* FEATURE: Let sites add a sitemap.xml file.
This PR adds the same features discourse-sitemap provides to core. Sitemaps are only added to the robots.txt file if the `enable_sitemap` setting is enabled and `login_required` disabled.
After merging discourse/discourse-sitemap#34, this change will take priority over the sitemap plugin because it will disable itself. We're also using the same sitemaps table, so our migration won't try to create it
again using `if_not_exists: true`.
We have a couple of site setting, `slow_down_crawler_user_agents` and `slow_down_crawler_rate`, that are meant to allow site owners to signal to specific crawlers that they're crawling the site too aggressively and that they should slow down.
When a crawler is added to the `slow_down_crawler_user_agents` setting, Discourse currently adds a `Crawl-delay` directive for that crawler in `/robots.txt`. Unfortunately, many crawlers don't support the `Crawl-delay` directive in `/robots.txt` which leaves the site owners no options if a crawler is crawling the site too aggressively.
This PR replaces the `Crawl-delay` directive with proper rate limiting for crawlers added to the `slow_down_crawler_user_agents` list. On every request made by a non-logged in user, Discourse will check the User Agent string and if it contains one of the values of the `slow_down_crawler_user_agents` list, Discourse will only allow 1 request every N seconds for that User Agent (N is the value of the `slow_down_crawler_rate` setting) and the rest of requests made within the same interval will get a 429 response.
The `slow_down_crawler_user_agents` setting becomes quite dangerous with this PR since it could rate limit lots if not all of anonymous traffic if the setting is not used appropriately. So to protect against this scenario, we've added a couple of new validations to the setting when it's changed:
1) each value added to setting must 3 characters or longer
2) each value cannot be a substring of tokens found in popular browser User Agent. The current list of prohibited values is: apple, windows, linux, ubuntu, gecko, firefox, chrome, safari, applewebkit, webkit, mozilla, macintosh, khtml, intel, osx, os x, iphone, ipad and mac.
DEV: Replace instances of Discourse.base_uri with Discourse.base_path
This is clearer because the base_uri is actually just a path prefix. This continues the work started in 555f467.
This stops crawlers from hitting tags and category rss feeds to discover
new content, instead they should focus on latest/posts if they need to
consume something regular
Crawlers love hitting the rss feeds (confirmed that both Google and Bing do)
Experimenting with the impact of blocking these feeds and forcing Crawlers to hit
the content direct. It is better if they hit the actual page to start with as opposed to
1. Hit RSS feed
2. Find new content
3. Hit post link
4. Get canonical
5. Hit canonical
Lots of pointless work.
We do not know for sure what impact this will have on newsreader apps,
we will listen for feedback.
Also moved to default crawl delay bing so no more than a req every 5 seconds is allowed
New site settings:
"slow_down_crawler_user_agents" - list of crawlers that will be slowed down
"slow_down_crawler_rate" - how many seconds to wait between requests
Not enforced server side yet
Although most user uploads are probably harmless, it's possible someone
has (either maliciously or not) uploaded sensitive information. Prevent
robots from indexing the uploads route.
