %s",
-			errHTTPStatusCodeNotOK, response.StatusCode, response.Status)
+		return data, fmt.Errorf("HTTP status code not OK: %d %s",
+			response.StatusCode, response.Status)
 	}
 
 	decoder := json.NewDecoder(response.Body)

internal/provider/mullvad/connection_test.go

@@ -22,20 +22,16 @@ func Test_Provider_GetConnection(t *testing.T) {
 
 	const provider = providers.Mullvad
 
-	errTest := errors.New("test error")
-
 	testCases := map[string]struct {
 		filteredServers []models.Server
 		storageErr      error
 		selection       settings.ServerSelection
 		ipv6Supported   bool
 		connection      models.Connection
-		errWrapped      error
 		errMessage      string
 	}{
 		"error": {
-			storageErr: errTest,
-			errWrapped: errTest,
+			storageErr: errors.New("test error"),
 			errMessage: "filtering servers: test error",
 		},
 		"default Wireguard port": {
@@ -70,9 +66,10 @@ func Test_Provider_GetConnection(t *testing.T) {
 
 			connection, err := provider.GetConnection(testCase.selection, testCase.ipv6Supported)
 
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 
 			assert.Equal(t, testCase.connection, connection)

internal/provider/mullvad/updater/api.go

@@ -3,16 +3,10 @@ package updater
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"net/http"
 )
 
-var (
-	ErrHTTPStatusCodeNotOK = errors.New("HTTP status code not OK")
-	ErrDecodeResponseBody  = errors.New("failed decoding response body")
-)
-
 type serverData struct {
 	Hostname string `json:"hostname"`
 	Country  string `json:"country_name"`
@@ -41,13 +35,12 @@ func fetchAPI(ctx context.Context, client *http.Client) (data []serverData, err
 	defer response.Body.Close()
 
 	if response.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("%w: %d %s", ErrHTTPStatusCodeNotOK,
-			response.StatusCode, response.Status)
+		return nil, fmt.Errorf("HTTP status code not OK: %d %s", response.StatusCode, response.Status)
 	}
 
 	decoder := json.NewDecoder(response.Body)
 	if err := decoder.Decode(&data); err != nil {
-		return nil, fmt.Errorf("%w: %s", ErrDecodeResponseBody, err)
+		return nil, fmt.Errorf("failed decoding response body: %s", err)
 	}
 
 	if err := response.Body.Close(); err != nil {

internal/provider/mullvad/updater/hosttoserver.go

@@ -12,20 +12,13 @@ import (
 
 type hostToServer map[string]models.Server
 
-var (
-	ErrNoIP                = errors.New("no IP address for VPN server")
-	ErrIPIsNotV4           = errors.New("IP address is not IPv4")
-	ErrIPIsNotV6           = errors.New("IP address is not IPv6")
-	ErrVPNTypeNotSupported = errors.New("VPN type not supported")
-)
-
 func (hts hostToServer) add(data serverData) (err error) {
 	if !data.Active {
 		return nil
 	}
 
 	if data.IPv4 == "" && data.IPv6 == "" {
-		return fmt.Errorf("%w", ErrNoIP)
+		return errors.New("no IP address for VPN server")
 	}
 
 	server, ok := hts[data.Hostname]
@@ -40,7 +33,7 @@ func (hts hostToServer) add(data serverData) (err error) {
 		// ignore bridge servers
 		return nil
 	default:
-		return fmt.Errorf("%w: %s", ErrVPNTypeNotSupported, data.Type)
+		return fmt.Errorf("VPN type not supported: %s", data.Type)
 	}
 
 	if data.IPv4 != "" {
@@ -48,7 +41,7 @@ func (hts hostToServer) add(data serverData) (err error) {
 		if err != nil {
 			return fmt.Errorf("parsing IPv4 address: %w", err)
 		} else if !ipv4.Is4() {
-			return fmt.Errorf("%w: %s", ErrIPIsNotV4, data.IPv4)
+			return fmt.Errorf("IP address is not IPv4: %s", data.IPv4)
 		}
 		server.IPs = append(server.IPs, ipv4)
 	}
@@ -58,7 +51,7 @@ func (hts hostToServer) add(data serverData) (err error) {
 		if err != nil {
 			return fmt.Errorf("parsing IPv6 address: %w", err)
 		} else if !ipv6.Is6() {
-			return fmt.Errorf("%w: %s", ErrIPIsNotV6, data.IPv6)
+			return fmt.Errorf("IP address is not IPv6: %s", data.IPv6)
 		}
 		server.IPs = append(server.IPs, ipv6)
 	}

internal/provider/nordvpn/updater/api.go

@@ -3,13 +3,10 @@ package updater
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"net/http"
 )
 
-var ErrHTTPStatusCodeNotOK = errors.New("HTTP status code not OK")
-
 func fetchAPI(ctx context.Context, client *http.Client,
 	limit uint,
 ) (data serversData, err error) {
@@ -28,7 +25,7 @@ func fetchAPI(ctx context.Context, client *http.Client,
 	defer response.Body.Close()
 
 	if response.StatusCode != http.StatusOK {
-		return serversData{}, fmt.Errorf("%w: %s", ErrHTTPStatusCodeNotOK, response.Status)
+		return serversData{}, fmt.Errorf("HTTP status code not OK: %s", response.Status)
 	}
 
 	decoder := json.NewDecoder(response.Body)

internal/provider/nordvpn/updater/models.go

@@ -168,11 +168,6 @@ func (s *serverData) ips() (ips []netip.Addr) {
 	return ips
 }
 
