Is there any way to detect if a link is invalid using webbot?
I need to tell the user that the link they provided was unreachable.
The only way to be completely sure that a url sends you to a valid page is to fetch that page and check it works. You could try making a request other than GET to try to avoid the wasted bandwith downloading the page, but not all servers will respond: the only way to be absolutely sure is to GET and see what happens. Something like:
import requests
from requests.exceptions import ConnectionError
def check_url(url):
try:
r = requests.get(url, timeout=1)
return r.status_code == 200
except ConnectionError:
return False
Is this a good idea? It's only a GET request, and get is supposed to idempotent, so you shouldn't cause anybody any harm. On the other hand, what if a user sets up a script to add a new link every second pointing to the same website? Then you're DDOSing that website. So when you allow users to cause your server to do things like this, you need to think how you might protect it. (In this case: you could keep a cache of valid links expiring every n seconds, and only look up if the cache doesn't hold the link.)
Note that if you just want to check the link points to a valid domain it's a bit easier: you can just do a dns query. (The same point about caching and avoiding abuse probably applies.)
Note that I used requests, because it is easy, but you likely want to do this in the bacground, either with requests in a thread, or with one of the asyncio http libraries and an asyncio event loop. Otherwise your code will block for at least timeout seconds.
(Another attack: this gets the whole page. What if a user links to a massive page? See this question for a discussion of protecting from oversize responses. For your use case you likely just want to get a few bytes. I've deliberately not complicated the example code here because I wanted to illustrate the principle.)
Note that this just checks that something is available on that page. What if it's one of the many dead links which redirects to a domain-name website? You could enforce 'no redirects'---but then some redirects are valid. (Likewise, you could try to detect redirects up to the main domain or to a blacklist of venders' domains, but this will always be imperfect.) There is a tradeoff here to consider, which depends on your concrete use case, but it's worth being aware of.
You could try sending an HTTP request, opening the result, and have a list of known error codes, 404, etc. You can easily implement this in Python and is efficient and quick. Be warned that SOMETIMES (quite rarely) a website might detect your scraper and artificially return an Error Code to confuse you.
Related
My python code used to work, but when I tried it today it did not work anymore.
I assume the website owner forbade non browsers requests recently.
code
import requests, bs4
res = requests.get('https://manga1001.com/日常-raw-free/')
res.raise_for_status()
print(res.text)
I read that adding header in the requests.get method may work, but I don't know which header info exactly I need to make it work.
error
---------------------------------------------------------------------------
HTTPError Traceback (most recent call last)
<ipython-input-15-ed1948d83d51> in <module>
3 # res = requests.get('https://manga1001.com/日常-raw-free/', headers=headers_dic)
4 res = requests.get('https://manga1001.com/日常-raw-free/')
----> 5 res.raise_for_status()
6 print(res.text)
7
~/opt/anaconda3/lib/python3.8/site-packages/requests/models.py in raise_for_status(self)
939
940 if http_error_msg:
--> 941 raise HTTPError(http_error_msg, response=self)
942
943 def close(self):
HTTPError: 403 Client Error: Forbidden for url: https://manga1001.com/%E6%97%A5%E5%B8%B8-raw-free/
Requests get a header argument
res = requests.get('https://manga1001.com/日常-raw-free/', headers="")
I think adding a proper value here could make it work, but I don't know what the value is.
I would really appreciate if you could tell you.
And if you know any other ways to make it work, that is also quite helpful.
Btw I have also tried the code below but it also didn't work.
code 2
from requests_html import HTMLSession
url = "https://search.yahoo.co.jp/realtime"
session = HTMLSession()
r = session.get(url)
r = r.html.render()
print(r)
FYI HTMLSession may not work on IDLE like Jupyter notebook so I tired it after saving it as a python file but it still did not work.
When I run first code without res.raise_for_status() then I can see in HTML with Why do I have to complete a CAPTCHA? and Cloudflare Ray ID which shows what is the problem. It uses Cloudflare to detect scripts/bots/hackers/spamers and it uses Captcha to check it. But if I use header 'User-Agent' with value from real browser or even with short 'Mozilla/5.0' then it get expected page.
It works for me with both pages.
import requests
headers = {
'User-Agent': 'Mozilla/5.0'
}
url = 'https://manga1001.com/日常-raw-free/'
#url = 'https://search.yahoo.co.jp/realtime'
res = requests.get(url, headers=headers)
print('status_code:', res.status_code)
print(res.text)
BTW:
If you will run it often for many links in short time then it may display again CAPTCHA and then you may need other methods to behave more like real human - ie. sleep() with random time, Session() to use cookies, first get main page (to get fresh cookies) and later get this page, add other headers.
I wanted to expand on the answer given by #Furas because I understand his fix will not be the solution in all cases. Yes, In this instance you're getting the 403 and Cloudflare/security captcha page when you make a request because of not "scoring" high enough on the security system (Your HTTP browser isn't similar enough to a real browser)
This creates a big question. What is a real browser and what score do I need to beat it? How do I increase my browser score and make my HTTP-request based browser look more real to the bot protection?
