go-multierror is a package for Go that provides a mechanism for
representing a list of error values as a single error.
This allows a function in Go to return an error that might actually
be a list of errors. If the caller knows this, they can unwrap the
list and access the errors. If the caller doesn't know, the error
formats to a nice human-readable format.
go-multierror implements the
errwrap interface so that it can
be used with that library, as well.
Install using go get github.com/hashicorp/go-multierror.
Full documentation is available at
http://godoc.org/github.com/hashicorp/go-multierror
go-multierror is easy to use and purposely built to be unobtrusive in
existing Go applications/libraries that may not be aware of it.
Building a list of errors
The Append function is used to create a list of errors. This function
behaves a lot like the Go built-in append function: it doesn't matter
if the first argument is nil, a multierror.Error, or any other error,
the function behaves as you would expect.
var result error
if err := step1(); err != nil {
result = multierror.Append(result, err)
}
if err := step2(); err != nil {
result = multierror.Append(result, err)
}
return result
Customizing the formatting of the errors
By specifying a custom ErrorFormat, you can customize the format
of the Error() string function:
var result *multierror.Error
// ... accumulate errors here, maybe using Append
if result != nil {
result.ErrorFormat = func([]error) string {
return "errors!"
}
}
Accessing the list of errors
multierror.Error implements error so if the caller doesn't know about
multierror, it will work just fine. But if you're aware a multierror might
be returned, you can use type switches to access the list of errors:
if err := something(); err != nil {
if merr, ok := err.(*multierror.Error); ok {
// Use merr.Errors
}
}
Returning a multierror only if there are errors
If you build a multierror.Error, you can use the ErrorOrNil function
to return an error implementation only if there are errors to return:
var result *multierror.Error
// ... accumulate errors here
// Return the `error` only if errors were added to the multierror, otherwise
// return nil since there are no errors.
return result.ErrorOrNil()