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Archiving URLs

Archiving the Web, because nothing lasts forever: statistics, online archive services, extracting URLs automatically from browsers, and creating a daemon to regularly back up URLs to multiple sources.

Links on the Internet last forever or a year, whichever inconveniences you more. This is a major problem for anyone serious about writing with good references, as link rot will cripple several percent of all links each year, and compounding.

To deal with link rot, I present my multi-pronged archival strategy using a combination of scripts, daemons, and Internet archival services: URLs are regularly dumped from both my web browser’s daily browsing and my website pages into an archival daemon I wrote, which pre-emptively downloads copies locally and attempts to archive them in the Internet Archive. This ensures a copy will be available indefinitely from one of several sources. Link rot is then detected by regular runs of linkchecker, and any newly dead links can be immediately checked for alternative locations, or restored from one of the archive sources.

As an additional flourish, my local archives are efficiently cryptographically timestamped using Bitcoin in case forgery is a concern, and I demonstrate a simple compression trick for substantially reducing sizes of large web archives such as crawls (particularly useful for repeated crawls such as my DNM archives).

Given my interest in long term content and extensive linking, link rot is an issue of deep concern to me. I need backups not just for my files1, but for the web pages I read and use—they’re all part of my exomind. It’s not much good to have an extensive essay on some topic where half the links are dead and the reader can neither verify my claims nor get context for my claims.

Detection

With every new spring
the blossoms speak not a word
yet expound the Law—
knowing what is at its heart
by the scattering storm winds.

Shōtetsu7

The first remedy is to learn about broken links as soon as they happen, which allows one to react quickly and scrape archives or search engine caches (‘lazy preservation’). I currently use linkchecker to spider Gwern.net looking for broken links. linkchecker is run in a cron job like so:

@monthly linkchecker --check-extern --timeout=35 --no-warnings --file-output=html \
                      --ignore-url=^mailto --ignore-url=^irc --ignore-url=http://.*\.onion \
                      --ignore-url=paypal.com --ignore-url=web.archive.org \
                     https://gwern.net

Just this command would turn up many false positives. For example, there would be several hundred warnings on Wikipedia links because I link to redirects; and linkchecker respects robots.txts which forbid it to check liveness, but emits a warning about this. These can be suppressed by editing ~/.linkchecker/linkcheckerrc to say ignorewarnings=http-moved-permanent,http-robots-denied (the available warning classes are listed in linkchecker -h).

The quicker you know about a dead link, the sooner you can look for replacements or its new home.

Prevention

Remote Caching

Anything you post on the internet will be there as long as it’s embarrassing and gone as soon as it would be useful.8

taejo

We can ask a third party to keep a cache for us. There are several archive site possibilities:

  1. the Internet Archive
  2. WebCite
  3. Perma.cc (highly limited; has lost some archives)
  4. Linterweb’s WikiWix9.
  5. Peeep.us (defunct as of 2018)
  6. Archive.is
  7. Pinboard (with the $22/year archiving option10)

There are other options but they are not available like Google11 or various commercial/government archives12

(An example would be bits.blogs.nytimes.com/2010/12/07/palm-is-far-from-game-over-says-former-chief/ being archived at webcitation.org/5ur7ifr12.)

These archives are also good for archiving your own website:

  1. you may be keeping backups of it, but your own website/server backups can be lost (I can speak from personal experience here), so it’s good to have external copies
  2. Another benefit is the reduction in ‘bus-factor’: if you were hit by a bus tomorrow, who would get your archives and be able to maintain the websites and understand the backups etc? While if archived in IA, people already know how to get copies and there are tools to download entire domains.
  3. A focus on backing up only one’s website can blind one to the need for archiving the external links as well. Many pages are meaningless or less valuable with broken links. A linkchecker script/daemon can also archive all the external links.

So there are several benefits to doing web archiving beyond simple server backups.

My first program in this vein of thought was a bot which fired off WebCite, Internet Archive/Alexa, & Archive.is requests: Wikipedia Archiving Bot, quickly followed up by a RSS version. (Or you could install the Alexa Toolbar to get automatic submission to the Internet Archive, if you have ceased to care about privacy.)

The core code was quickly adapted into a gitit wiki plugin which hooked into the save-page functionality and tried to archive every link in the newly-modified page, Interwiki.hs

Finally, I wrote archiver, a daemon which watches13/reads a text file. Source is available via git clone https://github.com/gwern/archiver-bot.git. (A similar tool is Archiveror; the Python package archivenow does something similar & as of January 2021 is probably better.)

The library half of archiver is a simple wrapper around the appropriate HTTP requests; the executable half reads a specified text file and loops as it (slowly) fires off requests and deletes the appropriate URL.

That is, archiver is a daemon which will process a specified text file, each line of which is a URL, and will one by one request that the URLs be archived or spidered

Usage of archiver might look like archiver ~/.urls.txt gwern@gwern.net. In the past, archiver would sometimes crash for unknown reasons, so I usually wrap it in a while loop like so: while true; do archiver ~/.urls.txt gwern@gwern.net; done. If I wanted to put it in a detached GNU screen session: screen -d -m -S "archiver" sh -c 'while true; do archiver ~/.urls.txt gwern@gwern.net; done'. Finally, rather than start it manually, I use a cron job to start it at boot, for a final invocation of

@reboot sleep 4m && screen -d -m -S "archiver" sh -c 'while true; do archiver ~/.urls.txt \
        "cd ~/www && nice -n 20 ionice -c3 wget --unlink --limit-rate=20k --page-requisites --timestamping \
        -e robots=off --reject .iso,.exe,.gz,.xz,.rar,.7z,.tar,.bin,.zip,.jar,.flv,.mp4,.avi,.webm \
        --user-agent='Firefox/4.9'" 500; done'

Local Caching

Remote archiving, while convenient, has a major flaw: the archive services cannot keep up with the growth of the Internet and are woefully incomplete. I experience this regularly, where a link on Gwern.net goes dead and I cannot find it in the Internet Archive or WebCite, and it is a general phenomenon: Ainsworth et al 2012 find <35% of common Web pages ever copied into an archive service, and typically only one copy exists.