-var (
-	ErrWireguardPublicKeyMalformed = errors.New("wireguard public key is malformed")
-	ErrWireguardPublicKeyNotFound  = errors.New("wireguard public key not found")
-)
-
 // wireguardPublicKey returns the Wireguard public key for the server.
 func (s *serverData) wireguardPublicKey(technologies map[uint32]technologyData) (
 	wgPubKey string, err error,
@@ -189,11 +184,10 @@ func (s *serverData) wireguardPublicKey(technologies map[uint32]technologyData)
 			wgPubKey = metadata.Value
 			_, err = base64.StdEncoding.DecodeString(wgPubKey)
 			if err != nil {
-				return "", fmt.Errorf("%w: %s cannot be decoded: %s",
-					ErrWireguardPublicKeyMalformed, wgPubKey, err)
+				return "", fmt.Errorf("wireguard public key is malformed: %s cannot be decoded: %s", wgPubKey, err)
 			}
 			return metadata.Value, nil
 		}
 	}
-	return "", fmt.Errorf("%w", ErrWireguardPublicKeyNotFound)
+	return "", errors.New("wireguard public key not found")
 }

internal/provider/nordvpn/updater/name.go

@@ -7,10 +7,7 @@ import (
 	"strings"
 )
 
-var (
-	ErrNoIDInServerName      = errors.New("no ID in server name")
-	ErrInvalidIDInServerName = errors.New("invalid ID in server name")
-)
+var ErrNoIDInServerName = errors.New("no ID in server name")
 
 func parseServerName(serverName string) (number uint16, err error) {
 	i := strings.IndexRune(serverName, '#')
@@ -21,7 +18,7 @@ func parseServerName(serverName string) (number uint16, err error) {
 	idString := serverName[i+1:]
 	idUint64, err := strconv.ParseUint(idString, 10, 16)
 	if err != nil {
-		return 0, fmt.Errorf("%w: %s", ErrInvalidIDInServerName, serverName)
+		return 0, fmt.Errorf("invalid ID in server name: %s", serverName)
 	}
 
 	number = uint16(idUint64)

internal/provider/nordvpn/updater/servers.go

@@ -11,8 +11,6 @@ import (
 	"github.com/qdm12/gluetun/internal/provider/common"
 )
 
-var ErrNotIPv4 = errors.New("IP address is not IPv4")
-
 func (u *Updater) FetchServers(ctx context.Context, minServers int) (
 	servers []models.Server, err error,
 ) {

internal/provider/privateinternetaccess/portforward.go

@@ -21,8 +21,6 @@ import (
 	"github.com/qdm12/gluetun/internal/provider/utils"
 )
 
-var ErrServerNameNotFound = errors.New("server name not found in servers")
-
 // PortForward obtains a VPN server side port forwarded from PIA.
 func (p *Provider) PortForward(ctx context.Context,
 	objects utils.PortForwardObjects,
@@ -42,7 +40,7 @@ func (p *Provider) PortForward(ctx context.Context,
 	logger := objects.Logger
 
 	if !objects.CanPortForward {
-		return nil, fmt.Errorf("%w: for server %s", ErrServerNameNotFound, serverName)
+		return nil, fmt.Errorf("server name %s not found in servers", serverName)
 	}
 
 	privateIPClient, err := newHTTPClient(serverName)
@@ -91,8 +89,6 @@ func (p *Provider) PortForward(ctx context.Context,
 	return map[uint16]uint16{data.Port: data.Port}, nil
 }
 
-var ErrPortForwardedExpired = errors.New("port forwarded data expired")
-
 func (p *Provider) KeepPortForward(ctx context.Context,
 	objects utils.PortForwardObjects,
 ) (err error) {
@@ -136,14 +132,12 @@ func (p *Provider) KeepPortForward(ctx context.Context,
 			}
 			keepAliveTimer.Reset(keepAlivePeriod)
 		case <-expiryTimer.C:
-			return fmt.Errorf("%w: on %s", ErrPortForwardedExpired,
+			return fmt.Errorf("port forwarded data expired on %s",
 				data.Expiration.Format(time.RFC1123))
 		}
 	}
 }
 
-var errAPIIPNotFound = errors.New("API IP address not found")
-
 func findAPIIP(ctx context.Context, client *http.Client, gateway netip.Addr) (
 	apiIP netip.Addr, err error,
 ) {
@@ -188,7 +182,7 @@ func findAPIIP(ctx context.Context, client *http.Client, gateway netip.Addr) (
 		return ip, nil
 	}
 
-	return netip.Addr{}, fmt.Errorf("%w: %w", errAPIIPNotFound, errors.Join(errs...))
+	return netip.Addr{}, fmt.Errorf("API IP address not found: %w", errors.Join(errs...))
 }
 
 func refreshPIAPortForwardData(ctx context.Context, client, privateIPClient *http.Client,
@@ -290,8 +284,6 @@ func packPayload(port uint16, token string, expiration time.Time) (payload strin
 	return payload, nil
 }
 
-var errEmptyToken = errors.New("token received is empty")
-
 func fetchToken(ctx context.Context, client *http.Client,
 	username, password string,
 ) (token string, err error) {
@@ -340,7 +332,7 @@ func fetchToken(ctx context.Context, client *http.Client,
 	}
 
 	if result.Token == "" {
-		return "", errEmptyToken
+		return "", errors.New("token received is empty")
 	}
 	return result.Token, nil
 }
@@ -391,7 +383,7 @@ func fetchPortForwardData(ctx context.Context, client *http.Client, apiIP netip.
 	}
 
 	if data.Status != "OK" {
-		return 0, "", expiration, fmt.Errorf("%w: status is: %s", ErrBadResponse, data.Status)
+		return 0, "", expiration, fmt.Errorf("bad response received with status %s", data.Status)
 	}
 
 	port, _, expiration, err = unpackPayload(data.Payload)
@@ -401,8 +393,6 @@ func fetchPortForwardData(ctx context.Context, client *http.Client, apiIP netip.
 	return port, data.Signature, expiration, err
 }
 
