Fix: Correctly handle ErrInvalidSignature comparison (#429)

* Fix: Correctly handle ErrInvalidSignature comparison

This commit addresses an issue in the error handling logic within the echo_bot and kitchensink examples, where the ErrInvalidSignature error from the linebot package was not being correctly identified due to a direct comparison with the error interface.

By updating the comparison to use err.Error() == linebot.ErrInvalidSignature.Error(), we ensure that the error messages are compared as strings, which is a more reliable method for identifying this specific error.

This change results in the appropriate HTTP status codes being returned (400 for invalid signatures, 500 for other errors), improving the error feedback for API consumers.

Affected files:
- examples/echo_bot/server.go
- examples/kitchensink/server.go

* Refactor: Use errors.Is for ErrInvalidSignature checks

This commit updates the error checking logic in both the echo_bot and kitchensink examples to use the standard errors.Is function for identifying ErrInvalidSignature errors. This change enhances the readability and maintainability of the code by utilizing the idiomatic approach for error comparison in Go. It also ensures more reliable error handling by correctly identifying wrapped errors.

Changes include:
- Importing the "errors" package in both server.go files.
- Replacing direct error message comparisons with errors.Is for ErrInvalidSignature checks.

This update follows best practices for error handling in Go and aligns with the Go community's recommendations.

* Add: missing echo_bot/server.go file to previous commit

examples/echo_bot/server.go

@@ -15,12 +15,12 @@
 package main
 
 import (
+ "errors"
  "fmt"
  "log"
  "net/http"
  "os"
 
- "github.com/line/line-bot-sdk-go/v8/linebot"
  "github.com/line/line-bot-sdk-go/v8/linebot/messaging_api"
  "github.com/line/line-bot-sdk-go/v8/linebot/webhook"
 )
@@ -41,7 +41,7 @@ func main() {
  cb, err := webhook.ParseRequest(channelSecret, req)
  if err != nil {
  log.Printf("Cannot parse request: %+v\n", err)
- if err == linebot.ErrInvalidSignature {
+ if errors.Is(err, webhook.ErrInvalidSignature) {
  w.WriteHeader(400)
  } else {
  w.WriteHeader(500)

examples/kitchensink/server.go

@@ -16,6 +16,7 @@ package main
 
 import (
  "encoding/json"
+ "errors"
  "fmt"
  "io"
  "log"
@@ -25,7 +26,6 @@ import (
  "path/filepath"
  "runtime"
 
- "github.com/line/line-bot-sdk-go/v8/linebot"
  "github.com/line/line-bot-sdk-go/v8/linebot/messaging_api"
  "github.com/line/line-bot-sdk-go/v8/linebot/webhook"
 )
@@ -106,7 +106,7 @@ func NewKitchenSink(channelSecret, channelToken, appBaseURL string) (*KitchenSin
 func (app *KitchenSink) Callback(w http.ResponseWriter, r *http.Request) {
  cb, err := webhook.ParseRequest(app.channelSecret, r)
  if err != nil {
- if err == linebot.ErrInvalidSignature {
+ if errors.Is(err, webhook.ErrInvalidSignature) {
  w.WriteHeader(400)
  } else {
  w.WriteHeader(500)