README
¶
go-multierror
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 is fully compatible with the Go standard library
errors package, including the
functions As, Is, and Unwrap. This provides a standardized approach
for introspecting on error values.
Installation and Docs
Install using go get github.com/hashicorp/go-multierror.
Full documentation is available at https://pkg.go.dev/github.com/hashicorp/go-multierror
Requires go version 1.13 or newer
go-multierror requires go version 1.13 or newer. Go 1.13 introduced
error wrapping, which
this library takes advantage of.
If you need to use an earlier version of go, you can use the v1.0.0 tag, which doesn't rely on features in go 1.13.
If you see compile errors that look like the below, it's likely that you're on an older version of go:
/go/src/github.com/hashicorp/go-multierror/multierror.go:112:9: undefined: errors.As
/go/src/github.com/hashicorp/go-multierror/multierror.go:117:9: undefined: errors.Is
Usage
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
}
}
You can also use the standard errors.Unwrap
function. This will continue to unwrap into subsequent errors until none exist.
Extracting an error
The standard library errors.As
function can be used directly with a multierror to extract a specific error:
// Assume err is a multierror value
err := somefunc()
// We want to know if "err" has a "RichErrorType" in it and extract it.
var errRich RichErrorType
if errors.As(err, &errRich) {
// It has it, and now errRich is populated.
}
Checking for an exact error value
Some errors are returned as exact errors such as the ErrNotExist
error in the os package. You can check if this error is present by using
the standard errors.Is function.
// Assume err is a multierror value
err := somefunc()
if errors.Is(err, os.ErrNotExist) {
// err contains os.ErrNotExist
}
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()
Documentation
¶
Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func ListFormatFunc ¶
ListFormatFunc is a basic formatter that outputs the number of errors that occurred along with a bullet point list of the errors.
Types ¶
type Error ¶
type Error struct {
Errors []error
ErrorFormat ErrorFormatFunc
}
Error is an error type to track multiple errors. This is used to accumulate errors in cases and return them as a single "error".
func Append ¶
Append is a helper function that will append more errors onto an Error in order to create a larger multi-error.
If err is not a multierror.Error, then it will be turned into one. If any of the errs are multierr.Error, they will be flattened one level into err. Any nil errors within errs will be ignored. If err is nil, a new *Error will be returned.
func (*Error) ErrorOrNil ¶
ErrorOrNil returns an error interface if this Error represents a list of errors, or returns nil if the list of errors is empty. This function is useful at the end of accumulation to make sure that the value returned represents the existence of errors.
func (*Error) Unwrap ¶ added in v1.1.0
Unwrap returns an error from Error (or nil if there are no errors). This error returned will further support Unwrap to get the next error, etc. The order will match the order of Errors in the multierror.Error at the time of calling.
The resulting error supports errors.As/Is/Unwrap so you can continue to use the stdlib errors package to introspect further.
This will perform a shallow copy of the errors slice. Any errors appended to this error after calling Unwrap will not be available until a new Unwrap is called on the multierror.Error.
func (*Error) WrappedErrors ¶
WrappedErrors returns the list of errors that this Error is wrapping. It is an implementation of the errwrap.Wrapper interface so that multierror.Error can be used with that library.
This method is not safe to be called concurrently. Unlike accessing the Errors field directly, this function also checks if the multierror is nil to prevent a null-pointer panic. It satisfies the errwrap.Wrapper interface.
type ErrorFormatFunc ¶
ErrorFormatFunc is a function callback that is called by Error to turn the list of errors into a string.
type Group ¶ added in v1.1.0
type Group struct {
// contains filtered or unexported fields
}
Group is a collection of goroutines which return errors that need to be coalesced.
Source Files