-var ErrBadResponse = errors.New("bad response received")
-
 func bindPort(ctx context.Context, client *http.Client, apiIPAddress netip.Addr, data piaPortForwardData) (err error) {
 	// Define a timeout since the default client has a large timeout and we don't
 	// want to wait too long.
@@ -455,7 +445,7 @@ func bindPort(ctx context.Context, client *http.Client, apiIPAddress netip.Addr,
 	}
 
 	if responseData.Status != "OK" {
-		return fmt.Errorf("%w: %s: %s", ErrBadResponse, responseData.Status, responseData.Message)
+		return fmt.Errorf("bad response received with status %q and message %q", responseData.Status, responseData.Message)
 	}
 
 	return nil
@@ -464,7 +454,7 @@ func bindPort(ctx context.Context, client *http.Client, apiIPAddress netip.Addr,
 // replaceInErr is used to remove sensitive information from errors.
 func replaceInErr(err error, substitutions map[string]string) error {
 	s := replaceInString(err.Error(), substitutions)
-	return errors.New(s) //nolint:err113
+	return errors.New(s)
 }
 
 // replaceInString is used to remove sensitive information.
@@ -475,8 +465,6 @@ func replaceInString(s string, substitutions map[string]string) string {
 	return s
 }
 
-var ErrHTTPStatusCodeNotOK = errors.New("HTTP status code is not OK")
-
 func makeNOKStatusError(response *http.Response, substitutions map[string]string) (err error) {
 	url := response.Request.URL.String()
 	url = replaceInString(url, substitutions)
@@ -487,7 +475,6 @@ func makeNOKStatusError(response *http.Response, substitutions map[string]string
 	shortenMessage = strings.ReplaceAll(shortenMessage, "  ", " ")
 	shortenMessage = replaceInString(shortenMessage, substitutions)
 
-	return fmt.Errorf("%w: %s: %d %s: response received: %s",
-		ErrHTTPStatusCodeNotOK, url, response.StatusCode,
-		response.Status, shortenMessage)
+	return fmt.Errorf("HTTP status code not OK: %s: %d %s: response received: %s",
+		url, response.StatusCode, response.Status, shortenMessage)
 }

internal/provider/privateinternetaccess/updater/api.go

@@ -4,15 +4,12 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"net/http"
 	"net/netip"
 )
 
-var ErrHTTPStatusCodeNotOK = errors.New("HTTP status code not OK")
-
 type apiData struct {
 	Regions []regionData `json:"regions"`
 }
@@ -50,7 +47,7 @@ func fetchAPI(ctx context.Context, client *http.Client) (
 	defer response.Body.Close()
 
 	if response.StatusCode != http.StatusOK {
-		return data, fmt.Errorf("%w: %d %s", ErrHTTPStatusCodeNotOK,
+		return data, fmt.Errorf("HTTP status code not OK: %d %s",
 			response.StatusCode, response.Status)
 	}
 

internal/provider/privatevpn/portforward.go

@@ -11,14 +11,11 @@ import (
 	"strconv"
 	"time"
 
-	"github.com/qdm12/gluetun/internal/provider/common"
 	"github.com/qdm12/gluetun/internal/provider/utils"
 )
 
 var regexPort = regexp.MustCompile(`[1-9][0-9]{0,4}`)
 
-var ErrPortForwardedNotFound = errors.New("port forwarded not found")
-
 // PortForward obtains a VPN server side port forwarded from the PrivateVPN API.
 // It returns 0 if all ports are to forwarded on a dedicated server IP.
 func (p *Provider) PortForward(ctx context.Context, objects utils.PortForwardObjects) (
@@ -42,8 +39,7 @@ func (p *Provider) PortForward(ctx context.Context, objects utils.PortForwardObj
 	}
 
 	if response.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("%w: %d %s", common.ErrHTTPStatusCodeNotOK,
-			response.StatusCode, response.Status)
+		return nil, fmt.Errorf("HTTP status code not OK: %d %s", response.StatusCode, response.Status)
 	}
 
 	defer response.Body.Close()
@@ -62,12 +58,12 @@ func (p *Provider) PortForward(ctx context.Context, objects utils.PortForwardObj
 		return nil, fmt.Errorf("decoding JSON response: %w; data is: %s",
 			err, string(bytes))
 	} else if !data.Supported {
-		return nil, fmt.Errorf("%w for this VPN server", common.ErrPortForwardNotSupported)
+		return nil, errors.New("port forwarding not supported for this VPN server")
 	}
 
 	portString := regexPort.FindString(data.Status)
 	if portString == "" {
-		return nil, fmt.Errorf("%w: in status %q", ErrPortForwardedNotFound, data.Status)
+		return nil, fmt.Errorf("port forwarded not found in status %q", data.Status)
 	}
 
 	const base, bitSize = 10, 16

internal/provider/privatevpn/portforward_test.go

@@ -22,8 +22,6 @@ func (s roundTripFunc) RoundTrip(r *http.Request) (*http.Response, error) {
 func Test_Provider_PortForward(t *testing.T) {
 	t.Parallel()
 
-	errTest := errors.New("test error")
-
 	canceledCtx, cancel := context.WithCancel(context.Background())
 	cancel()
 
