I am struggling to understand when does the server return XML data vs HTML text data, and how come responseXML can return both? Is XML data returned only when making a POST request?
It's hard to actually test these, because I couldn't properly setup a PHP server, and making a POST request keeps returning 404 bad request, but when I make a GET request, I always get the HTML document in the responseText property, but when I try to use responseXML, I get null. So, if responseXML can return either HTML or XML, why does it not return the HTML document then?
Note: Before you accuse me of not doing any research. Let me tell you that I have been doing research for the past 3 days, and the book I'm reading just doesn't clarify these differences, and does not explain what exactly is XML in the first place. It says that XML data needs to be parsed to be displayed as a text, but doesn't explain why. It's all very ambiguous. So, I would appreciate if someone could clarify things for me.
POST requests return XML data, if the backend server is configured to return XML data. Completely depends on the server you're talking to, there's no way of predicting the behavior otherwise. Also, it's worth noting that every input can change the behavior of the server. E.g. if you provide a query with a specific value, the server could also return a CSS file, instead of an HTML or XML one.
This is an example of getting HTML from server response using fetch API.
fetch('https://someweb.com/api/list').then(function (response) {
// The API call was successful!
return response.text();
}).then(function (html) {
// Convert the HTML string into a document object
var parser = new DOMParser();
var doc = parser.parseFromString(html, 'text/html');
}).catch(function (err) {
// There was an error
console.warn('Something went wrong.', err);
});
Specifically I am interested in changing all responses with code 403 to code 404, and changing all responses with code 301 to 302. I do not want any other part of the response to change, except the status text (which I want to be empty). Below is my own attempt at this:
addEventListener("fetch", event => {
event.respondWith(fetchAndModify(event.request));
});
async function fetchAndModify(request) {
// Send the request on to the origin server.
const response = await fetch(request);
const body = await response.body
newStatus = response.status
if (response.status == 403) {
newStatus = 404
} else if (response.status == 301) {
newStatus = 302
}
// Return modified response.
return new Response(body, {
status: newStatus,
statusText: "",
headers: response.headers
});
}
I have confirmed that this code works. I would like to know if there is any possibility at all that this overwrites part of the response other than the status code or text, and if so, how can I avoid that? If this goes against certain best practices of Cloudflare workers or javascript, please describe which ones and why.
You've stumbled on a real problem with the Fetch API spec as it is written today.
As of now, status, statusText, and headers are the only standard properties of Response's init structure. However, there's no guarantee that they will remain the only properties forever, and no guarantee that an implementation doesn't provide additional non-standard or not-yet-standard properties.
In fact, Cloudflare Workers today implements a non-standard property: webSocket, which is used to implement WebSocket proxying. This property is present if the request passed to fetch() was a WebSocket initiation request and the origin server completed a WebSocket handshake. In this case, if you drop the webSocket field from the Response, WebSocket proxying will break -- which may or may not matter to you.
Unfortunately, the standard does not specify any good way to rewrite a single property of a Response without potentially dropping unanticipated properties. This differs from Request objects, which do offer a (somewhat awkward) way to do such rewrites: Request's constructor can take another Request object as the first parameter, in which case the second parameter specifies only the properties to modify. Alternately, to modify only the URL, you can pass the URL as the first parameter and a Request object as the second parameter. This works because a Request object happens to be the same "shape" as the constructor's initializer structure (it's unclear if the spec authors intended this or if it was a happy accident). Exmaples:
// change URL
request = new Request(newUrl, request);
// change method (or any other property)
request = new Request(request, {method: "GET"});
But for Response, you cannot pass an existing Response object as the first parameter to Response's constructor. There are straightforward ways to modify the body and headers:
// change response body
response = new Response(newBody, response);
// change response headers
// Making a copy of a Response object makes headers mutable.
response = new Response(response.body, response);
response.headers.set("Foo", "bar");
But if you want to modify status... well, there's a trick you can do, but it's not pretty:
// Create an initializer by copying the Response's enumerable fields
// into a new object.
let init = {...response};
// Modify it.
init.status = 404;
init.statusText = "Not Found";
// Work around a bug where `webSocket` is `null` but needs to be `undefined`.
