encoding/xml: implement dual of 'omitempty' for unmarshalling «optional» fields #13417
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To be precise, what I'd like to have is type Foo struct {
Bar *int `xml:"BAR,allowempty"`
}which will parse |
quentinmit
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NeedsFix
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I am happy to take this if nobody is working on it already. I would think that the unmarshaling behavior for Is there a use case that I’m missing for the error that unmarshaling Please correct me if I misunderstand the issue. |
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Nvm. ^ goes against xml spec. |
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CL https://golang.org/cl/38386 mentions this issue. |
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CL https://golang.org/cl/39607 mentions this issue. |
gopherbot
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Apr 5, 2017
…ntax, like Go 1.7
Consider this struct, which expects an attribute A and a child C both ints:
type X struct {
XMLName xml.Name `xml:"X"`
A int `xml:",attr"`
C int
}
Go 1.2 through Go 1.7 were consistent: attributes unchecked,
children strictly checked:
$ go1.7 run /tmp/x.go
<X></X> ok
<X A=""></X> ok
<X A="bad"></X> ok
<X></X> ok
<X><C></C></X> ERROR strconv.ParseInt: parsing "": invalid syntax
<X><C/></X> ERROR strconv.ParseInt: parsing "": invalid syntax
<X><C>bad</C></X> ERROR strconv.ParseInt: parsing "bad": invalid syntax
$
Go 1.8 made attributes strictly checked, matching children:
$ go1.8 run /tmp/x.go
<X></X> ok
<X A=""></X> ERROR strconv.ParseInt: parsing "": invalid syntax
<X A="bad"></X> ERROR strconv.ParseInt: parsing "bad": invalid syntax
<X></X> ok
<X><C></C></X> ERROR strconv.ParseInt: parsing "": invalid syntax
<X><C/></X> ERROR strconv.ParseInt: parsing "": invalid syntax
<X><C>bad</C></X> ERROR strconv.ParseInt: parsing "bad": invalid syntax
$
but this broke XML code that had empty attributes (#19333).
In Go 1.9 we plan to start allowing empty children (#13417).
The fix for that will also make empty attributes work again:
$ go run /tmp/x.go # Go 1.9 development
<X></X> ok
<X A=""></X> ok
<X A="bad"></X> ERROR strconv.ParseInt: parsing "bad": invalid syntax
<X></X> ok
<X><C></C></X> ok
<X><C/></X> ok
<X><C>bad</C></X> ERROR strconv.ParseInt: parsing "bad": invalid syntax
$
For Go 1.8.1, we want to restore the empty attribute behavior
to match Go 1.7 but not yet change the child behavior as planned for Go 1.9,
since that change hasn't been through release testing.
Instead, restore the more lax Go 1.7 behavior, so that XML files
with empty attributes will not be broken until Go 1.9:
$ go run /tmp/x.go # after this CL
<X></X> ok
<X A=""></X> ok
<X A="bad"></X> ok
<X></X> ok
<X><C></C></X> ERROR strconv.ParseInt: parsing "": invalid syntax
<X><C/></X> ERROR strconv.ParseInt: parsing "": invalid syntax
<X><C>bad</C></X> ERROR strconv.ParseInt: parsing "bad": invalid syntax
$
Fixes #19333.
Change-Id: I3d38ebd2509f5b6ea3fd4856327f887f9a1a8085
Reviewed-on: https://go-review.googlesource.com/39607
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Sarah Adams <shadams@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
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XML is often used in legacy APIs, which are often not very consistent in the data format they output. One of such inconsistencies is emitting of nodes with empty data in case it is missing, so
<tag>123</tag>becomes<tag></tag>, instead of being omitted entirely.If node data type is non-string, the only way to handle this in Go currently is to mark node data type as
string, and handle the parsing by hand. This is verbose, error-prone and in contrast with the rest of parsing, which is quite declarative.Go 1.5.1 // #8333, #8334
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