@@ -59,7 +57,7 @@ func Test_Provider_PortForward(t *testing.T) {
 						assert.Equal(t,
 							"https://connect.pvdatanet.com/v3/Api/port?ip[]=10.10.10.10",
 							r.URL.String())
-						return nil, errTest
+						return nil, errors.New("test error")
 					}),
 				},
 			},
@@ -156,7 +154,7 @@ func Test_Provider_PortForward(t *testing.T) {
 					}),
 				},
 			},
-			errMessage: "port forwarded not found: in status \"no port here\"",
+			errMessage: "port forwarded not found in status \"no port here\"",
 		},
 		"port_too_big": {
 			ctx: context.Background(),

internal/provider/privatevpn/updater/filename.go

@@ -1,7 +1,6 @@
 package updater
 
 import (
-	"errors"
 	"fmt"
 	"regexp"
 	"strings"
@@ -9,12 +8,6 @@ import (
 
 var trailingNumber = regexp.MustCompile(` [0-9]+$`)
 
-var (
-	errBadPrefix      = errors.New("bad prefix in file name")
-	errBadSuffix      = errors.New("bad suffix in file name")
-	errNotEnoughParts = errors.New("not enough parts in file name")
-)
-
 func parseFilename(fileName string) (
 	countryCode, city string, err error,
 ) {
@@ -22,7 +15,7 @@ func parseFilename(fileName string) (
 
 	const prefix = "PrivateVPN-"
 	if !strings.HasPrefix(fileName, prefix) {
-		return "", "", fmt.Errorf("%w: %s", errBadPrefix, fileName)
+		return "", "", fmt.Errorf("bad prefix in file name %s", fileName)
 	}
 	s := strings.TrimPrefix(fileName, prefix)
 
@@ -34,7 +27,7 @@ func parseFilename(fileName string) (
 	case strings.HasSuffix(fileName, udpSuffix):
 		s = strings.TrimSuffix(s, udpSuffix)
 	default:
-		return "", "", fmt.Errorf("%w: %s", errBadSuffix, fileName)
+		return "", "", fmt.Errorf("bad suffix in file name %s", fileName)
 	}
 
 	s = trailingNumber.ReplaceAllString(s, "")
@@ -42,7 +35,7 @@ func parseFilename(fileName string) (
 	parts := strings.Split(s, "-")
 	const minParts = 2
 	if len(parts) < minParts {
-		return "", "", fmt.Errorf("%w: %s", errNotEnoughParts, fileName)
+		return "", "", fmt.Errorf("not enough parts in file name %s", fileName)
 	}
 	countryCode, city = parts[0], parts[1]
 

internal/provider/protonvpn/portforward.go

@@ -12,8 +12,6 @@ import (
 	"github.com/qdm12/gluetun/internal/provider/utils"
 )
 
-var ErrServerPortForwardNotSupported = errors.New("server does not support port forwarding")
-
 const nonSymmetricPortStart uint16 = 56789
 
 // PortForward obtains a VPN server side port forwarded from ProtonVPN gateway.
@@ -21,7 +19,7 @@ func (p *Provider) PortForward(ctx context.Context, objects utils.PortForwardObj
 	internalToExternalPorts map[uint16]uint16, err error,
 ) {
 	if !objects.CanPortForward {
-		return nil, fmt.Errorf("%w", ErrServerPortForwardNotSupported)
+		return nil, errors.New("server does not support port forwarding")
 	}
 
 	client := natpmp.New()
@@ -104,11 +102,6 @@ func checkExternalPorts(logger utils.Logger, udpPort, tcpPort uint16) {
 	}
 }
 
-var (
-	ErrInternalPortChanged = errors.New("internal port changed")
-	ErrExternalPortChanged = errors.New("external port changed")
-)
-
 func (p *Provider) KeepPortForward(ctx context.Context,
 	objects utils.PortForwardObjects,
 ) (err error) {
@@ -135,11 +128,10 @@ func (p *Provider) KeepPortForward(ctx context.Context,
 				}
 				checkLifetime(logger, networkProtocol, lifetime, assignedLiftetime)
 				if externalPort != assignedExternalPort {
-					return fmt.Errorf("%w: %d changed to %d",
-						ErrExternalPortChanged, externalPort, assignedExternalPort)
+					return fmt.Errorf("external port changed from %d to %d", externalPort, assignedExternalPort)
 				} else if internalPort != assignedInternalPort {
-					return fmt.Errorf("%w: %d (for external port %d) changed to %d",
-						ErrInternalPortChanged, internalPort, externalPort, assignedInternalPort)
+					return fmt.Errorf("internal port changed from %d (for external port %d) to %d",
+						internalPort, externalPort, assignedInternalPort)
 				}
 			}
 			objects.Logger.Debug(fmt.Sprintf("port forwarded %d maintained", externalPort))

internal/provider/protonvpn/updater/api.go

@@ -60,8 +60,6 @@ func newAPIClient(ctx context.Context, httpClient *http.Client) (client *apiClie
 	}, nil
 }
 
-var ErrCodeNotSuccess = errors.New("response code is not success")
-
 // setHeaders sets the minimal necessary headers for Proton API requests
 // to succeed without being blocked by their "security" measures.
 // See for example [getMostRecentStableTag] on how the app version must
@@ -126,8 +124,6 @@ func (c *apiClient) authenticate(ctx context.Context, email, password string,
 	return authCookie, nil
 }
 
-var ErrSessionIDNotFound = errors.New("session ID not found in cookies")
-
 func (c *apiClient) getSessionID(ctx context.Context) (sessionID string, err error) {
 	const url = "https://account.proton.me/vpn"
 	request, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
@@ -150,11 +146,9 @@ func (c *apiClient) getSessionID(ctx context.Context) (sessionID string, err err
 		}
 	}
 
