Fun with `encoding/xml`

For the first time I’ve felt betrayed somewhat by Go’s standard library. The encoding/xml package’s namespace support seems to be half baked, and I’ve been unable to work around some issues.

Quick Recap

Here’s an example of using encoding/xml

package main

import (
	"encoding/xml"
	"fmt"
)

type XMLDoc struct {
	XMLName xml.Name `xml:"document"`
	Field   string   `xml:"field"`
}

func main() {
	input := `<document><field>field_value</field></document>`
	var parsed XMLDoc
	xml.Unmarshal([]byte(input), &parsed)
	fmt.Printf("%#v", parsed)
}

main.XMLDoc{XMLName:xml.Name{Space:"", Local:"document"}, Field:"field_value"}

Simple enough. Here’s how you would modify this to use namespaces, demonstrating two equivalent ways to specify the namespace.

package main

import (
	"encoding/xml"
	"fmt"
)

type XMLDoc struct {
	XMLName xml.Name `xml:"document"`
	Field   string   `xml:"https://example.com/xmlschema field"`
}

func parse(input string) {
	var parsed XMLDoc
	xml.Unmarshal([]byte(input), &parsed)
	fmt.Printf("%#v\n", parsed)
}

func main() {
	parse(`
		<document xmlns:examplenamespace="https://example.com/xmlschema">
			<examplenamespace:field>field_value</examplenamespace:field>
		</document>
	`)

	parse(`
		<document>
			<field xmlns="https://example.com/xmlschema">field_value</field>
		</document>
	`)
}

main.XMLDoc{XMLName:xml.Name{Space:"", Local:"document"}, Field:"field_value"}
main.XMLDoc{XMLName:xml.Name{Space:"", Local:"document"}, Field:"field_value"}

The Problem

The issue is when you need to mix namespaced and non-namespaced tags.

Watch this magic trick, this works as expected:

package main

import (
	"encoding/xml"
	"fmt"
)

type XMLDoc struct {
	XMLName         xml.Name `xml:"document"`
	NamespacedField string   `xml:"https://example.com/xmlschema field"`
	Field           string   `xml:"field"`
}

func parse(input string) XMLDoc {
	var parsed XMLDoc
	xml.Unmarshal([]byte(input), &parsed)
	fmt.Printf("\n%#v\n", parsed)
	return parsed
}

func main() {
	parse(`
		<document xmlns:examplenamespace="https://example.com/xmlschema">
			<examplenamespace:field>namespaced_field_value</examplenamespace:field>
			<field>field_value</field>
		</document>
	`)

	parse(`
		<document>
			<field xmlns="https://example.com/xmlschema">namespaced_field_value</field>
			<field>field_value</field>
		</document>
	`)

}

main.XMLDoc{XMLName:xml.Name{Space:"", Local:"document"}, NamespacedField:"namespaced_field_value", Field:"field_value"}

main.XMLDoc{XMLName:xml.Name{Space:"", Local:"document"}, NamespacedField:"namespaced_field_value", Field:"field_value"}

All good, but watch what happens when I flip the order of Field and NamespacedField in the struct:

package main

import (
	"encoding/xml"
	"fmt"
)

type XMLDoc struct {
	XMLName         xml.Name `xml:"document"`
	Field           string   `xml:"field"`
	NamespacedField string   `xml:"https://example.com/xmlschema field"`
}

func parse(input string) XMLDoc {
	var parsed XMLDoc
	xml.Unmarshal([]byte(input), &parsed)
	fmt.Printf("\n%#v\n", parsed)
	return parsed
}

func main() {
	parse(`
		<document xmlns:examplenamespace="https://example.com/xmlschema">
			<examplenamespace:field>namespaced_field_value</examplenamespace:field>
			<field>field_value</field>
		</document>
	`)

	parse(`
		<document>
			<field xmlns="https://example.com/xmlschema">namespaced_field_value</field>
			<field>field_value</field>
		</document>
	`)

}

main.XMLDoc{XMLName:xml.Name{Space:"", Local:"document"}, Field:"field_value", NamespacedField:""}

main.XMLDoc{XMLName:xml.Name{Space:"", Local:"document"}, Field:"field_value", NamespacedField:""}

Yikes! Now NamespacedField isn’t correctly deserialized!

We’ve found an 11 year old bug in encoding/xml that Google seemingly has no desire to fix.

`CDATA`

If you use this, you apparently have to have xmlns:content="http://purl.org/rss/1.0/modules/content/" in your <rss> tag. I don’t really understand this because the CDATA thing appears to be an XML thing, and if it is needed, why doesn’t encoding/xml include it?

WTF is going on with date formats?

The RSS spec says the date format should be RFC 822 with the example Mon, 10 Oct 2005 14:10:00 GMT. Apple says it should be RFC 2822 and gives the example Sat, 01 Apr 2023 19:00:00 GMT

Go helpfully provides a time.RFC822 format specifier, but when I use it Apple Podcasts defaults to a date in 2000. Looking at the format specifier, it is 02 Jan 06 15:04 MST, which doesn’t appear to match. Browsing the stdlib I see RFC1123 which does appear to have the right format (Mon, 02 Jan 2006 15:04:05 MST), so I used that and it worked in Apple Podcasts.

Except the podcast.ai feed validator complains that:

The “lastBuildDate” value “Sat, 31 May 2025 10:41:05 MDT” does not conform to RFC 2822.

Apple Podcasts App

To test I’ve been manually adding my feed URL to the Apple Podcast app and removing it when I want to apply some changes.

Unfortunately, there is some kind of caching going on; so if I re-add the same URL immediately sometimes it shows the old version and sometimes it just doesn’t do anything at all.

Buggy Podcast Validator Tools

https://podcastai.com/feed-validator
- Appears to not understand XML namespaces, ie complains about itunes:image missing when ` ` it there and the Apple Podcast app understands it
- Complains about dates that seem valid?
https://www.castfeedvalidator.com/validate.php
- Does not like it when your file doesn’t end with xml
- Appears to understand XML namespaces though
https://podba.se/validate/?
- Complains about missing “Atom” namespace was not found when it is 100% there
- Appears to not understand XML namespaces
- Got this confusing error:
  
  The feed’s is missing an . To be featured by Apple Podcasts, feeds must have valid author information.
https://validator.w3.org/
- Appears to work
https://validator.livewire.io
- Really doesn’t understand XML namespaces
  
  Bad item attribute name: xmlns[itunes]
  
  Except it does parse some later?
  
  Found 5 podcast namespace tags: , , , , [podcastindex]
https://www.feedvalidator.org
- This is just, wrong? According to Apple’s spec?
  
  line 41, column 34: itunes:explicit must be “yes”, “no”, or “clean”: false
- Doesn’t know about https://podcastindex.org/namespace/1.0 namespace

Conclusion

This is annoying.

Fun with encoding/xml