Error Handling in Golang: How to Prevent Application Stop
Tags: go, programming, learning
Published: 2023-05-17 13:47:52

Golang is a programming language that has gained immense popularity among developers due to its robust performance and simplicity. However, like any other programming language, Golang handles errors in its own way. 
 
In this article, we’ll dive deep into how Golang handles errors and explore some effective ways to prevent your application from stopping. 
 
### Error Handling in Golang 
 
In Golang, errors are represented as values of the built-in  error  type. Golang provides a simple, yet effective, way of handling errors using the  err  syntax:

```
if err != nil {
    // handle the error
}
```
This syntax checks if the value of the error is  nil , which means there was no error. If the error is not  nil , the code inside the  if  block is executed, which handles the error. 
 
However, one of the biggest mistakes that developers make while handling errors in Golang is to ignore them. Ignoring errors can lead to unexpected application behavior, and in some cases, even result in application stop. 
 
### Preventing Application Stop 
 
#### 1. Logging Errors 
 
One of the most common ways to prevent application stop due to errors is by logging errors. You can use the  log  package provided by Golang to log errors to the console or a file. Here is an example:

```
import (
    "log"
    "os"
)
 func main() {
    file, err := os.Open("file.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()
     // your code here
}
```
In this example, we’re using the  log.Fatal()  method to log the error and stop the application. 
 
#### 2. Recovering from Panics 
 
Another way to prevent application stop is by recovering from panics. A panic is a built-in function in Golang that stops the current goroutine and starts the panic sequence. To recover from a panic sequence, you can use the  recover()  function.

```
func main() {
    defer func() {
        if r := recover(); r != nil {
            log.Println("Recovered from panic:", r)
        }
    }()
     panic("Something went wrong")
}
```
In this example, we’re using the  defer  statement to register a function that will be called when the panic sequence starts. This function uses the  recover()  function to stop the panic sequence and log the error. 
 
#### 3. Graceful Shutdown 
 
The third way to prevent application stop is by using graceful shutdown. Graceful shutdown is a technique used to stop an application gracefully without losing any data. Here’s an example of how to implement graceful shutdown in Golang:

```
import (
    "context"
    "os"
    "os/signal"
    "syscall"
)
 func main() {
    ctx, cancel := context.WithCancel(context.Background())
     c := make(chan os.Signal, 1)
    signal.Notify(c, os.Interrupt, syscall.SIGTERM)
     go func() {
        <-c
        cancel()
    }()
     // your code here
     <-ctx.Done()
    log.Println("Application stopped gracefully")
}
```
In this example, we’re creating a  context  object and a  cancel  function. We’re also creating a channel to listen for signals that may cause the application to stop, like  SIGTERM  or  os.Interrupt . When one of these signals is received, the  cancel  function is called to stop the application gracefully. 

### Some best practices for error handling in Golang

 1 - **Always handle errors**: In Golang, it's essential to handle errors correctly. Ignoring errors can lead to unexpected behavior and even cause your application to crash. When you encounter an error, you should handle it appropriately. You can log the error, return an error value to the caller, or use panic and recover to handle errors. 

```
file, err := os.Open("filename.txt")
if err != nil {
   log.Fatal(err)
}
defer file.Close()
// your code here
```
In this example, we're using the  os.Open()  function to open a file. If an error occurs, we log the error and stop the program. If there's no error, we defer closing the file and continue with our code.

 2 - **Use descriptive error messages**: When you encounter an error, make sure the error message is descriptive and helpful. The error message should contain information about what went wrong and where the error occurred. This information can help you debug the error and fix it quickly.

```
_, err := http.Get("http://example.com")
if err != nil {
   log.Printf("Error making HTTP request: %s", err)
}
```
In this example, we're making an HTTP request using the  http.Get()>  function. If an error occurs, we log the error with a descriptive message. 
 
 3 - **Wrap errors**: When you call a function that returns an error, it's a good practice to wrap the error with additional information. Wrapping errors can help you understand the context in which the error occurred and help you debug the error more easily. 

```
func doSomething() error {
   _, err := someFunction()
   if err != nil {
      return fmt.Errorf("Error doing something: %w", err)
   }
   // your code here
   return nil
}
```
In this example, we're wrapping the error returned by the  someFunction()  function with additional context information using the  fmt.Errorf()  function. 

 4 - **Use error types**: In Golang, you can define custom error types. Using error types can make your error handling more robust and help you distinguish between different types of errors. For example, you can define an error type for network errors, database errors, or file system errors. 

```
type MyError struct {
   Msg string
   Code int
}
func (e *MyError) Error() string {
   return e.Msg
}
func doSomething() error {
   _, err := someFunction()
   if err != nil {
      return &MyError{
         Msg: "Error doing something",
         Code: 500,
      }
   }
   // your code here
   return nil
}
```
In this example, we're defining a custom error type  MyError  and using it to return a specific error when an error occurs in the  doSomething()  function. 

 5 - **Use defer**: Defer is a built-in function in Golang that allows you to schedule a function call to execute after the current function returns. Using defer can help you avoid forgetting to handle errors by ensuring that the error handling code is always executed. 

```
file, err := os.Open("filename.txt")
if err != nil {
   log.Fatal(err)
}
defer file.Close()
// your code here
```
In this example, we're using  defer  to ensure that the  file.Close()  function is always called, even if an error occurs.

 6 - **Use context**: Context is a powerful concept in Golang that allows you to propagate deadlines and other request-scoped values across API boundaries and between processes. Using context can help you manage errors more effectively by providing a way to cancel an operation or request if it takes too long to complete. 

```
func doSomething(ctx context.Context) error {
   // set a deadline of 10 seconds
   ctx, cancel := context.WithDeadline(ctx, time.Now().Add(10*time.Second))
   defer cancel() // cancel the context when the function returns
   // your code here
   return nil
}
```
In this example, we're using  context  to set a deadline of 10 seconds for an operation. If the operation takes longer than 10 seconds, the context is canceled and an error is returned.
 
By following these best practices, you can ensure that your Golang code is more robust and that your error handling is effective.
 
### Conclusion 
 
Error handling is an essential part of any programming language, and Golang is no exception. By following the methods outlined in this article, you can effectively handle errors in your Golang applications and prevent them from stopping unexpectedly.