I have the feeling, in every RSS.xml file, both the pubDate and the lastBuildDate match.
I am sure that this one, is not always true...
So firstly, what is the difference between those two above?
Secondly, the RSS readers, sort the content by Date, based on the pubDate or the lastBuildDate?
pubDate:
The original publication date for the channel or item. (optional)
lastBuildDate:
The most recent time the content of the channel was modified. (optional)
Here are some docs for the optional items in the RSS 2.0 spec.
Answers here are all over the place. Some people are getting confused by the fact that item has a pubDate as well. I believe the OP is specifically asking about the difference between lastBuildDate and pubDate at the channel level.
From the best of my understanding of the RSS spec, which is notorious for ambiguous explanations, lastBuildDate would be the last time the feed was created. For example, if you cache a copy of it on your server for some period of time, lastBuildDate would the time that cached copy was created.
pubDate, on the other hand, seems to be basically the last time any actual content within the feed has changed. For the most part it's pretty much going to be the latest pubDate value from the items in the feed, since generally, the feed content is only changing when some new item gets published. However, it could also be a date when you made some change to the channel, itself, such as changing the channel title, description, etc.
lastBuildDate specifies the last date/time the entry was modified. pubDate specifies the actual publication date/time.
The reason you see these as generally the same is because by the time you get the RSS feed, there hasn't been any edit to the article.
I can't find the RSS spec on this unfortunately, but I am pretty positive that's what they are.
By RSS 2.0 specification, it seems they are roughly equivalent:
lastBuildDate:
The last time the content of the channel changed.
pubDate:
The publication date for the content in the channel. ...
The difference is subtle: They tell us about the method that was used. In case of <pubDate>, the channel is published manually or in fixed period. In case of <lastBuildDate>, the channel is built automatically upon new article being added on the website, adding it as new item.
While the other answers here do provide some good information, I feel the need to elaborate just a little bit for any future visitors.
pubDate
The publication date for the content in the channel. For example, the New York Times publishes on a daily basis, the publication date flips once every 24 hours. That's when the pubDate of the channel changes.
lastBuildDate
The last time the content of the channel changed.
So, taking the New York Times as an example again, the <pubDate> is the date the feed was published while the <lastBuildDate> would be the date the content inside the feed changed. In the end, I would view the <pubDate> as the date the feed is published and the <lastBuildDate> as the date any content in the feed was last modified.
Related
I have a large set of podcast feed URLs which I'm periodically polling to check for updates. I'm really struggling to find a robust way to detect if a feed has changed that doesn't have any false positives. I'd like to be able to detect not just if there is a new episode, but also if an existing episode was updated.
RSS and Atom feeds provide pubDate, lastBuildDate or updated elements. However, I'm finding these frequently misused so that the feed is actually inserting the current date time into these fields each request. This makes them difficult to rely on to detect changes.
My next thought was to strip all date information from the podcasts, then MD5 hash the feed contents. I can then compare the feed hashes to detect changes to the feeds.
This seems to work for about 90% of the cases. However, there are still hundreds of podcasts that insert dynamic data into their feeds.
One podcast has the following as their podcast cover art:
http://erikglassman.hipcast.com/albumart/1000.1439649026.jpg
Where 1439649026 is what I assume is a timestamp. This second number changes with each request of their feed.
This is starting to seem like a losing battle. If I can't reliably trust the date fields of a podcast feed, and if some percentage of podcasts insert dynamic data into their feed text, how can I reliably detect changes to a feed in a robust way?
Everything you say is true, so it's not a good idea to try to detect changes at the feed level, instead look for them at the item level.
That generally works, if it doesn't the feed can't be used by anyone, so the source of the feed is likely to have fixed any problem. That's why I think it works so well.
I've been writing feed readers as long as they have existed, my current product is called River4, it's available as open source, MIT License, so you can use it as example code, for this and other issues.
This is where it checks if an item is new:
https://github.com/scripting/river4/blob/master/river4.js#L1411
That might move around as the code changes, so look for a routine called getItemGuid. It shows you how to get a value that uniquely identifies the item. I use this code for my podcatcher, http://podcatch.com/, and it seems to catch the new items, and doesn't get false positives.
Hope this helps! :-)
I have a page which displays a random post every day, and I have made a custom RSS feed page for it. My question is how Mailchimp and similar services (such as IFTTT) that uses RSS feeds detects "New Items"?
Cause my RSS feed looks like this:
<channel>
<title><b>Quote of the Day</b></title>
<atom:link rel="self" href="http://www.mysite.com/qotd/feed-2" type="application/rss+xml"/>
<link>http:/mysite.com/qotd/feed-2</link>
<description>Textt</description>
<language>en-us</language>
<pubDate>Wed, 22 Jan 2014 21:30:45 +0000</pubDate>
<lastBuildDate>Wed, 22 Jan 2014 21:30:45 +0000</lastBuildDate>
<item>
<link>http://www.mysite.com/412</link>
<pubDate>Wed, 20 Jan 2014 07:17:45 +0000</pubDate>
<description><![CDATA[]]></description>
<guid>http://www.mysite.com/412</guid>
</item>
</channel>
</rss>
Every 24h, the feed updates with a new item. The problem is that there will always be 1 item in total, and the pubdate might be an older date before, depending on which random post it pulls. Will services that uses RSS still detect it as if a new item has been added?
It's not considered good practice to have only a single item in your feed. It exposes you to the risk of missed update if a given service polls the feed unfrequently enough.