Caching Proxy

The most ambitious & total approach to local caching is to set up a proxy to do your browsing through, and record literally all your web traffic; for example, using Live Archiving Proxy (LAP) or WarcProxy which will save as WARC files every page you visit through it. (Zachary Vance explains how to set up a local HTTPS certificate to MITM your HTTPS browsing as well.)

One may be reluctant to go this far, and prefer something lighter-weight, such as periodically extracting a list of visited URLs from one’s web browser and then attempting to archive them.

Batch Job Downloads

For a while, I used a shell script named, imaginatively enough, local-archiver:

#!/bin/sh
set -euo pipefail

cp `find ~/.mozilla/ -name "places.sqlite"` ~/
sqlite3 places.sqlite "SELECT url FROM moz_places, moz_historyvisits \
                       WHERE moz_places.id = moz_historyvisits.place_id \
                             and visit_date > strftime('%s','now','-1.5 month')*1000000 ORDER by \
                       visit_date;" | filter-urls >> ~/.tmp
rm ~/places.sqlite
split -l500 ~/.tmp ~/.tmp-urls
rm ~/.tmp

cd ~/www/
for file in ~/.tmp-urls*;
 do (wget --unlink --continue --page-requisites --timestamping --input-file $file && rm $file &);
done

find ~/www -size +4M -delete

The code is not the prettiest, but it’s fairly straightforward:

  1. the script grabs my Firefox browsing history by extracting it from the history SQL database file14, and feeds the URLs into wget.

    wget is not the best tool for archiving as it will not run JavaScript or Flash or download videos etc. It will download included JS files but the JS will be obsolete when run in the future and any dynamic content will be long gone. To do better would require a headless browser like PhantomJS which saves to MHT/MHTML, but PhantomJS refuses to support it and I’m not aware of an existing package to do this. In practice, static content is what is most important to archive, most JS is of highly questionable value in the first place, and any important YouTube videos can be archived manually with youtube-dl, so wget’s limitations haven’t been so bad.

  2. The script splits the long list of URLs into a bunch of files and runs that many wgets in parallel because wget apparently has no way of simultaneously downloading from multiple domains. There’s also the chance of wget hanging indefinitely, so parallel downloads continues to make progress.

  3. The filter-urls command is another shell script, which removes URLs I don’t want archived. This script is a hack which looks like this:

    #!/bin/sh
    set -euo pipefail
    cat /dev/stdin | sed -e "s/#.*//" | sed -e "s/&sid=.*$//" | sed -e "s/\/$//" | grep -v -e 4chan -e reddit ...
  4. delete any particularly large (>4MB) files which might be media files like videos or audios (podcasts are particular offenders)

A local copy is not the best resource—what if a link goes dead in a way your tool cannot detect so you don’t know to put up your copy somewhere? But it solves the problem decisively.

The downside of this script’s batch approach soon became apparent to me:

  1. not automatic: you have to remember to invoke it and it only provides a single local archive, or if you invoke it regularly as a cron job, you may create lots of duplicates.
  2. unreliable: wget may hang, URLs may be archived too late, it may not be invoked frequently enough, >4MB non-video/audio files are increasingly common…
  3. I wanted copies in the Internet Archive & elsewhere as well to let other people benefit and provide redundancy to my local archive

It was to fix these problems that I began working on archiver—which would run constantly archiving URLs in the background, archive them into the IA as well, and be smarter about media file downloads. It has been much more satisfactory.

Daemon

archiver has an extra feature where any third argument is treated as an arbitrary sh command to run after each URL is archived, to which is appended said URL. You might use this feature if you wanted to load each URL into Firefox, or append them to a log file, or simply download or archive the URL in some other way.

For example, instead of a big local-archiver run, I have archiver run wget on each individual URL: screen -d -m -S "archiver" sh -c 'while true; do archiver ~/.urls.txt gwern@gwern.net "cd ~/www && wget --unlink --continue --page-requisites --timestamping -e robots=off --reject .iso,.exe,.gz,.xz,.rar,.7z,.tar,.bin,.zip,.jar,.flv,.mp4,.avi,.webm --user-agent='Firefox/3.6' 120"; done'. (For private URLs which require logins, such as darknet markets, wget can still grab them with some help: installing the Firefox extension Export Cookies, logging into the site in Firefox like usual, exporting one’s cookies.txt, and adding the option --load-cookies cookies.txt to give it access to the cookies.)

Alternately, you might use curl or a specialized archive downloader like the Internet Archive’s crawler Heritrix.

Cryptographic Timestamping Local Archives

We may want cryptographic timestamping to prove that we created a file or archive at a particular date and have not since altered it. Using a timestamping service’s API, I’ve written 2 shell scripts which implement downloading (wget-archive) and timestamping strings or files (timestamp). With these scripts, extending the archive bot is as simple as changing the shell command:

@reboot sleep 4m && screen -d -m -S "archiver" sh -c 'while true; do archiver ~/.urls.txt gwern2@gwern.net \
        "wget-archive" 200; done'

Now every URL we download is automatically cryptographically timestamped with ~1-day resolution for free.

