How do I access the response body after doing multiple res.write()s? Simplified example:
endpoint(req, res) {
res.set('Content-Type', 'application/json')
res.write('{"resdata":')
//Stream data, format it, and then add to the response
res.write(stream1)
res.write(', "resdata2":')
//Stream some other data, format it, and then add to the response:
res.write(stream2)
res.write('}')
var savedBody = res.getBody() //Is there a way to extract the response body here from all the res.writes()?
res.end()
doSomethingElseWithResponseBody(savedBody)
}
Technically, I could create my own JSON and then do a single res.send at the end -- I know -- but in the specific implementation of this, it's very difficult to use that method; the res.writes() need to be kept.
Appreciate any tips!
Related
I have a client-side script running to send the string "Y" to the server. I set up a console.log on the client-side (which you can see below) and another on the server-side. The one on the client-side works, but the one logs an "empty" object.. it just shows "{}".
How do I get my data to stay in the object?
const status = "Y";
const options = {
method: 'POST',
headers: {
'Content-type': 'application/json'
},
body: status
fetch('/events/<%- event.id %>/prompt', options)
console.log(options.body)
Here's my route for context:
router.route('events/:id/prompt')
.get(catchAsync(events.showPrompt))
.post(catchAsync(events.checkIn))
And my controller:
module.exports.checkIn = async(req, res) => {
console.log(req.body);
}
How do I get the object to come through to the server?
For sending "y" as the content and receiving that in Express, you need two things:
You need to make sure the content-type is set to text/plain on the request.
You need the appropriate middleware that will read that text/plain body.
app.use(express.text())
Then, you will find the body in req.body within any express request handler registered after the above middleware.
You could pick different content-types also such as application/json, the corresponding middleware for that content-type app.use(express.json())` and then format the body data in that format.
It's important to realize that Express does not by itself read the body of an incoming request. It reads the headers, but not the body by default. If you want the body to be read, then you need middleware that is looking for whatever content-type the incoming request has, reads the body, parses it from whatever it's format is and puts the resulting parsed data into req.body. Express comes with a number of built-in middleware for popular content-types.
Status is a string. However body have to take a object with key-value pair. If send like with like below, then you get object which contains status on the backend side.
body: {status: status}
Problem from :
Client : you choose Content-type': 'application/json' , so your body must be json format , something like body : { status } . Make sure you sent exact object with browser debug , because some call api package can change value of request.
Server : Some nodejs framework need parse the value is sent from client before read it (Exp : app.use(express.json()) with Express)
I am writing the server side code to handle incoming post requests (using NodeJS and Express).
If the request coming into the server is formatted as JSON data, then I want to use JSON.parse, but if the data coming in is formatted as a URL encoded query string, then using JSON.parse on that data gives me the error below. Any suggestions? Code at the bottom.
app.post("/", (req, res) => {
let parsedData;
// if request.body is received as JSON data, I want to put it inside the loop below and parse it and then set parsedData equal to that parsed data.
// if the request.body is received as url encoded data, I just want to set parsedData = req.body
for (var key in req.body) {
parsedData = JSON.parse(key);
}
})
Actually I was able to figure it out! Basically I created a separate function to see if I could JSON PARSE the req.body
function isJSONObject(value) {
try {
JSON.parse(value)
} catch {
return false;
}
return true;
}
I need some clarification on JSON objects. Inside my node backend, I receive a JSON object and after I'm done going through which key/value pairs I need, I send it off to the frontend. This is where I'm getting confused- I still need to turn that response object into json via response.json(). Why? If the backend is passing JSON, then why would I need to turn the response obj into JSON?
// test.js (node)
const testObj = {
"test1": {
"1": "Hello there"
}
}
app.get('some-route', async(req,res) =>{
res.send(testObj)
}
// front.js (React)
async someFunc(){
const response = await fetch('/some-route');
const data = await response.json(); //why?
}
Because on your front-end, the fetch API receives a buffer -- an array of bytes, which could contain any payload. It could be an image, plain text, a file, or a JSON payload.
Knowing what your back-end is going to send down, you need to receive the buffer of the data and then perform the .json() API on it, essentially asking that the buffer be interpreted as a serialized string representing a JSON object, and then having the Javascript engine evaluate (deserialize) that string into an object.
Fetch is a multi-purpose API that doesn't have any prior knowledge about the payload that the server is going to send. You are instructing it to treat the payload as JSON by using the .json() function.