// (Sorry, I only just noticed this when testing this answer! We'll fix this
// in the future.)
init.webSocket = init.webSocket || undefined;
// Create a new Response.
response = new Response(response.body, init);
But, ugh, that sure was ugly.
I have proposed improvements to the Fetch API to solve this, but I haven't yet had time to follow through on them. :(
How do I access a page's HTTP response headers via JavaScript?
Related to this question, which was modified to ask about accessing two specific HTTP headers.
Related:
How do I access the HTTP request header fields via JavaScript?
It's not possible to read the current headers. You could make another request to the same URL and read its headers, but there is no guarantee that the headers are exactly equal to the current.
Use the following JavaScript code to get all the HTTP headers by performing a get request:
var req = new XMLHttpRequest();
req.open('GET', document.location, false);
req.send(null);
var headers = req.getAllResponseHeaders().toLowerCase();
alert(headers);
Unfortunately, there isn't an API to give you the HTTP response headers for your initial page request. That was the original question posted here. It has been repeatedly asked, too, because some people would like to get the actual response headers of the original page request without issuing another one.
For AJAX Requests:
If an HTTP request is made over AJAX, it is possible to get the response headers with the getAllResponseHeaders() method. It's part of the XMLHttpRequest API. To see how this can be applied, check out the fetchSimilarHeaders() function below. Note that this is a work-around to the problem that won't be reliable for some applications.
myXMLHttpRequest.getAllResponseHeaders();
The API was specified in the following candidate recommendation for XMLHttpRequest: XMLHttpRequest - W3C Candidate Recommendation 3 August 2010
Specifically, the getAllResponseHeaders() method was specified in the following section: w3.org: XMLHttpRequest: the getallresponseheaders() method
The MDN documentation is good, too: developer.mozilla.org: XMLHttpRequest.
This will not give you information about the original page request's HTTP response headers, but it could be used to make educated guesses about what those headers were. More on that is described next.
Getting header values from the Initial Page Request:
This question was first asked several years ago, asking specifically about how to get at the original HTTP response headers for the current page (i.e. the same page inside of which the javascript was running). This is quite a different question than simply getting the response headers for any HTTP request. For the initial page request, the headers aren't readily available to javascript. Whether the header values you need will be reliably and sufficiently consistent if you request the same page again via AJAX will depend on your particular application.
The following are a few suggestions for getting around that problem.
1. Requests on Resources which are largely static
If the response is largely static and the headers are not expected to change much between requests, you could make an AJAX request for the same page you're currently on and assume that they're they are the same values which were part of the page's HTTP response. This could allow you to access the headers you need using the nice XMLHttpRequest API described above.
function fetchSimilarHeaders (callback) {
var request = new XMLHttpRequest();
request.onreadystatechange = function () {
if (request.readyState === XMLHttpRequest.DONE) {
//
// The following headers may often be similar
// to those of the original page request...
//
if (callback && typeof callback === 'function') {
callback(request.getAllResponseHeaders());
}
}
};
//
// Re-request the same page (document.location)
// We hope to get the same or similar response headers to those which
// came with the current page, but we have no guarantee.
// Since we are only after the headers, a HEAD request may be sufficient.
//
request.open('HEAD', document.location, true);
request.send(null);
}
This approach will be problematic if you truly have to rely on the values being consistent between requests, since you can't fully guarantee that they are the same. It's going to depend on your specific application and whether you know that the value you need is something that won't be changing from one request to the next.
2. Make Inferences
There are some BOM properties (Browser Object Model) which the browser determines by looking at the headers. Some of these properties reflect HTTP headers directly (e.g. navigator.userAgent is set to the value of the HTTP User-Agent header field). By sniffing around the available properties you might be able to find what you need, or some clues to indicate what the HTTP response contained.
3. Stash them
If you control the server side, you can access any header you like as you construct the full response. Values could be passed to the client with the page, stashed in some markup or perhaps in an inlined JSON structure. If you wanted to have every HTTP request header available to your javascript, you could iterate through them on the server and send them back as hidden values in the markup. It's probably not ideal to send header values this way, but you could certainly do it for the specific value you need. This solution is arguably inefficient, too, but it would do the job if you needed it.
