53 lines
2.2 KiB
Markdown
53 lines
2.2 KiB
Markdown
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# errors [](https://travis-ci.org/pkg/errors) [](http://godoc.org/github.com/pkg/errors) [](https://goreportcard.com/report/github.com/pkg/errors)
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Package errors implements functions for manipulating errors.
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The traditional error handling idiom in Go is roughly akin to
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```
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if err != nil {
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return err
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}
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```
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which applied recursively up the call stack results in error reports without context or debugging information. The errors package allows programmers to add context to the failure path in their code in a way that does not destroy the original value of the error.
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## Adding context to an error
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The errors.Wrap function returns a new error that adds context to the original error. For example
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```
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_, err := ioutil.ReadAll(r)
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if err != nil {
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return errors.Wrap(err, "read failed")
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}
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```
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In addition, `errors.Wrap` records the file and line where it was called, allowing the programmer to retrieve the path to the original error.
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## Retrieving the cause of an error
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Using `errors.Wrap` constructs a stack of errors, adding context to the preceding error. Depending on the nature of the error it may be necessary to recurse the operation of errors.Wrap to retrieve the original error for inspection. Any error value which implements this interface can be inspected by `errors.Cause`.
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```
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type causer interface {
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Cause() error
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}
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```
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`errors.Cause` will recursively retrieve the topmost error which does not implement `causer`, which is assumed to be the original cause. For example:
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```
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switch err := errors.Cause(err).(type) {
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case *MyError:
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// handle specifically
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default:
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// unknown error
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}
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```
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Would you like to know more? Read the [blog post](http://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully).
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## Contributing
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We welcome pull requests, bug fixes and issue reports. With that said, the bar for adding new symbols to this package is intentionally set high.
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Before proposing a change, please discuss your change by raising an issue.
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## Licence
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MIT
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