Besides .json(), there are other helper methods to read and parse a variety of other possible response types; for example, .text() for plain text, .formData() for form encoded data (similar to querystring values), .blob(), and .arrayBuffer() for byte-level access to the returned data. You will use the appropriate method based on the response type that you're expecting from the API.
https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API
The response object isn't whatever you sent from the backend, it will be a Response object. That's how the Fetch API works. That Response object will have lots of metadata on it, and some methods, including .json which Takes a Response stream and reads it to completion. It returns a promise that resolves with the result of parsing the body text as JSON.
If you don't want to have to go through these two steps, just write this function.
const fetchJson = async url => {
const response = await fetch(url)
return response.json()
}
and use it like this:
async someFunc(){
const data = await fetchJson('/some-route')
}
A response object is more than just its JSON part. It contains all HTTP protocol elements, like headers, the state of the response and so on.
When you use res.json() you are telling your code to separate only the JSON part from all these other things.
To understand a bit more about an HTTP response, I suggest you to read this.
Good question!
When you send data to the front-end from the back-end, you're not just sending the data payload you created in your testObj. What's actually being returned is a response object, which will look something like:
{
type: "cors",
url: "http://some-url.com/some-api",
redirected: false,
status: 200,
ok: true,
body: ReadableStream,
...
headers: Headers,
json: json(),
...
}
where the value of response.json is the body deserializer method in the response object. You can see for yourself; try to console.log(data) from your example after removing the .json() bit, and you'll get a look at the response object in its entirety.
As you can see, the response's body - or the payload you sent from the server - is received by the client as a ReadableStream object, which then needs to be deserialized once the entire object has reached the client. The response.json() method simply deserializes the response.body ReadableStream object from serialized byte data into JSON, which you can then parse in your application.
I'm trying to use a Cloudflare Worker to proxy a POST request to another server.
It is throwing a JS exception – by wrapping in a try/catch blog I've established that the error is:
TypeError: A request with a one-time-use body (it was initialized from a stream, not a buffer) encountered a redirect requiring the body to be retransmitted. To avoid this error in the future, construct this request from a buffer-like body initializer.
I would have thought this could be solved by simply copying the Response so that it's unused, like so:
return new Response(response.body, { headers: response.headers })
That's not working. What am I missing about streaming vs buffering here?
addEventListener('fetch', event => {
var url = new URL(event.request.url);
if (url.pathname.startsWith('/blog') || url.pathname === '/blog') {
if (reqType === 'POST') {
event.respondWith(handleBlogPost(event, url));
} else {
handleBlog(event, url);
}
} else {
event.respondWith(fetch(event.request));
}
})
async function handleBlog(event, url) {
var newBlog = "https://foo.com";
var originUrl = url.toString().replace(
'https://www.bar.com/blog', newBlog);
event.respondWith(fetch(originUrl));
}
async function handleBlogPost(event, url) {
try {
var newBlog = "https://foo.com";
var srcUrl = "https://www.bar.com/blog";
const init = {
method: 'POST',
headers: event.request.headers,
body: event.request.body
};
var originUrl = url.toString().replace( srcUrl, newBlog );
const response = await fetch(originUrl, init)
return new Response(response.body, { headers: response.headers })
} catch (err) {
// Display the error stack.
return new Response(err.stack || err)
}
}
A few issues here.
First, the error message is about the request body, not the response body.
By default, Request and Response objects received from the network have streaming bodies -- request.body and response.body both have type ReadableStream. When you forward them on, the body streams through -- chunks are received from the sender and forwarded to the eventual recipient without keeping a copy locally. Because no copies are kept, the stream can only be sent once.
The problem in your case, though, is that after streaming the request body to the origin server, the origin responded with a 301, 302, 307, or 308 redirect. These redirects require that the client re-transmit the exact same request to the new URL (unlike a 303 redirect, which directs the client to send a GET request to the new URL). But, Cloudflare Workers didn't keep a copy of the request body, so it can't send it again!
You'll notice this problem doesn't happen when you do fetch(event.request), even if the request is a POST. The reason is that event.request's redirect property is set to "manual", meaning that fetch() will not attempt to follow redirects automatically. Instead, fetch() in this case returns the 3xx redirect response itself and lets the application deal with it. If you return that response on to the client browser, the browser will take care of actually following the redirect.
