`Case 5:18-md-02834—BLF Document 507-7 Filed 08/26/19 Page 1 of 5
`
`
`
`
`EXHIBIT 6
`
`EXHIBIT 6
`
`
`
`Case 5:18-md-02834-BLF Document 507-7 Filed 08/26/19 Page 2 of 5
`
`
`
`
`
`EXPERT REPORT OF
`PATRICK MCCLORY
`
`
`IN THE MATTER OF:
`
`
`PERSONALWEB TECHNOLOGIES, LLC, and
`LEVEL 3 COMMUNICATIONS, LLC
`adv.
`TWITCH INTERACTIVE, INC.
`
`
`
`
`UNITED STATES DISTRICT COURT
`NORTHERN DISTRICT OF CALIFORNIA
`CASE NO. 5:18-CV-05619-BLF
`
`
`
`AUGUST 23, 2019
`
`
`
`Case 5:18-md-02834-BLF Document 507-7 Filed 08/26/19 Page 3 of 5
`PERSONALWEB TECHNOLOGIES, LLC, ET AL., v. TWITCH INTERACTIVE, INC.
`EXPERT REPORT OF PATRICK MCCLORY
`
`
`71.
`
`If I am being precise, the ‘standard’ for web servers clearly is the file node
`
`+ last-modified time + size (for directly served static content, not coming from an
`
`application server).
`
`72.
`
`It is fairly rare to have a standalone web server with no app server,
`
`especially in the 2012-2014 timeframe.
`
`73.
`
`For specific HTTP servers, if an ETag is not present for a file, the web
`
`server will generate an ETag for the asset:
`
`● Litespeed: file inode, last-modified time + size—see
`
`https://www.litespeedtech.com/docs/webserver/config/tuning#fileETag (Exhibit
`
`16).
`
`● Apache: file inode, last-modified time + size—see
`
`https://httpd.apache.org/docs/2.4/mod/core.html#fileetag (Exhibit 17).
`
`● Nginx: file inode, last-modified time + size—see
`
`http://lxr.nginx.org/source/src/http/ngx_http_core_module.c#1582 (Exhibit 18).
`
`74.
`
`That being said, this default HTTP server behavior happens when an
`
`ETag is not present, and one would have to look at what the application is passing to
`
`the web server for a given request.
`
`75.
`
`There are many, many examples of file-content based ETags in PHP apps
`
`dating back many years:
`
`● https://gist.github.com/oliworx/4951478 (Exhibit 19)
`
`● https://css-tricks.com/snippets/php/intelligent-php-cache-control/ (Exhibit 20)
`
`
`
`26
`
`
`
`Case 5:18-md-02834-BLF Document 507-7 Filed 08/26/19 Page 4 of 5
`PERSONALWEB TECHNOLOGIES, LLC, ET AL., v. TWITCH INTERACTIVE, INC.
`EXPERT REPORT OF PATRICK MCCLORY
`
`
`● https://stackoverflow.com/questions/18218643/php-etag-generation-using-php
`
`(Exhibit 21)
`
`76. Additionally, a few popular PHP frameworks from 2012 also used file-
`
`content based ETags:
`
`● Kohana uses an SHA1 of the rendered content: see
`
`https://github.com/kohana/core/blob/bdbe81afb5a09cee4269d2e2210a0d293265
`
`231a/classes/Kohana/Response.php#L650 (Exhibit 22).
`
`● Symfony uses a weak ETag: see
`
`https://github.com/symfony/symfony/blob/2.0/src/Symfony/Component/HttpFound
`
`ation/Response.php#L674 (Exhibit 23).
`
`● Laravel uses an MD5 of the rendered content: see
`
`https://github.com/laravel/framework/blob/5.8/src/Illuminate/Http/Middleware/Set
`
`CacheHeaders.php#L32 (Exhibit 24).
`
`● Python has a number of toolsets, but Django and Flask are two very popular
`
`frameworks:
`
`○ Python Django uses the response content’s md5—see
`
`https://github.com/django/django/blob/master/django/utils/cache.py#L100-
`
`L103 (Exhibit 25).
`
`○ The same Python Django framework, but from 2012, uses the response
`
`content’s md5: see
`
`https://github.com/django/django/blob/4b27813198ae31892f1159d437e49
`
`2f7745761a0/django/utils/cache.py#L97-L100 (Exhibit 26).
`
`
`
`27
`
`
`
`Case 5:18-md-02834-BLF Document 507-7 Filed 08/26/19 Page 5 of 5
`PERSONALWEB TECHNOLOGIES, LLC, ET AL., v. TWITCH INTERACTIVE, INC.
`EXPERT REPORT OF PATRICK MCCLORY
`
`
`○ Flask uses the Werkzeug web server and Werkzeug, by default,
`
`generates ETags via an MD5 of the response data (body)—see
`
`https://github.com/pallets/werkzeug/blob/71cf9902012338f8ee98338fa7bb
`
`a50572606637/src/werkzeug/http.py#L775 (Exhibit 27).
`
`77. Rack, the web server commonly paired with Ruby on Rails, directly
`
`digests the content body to generate ETags:
`
`● Version 1.2: see https://github.com/rack/rack/blob/rack-1.2/lib/rack/etag.rb#L14
`
`(Exhibit 28).
`
`● Version 1.3: see https://github.com/rack/rack/blob/rack-1.3/lib/rack/etag.rb#L26
`
`(Exhibit 29).
`
`● … Version 1.6: see https://github.com/rack/rack/blob/1-6-
`
`stable/lib/rack/etag.rb#L28 (Exhibit 30).
`
`● The latest version is 2.0: see https://github.com/rack/rack/blob/2-0-
`
`stable/lib/rack/etag.rb#L29 (Exhibit 31).
`
`78. Apache Tomcat (Java) has historically defaulted to a weak ETag with the
`
`ability to override. Websphere (IBM) utilizes the underlying setup in their web server
`
`based on apache tomcat: see
`
`https://developer.ibm.com/answers/questions/334787/using-etag-with-websphere-
`
`portal/ (Exhibit 32).
`
`79.
`
`The ETag workflow seems less mature in the ASP.net/IIS world with lots
`
`of ‘here is how I implemented it’ docs along with a lot of weak ETag defaults.
`
`
`
`28
`
`
Accessing this document will incur an additional charge of $.
After purchase, you can access this document again without charge.
Accept $ Charge
Still Working On It
This document is taking longer than usual to download. This can happen if we need to contact the court directly to obtain the document and their servers are running slowly.
Give it another minute or two to complete, and then try the refresh button.
A few More Minutes ... Still Working
It can take up to 5 minutes for us to download a document if the court servers are running slowly.
Thank you for your continued patience.
This document could not be displayed.
We could not find this document within its docket. Please go back to the docket page and check the link. If that does not work, go back to the docket and refresh it to pull the newest information.
Your account does not support viewing this document.
You need a Paid Account to view this document. Click here to change your account type.
Your account does not support viewing this document.
Set your membership
status to view this document.
With a Docket Alarm membership, you'll
get a whole lot more, including:
- Up-to-date information for this case.
- Email alerts whenever there is an update.
- Full text search for other cases.
- Get email alerts whenever a new case matches your search.
One Moment Please
The filing “” is large (MB) and is being downloaded.
Please refresh this page in a few minutes to see if the filing has been downloaded. The filing will also be emailed to you when the download completes.
Your document is on its way!
If you do not receive the document in five minutes, contact support at support@docketalarm.com.
Sealed Document
We are unable to display this document, it may be under a court ordered seal.
If you have proper credentials to access the file, you may proceed directly to the court's system using your government issued username and password.
Access Government Site
