refactor: move from io/ioutil to io and os packages

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

alerting/provider/custom/custom.go

@@ -3,7 +3,7 @@ package custom
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"strings"
 
@@ -105,7 +105,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 		return err
 	}
 	if response.StatusCode > 399 {
-		body, _ := ioutil.ReadAll(response.Body)
+		body, _ := io.ReadAll(response.Body)
 		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
 	}
 	return err

alerting/provider/custom/custom_test.go

@@ -1,7 +1,7 @@
 package custom
 
 import (
-	"io/ioutil"
+	"io"
 	"net/http"
 	"testing"
 
@@ -113,7 +113,7 @@ func TestAlertProvider_buildHTTPRequestWhenResolved(t *testing.T) {
 	if request.URL.String() != ExpectedURL {
 		t.Error("expected URL to be", ExpectedURL, "was", request.URL.String())
 	}
-	body, _ := ioutil.ReadAll(request.Body)
+	body, _ := io.ReadAll(request.Body)
 	if string(body) != ExpectedBody {
 		t.Error("expected body to be", ExpectedBody, "was", string(body))
 	}
@@ -133,7 +133,7 @@ func TestAlertProvider_buildHTTPRequestWhenTriggered(t *testing.T) {
 	if request.URL.String() != ExpectedURL {
 		t.Error("expected URL to be", ExpectedURL, "was", request.URL.String())
 	}
-	body, _ := ioutil.ReadAll(request.Body)
+	body, _ := io.ReadAll(request.Body)
 	if string(body) != ExpectedBody {
 		t.Error("expected body to be", ExpectedBody, "was", string(body))
 	}
@@ -158,7 +158,7 @@ func TestAlertProvider_buildHTTPRequestWithCustomPlaceholder(t *testing.T) {
 	if request.URL.String() != ExpectedURL {
 		t.Error("expected URL to be", ExpectedURL, "was", request.URL.String())
 	}
-	body, _ := ioutil.ReadAll(request.Body)
+	body, _ := io.ReadAll(request.Body)
 	if string(body) != ExpectedBody {
 		t.Error("expected body to be", ExpectedBody, "was", string(body))
 	}
@@ -205,7 +205,7 @@ func TestAlertProvider_isBackwardCompatibleWithServiceRename(t *testing.T) {
 	if request.URL.String() != ExpectedURL {
 		t.Error("expected URL to be", ExpectedURL, "was", request.URL.String())
 	}
-	body, _ := ioutil.ReadAll(request.Body)
+	body, _ := io.ReadAll(request.Body)
 	if string(body) != ExpectedBody {
 		t.Error("expected body to be", ExpectedBody, "was", string(body))
 	}

alerting/provider/discord/discord.go

@@ -3,7 +3,7 @@ package discord
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 
 	"github.com/TwiN/gatus/v3/alerting/alert"
@@ -37,7 +37,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 		return err
 	}
 	if response.StatusCode > 399 {
-		body, _ := ioutil.ReadAll(response.Body)
+		body, _ := io.ReadAll(response.Body)
 		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
 	}
 	return err

alerting/provider/mattermost/mattermost.go

@@ -3,7 +3,7 @@ package mattermost
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 
 	"github.com/TwiN/gatus/v3/alerting/alert"
@@ -43,7 +43,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 		return err
 	}
 	if response.StatusCode > 399 {
-		body, _ := ioutil.ReadAll(response.Body)
+		body, _ := io.ReadAll(response.Body)
 		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
 	}
 	return err

alerting/provider/messagebird/messagebird.go

@@ -3,7 +3,7 @@ package messagebird
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 
 	"github.com/TwiN/gatus/v3/alerting/alert"
@@ -45,7 +45,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 		return err
 	}
 	if response.StatusCode > 399 {
-		body, _ := ioutil.ReadAll(response.Body)
+		body, _ := io.ReadAll(response.Body)
 		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
 	}
 	return err

alerting/provider/pagerduty/pagerduty.go

@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"net/http"
 
@@ -64,7 +64,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 		return err
 	}
 	if response.StatusCode > 399 {
-		body, _ := ioutil.ReadAll(response.Body)
+		body, _ := io.ReadAll(response.Body)
 		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
 	}
 	if alert.IsSendingOnResolved() {
@@ -73,7 +73,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 			alert.ResolveKey = ""
 		} else {
 			// We need to retrieve the resolve key from the response
-			body, err := ioutil.ReadAll(response.Body)
+			body, err := io.ReadAll(response.Body)
 			var payload pagerDutyResponsePayload
 			if err = json.Unmarshal(body, &payload); err != nil {
 				// Silently fail. We don't want to create tons of alerts just because we failed to parse the body.

alerting/provider/slack/slack.go

@@ -3,7 +3,7 @@ package slack
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 
 	"github.com/TwiN/gatus/v3/alerting/alert"
@@ -37,7 +37,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 		return err
 	}
 	if response.StatusCode > 399 {
-		body, _ := ioutil.ReadAll(response.Body)
+		body, _ := io.ReadAll(response.Body)
 		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
 	}
 	return err

alerting/provider/teams/teams.go

@@ -3,7 +3,7 @@ package teams
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 
 	"github.com/TwiN/gatus/v3/alerting/alert"
@@ -37,7 +37,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 		return err
 	}
 	if response.StatusCode > 399 {
-		body, _ := ioutil.ReadAll(response.Body)
+		body, _ := io.ReadAll(response.Body)
 		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
 	}
 	return err

alerting/provider/telegram/telegram.go

@@ -3,7 +3,7 @@ package telegram
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 
 	"github.com/TwiN/gatus/v3/alerting/alert"
@@ -38,7 +38,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 		return err
 	}
 	if response.StatusCode > 399 {
-		body, _ := ioutil.ReadAll(response.Body)
+		body, _ := io.ReadAll(response.Body)
 		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
 	}
 	return err

alerting/provider/twilio/twilio.go

@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"encoding/base64"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/url"
 
@@ -43,7 +43,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 		return err
 	}
 	if response.StatusCode > 399 {
-		body, _ := ioutil.ReadAll(response.Body)
+		body, _ := io.ReadAll(response.Body)
 		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
 	}
 	return err