-	return "", fmt.Errorf("%w", ErrSessionIDNotFound)
+	return "", errors.New("session ID not found in cookies")
 }
 
-var ErrDataFieldMissing = errors.New("data field missing in response")
-
 func (c *apiClient) getUnauthSession(ctx context.Context, sessionID string) (
 	tokenType, accessToken, refreshToken, uid string, err error,
 ) {
@@ -198,24 +192,22 @@ func (c *apiClient) getUnauthSession(ctx context.Context, sessionID string) (
 	const successCode = 1000
 	switch {
 	case data.Code != successCode:
-		return "", "", "", "", fmt.Errorf("%w: expected %d got %d",
-			ErrCodeNotSuccess, successCode, data.Code)
+		return "", "", "", "", fmt.Errorf("response code %d is not expected success code %d",
+			data.Code, successCode)
 	case data.AccessToken == "":
-		return "", "", "", "", fmt.Errorf("%w: access token is empty", ErrDataFieldMissing)
+		return "", "", "", "", errors.New("access token is empty in response")
 	case data.RefreshToken == "":
-		return "", "", "", "", fmt.Errorf("%w: refresh token is empty", ErrDataFieldMissing)
+		return "", "", "", "", errors.New("refresh token is empty in response")
 	case data.TokenType == "":
-		return "", "", "", "", fmt.Errorf("%w: token type is empty", ErrDataFieldMissing)
+		return "", "", "", "", errors.New("token type is empty in response")
 	case data.UID == "":
-		return "", "", "", "", fmt.Errorf("%w: UID is empty", ErrDataFieldMissing)
+		return "", "", "", "", errors.New("UID is empty in response")
 	}
 	// Ignore Scopes and LocalID fields, we don't use them.
 
 	return data.TokenType, data.AccessToken, data.RefreshToken, data.UID, nil
 }
 
-var ErrUIDMismatch = errors.New("UID in response does not match request UID")
-
 func (c *apiClient) cookieToken(ctx context.Context, sessionID, tokenType, accessToken,
 	refreshToken, uid string,
 ) (cookieToken string, err error) {
@@ -282,11 +274,11 @@ func (c *apiClient) cookieToken(ctx context.Context, sessionID, tokenType, acces
 	const successCode = 1000
 	switch {
 	case cookies.Code != successCode:
-		return "", fmt.Errorf("%w: expected %d got %d",
-			ErrCodeNotSuccess, successCode, cookies.Code)
+		return "", fmt.Errorf("response code %d is not expected success code %d",
+			cookies.Code, successCode)
 	case cookies.UID != requestBody.UID:
-		return "", fmt.Errorf("%w: expected %s got %s",
-			ErrUIDMismatch, requestBody.UID, cookies.UID)
+		return "", fmt.Errorf("UID %s in response does not match request UID %s",
+			cookies.UID, requestBody.UID)
 	}
 	// Ignore LocalID and RefreshCounter fields, we don't use them.
 
@@ -296,11 +288,9 @@ func (c *apiClient) cookieToken(ctx context.Context, sessionID, tokenType, acces
 		}
 	}
 
-	return "", fmt.Errorf("%w", ErrAuthCookieNotFound)
+	return "", errors.New("auth cookie not found")
 }
 
-var ErrUsernameDoesNotExist = errors.New("username does not exist")
-
 // authInfo fetches SRP parameters for the account.
 func (c *apiClient) authInfo(ctx context.Context, email string, unauthCookie cookie) (
 	username, modulusPGPClearSigned, serverEphemeralBase64, saltBase64, srpSessionHex string,
@@ -358,20 +348,20 @@ func (c *apiClient) authInfo(ctx context.Context, email string, unauthCookie coo
 	const successCode = 1000
 	switch {
 	case info.Code != successCode:
-		return "", "", "", "", "", 0, fmt.Errorf("%w: expected %d got %d",
-			ErrCodeNotSuccess, successCode, info.Code)
+		return "", "", "", "", "", 0, fmt.Errorf("response code %d is not expected success code %d",
+			info.Code, successCode)
 	case info.Modulus == "":
-		return "", "", "", "", "", 0, fmt.Errorf("%w: modulus is empty", ErrDataFieldMissing)
+		return "", "", "", "", "", 0, errors.New("modulus is empty in response")
 	case info.ServerEphemeral == "":
-		return "", "", "", "", "", 0, fmt.Errorf("%w: server ephemeral is empty", ErrDataFieldMissing)
+		return "", "", "", "", "", 0, errors.New("server ephemeral is empty in response")
 	case info.Salt == "":
-		return "", "", "", "", "", 0, fmt.Errorf("%w (salt data field is empty)", ErrUsernameDoesNotExist)
+		return "", "", "", "", "", 0, errors.New("salt is empty in response")
 	case info.SRPSession == "":
-		return "", "", "", "", "", 0, fmt.Errorf("%w: SRP session is empty", ErrDataFieldMissing)
+		return "", "", "", "", "", 0, errors.New("SRP session is empty in response")
 	case info.Username == "":
-		return "", "", "", "", "", 0, fmt.Errorf("%w: username is empty", ErrDataFieldMissing)
+		return "", "", "", "", "", 0, errors.New("username is empty in response")
 	case info.Version == nil:
-		return "", "", "", "", "", 0, fmt.Errorf("%w: version is missing", ErrDataFieldMissing)
+		return "", "", "", "", "", 0, errors.New("version is missing in response")
 	}
 
 	version = int(*info.Version) //nolint:gosec
@@ -399,13 +389,7 @@ func (c *cookie) String() string {
 	return s
 }
 
-var (
-	// ErrServerProofNotValid indicates the M2 from the server didn't match the expected proof.
-	ErrServerProofNotValid = errors.New("server proof from server is not valid")
-	ErrVPNScopeNotFound    = errors.New("VPN scope not found in scopes")
-	ErrTwoFANotSupported   = errors.New("two factor authentication not supported in this client")
-	ErrAuthCookieNotFound  = errors.New("auth cookie not found")
-)
+// ErrServerProofNotValid indicates the M2 from the server didn't match the expected proof.
 