Using XmlHttpRequest you can pull up the current page and then examine the http headers of the response.
Best case is to just do a HEAD request and then examine the headers.
For some examples of doing this have a look at http://www.jibbering.com/2002/4/httprequest.html
Just my 2 cents.
A solution with Service Workers
Service workers are able to access network information, which includes headers. The good part is that it works on any kind of request, not just XMLHttpRequest.
How it works:
Add a service worker on your website.
Watch every request that's being sent.
Make the service worker fetch the request with the respondWith function.
When the response arrives, read the headers.
Send the headers from the service worker to the page with the postMessage function.
Working example:
Service workers are a bit complicated to understand, so I've built a small library that does all this. It is available on github: https://github.com/gmetais/sw-get-headers.
Limitations:
the website needs to be on HTTPS
the browser needs to support the Service Workers API
the same-domain/cross-domain policies are in action, just like on XMLHttpRequest
Another way to send header information to JavaScript would be through cookies. The server can extract whatever data it needs from the request headers and send them back inside a Set-Cookie response header — and cookies can be read in JavaScript. As keparo says, though, it's best to do this for just one or two headers, rather than for all of them.
(2021) An answer without additional HTTP call
While it's not possible in general to read arbitrary HTTP response headers of the top-level HTML navigation, if you control the server (or middleboxes on the way) and want to expose some info to JavaScript that can't be exposed easily in any other way than via a header:
You may use Server-Timing header to expose arbitrary key-value data, and it will be readable by JavaScript.
(*in supported browsers: Firefox 61, Chrome 65, Edge 79; no Safari yet and no immediate plans for shipping as of 2021.09; no IE)
Example:
server-timing: key;desc="value"
You can use this header multiple times for multiple pieces of data:
server-timing: key1;desc="value1"
server-timing: key2;desc="value2"
or use its compact version where you expose multiple pieces of data in one header, comma-separated.
server-timing: key1;desc="value1", key2;desc="value2"
Example of how Wikipedia uses this header to expose info about cache hit/miss:
Code example (need to account for lack of browser support in Safari and IE):
if (window.performance && performance.getEntriesByType) { // avoid error in Safari 10, IE9- and other old browsers
let navTiming = performance.getEntriesByType('navigation')
if (navTiming.length > 0) { // still not supported as of Safari 14...
let serverTiming = navTiming[0].serverTiming
if (serverTiming && serverTiming.length > 0) {
for (let i=0; i<serverTiming.length; i++) {
console.log(`${serverTiming[i].name} = ${serverTiming[i].description}`)
}
}
}
}
This logs cache = hit-front in supported browsers.
Notes:
as mentioned on MDN, the API is only supported over HTTPS
if your JS is served from another domain, you have to add Timing-Allow-Origin response header to make the data readable to JS (Timing-Allow-Origin: * or Timing-Allow-Origin: https://www.example.com)
Server-Timing headers support also dur(header) field, readable as duration on JS side, but it's optional and defaults to 0 in JS if not passed
regarding Safari support: see bug 1 and bug 2 and bug 3
You can read more on server-timing in this blog post
Note that performance entries buffers might get cleaned by JS on the page (via an API call), or by the browser, if the page issues too many calls for subresources. For that reason, you should capture the data as soon as possible, and/or use PerformanceObserver API instead. See the blog post for details.
For those looking for a way to parse all HTTP headers into an object that can be accessed as a dictionary headers["content-type"], I've created a function parseHttpHeaders:
function parseHttpHeaders(httpHeaders) {
return httpHeaders.split("\n")
.map(x=>x.split(/: */,2))
.filter(x=>x[0])
.reduce((ac, x)=>{ac[x[0]] = x[1];return ac;}, {});
}
var req = new XMLHttpRequest();
req.open('GET', document.location, false);
req.send(null);
var headers = parseHttpHeaders(req.getAllResponseHeaders());
// Now we can do: headers["content-type"]
You can't access the http headers, but some of the information provided in them is available in the DOM. For example, if you want to see the http referer (sic), use document.referrer. There may be others like this for other http headers. Try googling the specific thing you want, like "http referer javascript".
