This is the goal that I have no idea how to achieve. As an iOS reverse engineer, my idea is that if I know in the source code how/where the server sends this image, I can track back and see where the server loads this image locally. But I read Ruby like reading seudo code, so locating where the server sends this image becomes a great great task for me 
That should be a lot easier for a person whoâre familiar with the source code though
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In discourse/upload.rb at master ¡ discourse/discourse ¡ GitHub
I saw the table uploads which stored all the uploads of a user. For user Baal998 whose user ID is 1637, I then run SELECT * FROM uploads WHERE user_id = '1637'; and the result is
id | user_id | original_filename | filesize | width | height | url | created_at | updated_at | sha1 | origin | retain_hours | extension | thumbnail_width | thumbnail_height | etag | secure | access_control_post_id | original_sha1 | animated | verified | verification_status
------+---------+-------------------+----------+-------+--------+-----------------------------------------------------------------------------+----------------------------+----------------------------+------------------------------------------+--------+--------------+-----------+-----------------+------------------+------+--------+------------------------+---------------+----------+----------+---------------------
2210 | 1637 | 2.pic.jpg | 60610 | | | /uploads/default/original/2X/c/cb2188eaeecc3a648f021fa00da4734bd60ca183.jpg | 2016-08-08 09:37:13.937306 | 2018-01-05 02:38:49.498264 | cb2188eaeecc3a648f021fa00da4734bd60ca183 | | | jpg | | | | f | | | | | 1
(1 row)
Which is the same to running Upload.find(user_avatar.custom_upload_id).url with rails.
My guess is that after the user uploaded avatar, discourse will do something to the original avatar file and store the optimized files in somewhere else?
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In table optimized_images this row seemed suspicious
id | sha1 | extension | width | height | upload_id | url | filesize | etag | version | created_at | updated_at
-------+------------------------------------------+-----------+-------+--------+-----------+----------------------------------------------------------------------------------------+----------+------+---------+----------------------------+----------------------------
49538 | e6dc9b0d6c18f2a4c3c0d2027534d01cfc89c84e | .jpg | 135 | 135 | 2210 | /uploads/default/optimized/2X/c/cb2188eaeecc3a648f021fa00da4734bd60ca183_2_135x135.jpg | 10968 | | 2 | 2016-08-08 09:37:13.937306 | 2016-08-08 09:37:13.937306
(1 row)
The sha1 and filesize matches https://iosre.com/user_avatar/iosre.com/baal998/135/2210_2.png , but on server this file doesnât exist.
root@iosre:/var/discourse/shared/standalone# ls /uploads/default/optimized/2X/c/cb2188eaeecc3a648f021fa00da4734bd60ca183_2_135x135.jpg
ls: cannot access /uploads/default/optimized/2X/c/cb2188eaeecc3a648f021fa00da4734bd60ca183_2_135x135.jpg: No such file or directory
No idea what was wrong.
Problem solved:
Someone from my forum told me that this avatar image might be stored in nginx cache under proxy_cache_path, which was usually /var/nginx/cache, but I couldnât find either proxy_cache_path or /var/nginx/cache.
I was inspired by him that I entered the discourse app via launcher enter app and then found nginx cache:
root@iosre:/var/discourse/shared# /var/discourse/launcher enter app
WARNING: Docker version 17.05.0-ce deprecated, recommend upgrade to 17.06.2 or newer.
root@iosre-app:/var/www/discourse# cd /var/nginx/cache
root@iosre-app:/var/nginx/cache# ls
0 1 2 3 4 5 6 7 8 9 a b c d e f
root@iosre-app:/var/nginx/cache#
And deleted all the caches:
root@iosre-app:/var/nginx/cache# ls
root@iosre-app:/var/nginx/cache#
The image was gone.
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