Firstly, it's important to understand that these 403/Security blocks are based on different levels on security. Something you do on one site may not work on the other due to different security configurations/version. Two sites may use the same security system and still the request you make may only work on one.
Why would they have different configurations and everyone not use the highest security available? Because with each additional security measure, there's more false-positives and challenges to pass, on a large scale or for an e-commerce store this can mean lost sales due to a poor user-experience or additional bugs/downtime which are introduced via the security program.
What is a real browser?
A real browser can perform SSL/TLS handshakes, parse and run Javascript and make TCP/requests. Along with this, the security programs will analyze the patterns and timings of everything from Layer 2 to see if you're a "real" human. When you use something like Python to make a request that is only performing a HTTP(s) request it's really easy for these security programs to recognise you as a bot without some heavy configuration.
One way that security systems combat bots is by putting a Javascript challenge as a proxy between the bot and a site, this requires running client-side Javascript which bots cannot do by default, not only do you need to run the client-side Javascript, it also needs to be similar to one that your own browser would generate, the challenge can typically consist of a few hundred individual "browser" challenges or/along with a manual captcha to fingerprint and track your browser to see if you're a human (This is the page you're seeing).
The typical and more lower-standard security systems/configurations can be beaten by using the correct headers (with capitalization, header order and HTTP versions. Like #Furas mentioned, using consistent sessions can also help create longer-lasting sessions before getting another 403. More advanced and higher-level security configurations can do tracking on lower-levels by looking at some flags (Such as WindowSize) of the TCP connection and JA3 fingerprinting analyzing the TLS handshake which will look at your cipher suites and ALPN amongst other things. Security systems can see characteristics which differentiate between browsers, browser-versions and operating systems and compare these all together to generate your realness score. Your IP can also be an important factor, requests can be cross-checked with other sites, intervals, older requests you tried before and much more, you can use proxies to divide your requests between and look less suspicious, but this can come with additional problems and affect your request also causing it to be fingerprinted and blocked.
To understand this better, here's a great site you can go to in your browser and also make a GET request to, check your browser "Rank" and look at the different values which can be seen just from the TLS request alone.
I hope this provides some insight into why a block might appear, although it's impossible to tell from a single URL since blocks can appear for such a variety of different reasons.
I would like to try send requests.get to this website:
requests.get('https://rent.591.com.tw')
and I always get
<Response [404]>
I knew this is a common problem and tried different way but still failed.
but all of other website is ok.
any suggestion?
Webservers are black boxes. They are permitted to return any valid HTTP response, based on your request, the time of day, the phase of the moon, or any other criteria they pick. If another HTTP client gets a different response, consistently, try to figure out what the differences are in the request that Python sends and the request the other client sends.
That means you need to:
Record all aspects of the working request
Record all aspects of the failing request
Try out what changes you can make to make the failing request more like the working request, and minimise those changes.
I usually point my requests to a http://httpbin.org endpoint, have it record the request, and then experiment.
For requests, there are several headers that are set automatically, and many of these you would not normally expect to have to change:
Host; this must be set to the hostname you are contacting, so that it can properly multi-host different sites. requests sets this one.
Content-Length and Content-Type, for POST requests, are usually set from the arguments you pass to requests. If these don't match, alter the arguments you pass in to requests (but watch out with multipart/* requests, which use a generated boundary recorded in the Content-Type header; leave generating that to requests).
Connection: leave this to the client to manage
Cookies: these are often set on an initial GET request, or after first logging into the site. Make sure you capture cookies with a requests.Session() object and that you are logged in (supplied credentials the same way the browser did).
Everything else is fair game but if requests has set a default value, then more often than not those defaults are not the issue. That said, I usually start with the User-Agent header and work my way up from there.
In this case, the site is filtering on the user agent, it looks like they are blacklisting Python, setting it to almost any other value already works:
>>> requests.get('https://rent.591.com.tw', headers={'User-Agent': 'Custom'})
<Response [200]>
Next, you need to take into account that requests is not a browser. requests is only a HTTP client, a browser does much, much more. A browser parses HTML for additional resources such as images, fonts, styling and scripts, loads those additional resources too, and executes scripts. Scripts can then alter what the browser displays and load additional resources. If your requests results don't match what you see in the browser, but the initial request the browser makes matches, then you'll need to figure out what other resources the browser has loaded and make additional requests with requests as needed. If all else fails, use a project like requests-html, which lets you run a URL through an actual, headless Chromium browser.
The site you are trying to contact makes an additional AJAX request to https://rent.591.com.tw/home/search/rsList?is_new_list=1&type=1&kind=0&searchtype=1®ion=1, take that into account if you are trying to scrape data from this site.
Next, well-built sites will use security best-practices such as CSRF tokens, which require you to make requests in the right order (e.g. a GET request to retrieve a form before a POST to the handler) and handle cookies or otherwise extract the extra information a server expects to be passed from one request to another.