Resource Consumption

The space consumed by such a backup is not that bad; only 30–50 gigabytes for a year of browsing, and less depending on how hard you prune the downloads. (More, of course, if you use linkchecker to archive entire sites and not just the pages you visit.) Storing this is quite viable in the long term; while page sizes have increased 7× between 2003 and 2011 and pages average around 400kb15, Kryder’s law has also been operating and has increased disk capacity by ~128×—in 2011, $107.5617523$802011 will buy you at least 2 terabytes, that works out to 4 cents a gigabyte or 80 cents for the low estimate for downloads; that is much better than the annual fee that somewhere like Pinboard charges. Of course, you need to back this up yourself. We’re relatively fortunate here—most Internet documents are ‘born digital’ and easy to migrate to new formats or inspect in the future. We can download them and worry about how to view them only when we need a particular document, and Web browser backwards-compatibility already stretches back to files written in the early 1990s. (Of course, we’re probably screwed if we discover the content we wanted was dynamically presented only in Adobe Flash or as an inaccessible ‘cloud’ service.) In contrast, if we were trying to preserve programs or software libraries instead, we would face a much more formidable task in keeping a working ladder of binary-compatible virtual machines or interpreters16. The situation with digital movie preservation hardly bears thinking on.

There are ways to cut down on the size; if you tar it all up and run 7-Zip with maximum compression options, you could probably compact it to 1⁄5th the size. I found that the uncompressed files could be reduced by around 10% by using fdupes to look for duplicate files and turning the duplicates into a space-saving hard link to the original with a command like fdupes --recurse --hardlink ~/www/. (Apparently there are a lot of bit-identical JavaScript (eg. JQuery) and images out there.)

Good filtering of URL sources can help reduce URL archiving count by a large amount. Examining my manual backups of Firefox browsing history, over the 1153 days from 2014-02-25 to 2017-04-22, I visited 2,370,111 URLs or 2055 URLs per day; after passing through my filtering script, that leaves 171,446 URLs, which after de-duplication yields 39,523 URLs or ~34 unique URLs per day or 12,520 unique URLs per year to archive.

This shrunk my archive by 9GB from 65GB to 56GB, although at the cost of some archiving fidelity by removing many filetypes like CSS or JavaScript or GIF images. As of 2017-04-22, after ~6 years of archiving, between xz compression (at the cost of easy searchability), aggressive filtering, occasional manual deletion of overly bulky domains I feel are probably adequately covered in the IA etc, my full WWW archives weigh 55GB.

URL Sources

Browser History

There are a number of ways to populate the source text file. For example, I have a script firefox-urls:

#!/bin/sh
set -euo pipefail

cp --force `find ~/.mozilla/firefox/ -name "places.sqlite"|sort|head -1` ~/
sqlite3 -batch places.sqlite "SELECT url FROM moz_places, moz_historyvisits \
                       WHERE moz_places.id = moz_historyvisits.place_id and \
                       visit_date > strftime('%s','now','-1 day')*1000000 ORDER by \
                       visit_date;" | filter-urls
rm ~/places.sqlite

(filter-urls is the same script as in local-archiver. If I don’t want a domain locally, I’m not going to bother with remote backups either. In fact, because of WebCite’s rate-limiting, archiver is almost perpetually back-logged, and I especially don’t want it wasting time on worthless links like 4chan.)

This is called every hour by cron:

@hourly firefox-urls >> ~/.urls.txt

This gets all visited URLs in the last time period and prints them out to the file for archiver to process. Hence, everything I browse is backed-up through archiver.

Non-Firefox browsers can be supported with similar strategies; for example, Zachary Vance’s Chromium scripts likewise extracts URLs from Chromium’s SQL history & bookmarks.

Website Spidering

Sometimes a particular website is of long-term interest to one even if one has not visited every page on it; one could manually visit them and rely on the previous Firefox script to dump the URLs into archiver but this isn’t always practical or time-efficient. linkchecker inherently spiders the websites it is turned upon, so it’s not a surprise that it can build a site map or simply spit out all URLs on a domain; unfortunately, while linkchecker has the ability to output in a remarkable variety of formats, it cannot simply output a newline-delimited list of URLs, so we need to post-process the output considerably. The following is the shell one-liner I use when I want to archive an entire site (note that this is a bad command to run on a large or heavily hyper-linked site like the English Wikipedia or LessWrong!); edit the target domain as necessary:

linkchecker --check-extern -odot --complete -v --ignore-url=^mailto --no-warnings http://www.longbets.org
    | grep -F http #
    | grep -F -v -e "label=" -e "->" -e '" [' -e '" ]' -e "/ "
    | sed -e "s/href=\"//" -e "s/\",//" -e "s/ //"
    | filter-urls
    | sort --unique >> ~/.urls.txt

When linkchecker does not work, one alternative is to do a wget --mirror and extract the URLs from the filenames—list all the files and prefix with a “http://” etc.

Fixing Redirects

Redirected URLS (primarily HTTP 301) are not hard to fix, and are worth treating as broken links and updating/fixing:

  1. redirects are broken links in disguise:

    This is particularly obvious when every URL is redirected to a homepage or error page because they were too lazy to set up the correct redirects and decide to lie by masking the underlying 404 error. Some broken redirects are subtler and use longer URLs, but can be spotted by reading the final URL: often there will be a tell-tale word or parameter like paywall or accessDenied or ?cookie=missing. (It would be hard to detect these automatically by any content-based solution because they are site-specific, constantly changing, and in many cases preserve a ‘teaser’ or abstract, and simply hide the rest.)

