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implement ".Unwrap() error" on Error type #2525

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LeGEC opened this issue Oct 9, 2020 · 4 comments
Closed

implement ".Unwrap() error" on Error type #2525

LeGEC opened this issue Oct 9, 2020 · 4 comments

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@LeGEC
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@LeGEC LeGEC commented Oct 9, 2020

Description

The 'Error' type defined in errors.go does not implement ".Unwrap() error", which prevents the usage of "errors.Is()" and "errors.As()"

How to reproduce

package main

import (
	"github.com/gin-gonic/gin"
)

type TestStrErr string

func (e TestStrErr) Error() string { return string(e) }

func main() {
	testErr := TestStrErr("some error")

	err := &gin.Error{Err: testErr}

	if errors.Is(err, testErr) {
	    fmt.Println("match with testErr ok")
	}
	
	var unwrap TestStrErr
	if errors.As(err, &unwrap) {
	    fmt.Println("succesfully unwrapped as a TestStrErr")
	}
}

Expectations

output :

match with testErr ok
succesfully unwrapped as a TestStrErr

Actual result

no output

Environment

  • go version: go version go1.14.2 linux/amd64
  • gin version (or commit ref): 540b1ef
  • operating system: linux
LeGEC added a commit to LeGEC/gin that referenced this issue Oct 9, 2020
@LeGEC
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@LeGEC LeGEC commented Oct 13, 2020

A more useful use case was asked by this user on StackOverflow :
How to assert error type json.UnmarshalTypeError when caught by gin c.BindJSON ?

He wants to tell apart "this is a JSON parsing error" from "the JSON is ok, this is a validation error"

With the correct implementation of the .Unwrap() error method, this boils down to :

// gErr is a gin.Error
var jsErr *json.UnmarshalTypeError
if errors.As(gErr, &jsErr) {
    fmt.Println("the json is invalid")
} else {
    fmt.Println("this is something else")
}

@thejdavid
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@thejdavid thejdavid commented Oct 13, 2020

It would also help for other issues for other data types such as trying to un parse an invalid time.Time. in such case it wouldn't return a json parsing error but a time parsing error.
It might be useful to differentiate / group parsing errors from binding errors.

LeGEC added a commit to LeGEC/gin that referenced this issue Oct 14, 2020
thinkerou added a commit that referenced this issue Oct 17, 2020
Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>
Co-authored-by: thinkerou <thinkerou@gmail.com>
@thinkerou
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@thinkerou thinkerou commented Oct 18, 2020

#2526 merged

@thinkerou thinkerou closed this Oct 18, 2020
@jhannah-mm
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@jhannah-mm jhannah-mm commented Apr 14, 2021

@thejdavid wrote:

It would also help for other issues for other data types such as trying to un parse an invalid time.Time. in such case it wouldn't return a json parsing error but a time parsing error.
It might be useful to differentiate / group parsing errors from binding errors.

Ya, it seems that even under 1.7.1 there's still no useful information regarding where in a JSON POST the UnmarshalType casting failure occurred...

POST {
   "start_date": "invalid_date"    // time.Time
}
parsing time ""invalid_date"" as ""2006-01-02T15:04:05Z07:00"": cannot parse "invalid_date"" as "2006"

Hoping it would say start_date... somewhere / somehow

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5 participants
@LeGEC @thinkerou @thejdavid @jhannah-mm and others