However, in your worker, it appears fetch() is trying to follow the redirect automatically, and producing an error. The reason is that you didn't set the redirect property when you constructed your Request object:
const init = {
method: 'POST',
headers: event.request.headers,
body: event.request.body
};
// ...
await fetch(originUrl, init)
Since init.redirect wasn't set, fetch() uses the default behavior, which is the same as redirect = "automatic", i.e. fetch() tries to follow redirects. If you want fetch() to use manual redirect behavior, you could add redirect: "manual" to init. However, it looks like what you're really trying to do here is copy the whole request. In that case, you should just pass event.request in place of the init structure:
// Copy all properties from event.request *except* URL.
await fetch(originUrl, event.request);
This works because a Request has all of the fields that fetch()'s second parameter wants.
What if you want automatic redirects?
If you really do want fetch() to follow the redirect automatically, then you need to make sure that the request body is buffered rather than streamed, so that it can be sent twice. To do this, you will need to read the whole body into a string or ArrayBuffer, then use that, like:
const init = {
method: 'POST',
headers: event.request.headers,
// Buffer whole body so that it can be redirected later.
body: await event.request.arrayBuffer()
};
// ...
await fetch(originUrl, init)
A note on responses
I would have thought this could be solved by simply copying the Response so that it's unused, like so:
return new Response(response.body, { headers: response.headers })
As described above, the error you're seeing is not related to this code, but I wanted to comment on two issues here anyway to help out.
First, this line of code does not copy all properties of the response. For example, you're missing status and statusText. There are also some more-obscure properties that show up in certain situations (e.g. webSocket, a Cloudflare-specific extension to the spec).
Rather than try to list every property, I again recommend simply passing the old Response object itself as the options structure:
new Response(response.body, response)
The second issue is with your comment about copying. This code copies the Response's metadata, but does not copy the body. That is because response.body is a ReadableStream. This code initializes the new Respnose object to contain a reference to the same ReadableStream. Once anything reads from that stream, the stream is consumed for both Response objects.
Usually, this is fine, because usually, you only need one copy of the response. Typically you are just going to send it to the client. However, there are a few unusual cases where you might want to send the response to two different places. One example is when using the Cache API to cache a copy of the response. You could accomplish this by reading the whole Response into memory, like we did with requests above. However, for responses of non-trivial size, that could waste memory and add latency (you would have to wait for the entire response before any of it gets sent to the client).
Instead, what you really want to do in these unusual cases is "tee" the stream so that each chunk that comes in from the network is actually written to two different outputs (like the Unix tee command, which comes from the idea of a T junction in a pipe).
// ONLY use this when there are TWO destinations for the
// response body!
new Response(response.body.tee(), response)
Or, as a shortcut (when you don't need to modify any headers), you can write:
// ONLY use this when there are TWO destinations for the
// response body!
response.clone()
Confusingly, response.clone() does something completely different from new Response(response.body, response). response.clone() tees the response body, but keeps the Headers immutable (if they were immutable on the original). new Response(response.body, response) shares a reference to the same body stream, but clones the headers and makes them mutable. I personally find this pretty confusing, but it's what the Fetch API standard specifies.
I am POSTing a json file to a node.js listener, and I must not fully understand how POSTs are properly constructed, because in the code below the on('data') callback is never invoked. I can see the actual json string in the body, so I can work around the lack of a callback, but it seems like I'm doing something wrong with how I generate my POST request. [Postman details further below]
// Server initialization
var server = restify.createServer();
server.use(restify.queryParser());
server.use(CookieParser.parse);
server.use(restify.bodyParser());
// Later, at the point where I register callbacks.
this.server.post('receive', function (request, respond) {
console.log('Received POST');
console.log("Headers: %s", JSON.stringify(request.headers));
console.log("Body: %s", JSON.stringify(request.body));
var body = '' ;
var filePath = './data/notes.json';
// this event is never triggered.
request.on('data', function (data) {
console.log('Data received.');
body += data;
});
request.on('end', function () {
console.log('End of POST');
fs.writeFile(filePath, body, function () {
respond.end();
});
});
});
POST details:
I'm using Postman to create a POST request, Content-Type: application/json and the putting the json string in the raw body. What will normally trigger the 'data' event in a POST request? If I ignore data events and just read from the request body, will I run into issues?
Since you're using restify.bodyParser, that middleware would have already read the request body so there isn't any more for your handler to read (hence no data events). A stream, like request, can only be read once, until it's exhausted. You can't "re-read" it.
Which also means that you can just use request.body, which should be the (parsed) result of the JSON that you're posting.
As an aside: I don't know Postman very well, but it looks like you're sending a JSON-encoded string to the server, as opposed to a JSON-encoded object.
To send the latter, I would expect that this should be the raw body data:
{"body":"this is a test"}