  2. redirects are prelude to link breaking:

    Redirects signal changes in a website, and on the Internet, change is usually for the worse. Many domain moves, www→naked subdomain, or HTTP→HTTPS migrations will maintain redirects for a time, and then a later change will break them. (I don’t know if the webmasters in question regard the interim as ‘adequate time to fix’ or if later changes make it hard to maintain the redirect.) The ‘new’ webpage may be substantially different (assets like images are frequently broken in migrations) and needs to be checked to see if it is de facto dead. (This is especially true of Wikipedia articles: when a page is ‘redirected’ or ‘merged’, it usually comes out the worse.) Redirects risk bugs when part of a page’s infrastructure: if a resource is supposed to be loaded over HTTP but gets redirected by a site-wide redirect to HTTPS, say, or vice-versa, then a web browser may kill the request for security reasons, permanently breaking whatever that resource does. The new domain may be a spammer domain, who has purchased it to exploit you & your readers’ inbound traffic. Sometimes an old domain will be abandoned entirely and all its redirects break instantly.

  3. Redirects cause ambiguous, complex, & redundant names:

    If one links a URL and also a redirect to the URL, even stipulating that the redirect never breaks, this causes a wide variety of problems.

    Broadly: one will not get the benefits of the browser highlighting an already-visited link, so one may waste time clicking on a known reference. If one searches the corpus for one URL, they will miss the other hits. If one fixes a broken URL, one hasn’t fixed the redirects to that broken URL & they remain broken. It is harder to fix broken URLs in the first place: you might find that it’s not archived under one URL but an archive exists under the other URL, if only you knew to check.17 One (and one’s readers) may check the corpus for a reference & copy an outdated URL elsewhere like a comment, setting that comment up for all these problems down the line.

    Redirects interfere with many Gwern.net features: with my local archives & annotations, use of multiple URLs causes glitches: beyond the missing-archives, I might write a high-quality annotation for one URL while the other URL has no annotation or just an automatic (low-quality) annotation, or they might be the same annotation but diverge over time. Redundant entries cause issues with the similar-links recommendations, because of course if one version is similar to some other annotation, then the other versions will be near-identically similar. Use of redundant names also increases the risk of accidentally setting up redirect loops or redirecting to the wrong place. It clutters my link-checking reports, hiding broken links & bugs in other features (eg. there might be a bug where Gwern.net systematically generates the wrong links, which are fixed by redirects, hiding the bug, but remaining visible in link-checking reports—if it’s not buried under a ton of other redirects or errors). It can break tools like curl which by default won’t follow redirects (because that might be dangerous or wrong), and archiving tools may not work. The final URL/domain may act differently from the original (eg. it might set different X-Frame-Options headers, breaking my live-link functionality, as is especially likely given that newer web software tends to disable as much as possible—‘change is bad’, see #2).

    None of these are major problems, but each one is a paper-cut which comes up more & more the larger & more complex the Gwern.net corpus & website get. So it helps to squash redirects where I find them and keep URLs as canonical as possible.

  4. Redirects are slower:

    Each redirect costs some milliseconds, and if they cross domains, the lookup can take a while. It is not terribly hard for redirects to stack up: on Gwern.net, a link to an old document could easily incur 4+ redirects.18 Given how much one sweats to eliminate even 100ms from load-time, why tolerate redirects which can be fixed with the swipe of a search-and-replace?

Redirects are reported by linkchecker & the W3C linkchecker.

To fix a redirect, one can hand-edit case by case, but redirects are so pervasive that one should use some sort of globa l search-and-replace.

Gwern.net Redirect Fixing

Because Gwern.net is primarily text-file based and its codebase has unit-tests, I have scripts to heavily automate finding & fixing redirects—no need to edit the source files by hand! (Ain’t no one got time for that.)

For Gwern.net use, I wrote a simple site-wide string search-and-replace gwsed.sh to allow easy updates like gwsed.sh 'URL1' 'URL2'. (It includes a special case for the common scenario of a site-wide HTTP→HTTPS migration, to detect gwsed.sh 'http://DOMAIN/URL1' 'https://DOMAIN/URL2', where the two strings differ solely by a http vs https prefix, and rewrite it to do gwsed.sh 'http://DOMAIN' 'https://DOMAIN' instead to update all links to that domain. It also includes a special-case for the format of the W3C linkchecker: a command like gwsed.sh URL1 redirected to URL2 will be converted to gwsed.sh URL1 URL2 so I can simply copy-paste right into the terminal.) This also makes updates scriptable in bulk; for example, if I want to do a site-wide check instead of a page-by-page check with the linkchecker tools, I can extract the URLs from all site files, process in a loop to see if they have non-zero redirects when downloaded using curl, print out the old/new, review by eye to delete evil or spurious ones, and automatically string-rewrite the rest:

cd ~/wiki/
URLS=$(find ./ -type f -name "*.page" | \
    parallel runghc -istatic/build/ ./static/build/link-extractor.hs | \
    grep -E -e '^http' | head -500 | sort --unique)

for URL in "$URLS"; do
    URLNEW=$(curl --write-out '%{url_effective}\n' --head --location --silent --show-error \
            "$URL" --output /dev/null);
    if [ "$URL" != "$URLNEW" ]; then echo "$URL redirected to $URLNEW"; fi;
done

The link-icon & live-link features rely heavily on domain name matches, so they are vulnerable to websites changing; fixing redirects can silently break them. However, they include test suites with at least one example per rule and exercising all of the branches or domains that a rule matches, and the search-and-replace modifies those files as well; so if URLs update, the test-suites will show up on a diff, and if they break the rules, the test-suites will error out on the next sync. So I can simply toss off gwsed.sh calls and be sure that they won’t silently break anything.

Preemptive Local Archiving

In 2020-02, because of the increasing difficulty of repairing old links, I switched Gwern.net’s primary linkrot defense to preemptive local archiving: automatically mirroring locally all PDFs & web pages using manually-reviewed (and edited) SingleFile snapshots.

While it costs more time upfront (and presented some subtle UX problems like the “Arxiv problem”), it reduces total linkrot work.

