When server caches a page, I thought it worked like this, but apparently I'm wrong.
server stores http response contents in a cache-store with a key (that's generated for the endpoint)
one could create separate cache key for certain aspects of requests (such as user language)
when there's a request for the same key, and it's stored in cache-store (such as redis), webserver returns the cached response instead of recreating the response
I think the above understanding is flawed because,,
when I hit the endpoint with axios, first request is hit on the server, but the second request doesn't even hit the endpoint, it seems axios is reusing the previous response it received.
So, if I clear all cache store between two requests, the second request doesn't get to the request handler (view function in django)
for http request (browser reload) does work as I described in the above, it hits the web server and gets the cached response.
In django, I'm using from django.views.decorators.cache import cache_page
But the question is more of general working of web response cache
General web caching is explained very well here * https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching
I guess certain client never reaches out to server when cache-control timeout or expires is set, and some client does reach out to server..
Update: Collected my thoughts better
I'm generating a unique identifier (UUID) for each user in the Viewer Request Lambda, and then selecting a cached page to return based upon that UUID. This works.
Ideally, this user would always have the same UUID.
I must generate that UUID in the Viewer Request if it is not present in a cookie on that Viewer Request. I also need that UUID to be set as a cookie, which of course happens in the response not the request.
Without caching, my server simply handles taking a custom header and creating a Set-Cookie in the response header.
I am not finding a way to handle this if I want to cache the page. I can ignore the request header for caching and serve the correct cached page, but then the user does not persist that UUID as no cookie is set to be utilized in their next request.
Has anyone accomplished something like this?
Things I'm trying
There are a few angles I'm working on with this, but haven't been able to get to work yet:
Some sort of setting in Cloudfront I'm unaware of that handles the header or other data pass-through from Viewer Request to Viewer Response, which could be used in a second lambda in Cloudfront.
Modify the response object headers preemptively in the Viewer Request. I don't think this is possible, as they return headers are not yet created, unless there's some built-in Cloudfront methodology I'm missing.
An existing pass-through header of some sort, I don't know if that's even a thing since I'm not intimately familiar with this aspect of request-response handling, but worth a shot.
Possibly (haven't tried yet though) I could create the entire response object in the Client Request lambda and somehow serve the cached page from there, modifying the response headers then passing it into the callback method.
Tobin's answer actually works, but is not a solid solution. If the user is not storing or serving their cookies it becomes an infinite loop, plus I'd rather not throw a redirect up in front of all of my pages if I can avoid it
Somewhat-working concept
Viewer Request Lambda, when UUID not present in cookies, generates UUID
Viewer Request Lambda sets UUID in cookies on header in request object. Callback with updated request object passed in
Presence of UUID cookie busts Cloudfront cache
Origin Request Lambda is triggered with UUID present
Origin Request Lambda calls original request URL again via http.get with UUID cookie set (40KB limit makes doing this in the Viewer Request Lambda impractical)
Second scenario for Viewer Request Lambda, seeing UUID now present, strips the UUID cookie then continues the request normally
Second Origin Request if not yet cached - Cached response if cached, as cache-busting UUID is not present - returns actual page HTML to First Origin Request
First Origin Request receives response from http.get containing HTML
First Origin Request creates custom response object containing response body from http.get and Set-Cookie header set with our original UUID
Subsequent calls, having the UUID already set, will strip the UUID from the cookie (to prevent cache busting) and skip directly to the second-scenario in the Viewer Request Lambda which will directly load the cached version of the page.
I say "somewhat" because when I try to hit my endpoint, I get a binary file downloaded.
EDIT
This is because I was not setting the content-type header. I now have only a 302 redirect problem... if I overcome this I'll post a full answer.
Original question
I have a function on the Viewer Request that picks an option and sets some things in the request before it's retrieved from the cache or server.
That works, but I want it to remember that choice for future users. The thought is to simply set a cookie I can read the next time that user comes through. As this is on the Viewer Request and not the Viewer Response I haven't figured out how to make that happen, or if it even is possible via the Lambda itself.
Viewer Request ->
Lambda picks options (needs to set cookie) ->
gets corresponding content ->
returns to Viewer with set-cookie header intact
I have seen the examples and been able to set cookies successfully in the Viewer Response via a Lambda. That doesn't help me much as the decision needs to be made on the request. Quite unsurprisingly adding this code into the Viewer Request shows nothing in the response.
I would argue that the really correct way to set a nonexistent cookie would be to return a 302 redirect to the same URI with Set-Cookie, and let the browser redo the request. This probably would not have much of an impact since the browser can reuse the same connection to "follow" the redirect.
But if you insist on not doing it that way, then you can inject the cookie into the request with your Viewer Request trigger and then emit a Set-Cookie with the same value in your Viewer Response trigger.
The request object, in a viewer response event, can be found at the same place where it's found in the original request event, event.Records[0].cf.request.
In a viewer-response trigger, this part of the structure contains the "request that CloudFront received from the viewer and that might have been modified by the Lambda function that was triggered by a viewer request event."
Use caution to ensure that you handle the cookie header correctly. The Cookie request header requires careful and accurate manipulation because the browser can use multiple formats when multiple cookies exist.
Once upon a time, cookies were required to be sent as a single request header.
Cookie: foo=bar; buzz=fizz
Parse these by splitting the values on ; followed by <space>.
But the browser may also split them with multiple headers, like this:
Cookie: foo=bar
Cookie: buzz=fizz
In the latter case, the array event.Records[0].cf.request.headers.cookie will contain multiple members. You need to examine the value attribute of each object in that array, check for multiple values within each, as well as accommodating the fact that the array will be completely undefined (not empty) if no cookies exist.
