encoding/xml: XML tag name that consist of ':' doesn't get umarshaled properly

[ormergi]

What version of Go are you using (go version)?

$ go version
go version go1.19.9 linux/amd64

Does this issue reproduce with the latest release?

Reproduces using go 1.21 with go.dev/play

What operating system and processor architecture are you using (go env)?

go version go1.19.9 linux/amd64

go env Output

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN="/usr/bin"
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/root/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/root/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/gimme/.gimme/versions/go1.19.9.linux.amd64"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/gimme/.gimme/versions/go1.19.9.linux.amd64/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19.9"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/root/go/src/kubevirt.io/kubevirt/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3975233845=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Umarshaling XML to a struct that has attribute with XML tag whos name consist of : wont unmarshal correctly and end up empty.

For example:

type QemuDomain struct {
	XMLName xml.Name `xml:"domain"`
	XmlNs   string   `xml:"xmlns:qemu,attr,omitempty"` <------ XmlNs set as XML attribute, with a name consist of ':'
}

The XmlNs attribute end up with empty string.

Reproducer https://go.dev/play/p/5l9WHxVBO5S

What did you expect to see?

I expect the XmlNs attribute to umarshal correctly and wont end up empty.

What did you see instead?

The XmlNs attribute end up empty.

[dmitshur]

CC @rsc, @ianlancetaylor.

[jupenur]

@ormergi in the struct tag the namespace separator is space, i.e. xmlns qemu instead of xmlns:qemu: https://go.dev/play/p/FHqeA6az2AU

[ormergi]

@ormergi in the struct tag the namespace separator is space, i.e. xmlns qemu instead of xmlns:qemu: https://go.dev/play/p/FHqeA6az2AU

@jupenur thanks for the feedback
I have tried what you suggest but it seems that marshaling the object again result with XmlNs not as expected:

<domain xmlns:_xmlns="xmlns" _xmlns:qemu="http://libvirt.org/schemas/domain/qemu/1.0"></domain>

Instead of:

`<domain xmlns:qemu="http://libvirt.org/schemas/domain/qemu/1.0"></domain>`

https://go.dev/play/p/2zdkbKMAZC1

[seankhliao]

why aren't you using encoding/xml.Name.Space?

[zephyrtronium]

We just hit this as well. I can't speak to @ormergi's case, but we are generating about a thousand Go types from XSD for an unfortunately picky downstream API. That API appears to require namespace prefixes rather than xmlns attributes on all but the top level. Using xml.Name creates exactly those xmlns attributes. The only way we've found to marshal attributes with namespace prefixes is to put the prefix in the XML tag like xml:"pidx:Invoice", but this causes unmarshalling to ignore those elements, per this issue.

Related:

• encoding/xml: XML namespace prefixes not fully supported #6800
• encoding/xml: support for XML namespace prefixes #9519
• encoding/xml: Serializing XML with namespace prefix #11496
• encoding/xml: fix name spaces #13400

[ydnar]

We have a fix in #48641: encoding/xml: support xmlns prefixes

https://go-review.googlesource.com/c/go/+/355353

[SoMuchForSubtlety]

Has there been any progress on this?

[hellodword]

My workaround using encoding/xml: https://gist.github.com/hellodword/fa97208b0e81baed8a75f8e40fb2ffea

I must to say it's very dirty and not working for many cases, but it works for me. Hope it'll be helpful for someone :)