Around 2019, while working on a linkchecker report, and spending time tracking down one particularly elusive broken link and drumming my fingers waiting on the slow Wayback Machine website, and comparing the mess to the half-minute it’d’ve taken to make & upload a snapshot with SingleFile, I realized: it’s a lot harder to fix dead links than it is to archive live links. Prevention > cure.

Easier. If you take the linkrot risk estimates seriously (and having watched so many links die on Gwern.net, I believe them), then as long as fixing is >2–3× harder than archiving (it definitely is), you are better off just archiving from the start instead of wasting time on reports & manual fixing one by one.

Higher-quality. Worse, while the preemptive archiving can be refined & improved, the reactive approach is inherently one of “toil”—treading water. Throw in the reality that the archives often fail or are inadequate, and their decreasing efficacy at capturing web pages as pages get ever more baroque and complex, that archives are ‘un-opinionated’ in making no attempt to strip ads/spam19 or optimize the snapshots or work as a ‘live link’ popup (when the full page pops up inside an iframe cf. the screenshot failure), the public-good of providing an independent archive, the greater speed of loading links from Gwern.net instead of a foreign domain (especially the slow IA), and I had to concede that the cost-benefit had long since favored preemptive local archiving.

Ripping off the bandaid. I had hoped this would not be the case because I wanted to limit the number of archives I had to make or host, but the burden was becoming unsustainable when combined with other site maintenance needs. I had no excuse from expensive cloud storage (even 100GB would have near-zero marginal cost after my move to Hetzner dedicated hosting in 2017), rewriting links would be easy using the Pandoc API, SingleFile was working well when I used it manually & had a convenient CLI mode for scripting purposes like this, and working on fixing broken links was annoying me slightly more every time.

Local Snapshots

So after mulling over the design for a while, I pulled the trigger in 2020-02, creating LinkArchive.hs, which maintains a database of URL/archive/status tuples, and calls linkArchive.sh to lookup or generate the snapshots using SingleFile CLI. The snapshots are reviewed by hand to verify that they work & are readable; if they are not, I make a new one, and often invest some time in making a bunch of uBlock Origin rules to clean a page up.

While it did not solve existing broken links or breakage of links where SingleFile can’t make a good snapshot, and it is a bit annoying to curate snapshots, it is a dramatic improvement over the status quo and I expect the benefits to only increase with time.

Workflow

  1. Database+directories: A simple database of URLs is maintained, with their status: either the first-seen date, or their on-disk path.

    The URL’s snapshot lives at /doc/www/$DOMAIN/SHA1($URL).html; the hash makes it simple to encode the name without escaping issues or incurring the difficulties of imitating the target URL’s directory structure20, and the separate prefixed domain helped compatibility with the link-icon rules.21

  2. Compile-time archiving:

    When compiling a page, each link is checked to see if it is on the blacklist (because it is a link which cannot or should not be archived). If not, then if it has an archive, it is rewritten to point to the archive instead. (The original URL is stored in an HTML attribute for any other tools that need to know what that was, such as the popups.) If it doesn’t, then the date is checked: if it was first-seen >6022 days ago, then it is time to archive the URL. (I limit the number of archives per site compilation to 12, to spread out the burden.)

    The archiving script checks the URL. If the URL returns a PDF MIME type, then it downloads the PDF and (like my manually-hosted PDFs) runs ocrmypdf on it to ensure that it has decent OCR, is a standard PDF/A archival-quality PDF, and throws in JBIG2 compression which will often save 2–3× space. If it’s a regular HTML URL, it instead runs SingleFile CLI, which opens the URL in a local Chrome installation, loads all the JS and lazy images etc, and writes out a static snapshot. (In theory, this Chrome instance should have all my usual extensions enabled like uBlock & cookies enabling logins23, but in practice I’ve run into problems and I’m not sure what exactly is getting run because it is impossible to debug.)

  3. Manual review: The URL & its new snapshot (whether PDF or HTML) are then both opened in Firefox for manual review.

    A bad snapshot may require me to add the domain or URL to the blacklist. It may also just be broken (in many different ways, including reloading to a nonexistent URL!), in which case I have to find a replacement URL & do a global rewrite (and the replacement URL will eventually be archived).

    Alternately, I may need to make a new snapshot manually, after deleting sticky elements with Always Kill Sticky, scrolling the page to load lazy elements, or spending a while with the uBlock element-picker to delete the most obnoxious elements. (I tried initially to edit the raw HTML of the SingleFile snapshot, but the data-URI encoding of images, and the spaghetti architecture of the pages most in need of de-cruddification, meant that it was far harder to edit it in a text editor than to simply use uBlock or the built-in web tool ‘inspector’ to select & delete. This can also be done repeatedly: take a SingleFile snapshot, delete stuff with inspector, and save with SingleFile again.) Sometimes a page will fail in Chromium SingleFile, but then succeed in Firefox SingleFile. Taking the time to remove all the ads & bric-a-brac is useful because it makes the page less likely to break in the future, smaller & faster, more readable as a ‘live’ popup, easier to see if anything is missing, and amortizes across future snapshots (so the manual review gets a little easier every time as the blacklist & blocklist expand).

  4. Metadata/hiding: The local archives are treated mostly like regular files, while trying to minimize search engine or user exposure; this is because various entities might not appreciate the mirrors24, and I don’t want to have to maintain them indefinitely (particularly by setting up redirects to avoid breaking old hash-URLs due to churn). People will still link to them, but there’s only so much one can do.

    The Gwern.net web server (nginx) is instructed to set appropriate headers to block indexing (beyond just noindex):

    location /doc/www/               { add_header X-Robots-Tag "none, nosnippet, noarchive, nocache"; }

    And for good measure, robots.txt:

    User-agent: *
    Disallow: /doc/www/*
  5. Results: As of 2023-03-09, there are 14,352 targeted links weighing 47GB (including now-unused archives which will be removed at some point), which is no problem.

