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Table of Contents
Use the standard library errors for error judgment
Customize error types and implement wrappers
Best practices for wrong packaging
Home Backend Development Golang How to wrap errors in golang

How to wrap errors in golang

Jul 07, 2025 am 01:39 AM

In Go language, error handling realizes context transmission and type recognition through explicit wrapping and judgment. Use fmt.Errorf with the %w verb to preserve the original error and add context, which facilitates subsequent judgment or extraction of specific error types through errors.Is and errors.As; when customizing error types, you need to embed the original error and implement the Unwrap method to support chain judgment; best practices include avoiding redundant wrapping, retaining critical contexts, using %w with caution, and outputting a complete error chain with %v in the log.

How to wrap errors in golang

In Go language, error handling is an important part of program development. Go's design philosophy tends to handle errors explicitly rather than using exception mechanisms. Therefore, it becomes very important to "wrap" the error so that the location and context information of the error occurred can be clearly seen on the call chain.

How to wrap errors in golang

Wrapping error using fmt.Errorf

The most basic way is to use the fmt.Errorf function to add more information based on the original error and retain the original error. Starting from Go 1.13, fmt.Errorf supports %w verbs to wrap errors:

How to wrap errors in golang
 if err != nil {
    return fmt.Errorf("failed to read config: %w", err)
}

The benefits of doing this are:

  • The original error message is retained for subsequent inspection.
  • The original error type can be judged or extracted by errors.Is and errors.As .

It should be noted that %w should be used only if you want the external caller to be able to recognize and handle the original error . If you just want to add context and don't want to expose the original error, you can use %w instead of %v or other formats.

How to wrap errors in golang

Use the standard library errors for error judgment

After wrapping an error, we usually need to judge the error type at the upper layer of the call chain or obtain the error information of a specific type. At this time, errors.Is and errors.As are needed:

  • errors.Is(err, target error) : determines whether an error is equal to the target error.
  • errors.As(err, target interface{}) : Try to convert the error to a specific type.

For example:

 if errors.Is(err, os.ErrNotExist) {
    // Handle the case where the file does not exist}

var pathErr *fs.PathError
if errors.As(err, &pathErr) {
    // Handle path error}

These two functions will automatically traverse the wrapped error chain until a match is found.


Customize error types and implement wrappers

Sometimes you need to customize the error type to carry more context information, such as operation name, file path, etc. You can embed original errors in the structure to implement error chains:

 type MyError struct {
    Msg string
    Op string
    Err error
}

func (e *MyError) Error() string {
    return fmt.Sprintf("%s: %s (%v)", e.Op, e.Msg, e.Err)
}

func (e *MyError) Unwrap() error {
    return e.Err return e.
}

This way you can construct the error like this:

 return &MyError{Msg: "open failed", Op: "readFile", Err: os.ErrNotExist}

Then use errors.Is and errors.As to make the judgment, just like a normal error.


Best practices for wrong packaging

  • Don't over-package : adding once to each layer may cause redundant error messages.
  • Maintain the critical context : such as the error operation name, parameters, location, etc., this information is very helpful for troubleshooting problems.
  • Be cautious when using %w : not every error needs to be exposed to the caller.
  • Output a complete error chain when logging : print the error using % v formatting method, and you can see the complete stack information (if the underlying support).

Basically that's it. Although Go's error packaging mechanism is simple, if you want to use it well, you still need to pay more attention to context delivery and error type encapsulation.

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