Categorygithub.com/podpalinc/rss-feed-generatorparser
package
0.0.53
Repository: https://github.com/podpalinc/rss-feed-generator.git
Documentation: pkg.go.dev
Overview
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# README

Podpal Feed Parser

Based on this repository.

The Podpal Feed Parser is a robust feed parser that supports parsing both RSS, Atom and JSON feeds. The library provides a universal parser.Parser that will parse and convert all feed types into a hybrid parser.Feed model. You also have the option of utilizing the feed specific atom.Parser or rss.Parser or json.Parser parsers which generate atom.Feed, rss.Feed and json.Feed respectively.

Table of Contents

Features

Supported feed types:

  • RSS 0.90
  • Netscape RSS 0.91
  • Userland RSS 0.91
  • RSS 0.92
  • RSS 0.93
  • RSS 0.94
  • RSS 1.0
  • RSS 2.0
  • Atom 0.3
  • Atom 1.0
  • JSON 1.0
  • JSON 1.1

Extension Support

The Podpal Feed Parser library provides support for parsing several popular predefined extensions into ready-made structs, including Dublin Core and Apple’s iTunes.

It parses all other feed extensions in a generic way (see the Extensions section for more details).

Invalid Feeds

A best-effort attempt is made at parsing broken and invalid XML feeds. Currently, Podpal Feed Parser can succesfully parse feeds with the following issues:

  • Unescaped/Naked Markup in feed elements
  • Undeclared namespace prefixes
  • Missing closing tags on certain elements
  • Illegal tags within feed elements without namespace prefixes
  • Missing "required" elements as specified by the respective feed specs.
  • Incorrect date formats

Overview

The Podpal Feed Parser library is comprised of a universal feed parser and several feed specific parsers. Which one you choose depends entirely on your usecase. If you will be handling rss, atom and json feeds then it makes sense to use the parser.Parser. If you know ahead of time that you will only be parsing one feed type then it would make sense to use rss.Parser or atom.Parser or json.Parser.

Universal Feed Parser

The universal parser.Parser works in 3 stages: detection, parsing and translation. It first detects the feed type that it is currently parsing. Then it uses a feed specific parser to parse the feed into its true representation which will be either a rss.Feed or atom.Feed or json.Feed. These models cover every field possible for their respective feed types. Finally, they are translated into a parser.Feed model that is a hybrid of all feed types. Performing the universal feed parsing in these 3 stages allows for more flexibility and keeps the code base more maintainable by separating RSS, Atom and Json parsing into seperate packages.

Diagram

The translation step is done by anything which adheres to the parser.Translator interface. The DefaultRSSTranslator, DefaultAtomTranslator, DefaultJSONTranslator are used behind the scenes when you use the parser.Parser with its default settings. You can see how they translate fields from atom.Feed or rss.Feed json.Feed to the universal parser.Feed struct in the Default Mappings section. However, should you disagree with the way certain fields are translated you can easily supply your own parser.Translator and override this behavior. See the Advanced Usage section for an example how to do this.

Feed Specific Parsers

The Podpal Feed Parser library provides two feed specific parsers: atom.Parser, rss.Parser and json.Parser. If the hybrid parser.Feed model that the universal parser.Parser produces does not contain a field from the atom.Feed or rss.Feed or json.Feed model that you require, it might be beneficial to use the feed specific parsers. When using the atom.Parser or rss.Parser or json.Parser directly, you can access all of fields found in the atom.Feed, rss.Feed and json.Feed models. It is also marginally faster because you are able to skip the translation step.

Basic Usage

Universal Feed Parser

The most common usage scenario will be to use parser.Parser to parse an arbitrary RSS or Atom or JSON feed into the hybrid parser.Feed model. This hybrid model allows you to treat RSS, Atom and JSON feeds the same.

Parse a feed from an URL:
fp := parser.NewParser()
feed, _ := fp.ParseURL("http://feeds.twit.tv/twit.xml")
fmt.Println(feed.Title)
Parse a feed from a string:
feedData := `<rss version="2.0">
<channel>
<title>Sample Feed</title>
</channel>
</rss>`
fp := parser.NewParser()
feed, _ := fp.ParseString(feedData)
fmt.Println(feed.Title)
Parse a feed from an io.Reader:
file, _ := os.Open("/path/to/a/file.xml")
defer file.Close()
fp := parser.NewParser()
feed, _ := fp.Parse(file)
fmt.Println(feed.Title)
Parse a feed from an URL with a 60s timeout:
ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
defer cancel()
fp := parser.NewParser()
feed, _ := fp.ParseURLWithContext("http://feeds.twit.tv/twit.xml", ctx)
fmt.Println(feed.Title)
Parse a feed from an URL with a custom User-Agent:
fp := parser.NewParser()
fp.UserAgent = "MyCustomAgent 1.0"
feed, _ := fp.ParseURL("http://feeds.twit.tv/twit.xml")
fmt.Println(feed.Title)