The Arxiv Problem

One subtlety that came up after a while was the issue of ‘URL transforms’. In some cases, like BioRxiv, it’s best to simply rewrite URLs to the full-text HTML version (just append .full to the URL); this is simple & one can ensure it happens by including a global search-and-replace in the compilation process, and forget about it while linking BioRxiv normally. Unfortunately, sometimes a global search-and-replace is inadequate: there is a set of URLs where you link to one URL, but for archiving purposes, you want to archive an alternative, a transformation of that URL. The motivating example was ‘the Arxiv problem’, one of the most heavily-linked domains on Gwern.net, and a difficult one to solve: I wound up needing 3 separate URLs to handle browsing as conveniently as possible for both desktop & mobile users.

‘The Arxiv problem’ is the difficulty in presenting Arxiv links to both desktop & mobile users which is not (1) slow, (2) redundant, or (3) foisting a PDF on readers (especially mobile readers). It is polite to link to the Arxiv HTML landing page like /abs/$ID rather than its fulltext PDF under /pdf/$ID, but that would be useless to archive because I already extract most of the relevant information to present as the annotation popup. It would be a waste of reader time to hover over an Arxiv annotated link, read the annotation with the title/author/date/abstract, and then hover over the ‘live’ Arxiv link to… read the same thing, presumably wasting their time until they can navigate to the fulltext PDF which they must have decided is worth their time. Obviously, the ‘live’ link should be the PDF, which can then be a local optimized PDF.25 Straightforward, except Arxiv has an additional wrinkle: whether HTML landing page or PDF, it’s bad for mobile readers on smartphones, who really need a responsive dark mode-compatible HTML version of the paper—which often exists, as there is yet a third set of Arxiv URLs located at the experimental LaTeX → HTML service which covers most (but not all) Arxiv papers, ‘Ar5iv’ (ie. https://ar5iv.labs.arxiv.org/html/$ID)!26

Arxiv is the main problem, but there are a few other cases worth handling. The preprint website OpenReview operates similarly to Arxiv, with an HTML landing page & PDF. And Reddit turns out to archive very poorly by default even using the ‘old’ Reddit interface which is good for regular browsing; but I discovered that while the mobile Reddit (i.reddit.com) didn’t look great, it at least preserved the content reliably. (Particularly acute readers may note that LessWrongGreaterWrong is not mentioned, because that is treated like a Wikipedia popup in that the JS code calls a specialized API.)

Every CS Problem…

What to do? One could bite the bullet & link Arxiv PDFs (ignoring mobile readers), or link to the Ar5iv HTML version (pleasing mobile but annoying desktop), or always link the abstract as a lowest-common-denominator (wasting a bit of everyone’s time but not foisting PDFs on them). However, I came up with a 3-way approach which integrated seamlessly into my existing popup system approach to showing annotation → archive → live.

I chose to add a second layer of indirection to archive rewrites: links will be rewritten silently before archiving (so in the case of an Arxiv /abs/ link, it gets rewritten to the PDF & the PDF becomes the local archive), and the ‘original link’ may be rewritten (so the popups are lied to and told that Ar5iv was the ‘original’ URL and that is what gets shown as the ‘live’ link).

While tricky to get right and requiring some modifications to the JS, this solves the Arxiv problem for Gwern.net readers:

  1. I link the Arxiv /abs/ normally & conveniently.

  2. This automatically creates an annotation containing the landing page’s metadata (plus all my additions like tags, excerpts, backlinks, similar-link recommendations, etc).

    This popup/popin will satisfy most readers.

  3. For readers who want to go deeper and read the fulltext: the title of the popup (popin) is an archive link to a local PDF mirror.

    This PDF is small & fast, and will pop up in another ‘live’ popup or tab (fine for desktop readers), or to an external PDF reader on mobile (less fine).

  4. But—as an ‘archive’ link, it automatically comes with a [LIVE] link appended pointing to the original raw URL (which is actually the Ar5iv version).

    This is for readers who need to link the original, want to consult it, or when the local archive is unfortunately broken (having been grandfathered in back in 2020-02). In the case of an Ar5iv link, however, this instead says [HTML]: this tells mobile readers where to click for the HTML version they want.

While complicated to explain, it follows our design language of popups/popins, and satisfies all users with no wasted clicks or mouse movements—aside from users who do want to visit/copy the /abs/ URL specifically, which I consider a minor use-case worth sacrificing for the other readers.

Appendices

filter-urls

A raw dump of URLs, while certainly archivable, will typically result in a very large mirror of questionable value (is it really necessary to archive Google search queries or Wikipedia articles? usually, no) and worse, given the rate-limiting necessary to store URLs in the Internet Archive or other services, may wind up delaying the archiving of the important links & risking their total loss. Disabling the remote archiving is unacceptable, so the best solution is to simply take a little time to manually blacklist various domains or URL patterns.