 // auth performs the SRP proof submission (and optionally TOTP) to obtain tokens.
 func (c *apiClient) auth(ctx context.Context, unauthCookie cookie,
@@ -495,22 +479,22 @@ func (c *apiClient) auth(ctx context.Context, unauthCookie cookie,
 		return cookie{}, fmt.Errorf("decoding server proof: %w", err)
 	}
 	if !bytes.Equal(m2, proofs.ExpectedServerProof) {
-		return cookie{}, fmt.Errorf("%w: expected %x got %x",
-			ErrServerProofNotValid, proofs.ExpectedServerProof, m2)
+		return cookie{}, fmt.Errorf("server proof from server %x is not expected proof %x",
+			m2, proofs.ExpectedServerProof)
 	}
 
 	const successCode = 1000
 	switch {
 	case auth.Code != successCode:
-		return cookie{}, fmt.Errorf("%w: expected %d got %d",
-			ErrCodeNotSuccess, successCode, auth.Code)
+		return cookie{}, fmt.Errorf("response code %d is not expected success code %d",
+			auth.Code, successCode)
 	case auth.UID != unauthCookie.uid:
-		return cookie{}, fmt.Errorf("%w: expected %s got %s",
-			ErrUIDMismatch, unauthCookie.uid, auth.UID)
+		return cookie{}, fmt.Errorf("UID %s in response does not match request UID %s",
+			auth.UID, unauthCookie.uid)
 	case auth.TwoFactor != 0:
-		return cookie{}, fmt.Errorf("%w", ErrTwoFANotSupported)
+		return cookie{}, errors.New("two factor authentication not supported in this client")
 	case !slices.Contains(auth.Scopes, "vpn"):
-		return cookie{}, fmt.Errorf("%w: in %v", ErrVPNScopeNotFound, auth.Scopes)
+		return cookie{}, fmt.Errorf("VPN scope not found in scopes %v", auth.Scopes)
 	}
 
 	for _, setCookieHeader := range response.Header.Values("Set-Cookie") {
@@ -524,8 +508,7 @@ func (c *apiClient) auth(ctx context.Context, unauthCookie cookie,
 		}
 	}
 
-	return cookie{}, fmt.Errorf("%w: in HTTP headers %s",
-		ErrAuthCookieNotFound, httpHeadersToString(response.Header))
+	return cookie{}, fmt.Errorf("auth cookie not found in HTTP headers %s", httpHeadersToString(response.Header))
 }
 
 // generateLettersDigits mimicing Proton's own random string generator:
@@ -611,8 +594,6 @@ func (c *apiClient) fetchServers(ctx context.Context, cookie cookie) (
 	return data, nil
 }
 
-var ErrHTTPStatusCodeNotOK = errors.New("HTTP status code not OK")
-
 func buildError(httpCode int, body []byte) error {
 	prettyCode := http.StatusText(httpCode)
 	var protonError struct {
@@ -624,8 +605,8 @@ func buildError(httpCode int, body []byte) error {
 	decoder.DisallowUnknownFields()
 	err := decoder.Decode(&protonError)
 	if err != nil || protonError.Error == nil || protonError.Code == nil {
-		return fmt.Errorf("%w: %s: %s",
-			ErrHTTPStatusCodeNotOK, prettyCode, body)
+		return fmt.Errorf("HTTP status code not OK: %s: %s",
+			prettyCode, body)
 	}
 
 	details := make([]string, 0, len(protonError.Details))
@@ -633,6 +614,6 @@ func buildError(httpCode int, body []byte) error {
 		details = append(details, fmt.Sprintf("%s: %s", key, value))
 	}
 
-	return fmt.Errorf("%w: %s: %s (code %d with details: %s)",
-		ErrHTTPStatusCodeNotOK, prettyCode, *protonError.Error, *protonError.Code, strings.Join(details, ", "))
+	return fmt.Errorf("HTTP status code not OK: %s: %s (code %d with details: %s)",
+		prettyCode, *protonError.Error, *protonError.Code, strings.Join(details, ", "))
 }

internal/provider/protonvpn/updater/version.go

@@ -45,7 +45,7 @@ func getMostRecentStableTag(ctx context.Context, client *http.Client) (version s
 		}
 
 		if response.StatusCode != http.StatusOK {
-			return "", fmt.Errorf("%w: %s: %s", ErrHTTPStatusCodeNotOK, response.Status, data)
+			return "", fmt.Errorf("HTTP status code not OK: %s: %s", response.Status, data)
 		}
 
 		var tags []struct {

internal/provider/purevpn/updater/servers.go

@@ -17,7 +17,7 @@ func (u *Updater) FetchServers(ctx context.Context, minServers int) (
 	servers []models.Server, err error,
 ) {
 	if !u.ipFetcher.CanFetchAnyIP() {
-		return nil, fmt.Errorf("%w: %s", common.ErrIPFetcherUnsupported, u.ipFetcher.String())
+		return nil, fmt.Errorf("IP fetcher %s does not support fetching any IP", u.ipFetcher.String())
 	}
 
 	const url = "https://d11a57lttb2ffq.cloudfront.net/heartbleed/router/Recommended-CA2.zip"

internal/provider/surfshark/updater/api.go

@@ -3,7 +3,6 @@ package updater
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"net/http"
 