Bonus: Here's a function I wrote, that I believe correctly handles all cases including the case where there are no cookies. It will extract the cookie with the name you are looking for. Cookie names are case-sensitive.
// extract a cookie value from request headers, by cookie name
// const my_cookie_value = extract_cookie(event.Records[0].cf.request.headers,'MYCOOKIENAME');
// returns null if the cookie can't be found
// https://stackoverflow.com/a/55436033/1695906
function extract_cookie(headers, cname) {
const cookies = headers['cookie'];
if(!cookies)
{
console.log("extract_cookie(): no 'Cookie:' headers in request");
return null;
}
// iterate through each Cookie header in the request, last to first
for (var n = cookies.length; n--;)
{
// examine all values within each header value, last to first
const cval = cookies[n].value.split(/;\ /);
const vlen = cval.length;
for (var m = vlen; m--;)
{
const cookie_kv = cval[m].split('=');
if(cookie_kv[0] === cname)
{
return cookie_kv[1];
}
} // for m (each value)
} // for n (each header)
// we have no match if we reach this point
console.log('extract_cookie(): cookies were found, but the specified cookie is absent');
return null;
}
Are you able to add another directory: with the first cookie setter request, return (from the lambda) a redirect which includes the cookie-set header, that redirects to your actual content?
OK, long way round but:
Take cookie instruction from the incoming request
Set this somewhere (cache, etc)
Let the request get your object
on the Response, also call a function that reads the (cache) and sets the set-cookie header on the response if needed?
It's been more than one year since the question was published. I hope you found a solution and you can share it with us!
I am facing the same problem and I've thinking also about the infinite loop... What about this?
The viewer request event sends back a 302 response with the cookie set, e.g. uuid=whatever and a GET parameter added to the URL in the Location header, e.g. _uuid_set_=1.
In the next viewer request where the GET parameter _uuid_set_ is set (and equals 1, but this is not needed), there will be two options:
Either the cookie uuid is not set, in which case you can send back a response 500 to break the loop, or whatever fits your needs,
or the cookie is set, in which case you send another 302 back with the parameter _uuid_set_ removed, so that it is never seen by the end user and cannot be copy-pasted and shared and we all can sleep at night.
i'm sending GET requests to my local REST server and I'm trying to set the request Cookie header to something different each time.
however, it seems that postman is somehow caching something because whenever I modify my cookie header request contents to something new it sends the old cookie header request contents.
i have no idea why it doesn't pick up the new cookie header contents that I set. this is not with interceptor turned on.
I've run into a few problems with setting cookies, and based on the reading I've done, this should work, so I'm probably missing something important.
This situation:
Previously I received responses from my API and used JavaScript to save them as cookies, but then I found that using the set-cookie response header is more secure in a lot of situations.
I have 2 cookies: "nuser" (contains a username) and key (contains a session key). nuser shouldn't be httpOnly so that JavaScript can access it. Key should be httpOnly to prevent rogue scripts from stealing a user's session. Also, any request from the client to my API should contain the cookies.
The log-in request
Here's my current implementation: I make a request to my login api at localhost:8080/login/login (keep in mind that the web-client is hosted on localhost:80, but based on what I've read, port numbers shouldn't matter for cookies)
First the web-browser will make an OPTIONS request to confirm that all the headers are allowed. I've made sure that the server response includes access-control-allow-credentials to alert the browser that it's okay to store cookies.
Once it's received the OPTIONS request, the browser makes the actual POST request to the login API. It sends back the set-cookie header and everything looks good at this point.
The Problems
This set-up yields 2 problems. Firstly, though the nuser cookie is not httpOnly, I don't seem to be able to access it via JavaScript. I'm able to see nuser in my browser's cookie option menu, but document.cookie yeilds "".
Secondly, the browser seems to only place the Cookie request header in requests to the exact same API (the login API):
But, if I do a request to a different API that's still on my localhost server, the cookie header isn't present:
Oh, and this returns a 406 just because my server is currently configured to do that if the user isn't validated. I know that this should probably be 403, but the thing to focus on in this image is the fact that the "cookie" header isn't included among the request headers.
So, I've explained my implementation based on my current understanding of cookies, but I'm obviously missing something. Posting exactly what the request and response headers should look like for each task would be greatly appreciated. Thanks.
Okay, still not exactly what was causing the problem with this specific case, but I updated my localhost:80 server to accept api requests, then do a subsequent request to localhost:8080 to get the proper information. Because the set-cookie header is being set by localhost:80 (the client's origin), everything worked fine. From my reading before, I thought that ports didn't matter, but apparently they do.
I have a VB.NET app that sends a POST request to a script on my server that is running Cloudflare. I always get an error when sending the request from the app, however using a Firefox extension to simulate the request works fine. With the use of Fiddler I think I have found the cause of the problem:
When sending the request with the Firefox addon an extra header is attached to the request:
Cookie: __cfduidxxxxxxxxxxxx
This cookie is from Cloudflare, but where does it come from, ie. how can I get this cookie value and send it with my requests from the VB app? I tried copying and pasting the cookie into the app and it worked fine, so this leads me to conclude that I need this cookie, however this value is unique for each user so I cannot simply hardcode it into the app.
Quick side-note: Not sure if this helps, but if I send a GET request from the VB app it works fine without the __cfduid cookie.
Look for a Set-Cookie header coming back from the server on it's response. It will expect to get that value back on subsequent requests in a Cookie: header. This value is usually an opaque string that is classified by a path, although not always.