This blacklisting can be as simple as a command like filter-urls | grep -v en.wikipedia.org, but can be much more elaborate. The following shell script is the skeleton of my own custom blacklist, derived from manually filtering through several years of daily browsing as well as spiders of dozens of websites for various people & purposes, demonstrating a variety of possible techniques: regexps for domains & file-types & query-strings, sed-based rewrites, fixed-string matches (both blacklists and whitelists), etc:

#!/bin/sh

# USAGE: `filter-urls` accepts on standard input a list of newline-delimited URLs or filenames,
# and emits on standard output a list of newline-delimited URLs or filenames.
#
# This list may be shorter and entries altered. It tries to remove all unwanted entries, where 'unwanted'
# is a highly idiosyncratic list of regexps and fixed-string matches developed over hundreds of thousands
# of URLs/filenames output by my daily browsing, spidering of interesting sites, and requests
# from other people to spider sites for them.
#
# You are advised to test output to make sure it does not remove
# URLs or filenames you want to keep. (An easy way to test what is removed is to use the `comm` utility.)
#
# For performance, it does not sort or remove duplicates from output; both can be done by
# piping `filter-urls` to `sort --unique`.

set -euo pipefail

cat /dev/stdin \
    | sed -e "s/#.*//" -e 's/>$//' -e "s/&sid=.*$//" -e "s/\/$//" -e 's/$/\n/' -e 's/\?sort=.*$//' \
      -e 's/^[ \t]*//' -e 's/utm_source.*//' -e 's/https:\/\//http:\/\//' -e 's/\?showComment=.*//' \
    | grep "\." \
    | grep -F -v "*" \
    | grep -E -v -e '\/\.rss$' -e "\.tw$" -e "//%20www\." -e "/file-not-found" -e "258..\.com/$" \
       -e "3qavdvd" -e "://avdvd" -e "\.avi" -e "\.com\.tw" -e "\.onion" -e "\?fnid\=" -e "\?replytocom=" \
       -e "^lesswrong.com/r/discussion/comments$" -e "^lesswrong.com/user/gwern$" \
       -e "^webcitation.org/query$" \
       -e "ftp.*" -e "6..6\.com" -e "6..9\.com" -e "6??6\.com" -e "7..7\.com" -e "7..8\.com" -e "7..\.com" \
       -e "78..\.com" -e "7??7\.com" -e "8..8\.com" -e "8??8\.com" -e "9..9\.com" -e "9??9\.com" \
       -e gold.*sell -e vip.*club \
    | grep -F -v -e "#!" -e ".bin" -e ".mp4" -e ".swf" -e "/mediawiki/index.php?title=" -e "/search?q=cache:" \
      -e "/wiki/Special:Block/" -e "/wiki/Special:WikiActivity" -e "Special%3ASearch" \
      -e "Special:Search" -e "__setdomsess?dest="
      # ...

# prevent URLs from piling up at the end of the file
echo -e "\n"

filter-urls can be used on one’s local archive to save space by deleting files which may be downloaded by wget as dependencies. For example:

find ~/www | sort --unique >> full.txt && \
    find ~/www | filter-urls | sort --unique >> trimmed.txt
comm -23 full.txt trimmed.txt | xargs -d "\n" rm
rm full.txt trimmed.txt

sort Key Compression Trick

Moved to “The Sort Key Trick”.

Cryptographic Timestamping

Moved to “Easy Cryptographic Timestamping of Files”.


  1. I use duplicity & rdiff-backup to backup my entire home directory to a cheap 1.5TB hard drive (bought from Newegg using forre.st’s “Storage Analysis—GB/$ for different sizes and media” price-chart); a limited selection of folders are backed up to Backblaze B2 using duplicity.

    I used to semiannually tar up my important folders, add PAR2 redundancy, and burn them to DVD, but that’s no longer really feasible; if I ever get a Blu-ray burner, I’ll resume WORM backups. (Magnetic media doesn’t strike me as reliable over many decades, and it would ease my mind to have optical backups.)↩︎

  2. “When the Internet Is My Hard Drive, Should I Trust Third Parties?”, Wired:

    Bits and pieces of the web disappear all the time. It’s called ‘link rot’, and we’re all used to it. A friend saved 65 links in 1999 when he planned a trip to Tuscany; only half of them still work today. In my own blog, essays and news articles and websites that I link to regularly disappear—sometimes within a few days of my linking to them.

    ↩︎
  3. “Going, Going, Gone: Lost Internet References”; abstract:

    The extent of Internet referencing and Internet reference activity in medical or scientific publications was systematically examined in more than 1000 articles published between 2000 and 2003 in the New England Journal of Medicine, The Journal of the American Medical Association, and Science. Internet references accounted for 2.6% of all references (672⁄25548) and in articles 27 months old, 13% of Internet references were inactive.

    ↩︎
  4. The Million Dollar Homepage still gets a surprising amount of traffic, so one fun thing one could do is buy up expired domains which paid for particularly large links.↩︎

  5. By 2013-01-06, the number has increased to ~12,000 external links, ~7,200 to non-Wikipedia domains.↩︎

  6. If each link has a fixed chance of dying in each time period, such as 3%, then the total risk of death is an exponential distribution; over the time period 2011–2070 the cumulative chance it will beat each of the 3% risks is 0.1658. So in 2070, how many of the 2200 links will have beat the odds? Each link is independent, so they are like flipping a biased coin and form a binomial distribution. The binomial distribution, being discrete, has no easy equation, so we just ask R how many links survive at the 5th percentile/quantile (a lower bound) and how many survive at the 95th percentile (an upper bound):

    qbinom(c(0.05, 0.95), 2200, 0.97^(2070-2011))
    # [1] 336 394
    
    ## the 50% annual link rot hypothetical:
    qbinom(c(0.05, 0.50), 2200, 0.50^(2070-2011))
    # [1] 0 0
    ↩︎
  7. 101, ‘Buddhism related to Blossoms’; Unforgotten Dreams: Poems by the Zen monk Shōtetsu; trans. Steven D. Carter, ISBN 0-231-10576-2↩︎

  8. My variant: “Social media is a machine for selectively bitrotting everything good about you while preserving millions of copies of your worst tweet.”↩︎

  9. Which I suspect is only accidentally ‘general’ and would shut down access if there were some other way to ensure that Wikipedia external links still got archived.↩︎

  10. Since Pinboard is a bookmarking service more than an archive site, I asked in 2012 whether treating it as such would be acceptable and Maciej said “Your current archive size, growing at 20 GB a year, should not be a problem. I’ll put you on the heavy-duty server where my own stuff lives.”

