encoding/xml: does not check namespace constraints that do not require keeping extra state

[DemiMarie]

Go version

go version go1.21.11 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/user/.cache/go-build'
GOENV='/home/user/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/user/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/user/go'
GOPRIVATE=''
GOPROXY='direct'
GOROOT='/usr/lib/golang'
GOSUMDB='off'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/lib/golang/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.21.11'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3671854511=/tmp/go-build -gno-record-gcc-switches'

What did you do?

https://go.dev/play/p/FRIvYTU13fC

What did you see happen?

encoding/xml does not reject XML with the following violations of namespace constraints:

1. Binding a URL other than http://www.w3.org/XML/1998/namespace to the prefix xml:

   <!-- Ill-formed: cannot bind prefix xml: to a URL other than
        http://www.w3.org/XML/1998/namespace -->
   <a xmlns:xml="https://example.com"/>

2. Binding http://www.w3.org/XML/1998/namespace to a prefix other than xml:

   <!-- Ill-formed: cannot bind a prefix other than xml: to
        http://www.w3.org/XML/1998/namespace -->
   <a xmlns:a="http://www.w3.org/XML/1998/namespace"/>

3. Declaring http://www.w3.org/XML/1998/namespace as the default namespace:

   <!-- Ill-formed: cannot declare http://www.w3.org/XML/1998/namespace
        as default namespace -->
   <a xmlns="http://www.w3.org/XML/1998/namespace"/>

4. Declaring the prefix xmlns, whether it is with the correct URL http://www.w3.org/2000/xmlns/

   <!-- Ill-formed: cannot declare xmlns: prefix -->
   <a xmlns:xmlns="http://www.w3.org/2000/xmlns/"/>

   or with any other URL:

   <!-- Ill-formed: cannot declare xmlns: prefix -->
   <a xmlns:xmlns="https://example.com"/>

5. Binding the URL http://www.w3.org/2000/xmlns/ to any prefix:

   <!-- Ill-formed: cannot bind a prefix to
        http://www.w3.org/2000/xmlns/ -->
   <a xmlns:a="http://www.w3.org/2000/xmlns/"/>

6. Declaring http://www.w3.org/2000/xmlns/ as the default namespace:

   <!-- Ill-formed: cannot declare http://www.w3.org/2000/xmlns/
        as default namespace -->
   <a xmlns="http://www.w3.org/2000/xmlns/"/>

7. Using xmlns as the prefix for an element:

   <!-- Ill-formed: xmlns: cannot be the prefix of an element name -->
   <xmlns:a/>

8. Undeclaring a namespace prefix by binding the empty string

   <!-- Ill-formed: cannot bind a namespace to the empty string -->
   <a xmlns:a=""/>

What did you expect to see?

encoding/xml should reject these violations, whether Token or RawToken are used. Detecting these violations can be done without maintaining any additional state and without resolving prefixes to namespace URLs.

[gabyhelp]

Related Issues

• encoding/xml: accepts various ill-formed XML #68293
• encoding/xml: Decoder does not reject xml-ProcInst preceeded by other data #65691
• encoding/xml: createAttrPrefix should ban "XMLanything" case insensitive, not just "xmlanything" #35151 (closed)
• encoding/xml: empty namespace prefix definitions should be illegal #8068
• proposal: encoding/xml: allow caller to specify preferred namespace prefix #48821
• encoding/xml: Default namespaces are missing #5040 (closed)
• encoding/xml: does not reject duplicate attribute names #68295
• proposal: encoding/xml: Allow to omit default namespace declarations #11565 (closed)
• encoding/xml: disallow attributes named xmlns:* #8167
• encoding/xml: encoding a start token with a namespace set in Name and Attr results in invalid XML #42807

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[cagedmantis]

@rsc

[cagedmantis]

Please note this related comment #68293 (comment)

[DemiMarie]

Please note this related comment #68293 (comment)

#68299 is that proposal