What is the difference between a browser request and a curl request?

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https://psycnet.apa.org/record/2016-47119-002

When I access the above URL by chrome (in a private window), I can see the first request which corresponds to the following curl command. But when I call this curl command in the command line, it will be detected by distil network showing <div id="distilIdentificationBlock">&nbsp;</div> .

This looks strange to me as this is the first request. Unless there is a difference between the requests send by curl and chrome, there is no way by which distil network can tell what request is sent by a bot or by a real browser. Does anybody know what is the difference between the curl request and the chrome request?

curl 'https://psycnet.apa.org/record/2016-47119-002' \
  -H 'Connection: keep-alive' \
  -H 'Pragma: no-cache' \
  -H 'Cache-Control: no-cache' \
  -H 'Upgrade-Insecure-Requests: 1' \
  -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.61 Safari/537.36' \
  -H 'Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9' \
  -H 'Sec-Fetch-Site: none' \
  -H 'Sec-Fetch-Mode: navigate' \
  -H 'Sec-Fetch-User: ?1' \
  -H 'Sec-Fetch-Dest: document' \
  -H 'Accept-Language: en-US,en;q=0.9,zh-CN;q=0.8,zh;q=0.7' \
  --compressed

P.S. The problem is same if I use firefox to extract the corresponding curl command. So the difference between firefox request and curl request is also relevant.

firefox google-chrome curl http javascript
1 Answers

There is no difference.

To find out how Distill (their web-scraping protection system) works, you need to look at the initial response HTML:

When I make the request in Chrome and look at the initial response in the Dev Tools (make sure "Preserve log" is checked) I see that the response is actually a short web-page that contains an embedded <script> which performs some simple "is this user-agent a web-browser?" checks, like running scripts that look for JavaScript DOM objects that won't exist outside of a web-browser (assuming the HTTP user-agent is capable of running scripts at all - which cURL and wget aren't, by the way).

If the script considers your user-agent to be a web-browser then it performs another request for the real content using a dynamically generated password (I didn't look at the details for how that works) - which is why you can't re-request the real content using cURL or wget as the password is unique for each request.

Here's a screenshot of the <script> element in the initial page response, and notice the lack of real actual content in the page's HTML.

enter image description here

If you disable JavaScript in your browser you won't be able to access that web-page at all.

This kind of anti-scraping system protects web-pages against requests from user-agents that lack the means to evaluate JavaScript - so it will block curl, wget, HttpClient, and in-browser fetch/XMLHttpRequests (at least not without further work).

You'd think this system would render a site un-indexable by search-engine spiders - but that's an old (and entrenched) belief and practice: because until the late-2000s the main search engine spiders (Google, Bing/Windows Live Search, Yahoo, etc) only indexed raw HTML and didn't run JavaScript - but since then the search-engine spiders started running JavaScript and even started indexing sites not using custom-built spider HTML-parser engines but using actual web-browser engines (Google really started it, so that they could index script-heavy websites, especially single-page-applications using Angular, Vue, etc). When I worked at Microsoft I got to use the Bing crawler system for some product research projects and that used a special build of Internet Explorer to "run" web-pages that it visited.

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