I know this should be obvious, but I kept searching for stuff like "http headers javascript" when all I really wanted was the referer, and didn't get any useful results. I don't know how I didn't realize I could make a more specific query.
Like many people I've been digging the net with no real answer :(
I've nevertheless find out a bypass that could help others. In my case I fully control my web server. In fact it is part of my application (see end reference). It is easy for me to add a script to my http response. I modified my httpd server to inject a small script within every html pages. I only push a extra 'js script' line right after my header construction, that set an existing variable from my document within my browser [I choose location], but any other option is possible. While my server is written in nodejs, I've no doubt that the same technique can be use from PHP or others.
case ".html":
response.setHeader("Content-Type", "text/html");
response.write ("<script>location['GPSD_HTTP_AJAX']=true</script>")
// process the real contend of my page
Now every html pages loaded from my server, have this script executed by the browser at reception. I can then easily check from JavaScript if the variable exist or not. In my usecase I need to know if I should use JSON or JSON-P profile to avoid CORS issue, but the same technique can be used for other purposes [ie: choose in between development/production server, get from server a REST/API key, etc ....]
On the browser you just need to check variable directly from JavaScript as in my example, where I use it to select my Json/JQuery profile
// Select direct Ajax/Json profile if using GpsdTracking/HttpAjax server otherwise use JsonP
var corsbypass = true;
if (location['GPSD_HTTP_AJAX']) corsbypass = false;
if (corsbypass) { // Json & html served from two different web servers
var gpsdApi = "http://localhost:4080/geojson.rest?jsoncallback=?";
} else { // Json & html served from same web server [no ?jsoncallback=]
var gpsdApi = "geojson.rest?";
}
var gpsdRqt =
{key :123456789 // user authentication key
,cmd :'list' // rest command
,group :'all' // group to retreive
,round : true // ask server to round numbers
};
$.getJSON(gpsdApi,gpsdRqt, DevListCB);
For who ever would like to check my code:
https://www.npmjs.org/package/gpsdtracking
Allain Lalonde's link made my day.
Just adding some simple working html code here.
Works with any reasonable browser since ages plus IE9+ and Presto-Opera 12.
<!DOCTYPE html>
<title>(XHR) Show all response headers</title>
<h1>All Response Headers with XHR</h1>
<script>
var X= new XMLHttpRequest();
X.open("HEAD", location);
X.send();
X.onload= function() {
document.body.appendChild(document.createElement("pre")).textContent= X.getAllResponseHeaders();
}
</script>
Note: You get headers of a second request, the result may differ from the initial request.
Another way is the more modern fetch() API
https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch
Per caniuse.com it's supported by Firefox 40, Chrome 42, Edge 14, Safari 11
Working example code:
<!DOCTYPE html>
<title>fetch() all Response Headers</title>
<h1>All Response Headers with fetch()</h1>
<script>
var x= "";
if(window.fetch)
fetch(location, {method:'HEAD'})
.then(function(r) {
r.headers.forEach(
function(Value, Header) { x= x + Header + "\n" + Value + "\n\n"; }
);
})
.then(function() {
document.body.appendChild(document.createElement("pre")).textContent= x;
});
else
document.write("This does not work in your browser - no support for fetch API");
</script>
If we're talking about Request headers, you can create your own headers when doing XmlHttpRequests.
var request = new XMLHttpRequest();
request.setRequestHeader("X-Requested-With", "XMLHttpRequest");
request.open("GET", path, true);
request.send(null);
To get the headers as an object which is handier (improvement of Raja's answer):
var req = new XMLHttpRequest();
req.open('GET', document.location, false);
req.send(null);
var headers = req.getAllResponseHeaders().toLowerCase();
headers = headers.split(/\n|\r|\r\n/g).reduce(function(a, b) {
if (b.length) {
var [ key, value ] = b.split(': ');
a[key] = value;
}
return a;
}, {});
I've just tested, and this works for me using Chrome Version 28.0.1500.95.
