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feat: add package to handle end-user error messages.
Because - Connector errors produce an unfriendly output in VDP. - In order to trigger a pipeline, several repositories are involved in the execution. This commit - Implements a way to add and extract end-user messages to errors.
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# errmsg | ||
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Add end-user messages to errors. | ||
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`err.Error()` doesn't usually provide a human-friendly output. `errmsg` allows | ||
errors to carry an (extendable) end-user message that can be used in e.g. | ||
handlers. | ||
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Here is an example on how it can be used: | ||
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```go | ||
package connector | ||
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import ( | ||
// ... | ||
"github.com/instill-ai/x/errmsg" | ||
) | ||
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func (c *Client) sendReq(reqURL, method, contentType string, data io.Reader) ([]byte, error) { | ||
// ... | ||
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res, err := c.HTTPClient.Do(req) | ||
if err != nil { | ||
err := fmt.Errorf("failed to call connector vendor: %w", err) | ||
return nil, errmsg.AddMessage(err, "Failed to call Vendor API.") | ||
} | ||
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if res.StatusCode < 200 || res.StatusCode >= 300 { | ||
err := fmt.Errorf("vendor responded with status code %d", res.StatusCode) | ||
msg := fmt.Sprintf("Vendor responded with a %d status code.", res.StatusCode) | ||
return nil, errmsg.AddMessage(err, msg) | ||
} | ||
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// ... | ||
} | ||
``` | ||
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```go | ||
package handler | ||
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func (h *PublicHandler) DoAction(ctx context.Context, req *pb.DoActionRequest) (*pb.DoActionResponse, error) { | ||
resp, err := h.triggerActionSteps(ctx, req) | ||
if err != nil { | ||
resp.Outputs, resp.Metadata, err = h.triggerNamespacePipeline(ctx, req) | ||
return nil, status.Error(asGRPCStatus(err), errmsg.MessageOrErr(err)) | ||
} | ||
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return resp, nil | ||
} | ||
``` |
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package errmsg | ||
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import ( | ||
"errors" | ||
"fmt" | ||
) | ||
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// endUserError is an error that holds an end-user message. | ||
type endUserError struct { | ||
message string | ||
cause error | ||
} | ||
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// Error implements the error interface by returning the internal error message. | ||
func (e *endUserError) Error() string { return e.cause.Error() } | ||
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// Unwrap implements the Unwrap interface. | ||
func (e *endUserError) Unwrap() error { return e.cause } | ||
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// As implements the required function to ensure errors.As can properly match | ||
// endUserEror targets. | ||
func (e *endUserError) As(target any) bool { | ||
if tgt, ok := target.(**endUserError); ok { | ||
*tgt = e | ||
return true | ||
} | ||
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return false | ||
} | ||
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// AddMessage adds an end-user message to an error, prepending it to any | ||
// potential existing message. | ||
func AddMessage(err error, msg string) error { | ||
if msgInCause := Message(err); msgInCause != "" { | ||
msg = fmt.Sprintf("%s %s", msg, msgInCause) | ||
} | ||
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return &endUserError{ | ||
cause: err, | ||
message: msg, | ||
} | ||
} | ||
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// Message extracts an end-user message from the error. | ||
func Message(err error) string { | ||
for err != nil { | ||
eu := new(endUserError) | ||
if errors.As(err, &eu) && eu.message != "" { | ||
return eu.message | ||
} | ||
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err = errors.Unwrap(err) | ||
} | ||
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return "" | ||
} | ||
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// MessageOrErr extracts an end-user message from the error. If no message is | ||
// found, err.Error() is returned. | ||
func MessageOrErr(err error) string { | ||
msg := Message(err) | ||
if msg == "" { | ||
return err.Error() | ||
} | ||
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return msg | ||
} |
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package errmsg | ||
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import ( | ||
"errors" | ||
"fmt" | ||
"testing" | ||
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qt "github.com/frankban/quicktest" | ||
pkgerrors "github.com/pkg/errors" | ||
) | ||
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func TestAddAndExtractMessage(t *testing.T) { | ||
c := qt.New(t) | ||
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testcases := []struct { | ||
name string | ||
wantMsg string | ||
wantErr string | ||
err error | ||
}{ | ||
{ | ||
name: "no message", | ||
wantMsg: "boom", | ||
wantErr: "boom", | ||
err: errors.New("boom"), | ||
}, | ||
{ | ||
name: "message on top of stack", | ||
wantMsg: "Something went wrong.", | ||
wantErr: "boom", | ||
err: AddMessage(errors.New("boom"), "Something went wrong."), | ||
}, | ||
{ | ||
name: "message in wrapped error (fmt)", | ||
wantMsg: "Something went wrong.", | ||
wantErr: "bang: boom", | ||
err: fmt.Errorf( | ||
"bang: %w", | ||
AddMessage(errors.New("boom"), "Something went wrong."), | ||
), | ||
}, | ||
{ | ||
name: "message in wrapped error (pkgerrors.Wrap)", | ||
wantMsg: "Something went wrong.", | ||
wantErr: "bang: boom", | ||
err: pkgerrors.Wrap( | ||
AddMessage(pkgerrors.New("boom"), "Something went wrong."), | ||
"bang", | ||
), | ||
}, | ||
{ | ||
name: "message in joint error", | ||
wantMsg: "Something went wrong.", | ||
wantErr: "bang\nboom", | ||
err: errors.Join( | ||
errors.New("bang"), | ||
AddMessage(errors.New("boom"), "Something went wrong."), | ||
), | ||
}, | ||
{ | ||
name: "multi-message error", | ||
wantMsg: "An error happened. Something went wrong.", | ||
wantErr: "bang: boom", | ||
err: AddMessage( | ||
// handle error coming from downstream | ||
fmt.Errorf("bang: %w", | ||
// downstream error also contains message | ||
AddMessage(errors.New("boom"), "Something went wrong."), | ||
), | ||
// add message to downstream error | ||
"An error happened.", | ||
), | ||
}, | ||
} | ||
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for _, tc := range testcases { | ||
c.Run(tc.name, func(c *qt.C) { | ||
c.Check(MessageOrErr(tc.err), qt.Equals, tc.wantMsg) | ||
c.Check(tc.err, qt.ErrorMatches, tc.wantErr) | ||
}) | ||
} | ||
} |
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