Hi,
recently I've plugged in Tika's content detection into Common Crawl's crawler
(modified Nutch) with
the target to get clean and correct MIME type - the HTTP Content-Type may
contain garbage and isn't
always correct [1].
For the June 2017 crawl I've prepared a comparison of content types sent by the
server in the HTTP
header and as detected by Tika 1.15 [2]. It shows that content types by Tika
are definitely clean
(1,400 different content types vs. more than 6,000 content type "strings" from
HTTP headers).
A look on the "confusions" where Content-Type and Tika differ, shows a mixed
picture: some pairs are
plausible, e.g., if Tika changes the type to a more precise subtype or detects
the MIME at all:
Tika-1.15 HTTP-Content-Type
1001968023 application/xhtml+xml text/html
2298146 application/rss+xml text/xml
617435 application/rss+xml application/xml
613525 text/html unk
361525 application/xhtml+xml unk
297707 application/rdf+xml application/xml
However, there are a few dubious decisions, esp. the group of web server-side
scripting languages
(ASP, JSP, PHP, ColdFusion, etc.):
Tika-1.15 HTTP-Content-Type
2047739 text/x-php text/html
681629 text/asp text/html
193095 text/x-coldfusion text/html
172318 text/aspdotnet text/html
139033 text/x-jsp text/html
38415 text/x-cgi text/html
32092 text/x-php text/xml
18021 text/x-perl text/html
Of course, due to misconfigurations some servers may deliver the script files
unmodified but in
general I wouldn't expect that this happens for millions of pages. I've
checked some of the
affected URLs:
- HTML fragment (no declaration of <!DOCTYPE...> or <html> opening tag)
https://www.projectmanagement.com/profile/profile_contributions.cfm?profileID=46773580&popup=&c_b=0&c_mb=0&c_q=0&c_a=2&c_r=1&c_bc=1&c_wc=0&c_we=0&c_ar=0&c_ack=0&c_v=0&c_d=0&c_ra=2&c_p=0
http://www.privi.com/product-details.asp?cno=C10910011
http://mental-ray.de/Root_alt/Default.asp
http://ekyrs.org/support/index.php?action=profile
http://cwmorse.eu5.org/lineal/mostrar.php?contador=200
- (overlong) comment block at start of HTML which "masks" the HTML declaration
http://www.mannheim-virtuell.de/index.php?branchenID=2&rubrikID=24
http://www.exoduschurch.org/bbs/view.php?id=sunday_school&page=1&sn1=&divpage=1&sn=off&ss=on&sc=on&select_arrange=headnum&desc=asc&no=6
https://www.preventiongenetics.com/About/Resources/disease/MarfansSyndrome.php
https://de.e-stories.org/categories.php?&lan=nl&art=p
- HTML with some scripting fragments ("<?php?>") present:
http://www.eco-ani-yao.org/shien/
- others are clearly HTML (looks more like a bug, at least, there is no simple
explanation)
http://www.proedinc.com/customer/content.aspx?redid=9
http://cball.dyndns.org/wbb2/board.php?boardid=8&sid=bf3b7971faa23413fa1164be0c068f79
http://eusoma.org/Engx/Info/ContactUs.aspx?cont=contact
http://cball.dyndns.org/wbb2/map.php?sid=bf3b7971faa23413fa1164be0c068f79
Obviously certain file suffixes (.php, .aspx) should get less weight compared
to Content-Type sent
from the responding server.
Now my question: where's the best place to fix this: in the crawler [3] or in
Tika?
If anyone is interested in using the detected MIME types or anything else from
Common Crawl - I'm
happy to help! The URL index [4] contains now a new field "mime-detected"
which makes it easy to
search or grep for confusion pairs.
Thanks and best,
Sebastian
[1] https://github.com/commoncrawl/nutch/issues/3
[2]
s3://commoncrawl-dev/tika-content-type-detection/content-type-diff-tika-1.15-cc-main-2017-26.txt.xz
https://commoncrawl-dev.s3.amazonaws.com/tika-content-type-detection/content-type-diff-tika-1.15-cc-main-2017-26.txt.xz
[3]
https://github.com/apache/nutch/blob/master/src/java/org/apache/nutch/util/MimeUtil.java#L152
[4] http://commoncrawl.org/2015/04/announcing-the-common-crawl-index/