I was needing to download a file and read the file name. The file name is in the header so I did the following:
var xhr = new XMLHttpRequest();
xhr.open('POST', url, true);
xhr.responseType = "blob";
xhr.onreadystatechange = function () {
if (xhr.readyState == 4) {
success(xhr.response); // the function to proccess the response
console.log("++++++ reading headers ++++++++");
var headers = xhr.getAllResponseHeaders();
console.log(headers);
console.log("++++++ reading headers end ++++++++");
}
};
Output:
Date: Fri, 16 Aug 2013 16:21:33 GMT
Content-Disposition: attachment;filename=testFileName.doc
Content-Length: 20
Server: Apache-Coyote/1.1
Content-Type: application/octet-stream
This is my script to get all the response headers:
var url = "< URL >";
var req = new XMLHttpRequest();
req.open('HEAD', url, false);
req.send(null);
var headers = req.getAllResponseHeaders();
//Show alert with response headers.
alert(headers);
Having as a result the response headers.
This is a comparison test using Hurl.it:
Using mootools, you can use this.xhr.getAllResponseHeaders()
This is an old question. Not sure when support became more broad, but getAllResponseHeaders() and getResponseHeader() appear to now be fairly standard: http://www.w3schools.com/xml/dom_http.asp
As has already been mentioned, if you control the server side then it should be possible to send the initial request headers back to the client in the initial response.
In Express, for example, the following works:
app.get('/somepage', (req, res) => {
res.render('somepage.hbs', {headers: req.headers});
})
The headers are then available within the template, so could be hidden visually but included in the markup and read by clientside javascript.
I think the question went in the wrong way,
If you want to take the Request header from JQuery/JavaScript the answer is simply No. The other solutions is create a aspx page or jsp page then we can easily access the request header.
Take all the request in aspx page and put into a session/cookies then you can access the cookies in JavaScript page..
In a code for a GroupMe chat bot, the variable request is defined as follows:
var request = JSON.parse(this.req.chunks[0]);
I'm trying to figure out what this means. In particlar, what is req referring to?
EDIT: Here is the function where it shows up:
function respond() {
var request = JSON.parse(this.req.chunks[0]),
botRegex = /^deadline ([0-9]|0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/;
botRegex2 = /^\/oranges$/;
if(request.text && botRegex.test(request.text)) {
this.res.writeHead(200);
postDeadline();
this.res.end();
} else if (request.text && botRegex2.test(request.text)) {
this.res.writeHead(200);
postOranges();
this.res.end();
} else {
console.log("don't care");
this.res.writeHead(200);
this.res.end();
}
}
req is a property on this. So that depends on what this is in this context.
Usually, req is a naming convention kept for objects representing an incoming request.
req is short for request which would be the HTTP request data from the client.
Typically, the convention is req is part of the request object on an HTTP transaction. If I had to guess form just this small snippet of code, it's a streaming request that's being parsed as JSON. The request is called by the parent object, hence this. Most likely, it's piping JSON data from an HTTP request to an API (perhaps the GroupMe API), and parsing it into an object that can be more easily used by other functions within the code.
EDIT: Unlike this, req isn't a reserved keyword. It's a convention that's commonly used when referring to HTTP transactions, but may not always hold the same context, so to say it definitively refers to a single thing would be foolish without knowing its function.
I have an issue where I'm trying to make a post request using Restangular:
I'll setup the query like so:
var auth = Restangular.all('auth');
var check = auth.one('check');
Then I'll do the post request like so:
var user = {
email: 'randomemail#gmail.com',
pass: 'randompass'
}
check.post(user)
However, the request shows an error, when I check the network, the request is sent as so :
http://localhost/auth/check/[object object]
Why does the post request attach the object like a query parameter instead of sending it in the request body?
If i'm formatting this post request incorrectly, can someone point out the correct way to format a post request using one and all in Restangular.
Thanks!
When you post to a one(), post() is actually expecting a subElement as the first argument, which is why it's attaching the object passed to the path...
(from documentation)
post(subElement, elementToPost, [queryParams, headers]): Does a POST
and creates a subElement. Subelement is mandatory and is the nested
resource. Element to post is the object to post to the server
To post to /auth/check, you can use customPOST()...
auth.customPOST(user, 'check');
Edit - Here are a couple of examples if you are set on using post()...
Restangular.one('auth').post('check', user);
Or
auth.all('check').post(user);