Feed Specific Parsers

You can easily use the rss.Parser, atom.Parser or json.Parser directly if you have a usage scenario that requires it:

Parse a RSS feed into a rss.Feed
feedData := `<rss version="2.0">
<channel>
<webMaster>[email protected] (Example Name)</webMaster>
</channel>
</rss>`
fp := rss.Parser{}
rssFeed, _ := fp.Parse(strings.NewReader(feedData))
fmt.Println(rssFeed.WebMaster)
Parse an Atom feed into a atom.Feed
feedData := `<feed xmlns="http://www.w3.org/2005/Atom">
<subtitle>Example Atom</subtitle>
</feed>`
fp := atom.Parser{}
atomFeed, _ := fp.Parse(strings.NewReader(feedData))
fmt.Println(atomFeed.Subtitle)
Parse a JSON feed into a json.Feed
feedData := `{"version":"1.0", "home_page_url": "https://daringfireball.net"}`
fp := json.Parser{}
jsonFeed, _ := fp.Parse(strings.NewReader(feedData))
fmt.Println(jsonFeed.HomePageURL)

Advanced Usage

Parse a feed while using a custom translator

The mappings and precedence order that are outlined in the Default Mappings section are provided by the following two structs: DefaultRSSTranslator, DefaultAtomTranslator and DefaultJSONTranslator. If you have fields that you think should have a different precedence, or if you want to make a translator that is aware of an unsupported extension you can do this by specifying your own RSS or Atom or JSON translator when using the parser.Parser.

Here is a simple example of creating a custom Translator that makes the /rss/channel/itunes:author field have a higher precedence than the /rss/channel/managingEditor field in RSS feeds. We will wrap the existing DefaultRSSTranslator since we only want to change the behavior for a single field.

First we must define a custom translator:


import (
    "fmt"

    "github.com/podpalinc/rss-feed-generator"
    "github.com/podpalinc/rss-feed-generator/rss"
)

type MyCustomTranslator struct {
    defaultTranslator *parser.DefaultRSSTranslator
}

func NewMyCustomTranslator() *MyCustomTranslator {
  t := &MyCustomTranslator{}

  // We create a DefaultRSSTranslator internally so we can wrap its Translate
  // call since we only want to modify the precedence for a single field.
  t.defaultTranslator = &parser.DefaultRSSTranslator{}
  return t
}

func (ct* MyCustomTranslator) Translate(feed interface{}) (*parser.Feed, error) {
	rss, found := feed.(*rss.Feed)
	if !found {
		return nil, fmt.Errorf("Feed did not match expected type of *rss.Feed")
	}

  f, err := ct.defaultTranslator.Translate(rss)
  if err != nil {
    return nil, err
  }

  if rss.ITunesExt != nil && rss.ITunesExt.Author != "" {
      f.Author = rss.ITunesExt.Author
  } else {
      f.Author = rss.ManagingEditor
  }
  return f
}

Next you must configure your parser.Parser to utilize the new parser.Translator:

feedData := `<rss version="2.0">
<channel>
<managingEditor>Ender Wiggin</managingEditor>
<itunes:author>Valentine Wiggin</itunes:author>
</channel>
</rss>`

fp := parser.NewParser()
fp.RSSTranslator = NewMyCustomTranslator()
feed, _ := fp.ParseString(feedData)
fmt.Println(feed.Author) // Valentine Wiggin

Extensions

Every element which does not belong to the feed's default namespace is considered an extension by Podpal Feed Parser. These are parsed and stored in a tree-like structure located at Feed.Extensions and Item.Extensions. These fields should allow you to access and read any custom extension elements.

In addition to the generic handling of extensions, Podpal Feed Parser also has built in support for parsing certain popular extensions into their own structs for convenience. It currently supports the Dublin Core and Apple iTunes extensions which you can access at Feed.ItunesExt, feed.DublinCoreExt and Item.ITunesExt and Item.DublinCoreExt

Default Mappings

The DefaultRSSTranslator, the DefaultAtomTranslator and the DefaultJSONTranslator map the following rss.Feed, atom.Feed and json.Feed fields to their respective parser.Feed fields. They are listed in order of precedence (highest to lowest):