The "default" behavior is to poll the feed regularly (every hour, every day... etc) and compare the <item> elements between 2 fetches. They will likely use the <guid> to determine whether an item has already been detected or not.
Additionally, many consuming apps (like IFTTT in your case but I'm not sure for Mailchimp) will support PubSubHubbub which is a webhook protocol so they know when a given feed has been updated. It saves them (and you!) resources because they won't have to poll the feed often and yet will always have timely updates.
Most of the time, the <pubDate> does not matter. Feel free to share the actual URL of your feed so we can tell you exactly what's going on.
That depends on the implementation, but usually they will compare the new item with all items stored locally to determine whether it was in the RSS earlier, and only display it if it's not, thus this should be fine (at least the two RSS feed readers I have used until now worked this way).
If you want the items to be displayed in the order they appeared on your website however you should use the current date instead of the actual date of the item.
There is a helpful troubleshooting guide by Mailchimp. It seems Mailchimp does evaluate the Pubdate to decide that items are published. From the page:
Make sure your pubDate tags are set up and populating correctly. If a pubDate is set in another time zone or a day off, MailChimp may not recognize that the items were posted before the next campaign is triggered.
Below is an example of the correct setup for your RSS feed. The pubDate is in English.We pull in the date for any of these tags, in this order: 'pubDate', 'pubdate', 'published', 'created', 'updated', 'date.'
I'm generating an RSS feed from my blog. I'm using node-rss. When I make a minor edit to one the posts listed in the feed, Google Reader lists the item as unread, even though I marked it as read a week ago.
My RSS feed contains title, description, link, guid and pubDate elements for each item. For guid, I'm just using the canonical URL to the item. The pubDate element is the date/time that the entry was first published, rather than the time of the last edit.
The feed itself contains lastBuildDate, which is set to the time that the RSS feed was generated (i.e. when it was requested).
As far as I can tell, there's nothing in the RSS feed that flags the item as being changed. So why does Google Reader think that the item has been updated, and why does it show it as unread again?
Does it look at the content (which has changed)? If so, can I do something in the RSS feed to mark this as a minor update, thus preventing Google Reader from showing it as unread?
If, in Google Reader, you mouse over the date in the top-right of each post, you'll see that it has "Received" and "Published" dates.
"Received" appears to be when the Google Reader server saw the new content, whereas "Published" comes from the feed itself.
Google Reader appears to use the "Received" date to decide whether something is new.
So, to get the correct behaviour
Don't put anything in the feed that's older than (say) 6 months.
Limit the feed XML to the most-recent 10 or so items.
Of course, the second could imply the first...
I am building RSS feed for the first time and I have some simple, direct questions that I was unable to find on the web, well at list in a sense that would be clear to me. Can you help me understand following
Which items should I include in RSS generation? should I always put in all the articles or what is the criteria when I query my articles for the feed?
What value should I set for pubDate? The specification says "The publication date for the content in the channel. For example, the New York Times publishes on a daily basis, the publication date flips once every 24 hours. That's when the pubDate of the channel changes.". I do not quite understand how to apply this to my feed. I have new articles daily, should I set the pubDate to let say 06:00 AM today and update it every day?
lastBuildDate: if I understand this right is the date of the latest updated item?
Which items should I include in RSS generation?
You should have one generic feed with all the new articles you post (for example: news). Additionally if you got your webpage split into categories, or you have some specific feeds (eg. calendar of the events) then it's good to create additional separate RSS for each one of them
What value should I set for pubDate? I do not quite understand how to apply this to my feed. I have new articles daily, should I set the pubDate to let say 06:00 AM today and update it every day?
Always set pubDate to the time when your news/articles went online. So if you have new articles daily pubDate should be a date when they were released to the public. Not random hour in the morning. Not the moment when you started writing them.
lastBuildDate: if I understand this right is the date of the latest updated item?
lastBuildDate is the most recent date when any of the results was posted or modified. Usually you should skip it - especially if your lastBuildDate will be simply a most recent pubDate. It's an optional parameter.
I use lastBuildDate only for calendar RSS feeds to show when the calendar was updated (as in calendars you not only add new entries but also often edit existing).
You should put every article, but the best is to provide different feeds for different categories, even search keywords. You can build it like any dynamic page, with a querystring.
that's not super important, you can put whatever. I don't think may feed readers use it.
theoretically it's the date the content changed. So the date of the latest updated item should work.
Something super important, since people are going to do polling on this page (meaning a lot of requests on the page)
- Cache it on your server
- Serve and Etag header and/or a LastModifiedDate. That way your server can respond with just a "not modified" if the client has it in cache already.
I'm using feedparser for working with RSS.
I'm getting regularly (e.g. every 15 minutes) RSS channel with items and store it. In the channels there aren't often any new items. So, it's unefficient.
Is there a way to detect quickly if there are some new items in the channel and if not, do nothing with this channel?
thank you
For RSS 2.0, the channel element has an optional lastBuildDate eleement. For atom, there's a similar "atom:updated" element, but the standard does state that this is when "an entry or feed was modified in a way the publisher considers significant. Therefore, not all modifications necessarily result in a changed atom:updated value".
There's also a PubDate element in RSS 2.0, also optional, but lastBuildDate should be the one to use, assuming it's there and the publisher is using it correctly.
You can store the previous one and compare the newly retrieved value with the old one.
Added material on feedparser:
For feedparser, see feed-updated_parsed and feed-updated.