Carl

Carl Mastrangelo

Hi, My name is Carl and I'm a software engineer and aspiring artist.


Markdown and Upload

I’m trying out using Markdown on my blog, and to experiment, I have enumerated the steps needed to upload a picture to an image site I used to run. I have listed the details here because it is full of corner cases and non intuitive setups found in shared hosting environments.

Upload Steps

This document describes the file upload procedure to the Server

  1. Validate User Session
    1. If the session key and id are present, use them as a Lookup
    2. Lookup the session by key and id
      • If the session is not found, or is not valid, Look-up session by IP address
      • If looking up by IP address fails, create a new session
      • If creating a new session fails, explode.
  2. Extract and Clean Tags
    1. Take each tag, and transliterate from UTF-8 to ASCII
    2. Take eash tag, and trim leading and trailing white space
    3. Take each tag, and lowercase
    4. Remove all empty tags
    5. Remove all duplicate tags
    6. Check that there are no more than the maximum tags, to avoid abuse.
    7. Check that there are at least the minimum number of tags.
  3. Extract and validate the Category Id
  4. Check that the IP hasn’t exceeded that max uploads per unit time (not the session id!)
  5. Get a local copy of the Uploaded picture data
    • If the picture came from a file upload
      1. Make sure the upload didn’t have an error
      2. The the file name (as provided by the client) and the file path (location in /tmp)
    • If a file URL was provided
      1. Record the referrer, and other meta data about where the picture came from.
      2. Attempt to download the file. On success get the file path
      3. If the file download had a Content-disposition file name, use it.
      4. If the file did not have a filename, or didn’t from from HTTP, use the URL basename.
  6. Check if the file size is too small.
  7. Check that the file name doesn’t have php in it.
  8. Check that the file is of a valid type (GIF, PNG, or JPEG)
  9. Calculate the file hash, and lookup to see if the image already exists
  10. Check to see (using the hash) to see if the file has been previously deleted.
  11. Insert the Image post data into the database, and get a post ID
  12. Rename the temp Image file to the post ID and file extension
  13. Update the bump ordering using the post ID
  14. Record that the IP address has uploaded a picture for use in step #4
  15. Store references from step #5 if present
  16. Insert all tags from step #2
  17. Add “Goats” (the currency of the site) to the session based on how many tags were provided
  18. Record in the session that it was last used at this time. (for Garbage collection policy)
  19. Create a thumbnail image of the picture
  20. Invalidate the Index HTML cache
  21. If requested, redirect the user back to the index.

Some points that you might have noticed:

And, some points that you may not have noticed:


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