parser.FeedRSSAtomJSON
Title/rss/channel/title
/rdf:RDF/channel/title
/rss/channel/dc:title
/rdf:RDF/channel/dc:title		/feed/title/title
Description/rss/channel/description
/rdf:RDF/channel/description
/rss/channel/itunes:subtitle		/feed/subtitle
/feed/tagline		/description
Link/rss/channel/link
/rdf:RDF/channel/link		/feed/link[@rel=”alternate”]/@href
/feed/link[not(@rel)]/@href		/home_page_url
FeedLink/rss/channel/atom:link[@rel="self"]/@href
/rdf:RDF/channel/atom:link[@rel="self"]/@href		/feed/link[@rel="self"]/@href/feed_url
Updated/rss/channel/lastBuildDate
/rss/channel/dc:date
/rdf:RDF/channel/dc:date		/feed/updated
/feed/modified		/items[0]/date_modified
Published/rss/channel/pubDate/items[0]/date_published
Author/rss/channel/managingEditor
/rss/channel/webMaster
/rss/channel/dc:author
/rdf:RDF/channel/dc:author
/rss/channel/dc:creator
/rdf:RDF/channel/dc:creator
/rss/channel/itunes:author		/feed/authors[0]/author
Authors/rss/channel/managingEditor
/rss/channel/webMaster
/rss/channel/dc:author
/rdf:RDF/channel/dc:author
/rss/channel/dc:creator
/rdf:RDF/channel/dc:creator
/rss/channel/itunes:author		/feed/authors/authors
/author
Language/rss/channel/language
/rss/channel/dc:language
/rdf:RDF/channel/dc:language		/feed/@xml:lang/language
Image/rss/channel/image
/rdf:RDF/image
/rss/channel/itunes:image		/feed/logo/icon
Copyright/rss/channel/copyright
/rss/channel/dc:rights
/rdf:RDF/channel/dc:rights		/feed/rights
/feed/copyright
Generator/rss/channel/generator/feed/generator
Categories/rss/channel/category
/rss/channel/itunes:category
/rss/channel/itunes:keywords
/rss/channel/dc:subject
/rdf:RDF/channel/dc:subject		/feed/category
parser.ItemRSSAtomJSON
Title/rss/channel/item/title
/rdf:RDF/item/title
/rdf:RDF/item/dc:title
/rss/channel/item/dc:title		/feed/entry/title/items/title
Description/rss/channel/item/description
/rdf:RDF/item/description
/rss/channel/item/dc:description
/rdf:RDF/item/dc:description		/feed/entry/summary/items/summary
Content/rss/channel/item/content:encoded/feed/entry/content/items/content_html
Link/rss/channel/item/link
/rdf:RDF/item/link		/feed/entry/link[@rel=”alternate”]/@href
/feed/entry/link[not(@rel)]/@href		/items/url
Updated/rss/channel/item/dc:date
/rdf:RDF/rdf:item/dc:date		/feed/entry/modified
/feed/entry/updated		/items/date_modified
Published/rss/channel/item/pubDate
/rss/channel/item/dc:date		/feed/entry/published
/feed/entry/issued		/items/date_published
Author/rss/channel/item/author
/rss/channel/item/dc:author
/rdf:RDF/item/dc:author
/rss/channel/item/dc:creator
/rdf:RDF/item/dc:creator
/rss/channel/item/itunes:author		/feed/entry/author/items/author/name
Authors/rss/channel/item/author
/rss/channel/item/dc:author
/rdf:RDF/item/dc:author
/rss/channel/item/dc:creator
/rdf:RDF/item/dc:creator
/rss/channel/item/itunes:author		/feed/entry/authors[0]/items/authors
/items/author/name
GUID/rss/channel/item/guid/feed/entry/id/items/id
Image/rss/channel/item/itunes:image
/rss/channel/item/media:image		/items/image
/items/banner_image
Categories/rss/channel/item/category
/rss/channel/item/dc:subject
/rss/channel/item/itunes:keywords
/rdf:RDF/channel/item/dc:subject		/feed/entry/category/items/tags
Enclosures/rss/channel/item/enclosure/feed/entry/link[@rel=”enclosure”]/items/attachments

Dependencies

# Packages

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# Functions

DetectFeedType attempts to determine the type of feed by looking for specific xml elements unique to the various feed types.
NewParser creates a universal feed parser.

# Constants

FeedTypeAtom repesents an Atom feed.
FeedTypeJSON represents a JSON feed.
FeedTypeRSS represents an RSS feed.
FeedTypeUnknown represents a feed that could not have its type determiend.

# Variables

ErrFeedTypeNotDetected is returned when the detection system can not figure out the Feed format.

# Structs

DefaultAtomTranslator converts an atom.Feed struct into the generic Feed struct.
DefaultJSONTranslator converts an json.Feed struct into the generic Feed struct.
DefaultRSSTranslator converts an rss.Feed struct into the generic Feed struct.
Enclosure is a file associated with a given Item.
Feed is the universal Feed type that atom.Feed and rss.Feed gets translated to.
HTTPError represents an HTTP error returned by a server.
Image is an image that is the artwork for a given feed or item.
Item is the universal Item type that atom.Entry and rss.Item gets translated to.
Parser is a universal feed parser that detects a given feed type, parsers it, and translates it to the universal feed type.
Person is an individual specified in a feed (e.g.

# Interfaces

Translator converts a particular feed (atom.Feed or rss.Feed of json.Feed) into the generic Feed struct.

# Type aliases

FeedType represents one of the possible feed types that we can detect.