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/updater/html/fetch.go

@@ -2,15 +2,12 @@ package html
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"net/http"
 
 	"golang.org/x/net/html"
 )
 
-var ErrHTTPStatusCodeNotOK = errors.New("HTTP status code is not OK")
-
 func Fetch(ctx context.Context, client *http.Client, url string) (
 	rootNode *html.Node, err error,
 ) {
@@ -25,7 +22,7 @@ func Fetch(ctx context.Context, client *http.Client, url string) (
 	}
 
 	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/updater/html/fetch_test.go

@@ -37,21 +37,18 @@ func Test_Fetch(t *testing.T) {
 		responseStatus int
 		responseBody   io.ReadCloser
 		rootNode       *html.Node
-		errWrapped     error
 		errMessage     string
 	}{
 		"context canceled": {
 			ctx:        canceledCtx,
 			url:        "https://example.com/path",
-			errWrapped: context.Canceled,
 			errMessage: `Get "https://example.com/path": context canceled`,
 		},
 		"response status not ok": {
 			ctx:            context.Background(),
 			url:            "https://example.com/path",
 			responseStatus: http.StatusNotFound,
-			errWrapped:     ErrHTTPStatusCodeNotOK,
-			errMessage:     `HTTP status code is not OK: 404 Not Found`,
+			errMessage:     `HTTP status code not OK: 404 Not Found`,
 		},
 		"success": {
 			ctx:            context.Background(),
@@ -86,9 +83,10 @@ func Test_Fetch(t *testing.T) {
 
 			rootNode, err := Fetch(testCase.ctx, client, testCase.url)
 
-			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.rootNode, rootNode)
 		})

internal/updater/loop/state.go

@@ -2,7 +2,6 @@ package loop
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"reflect"
 	"sync"
@@ -31,8 +30,6 @@ func (l *Loop) GetStatus() (status models.LoopStatus) {
 	return l.state.status
 }
 
-var ErrInvalidStatus = errors.New("invalid status")
-
 func (l *Loop) SetStatus(ctx context.Context, status models.LoopStatus) (outcome string, err error) {
 	l.state.statusMu.Lock()
 	defer l.state.statusMu.Unlock()
@@ -79,8 +76,8 @@ func (l *Loop) SetStatus(ctx context.Context, status models.LoopStatus) (outcome
 		l.state.status = newStatus
 		return status.String(), nil
 	default:
-		return "", fmt.Errorf("%w: %s: it can only be one of: %s, %s",
-			ErrInvalidStatus, status, constants.Running, constants.Stopped)
+		return "", fmt.Errorf("invalid status: %s: it can only be one of: %s, %s",
+			status, constants.Running, constants.Stopped)
 	}
 }
 

internal/updater/openvpn/extract.go

@@ -8,12 +8,6 @@ import (
 	"strings"
 )
 
-var (
-	ErrUnknownProto = errors.New("unknown protocol")
-	ErrNoRemoteHost = errors.New("remote host not found")
-	ErrNoRemoteIP   = errors.New("remote IP not found")
-)
-
 func ExtractProto(b []byte) (tcp, udp bool, err error) {
 	lines := strings.Split(string(b), "\n")
 	const protoPrefix = "proto "
@@ -30,7 +24,7 @@ func ExtractProto(b []byte) (tcp, udp bool, err error) {
 		case "udp", "udp4", "udp6":
 			return false, true, nil
 		default:
-			return false, false, fmt.Errorf("%w: %s", ErrUnknownProto, s)
+			return false, false, fmt.Errorf("unknown protocol: %s", s)
 		}
 	}
 
@@ -45,7 +39,7 @@ func ExtractHost(b []byte) (host, warning string, err error) {
 	)
 	hosts := extractRemoteHosts(b, rejectIP, rejectDomain)
 	if len(hosts) == 0 {
-		return "", "", ErrNoRemoteHost
+		return "", "", errors.New("remote host not found")
 	} else if len(hosts) > 1 {
 		warning = fmt.Sprintf(
 			"only using the first host %q and discarding %d other hosts",
@@ -58,7 +52,7 @@ func ExtractIPs(b []byte) (ips []netip.Addr, err error) {
 	const rejectIP, rejectDomain = false, true
 	ipStrings := extractRemoteHosts(b, rejectIP, rejectDomain)
 	if len(ipStrings) == 0 {
-		return nil, ErrNoRemoteIP
+		return nil, errors.New("remote IP not found")
 	}
 
 	sort.Slice(ipStrings, func(i, j int) bool {

internal/updater/openvpn/fetch.go

@@ -19,7 +19,7 @@ func FetchFile(ctx context.Context, client *http.Client, url string) (
 	const rejectDomain = false
 	hosts := extractRemoteHosts(b, rejectIP, rejectDomain)
 	if len(hosts) == 0 {
-		return "", fmt.Errorf("%w for url %s", ErrNoRemoteHost, url)
+		return "", fmt.Errorf("remote host not found for url %s", url)
 	}
 
 	return hosts[0], nil

internal/updater/providers.go

@@ -15,8 +15,6 @@ type Provider interface {
 	FetchServers(ctx context.Context, minServers int) (servers []models.Server, err error)
 }
 