@@ -38,8 +37,6 @@ func addServersFromAPI(ctx context.Context, client *http.Client,
 	return nil
 }
 
-var ErrHTTPStatusCodeNotOK = errors.New("HTTP status code not OK")
-
 type serverData struct {
 	Host     string `json:"connectionName"`
 	Region   string `json:"region"`
@@ -66,7 +63,7 @@ func fetchAPI(ctx context.Context, client *http.Client) (
 		defer response.Body.Close()
 
 		if response.StatusCode != http.StatusOK {
-			return nil, fmt.Errorf("%w: %d %s", ErrHTTPStatusCodeNotOK,
+			return nil, fmt.Errorf("HTTP status code not OK: %d %s",
 				response.StatusCode, response.Status)
 		}
 

internal/provider/surfshark/updater/location.go

@@ -1,20 +1,17 @@
 package updater
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/qdm12/gluetun/internal/provider/surfshark/servers"
 )
 
-var errHostnameNotFound = errors.New("hostname not found in hostname to location mapping")
-
 func getHostInformation(host string, hostnameToLocation map[string]servers.ServerLocation) (
 	data servers.ServerLocation, err error,
 ) {
 	locationData, ok := hostnameToLocation[host]
 	if !ok {
-		return locationData, fmt.Errorf("%w: %s", errHostnameNotFound, host)
+		return locationData, fmt.Errorf("hostname %s not found in hostname to location mapping", host)
 	}
 
 	return locationData, nil

internal/provider/utils/connection_test.go

@@ -19,8 +19,6 @@ import (
 func Test_GetConnection(t *testing.T) {
 	t.Parallel()
 
-	errTest := errors.New("test error")
-
 	testCases := map[string]struct {
 		provider        string
 		filteredServers []models.Server
@@ -30,12 +28,10 @@ func Test_GetConnection(t *testing.T) {
 		ipv6Supported   bool
 		randSource      rand.Source
 		connection      models.Connection
-		errWrapped      error
 		errMessage      string
 	}{
 		"storage filter error": {
-			filterError: errTest,
-			errWrapped:  errTest,
+			filterError: errors.New("test error"),
 			errMessage:  "filtering servers: test error",
 		},
 		"server without IPs": {
@@ -50,7 +46,6 @@ func Test_GetConnection(t *testing.T) {
 				OpenVPNUDPPort: 1,
 				WireguardPort:  1,
 			},
-			errWrapped: ErrNoConnectionToPickFrom,
 			errMessage: "no connection to pick from",
 		},
 		"OpenVPN server with hostname": {
@@ -199,9 +194,10 @@ func Test_GetConnection(t *testing.T) {
 				testCase.randSource)
 
 			assert.Equal(t, testCase.connection, connection)
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 		})
 	}

internal/provider/utils/nofetcher.go

@@ -2,7 +2,6 @@ package utils
 
 import (
 	"context"
-	"errors"
 	"fmt"
 
 	"github.com/qdm12/gluetun/internal/models"
@@ -18,10 +17,8 @@ func NewNoFetcher(providerName string) *NoFetcher {
 	}
 }
 
-var ErrFetcherNotSupported = errors.New("fetching of servers is not supported")
-
 func (n *NoFetcher) FetchServers(context.Context, int) (
 	servers []models.Server, err error,
 ) {
-	return nil, fmt.Errorf("%w: for %s", ErrFetcherNotSupported, n.providerName)
+	return nil, fmt.Errorf("fetching of servers is not supported for %s", n.providerName)
 }

internal/provider/utils/pick.go

@@ -11,8 +11,6 @@ import (
 	"github.com/qdm12/gluetun/internal/models"
 )
 
-var ErrNoConnectionToPickFrom = errors.New("no connection to pick from")
-
 // pickConnection picks a connection from a pool of connections.
 // If the VPN protocol is Wireguard and the target IP is set,
 // it finds the connection corresponding to this target IP.
@@ -23,7 +21,7 @@ func pickConnection(connections []models.Connection,
 	connection models.Connection, err error,
 ) {
 	if len(connections) == 0 {
-		return connection, ErrNoConnectionToPickFrom
+		return connection, errors.New("no connection to pick from")
 	}
 
 	var targetIP netip.Addr
@@ -56,8 +54,6 @@ func pickRandomConnection(connections []models.Connection,
 	return connections[rand.New(source).Intn(len(connections))] //nolint:gosec
 }
 
-var errTargetIPNotFound = errors.New("target IP address not found")
-
 func getTargetIPConnection(connections []models.Connection,
 	targetIP netip.Addr,
 ) (connection models.Connection, err error) {
@@ -66,6 +62,6 @@ func getTargetIPConnection(connections []models.Connection,
 			return connection, nil
 		}
 	}
-	return connection, fmt.Errorf("%w: in %d filtered connections",
-		errTargetIPNotFound, len(connections))
+	return connection, fmt.Errorf("target IP address not found: in %d filtered connections",
+		len(connections))
 }

internal/provider/vpnsecure/updater/website.go

@@ -33,8 +33,6 @@ func fetchServers(ctx context.Context, client *http.Client,
 	return servers, nil
 }
 
