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add Utility.HtmlDetect

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This will be used in youtube-dl integration, to tell when a html page has
been downloaded by addurl, in which case it is worth running youtube-dl
to see if it can extract media from it.

tagsoup is an almost free dependency, because yesod depends on it.
So, this only really adds a dep when git-annex is built without the
webapp.

I'd like this to as closely as possible match how browsers decide if a
page is html or not. Unfortunately, that is fairly heuristic, in order
to support malformed html. And, we don't want to falsely detect
something as html just because it has something that looks like a html
tag embedded somewhere in it. Probably any major video hosting site is
going to be serving html documents that at least start with a <html>
tag, so requiring that or a DOCTYPE should be good enough.

This commit was sponsored by Jeff Goeke-Smith on Patreon.
This commit is contained in:
Joey Hess 2017-11-28 12:50:30 -04:00
parent c37838d1b7
commit 57b4c5bdff
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35
Utility/HtmlDetect.hs Normal file
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@ -0,0 +1,35 @@
{- html detection
-
- Copyright 2017 Joey Hess <id@joeyh.name>
-
- License: BSD-2-clause
-}
module Utility.HtmlDetect where
import Text.HTML.TagSoup
import Data.Char
-- | Detect if a string is a html document.
--
-- The document many not be valid, and will still be detected as html,
-- as long as it starts with a "<html>" or "<!DOCTYPE html>" tag.
--
-- Html fragments like "<p>this</p>" are not detected as being html,
-- although some browsers may chose to render them as html.
isHtml :: String -> Bool
isHtml = evaluate . canonicalizeTags . parseTags . truncate
where
-- We only care about the beginning of the file,
-- so although tagsoup parses lazily anyway, truncate it.
truncate = take 16384
evaluate (TagOpen "!DOCTYPE" ((t, _):_):_) = map toLower t == "html"
evaluate (TagOpen "html" _:_) = True
-- Allow some leading whitespace before the tag.
evaluate (TagText t:rest)
| all isSpace t = evaluate rest
| otherwise = False
-- It would be pretty weird to have a html comment before the html
-- tag, but easy to allow for.
evaluate (TagComment _:rest) = evaluate rest
evaluate _ = False

1
debian/control vendored
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@ -25,6 +25,7 @@ Build-Depends:
libghc-dlist-dev,
libghc-uuid-dev,
libghc-aeson-dev,
libghc-tagsoup-dev,
libghc-unordered-containers-dev,
libghc-ifelse-dev,
libghc-bloomfilter-dev,

8
doc/todo/switch_from_quvi_to_youtube-dl.mdwn
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@ -23,6 +23,14 @@ Both of those changes would need changes to user's workflows and cron jobs.
git-annex could keep supporting quvi for some time, and warn when it uses
quvi, to help with the transition.
> Alternatively, git-annex addurl could download the url first, and then
> check the file to see if it looks like html. If so, run youtube-dl (which
> unfortunately has to download it again) and see if it manages to rip
> media from it. This way, addurl of non-html files does not have extra
> overhead, and the redundant download is fairly small compared to ripping
> the media. Only the unusual case where addurl is being used on html that
> does not contain media becomes more expensive.
Another gotcha is playlists. youtube-dl downloads playlists automatically.
But, git-annex needs to record an url that downloads a single file so that
`git annex get` works right. So, playlists will need to be disabled when

2
git-annex.cabal
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@ -347,6 +347,7 @@ Executable git-annex
persistent,
persistent-template,
aeson,
tagsoup,
unordered-containers,
feed (>= 0.3.9),
regex-tdfa,
@ -1001,6 +1002,7 @@ Executable git-annex
Utility.Glob
Utility.Gpg
Utility.Hash
Utility.HtmlDetect
Utility.HumanNumber
Utility.HumanTime
Utility.InodeCache