I have a service with a large proportion of requests with an empty value for HTTP_REFERER . I would like to correctly interpret this and wonder about the most common reasons for this.
I understand that HTTP_REFERER is an optional header field, but most browsers with default settings seem to send them.
Common reasons that I have found so far:
- proxies
- robots
- JavaScript links (all depend on this browser?)
- request from bookmarks or browser launch page
- user enters URL manually
- Flash Links
- Link from another application, such as an email client
- browser settings or privacy browser add-ons
- some personal filters for filtering firewalls
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- this
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