-var ErrHTMLServersDivNotFound = errors.New("HTML servers container div not found")
-
 const divString = "div"
 
 func parseHTML(rootNode *html.Node) (servers []models.Server,
@@ -43,7 +41,7 @@ func parseHTML(rootNode *html.Node) (servers []models.Server,
 	// Find div container for all servers, searching with BFS.
 	serversDiv := findServersDiv(rootNode)
 	if serversDiv == nil {
-		return nil, nil, htmlutils.WrapError(ErrHTMLServersDivNotFound, rootNode)
+		return nil, nil, htmlutils.WrapError(errors.New("HTML servers container div not found"), rootNode)
 	}
 
 	for countryNode := serversDiv.FirstChild; countryNode != nil; countryNode = countryNode.NextSibling {

internal/provider/vpnsecure/updater/website_test.go

@@ -31,12 +31,10 @@ func Test_fetchServers(t *testing.T) {
 		responseStatus int
 		responseBody   io.ReadCloser
 		servers        []models.Server
-		errWrapped     error
 		errMessage     string
 	}{
 		"context canceled": {
 			ctx:        canceledCtx,
-			errWrapped: context.Canceled,
 			errMessage: `fetching HTML code: Get "https://www.vpnsecure.me/vpn-locations/": context canceled`,
 		},
 		"success": {
@@ -105,9 +103,10 @@ func Test_fetchServers(t *testing.T) {
 
 			servers, err := fetchServers(testCase.ctx, client, warner)
 
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 			assert.Equal(t, testCase.servers, servers)
 		})
@@ -121,12 +120,10 @@ func Test_parseHTML(t *testing.T) {
 		rootNode   *html.Node
 		servers    []models.Server
 		warnings   []string
-		errWrapped error
 		errMessage string
 	}{
 		"empty html": {
 			rootNode:   parseTestHTML(t, ""),
-			errWrapped: ErrHTMLServersDivNotFound,
 			errMessage: `HTML servers container div not found: in HTML code: <html><head></head><body></body></html>`,
 		},
 		"test data": {
@@ -223,9 +220,10 @@ func Test_parseHTML(t *testing.T) {
 
 			assert.Equal(t, testCase.servers, servers)
 			assert.Equal(t, testCase.warnings, warnings)
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 		})
 	}

internal/provider/vyprvpn/updater/filename.go

@@ -1,19 +1,16 @@
 package updater
 
 import (
-	"errors"
 	"fmt"
 	"strings"
 )
 
-var errNotOvpnExt = errors.New("filename does not have the openvpn file extension")
-
 func parseFilename(fileName string) (
 	region string, err error,
 ) {
 	const suffix = ".ovpn"
 	if !strings.HasSuffix(fileName, suffix) {
-		return "", fmt.Errorf("%w: %s", errNotOvpnExt, fileName)
+		return "", fmt.Errorf("filename does not have the openvpn file extension: %s", fileName)
 	}
 
 	region = strings.TrimSuffix(fileName, suffix)

internal/provider/windscribe/connection_test.go

@@ -22,21 +22,17 @@ func Test_Provider_GetConnection(t *testing.T) {
 
 	const provider = providers.Windscribe
 
-	errTest := errors.New("test error")
-
 	testCases := map[string]struct {
 		filteredServers []models.Server
 		storageErr      error
 		selection       settings.ServerSelection
 		ipv6Supported   bool
 		connection      models.Connection
-		errWrapped      error
 		errMessage      string
 		panicMessage    string
 	}{
 		"error": {
-			storageErr: errTest,
-			errWrapped: errTest,
+			storageErr: errors.New("test error"),
 			errMessage: "filtering servers: test error",
 		},
 		"default OpenVPN TCP port": {
@@ -111,9 +107,10 @@ func Test_Provider_GetConnection(t *testing.T) {
 
 			connection, err := provider.GetConnection(testCase.selection, testCase.ipv6Supported)
 
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 
 			assert.Equal(t, testCase.connection, connection)

internal/provider/windscribe/updater/api.go

@@ -3,7 +3,6 @@ package updater
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"net/http"
 	"net/netip"
@@ -11,8 +10,6 @@ import (
 	"time"
 )
 
-var ErrHTTPStatusCodeNotOK = errors.New("HTTP status code not OK")
-
 type apiData struct {
 	Data []regionData `json:"data"`
 }
@@ -55,7 +52,7 @@ func fetchAPI(ctx context.Context, client *http.Client) (
 	defer response.Body.Close()
 
 	if response.StatusCode != http.StatusOK {
-		return data, fmt.Errorf("%w: %d %s", ErrHTTPStatusCodeNotOK,
+		return data, fmt.Errorf("HTTP status code not OK: %d %s",
 			response.StatusCode, response.Status)
 	}
 

internal/provider/windscribe/updater/servers.go

@@ -2,7 +2,6 @@ package updater
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"net/netip"
 	"sort"
@@ -12,8 +11,6 @@ import (
 	"github.com/qdm12/gluetun/internal/provider/common"
 )
 
-var ErrNoWireguardKey = errors.New("no wireguard public key found")
-
 func (u *Updater) FetchServers(ctx context.Context, minServers int) (
 	servers []models.Server, err error,
 ) {
@@ -51,7 +48,7 @@ func (u *Updater) FetchServers(ctx context.Context, minServers int) (
 				if !node.IP3.IsValid() { // Wireguard + Stealth
 					continue
 				} else if wgPubKey == "" {
-					return nil, fmt.Errorf("%w: for node %s", ErrNoWireguardKey, node.Hostname)
+					return nil, fmt.Errorf("no wireguard public key found: for node %s", node.Hostname)
 				}
 
 				server.VPN = vpn.Wireguard