    I ultimately did not take him up on this offer in part because Pinboard’s archives were relatively low-quality. Pinboard started being neglected around 2017 by Maciej, and as of mid-2022, errors are routine. I do not recommend use of Pinboard.↩︎

  11. Google Cache is generally recommended only as a last ditch resort because pages expire quickly from it. Personally, I’m convinced that Google would never just delete colossal amounts of Internet data—this is Google, after all, the epitome of storing unthinkable amounts of data—and that Google Cache merely ceases to make public its copies. And to request a Google spider visit, one has to solve a CAPTCHA—so that’s not a scalable solution.↩︎

  12. Which would not be publicly accessible or submittable; I know they exist, but because they hide themselves, I know only from random comments online eg. “years ago a friend of mine who I’d lost contact with caught up with me and told me he found a cached copy of a website I’d taken down in his employer’s equivalent to the Wayback Machine. His employer was a branch of the federal government.”.↩︎

  13. Version 0.1 of my archiver daemon didn’t simply read the file until it was empty and exit, but actually watched it for modifications with inotify. I removed this functionality when I realized that the required WebCite choking (just one URL every ~25 seconds) meant that archiver would never finish any reasonable workload.↩︎

  14. Much easier than it was in the past; Jamie Zawinski records his travails with the previous Mozilla history format in the aptly-named “when the database worms eat into your brain”.↩︎

  15. An older 2010 Google article put the average at 320kb, but that was an average over the entire Web, including all the old content.↩︎

  16. Already one runs old games like the classic LucasArts adventure games in emulators of the DOS operating system like DOSBox; but those emulators will not always be maintained. Who will emulate the emulators? Presumably in 2050, one will instead emulate some ancient but compatible OS—Windows 7 or Debian 6.0, perhaps—and inside that run DOSBox (to run the DOS which can run the game).↩︎

  17. Assiduously updating redirects can cause archive problems when the new URL breaks before archiving, or it was a lying link & you look up archives of a long-dead link. But you can always look through your version-control history for older URLs to try, and you may not be able to check newer URLs if you weren’t updating. So it’s better to update.↩︎

  18. Imagine a link to http://www.​gwern.net/docs/2010-anderson.pd created in 2015 by a user making a common typo; today it might bounce through the following sequence of redirects (I think): HTTP→HTTPS, www→root, /docs//doc/, ...pd...pdf, and /doc/ to /doc/statistics/prediction/ to reach its current URL of https://gwern​.net/doc/statistics/prediction/2010-anderson.pdf. And that’s just for now—the statistics/prediction tag is overloaded and needs refactoring into sub-tags, so Anderson & Sherman2010 will at some point probably be relocated to a Fermi estimate tag’s sub-directory, setting up a 6th redirect. If each redirect takes 50ms (optimistic), then that’s 0.3s spent just to get the URL!↩︎

  19. A surprisingly large fraction of Gwern.net readers—and readers in general—still do not use ad-blockers, especially on mobile where they need one most.↩︎

  20. It may be tempting to try to mirror a URL’s /foo/bar/baz.ext structure, but this is not as useful as it seems (since you will typically have relatively few archived URLs so the structure will be sparse, and you want to tag them anyway), and has many edge-cases in simply converting arbitrary URLs to usable on-disk filepaths. The fact is, it is not 1995, and a website is not a Unix directory. Contemporary URLs do not map, in any way, onto HTML filepaths: URLs are stuffed with dangerous characters which will should probably be escaped, punycode encoding of Unicode, website directories which are actually files/pages (the ubiquitous trailing slash), subdomains, query arguments, hash anchors (including the loathed and not completely defunct #! design pattern), redirects, and so on. Further, URLs change at the drop of a hat, including any implied ‘directory hierarchy’, rendering updates difficult—many redundant snapshots or contradictory implied paths. No, no, just resist the temptation to pun on URL ↔︎ filepath, and assign it an opaque unique ID and store that.↩︎

  21. No longer necessary with the final link-icon implementation, but this was necessary before when using CSS regexp rules, so rules like href=*"google.com" would match both https://www.google.com and /doc/www/www.google.com/XYZ.html.↩︎

  22. Down from 120 days, then 90, as I kept hitting moving paywalls or sites outright dying.↩︎

  23. This turned out to be a major flaw in archives of some websites like Reddit: there are few archives of the /r/DarkNetMarkets subreddit because it was set to over-18/NSFW, which meant that any cookie-less archiver like IA archived nothing but login-walls!↩︎

  24. I have thus far received only 1 DMCA takedown email, from, oddly, a local newspaper used in my DNM arrests census.↩︎

  25. Rehosting Arxiv PDFs is especially helpful because Arxiv PDFs can be very large (eg. the OFA paper is 35MB—most of my book scans are smaller), slow to download (in addition to the extra domain name lookup), and Arxiv is a nonprofit with minimal budget (so if one is encouraging readers to download PDFs profligately the way my popups do, you should rehost them).↩︎

  26. Ar5iv comes with its own caveats: it cannot render all Arxiv papers, sometimes the rendered one is broken, and it attempts renders with approximately a 1 month lag. Fortunately, it is capable of redirecting to the regular Arxiv landing page (append ?fallback=original), so it is safe to link to it—at worst, a mobile reader just winds where they would’ve ended up anyway.↩︎

  27. IA describes it as merely ‘closing 2 weeks early’ to save face, but they had originally said “This suspension will run through June 30, 2020, or the end of the US national emergency, whichever is later.”—the ‘US national emergency’, such as the closure of schools which was the primary rationale, was not over by 2020-06-30, needless to say, or that year (or the year after that).↩︎

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