Last but not least, if a site is blocking scripts from making requests, they probably are either trying to enforce terms of service that prohibit scraping, or because they have an API they rather have you use. Check for either, and take into consideration that you might be blocked more effectively if you continue to scrape the site anyway.
One thing to note: I was using requests.get() to do some webscraping off of links I was reading from a file. What I didn't realise was that the links had a newline character (\n) when I read each line from the file.
If you're getting multiple links from a file instead of a Python data type like a string, make sure to strip any \r or \n characters before you call requests.get("your link"). In my case, I used
with open("filepath", 'w') as file:
links = file.read().splitlines()
for link in links:
response = requests.get(link)
In my case this was due to fact that the website address was recently changed, and I was provided the old website address. At least this changed the status code from 404 to 500, which, I think, is progress :)
I'm using this script to randomize proxies in scrapy. The problem is that once it's allocated a proxy to a request, it won't allocate another one because of this code:
def process_request(self, request, spider):
# Don't overwrite with a random one (server-side state for IP)
if 'proxy' in request.meta:
return
That means that if there is a bad proxy which is not connecting to anything, then the request will fail. I'm intending to modify it like this:
if request.meta.get('retry_times',0) < 5:
return
thereby letting it allocate a new proxy if the current one fails 5 times. I'm assuming that if I set RETRY_TIMES to, say 20, in settings.py, then the request won't fail until 4 different proxies have each made 5 attempts.
I'd like to know if that will cause any problems. As I understand it, the reason that the check is there in the first place is for stateful transactions, such as those relying on log-ins, or perhaps cookies. Is that correct?
I bumped with the same problem.
I improved the aivarsk/scrapy-proxies. My middleware inherited by basic RetryMiddleware and trying to use one proxy RETRY_TIMES. If proxy is unavailable, the middleware change it.
Yes, I think the idea of that script was to check if the user is already defining a proxy on the meta parameter, so it can control it from the spider.
Setting it to change proxy every 5 times is ok, but I think you'll have to re login to the page, as most pages know when you changed from where you are making the request (proxy).
The idea if rotating proxies is not as easy as just selecting one randomly, because you could still end up using the same proxy, and also defining the rules for when a site "banned" you is not as simple as only checking statuses. This are the services I know for that thing you want: Crawlera and Proxymesh.
If you want direct functionality on scrapy for rotating proxies, I recommend to use Crawlera as it is already fully integrated.
I apologise if this is a daft question. I'm currently writing against a Django API (which I also maintain) and wish under certain circumstances to be able to generate multiple partial responses in the case where a single request yields a large number of objects, rather than sending the entire JSON structure as a single response.
Is there a technique to do this? It needs to follow a standard such that client systems using different request libraries would be able to make use of the functionality.
The issue is that the client system, at the point of asking, does not know the number of objects that will be present in the response.
If this is not possible, then I will have to chain requests on the client end - for example, getting the first 20 objects & if the response suggests there will be more, requesting the next 20 etc. This approach is an OK work-around, but any subsequent requests rely on the previous response. I'd rather ask once and have some kind of multi-part response.
As far as I know, No you can't send Multipart http response not yet atleast. Multipart response is only valid in http requests. Why? Because no browser as I know of completely supports this.
Firefox 3.5: Renders only the last part, others are ignored.
IE 8: Shows all the content as if it were text/plain, including the boundaries.
Chrome 3: Saves all the content in a single file, nothing is rendered.
Safari 4: Saves all the content in a single file, nothing is rendered.
Opera 10.10: Something weird. Starts rendering the first part as plain/text, and then clears everything. The loading progress bar hangs on 31%.
(Data credits Diego Jancic)
If I point Firefox at http://bitbucket.org/tortoisehg/stable/wiki/Home/ReleaseNotes, I get a page of HTML. But if I try this in Python:
import urllib
site = 'http://bitbucket.org/tortoisehg/stable/wiki/Home/ReleaseNotes'
req = urllib.urlopen(site)
text = req.read()
I get the following:
500 Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
What am I doing wrong?
You are not doing anything wrong, bitbucket does some user agent detection (to detect mercurial clients for example). Just changing the user agent fixes it (if it doesn't have urllib as a substring).
You should fill an issue regarding this: http://bitbucket.org/jespern/bitbucket/issues/new/
You're doing nothing wrong, on the surface, and as the error page says you should contact the site's administrators because they're the ones with the server logs which may explain what's happening. Fortunately, bitbucket's site admins are a friendly bunch!
No doubt there is some header or combination of headers that browsers set one way, urllib sets another way, and a bug on the server gets tickled in the latter case. You may want to see exactly what headers are being sent e.g. with firebug in firefox, and reproduce those until you isolate exactly the server bug; most likely it's going to be the user agent or some "accept"-ish header that's tickling that bug.
I don't think you're doing anything wrong -- it looks like this server was just down? Your script worked fine for me ('text' contained the same data as that displayed in the browser).