Does every HTTP request need to be paired with a response? When you do some POST or DELETE actions, my understanding is that sometimes you don't need to send back data. I've always been told to send back an empty object, but is that necessary? Also, is sending a status code considered a response?
Q1: Does every HTTP request need to be paired with a response?
Yes, unless client cancel the request. Actually, one HTTP request needs to be paired with one or more HTTP responses. According to RFC7231:
A server listens on a connection for a request, parses each message received, interprets the message semantics in relation to the identified request target, and responds to that request with one or more response messages.
Q2: When you do some POST or DELETE actions, my understanding is that sometimes you don't need to send back data. I've always been told to send back an empty object, but is that necessary?
It's NOT necessary to send back an empty object (payload). According to RFC7230, the response payload is not required:
A server responds to a client's request by sending one or more HTTP response messages, each beginning with... and finally a message body containing the payload body (if any).
However, although you don't have to "send back data", you still need to send back message, such as HTTP response statuc code and some necessary response headers.
Q3: is sending a status code considered a response?
Yes. Theoretically, a minimal HTTP response can only include HTTP protocol version, status code and status code textual phrase.
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I send some values using spring httpClient to other url. And about that question as I know if I send name=mister age=30 values, received page get that values not http status values, right?
Http status values are for sending page's not receive page's.
I mean, if I send those values, receiving page gets http values.
If receiving page want to get that values, I have send that values, is that right?
My team manager said to me that http has request and response so, if you send some values to other url, other url gets http status values.
But as I thought that is little bit anyway I can't understand my team manager's saying, please let me know, receiving page gets http status when I send some values.
Your team manager's statement is correct. ("the http status have to be written.", "http has request and response. so there should have that http status value result"). What he/she mentioned is HTTP response status code, which should be returned (with correct code) whatever the response is.
No matter your result (name=mister and age =30 etc.) is a static page or an Ajax response, the response code should be 200 OK when the result is generated successfully (correct business logic, no error happens). But when something bad happens, it is important to let client know why server failed to return result -- maybe it is because the request format is incorrect (400 Bad Request), there is a typo in request url (404 Not Found) or some error in server code (500 Internal Server Error). Send name=null and age=null to client with 200 OK is incorrect and bug prone. Without definition of these error status code in document, backend engineer have to communicate with frontend engineer during the development, API by API, case by case, which is very time consuming and inefficient.
I think your TODO is: for the API that accepts name=mister and age =30, define success case and different failure case, then assign correct response code to them.
I am having difficulties understanding the HTTP request and response flow. I am working with a system where I can "hijack" incoming HTTP request and give my own response. The problem I am having is that some type of GET request seem to assume that all data is sent back in first request.
For instance, JPEG image requests, no matter the size (my tests include 0-20 MB JPEG files) seems to assume that the entire data is sent in the first response. Even if I don't send any data and explicitly set range header to 0 I never get a response back from the client asking for the data.
Other data request types, such as mp4 video, the client seems perfectly fine with getting a response with only header information with no data and then sends a new request explicitly asking for byte range 0-.
Is there some kind of agreement between the the client and server that some types should be sent back in one request while others can be split up in a number of requests?
I am trying to create an HTTP parser, and I am interested to know how can I retrieve the URL from HTTP response message text. Does every response contain the URL of the page? Do I need to look at some fields in the header for that or just look at the packet's body? Do I need to save information from previous packets (such as location message)?
Requests have URLs, responses are data packets sent back to the client. But if you make an HTTP request, the immediate response will come from the same URL.
I realize this might sound like an odd question, but I'm seeing some odd results in my network calls so I'm trying to figure out if perhaps I'm misunderstanding something.
I see situations where in isolated incidents, when I'm uploading data, even though the response is 200, the data doesn't appear on the server. My guess is that the 200 response arrives during the initial HTTP handshake and then something goes wrong after the fact. Is that a correct interpretation of the order of events? Or is the 200 delivered once the server has collected whatever data the sending Header tells it is in the request? (cause if so then I'm back to the drawing board as to how I'm seeing what I'm seeing).
It means it has been successfully finished. From the HTTP /1.1 Spec
10.2.1 200 OK
The request has succeeded. The information returned with the response is dependent on the method used in the request, for example:
GET an entity corresponding to the requested resource is sent in the response;
HEAD the entity-header fields corresponding to the requested resource are sent in the response without any message-body;
POST an entity describing or containing the result of the action;
TRACE an entity containing the request message as received by the end server.
Finished. It doesn't make sense otherwise. Something might go wrong and the code could throw an error. How could the server send that error code when it already sent 200 OK.
What you experience might be lag, caching, detached thread running after the server sent the 200 etc.
A success reply, like 200, is not sent until after server has received and processed the full request. Error replies, on the other hand, may be sent before the request is fully received. If that happens, stop sending your request.
I read some articles about Comet tech. All of them mentioned that the long-life HTTP response should be Transfer-Encoding: chunked . I'm wondering why it should be chunked-encoded. If the response is not chunked-encoded, the client javascript can still read and parse the responded text, right?
Is there any special reason that Comet response should be chunked-encoded?
Chunked-encoded response is used when the length of the response is not known until the response is completed. An empty chunk indicates the end of the response. This is the only way the client can be notified for the end of response.
All this fit nicely with Comet. You send the first chunk when the request is received. You may also send additional "heartbeat" chunks while waiting for an action to complete. An empty chunk will notify the client that the response is completed.