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81 lines
2.5 KiB
Go
81 lines
2.5 KiB
Go
// Copyright 2013, 2014 Canonical Ltd.
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// Licensed under the LGPLv3, see LICENCE file for details.
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/*
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[godoc-link-here]
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The juju/errors provides an easy way to annotate errors without losing the
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orginal error context.
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The exported `New` and `Errorf` functions are designed to replace the
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`errors.New` and `fmt.Errorf` functions respectively. The same underlying
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error is there, but the package also records the location at which the error
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was created.
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A primary use case for this library is to add extra context any time an
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error is returned from a function.
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if err := SomeFunc(); err != nil {
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return err
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}
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This instead becomes:
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if err := SomeFunc(); err != nil {
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return errors.Trace(err)
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}
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which just records the file and line number of the Trace call, or
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if err := SomeFunc(); err != nil {
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return errors.Annotate(err, "more context")
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}
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which also adds an annotation to the error.
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When you want to check to see if an error is of a particular type, a helper
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function is normally exported by the package that returned the error, like the
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`os` package does. The underlying cause of the error is available using the
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`Cause` function.
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os.IsNotExist(errors.Cause(err))
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The result of the `Error()` call on an annotated error is the annotations joined
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with colons, then the result of the `Error()` method for the underlying error
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that was the cause.
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err := errors.Errorf("original")
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err = errors.Annotatef(err, "context")
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err = errors.Annotatef(err, "more context")
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err.Error() -> "more context: context: original"
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Obviously recording the file, line and functions is not very useful if you
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cannot get them back out again.
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errors.ErrorStack(err)
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will return something like:
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first error
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github.com/juju/errors/annotation_test.go:193:
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github.com/juju/errors/annotation_test.go:194: annotation
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github.com/juju/errors/annotation_test.go:195:
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github.com/juju/errors/annotation_test.go:196: more context
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github.com/juju/errors/annotation_test.go:197:
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The first error was generated by an external system, so there was no location
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associated. The second, fourth, and last lines were generated with Trace calls,
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and the other two through Annotate.
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Sometimes when responding to an error you want to return a more specific error
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for the situation.
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if err := FindField(field); err != nil {
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return errors.Wrap(err, errors.NotFoundf(field))
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}
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This returns an error where the complete error stack is still available, and
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`errors.Cause()` will return the `NotFound` error.
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*/
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package errors
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