-var ErrServerHasNotEnoughInformation = errors.New("server has not enough information")
-
 func (u *Updater) updateProvider(ctx context.Context, provider Provider,
 	minRatio float64,
 ) (err error) {

internal/updater/resolver/parallel.go

@@ -2,7 +2,6 @@ package resolver
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"net/netip"
 )
@@ -34,11 +33,6 @@ type parallelResult struct {
 	IPs  []netip.Addr
 }
 
-var (
-	ErrMinFound     = errors.New("not enough hosts found")
-	ErrMaxFailRatio = errors.New("maximum failure ratio reached")
-)
-
 func (pr *Parallel) Resolve(ctx context.Context, settings ParallelSettings) (
 	hostToIPs map[string][]netip.Addr, warnings []string, err error,
 ) {
@@ -90,7 +84,7 @@ func (pr *Parallel) Resolve(ctx context.Context, settings ParallelSettings) (
 	failureRatio := float64(len(warnings)) / float64(len(settings.Hosts))
 	if failureRatio > settings.MaxFailRatio {
 		return hostToIPs, warnings,
-			fmt.Errorf("%w: %.2f failure ratio reached", ErrMaxFailRatio, failureRatio)
+			fmt.Errorf("maximum failure ratio reached: %.2f failure ratio reached", failureRatio)
 	}
 
 	return hostToIPs, warnings, nil

internal/updater/resolver/repeat.go

@@ -2,7 +2,6 @@ package resolver
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"net"
 	"net/netip"
@@ -62,11 +61,6 @@ func (r *Repeat) Resolve(ctx context.Context, host string, settings RepeatSettin
 	return ips, nil
 }
 
-var (
-	ErrMaxNoNew = errors.New("reached the maximum number of no new update")
-	ErrMaxFails = errors.New("reached the maximum number of consecutive failures")
-)
-
 func (r *Repeat) resolveOnce(ctx, timedCtx context.Context, host string,
 	settings RepeatSettings, uniqueIPs map[string]struct{}, noNewCounter, failCounter int) (
 	newNoNewCounter, newFailCounter int, err error,
@@ -75,8 +69,8 @@ func (r *Repeat) resolveOnce(ctx, timedCtx context.Context, host string,
 	if err != nil {
 		failCounter++
 		if settings.MaxFails > 0 && failCounter == settings.MaxFails {
-			return noNewCounter, failCounter, fmt.Errorf("%w: %d failed attempts resolving %s: %s",
-				ErrMaxFails, settings.MaxFails, host, err)
+			return noNewCounter, failCounter, fmt.Errorf("reached the maximum number of consecutive failures: "+
+				"%d failed attempts resolving %s: %s", settings.MaxFails, host, err)
 		}
 		// it's fine to fail some of the resolutions
 		return noNewCounter, failCounter, nil
@@ -100,8 +94,9 @@ func (r *Repeat) resolveOnce(ctx, timedCtx context.Context, host string,
 		// we reached the maximum number of resolutions without
 		// finding any new IP address to our unique IP addresses set.
 		return noNewCounter, failCounter,
-			fmt.Errorf("%w: %d times no updated for %d IP addresses found",
-				ErrMaxNoNew, noNewCounter, len(uniqueIPs))
+			fmt.Errorf("reached the maximum number of no new update: "+
+				"%d times no updated for %d IP addresses found",
+				noNewCounter, len(uniqueIPs))
 	}
 
 	timer := time.NewTimer(settings.BetweenDuration)

internal/updater/unzip/fetch.go

@@ -2,14 +2,11 @@ package unzip
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"io"
 	"net/http"
 )
 
-var ErrHTTPStatusCodeNotOK = errors.New("HTTP status code not OK")
-
 func (u *Unzipper) FetchAndExtract(ctx context.Context, url string) (
 	contents map[string][]byte, err error,
 ) {
@@ -26,7 +23,7 @@ func (u *Unzipper) FetchAndExtract(ctx context.Context, url string) (
 	defer response.Body.Close()
 
 	if response.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("%w: %s: %d %s", ErrHTTPStatusCodeNotOK,
+		return nil, fmt.Errorf("HTTP status code not OK: %s: %d %s",
 			url, response.StatusCode, response.Status)
 	}