I am analyzing requests sent from a website and I want to decode the payload.
I know the content-encoding (from the header) :
Content-Encoding: 991f0418b7
(Which type of encoding is described by this?)
And the payload : a=1wPsj4z5HWKg%2FIwmZuJ9%2FT4XOr4eVRkvwk1KPngTbyEJeZZp8GrGSTu4Wsywmj%2BsbYdYxKCrFxs%2BtMQ3CKwVHy%2B7LtjXXAi0fRd97rNDj9cgHD1LY%2FUQtEQqRlSEjNniJxDJ8W4ivF8prpgXeY4LJEkUQV8DKINAVIUaeTfA7YA%2F82WGRgI%3D
I obviously also have all the client-side informations (cookies etc.).
Knowing this, how can I decode this payload?
Related
I want to send large amount of json over http to sever.
If I use "Content-Encoding":"GZIP" in my httpClient, does it automatically convert the request body to compressed format?
No, the RFC 7231 describes content encoding. If you are sending Content-Encoding you need to make sure that the content is in that encoding.
If you send Content-Encoding: gzip and the message in plain text you will (quite rightly) receive an HTTP 400. The body of a gzip message will always start with 0x1f 0x8b and if the server does not find that int he POST request it is right to complain.
Another reason for this is that you need an appropriate Content-Length header. This will not be the length of the original JSON, it must be the length (in bytes) of the gzipped JSON.
You need to perform the gzip of the JSON before sending anything since you need to know what to place in Content-Length beforehand.
Extra note: If the JSON is that huge (e.g. several gigabytes) you probably will need Transfer-Encoding: chunked, which comes with its own complications. (You do not send Content-Length but add the length of the chuck to the body itself.)
If it automatically does this, is 100% dependent on which http client you are using and if they implemented it that way. Usually setting a header will not automatically encode it, at least in the clients I regularly use.
The http spec says about the HEAD request:
The HEAD method is identical to GET except that the server MUST NOT
return a message-body in the response. The metainformation contained
in the HTTP headers in response to a HEAD request SHOULD be identical
to the information sent in response to a GET request.
And also:
The Content-Length entity-header field indicates the size of the
entity-body, in decimal number of OCTETs, sent to the recipient or, in
the case of the HEAD method, the size of the entity-body that would
have been sent had the request been a GET.
So if the requested resource is dynamically generated, for the HEAD request, will the resource ALSO be generated? Should there a Content-Length header or Transfer-Encoding: chunked header?
(I feel this is about how to implement the HTTP protocol.)
ADD 1
I don't see the spec mandates whether to send Content-Length header or how to send it for a dynamically generated resource. Such dynamic resource will be sent with chunked transfer encoding and there'll be no Content-Length header if accessed with a GET method. So, if HEAD response should mimic GET response, the Contnet-Length should not be sent either.
a) That's not the HTTP spec. It is the W3C copy of the now obsolete RFC 2616, dated 1999.
b) For the current spec, see https://greenbytes.de/tech/webdav/rfc7231.html#HEAD
To answer your question: if you don't know the payload size without actually generating it, not sending Content-Length in the HEAD response is ok.
What is the correct response for HTTP GET with a Content-Type? Should we respond with an error or should we ignore the Content-Type and process the request?
According to RFC 7231 section 3.1.1.5:
A sender that generates a message containing a payload body SHOULD
generate a Content-Type header field in that message unless the
intended media type of the enclosed representation is unknown to the
sender. If a Content-Type header field is not present, the recipient
MAY either assume a media type of "application/octet-stream"
([RFC2046], Section 4.5.1) or examine the data to determine its type.
So, anything that has a "body", a payload, in the request, should pass in a Content-type.
GET, DELETE, HEAD, OPTIONS most often don't have such a payload. But the might. So depending on the request method to determine if there is a body or not is not a very safe way.
If your server receives a GET, and it has a body, and that body is not application/octet-stream then it should have a Content-Type header. It is safe to send a 406 - Not Accepted back when you receive such a request.
On the other hand, if your server does not handle body on a GET, then it would be safe to send a 406 - Not Accepted back too.
For requests not sent by HTML forms, does HTTP limit the Content-Type of a request to application/x-www-form-urlencoded for non-file uploads, or is that MIME type "right"/standard/semantically meaningful in any other way?
For example, PHP automatically parses the content into $_POST, which seems to indicate that x-www-form-urlencoded is expected by the server. On the other hand, I could use Ajax to send a JSON object in the HTTP request content and set the Content-Type to application/json. At least some server technologies (e.g. WSGI) would not try to parse that, and instead provide it in original form to the script.
What MIME type should I use in POST and PUT requests in a RESTful API to ensure compliance with all server implementations of HTTP? I'm disregarding such technologies as SOAP and JSON-RPC because they tunnel protocols through HTTP instead of using HTTP as intended.
Short Answer
You should specify whichever content type best describes the HTTP message entity body.
Long Answer
For example, PHP automatically parses the content into $_POST, which seems to indicate that x-www-form-urlencoded is expected by the server.
The server is not "expecting" x-www-form-urlencoded. PHP -- in an effort to make the lives of developers simpler -- will parse the form-encoded entity body into the $_POST superglobal if and only if Content-Type: x-www-form-urlencoded AND the entity body is actually a urlencoded key-value string. A similar process is followed for messages arriving with Content-Type: multipart/form-data to generate the $_FILES array. While helpful, these superglobals are unfortunately named and they obfuscate what's really happening in terms of the actual HTTP transactions.
What MIME type should I use in POST and PUT requests in a RESTful API
to ensure compliance with all server implementations of HTTP?
You should specify whichever content type best describes the HTTP message entity body. Always adhere to the official HTTP specification -- you can't go wrong if you do that. From RFC 2616 Sec 7.2.1 (emphasis added):
Any HTTP/1.1 message containing an entity-body SHOULD include a
Content-Type header field defining the media type of that body. If and
only if the media type is not given by a Content-Type field, the
recipient MAY attempt to guess the media type via inspection of its
content and/or the name extension(s) of the URI used to identify the
resource. If the media type remains unknown, the recipient SHOULD
treat it as type "application/octet-stream".
Any mainstream server technology will adhere to these rules. Thoughtful web applications will not trust your Content-Type header, because it may or may not be correct. The originator of the message is free to send a totally bogus value. Usually the Content-Type header is checked as a preliminary validation measure, but the content is further verified by parsing the actual data. For example, if you're PUTing JSON data to a REST service, the endpoint might first check to make sure that you've sent Content-Type: application/json, but then actually parse the entity body of your message to ensure it really is valid JSON.
What status code should be returned if a client sends an HTTP request and specifies a Content-Encoding header which cannot be decoded by the server?
Example
A client POSTs JSON data to a REST resource and encodes the entity body using the gzip coding. However, the server can only decode DEFLATE codings because it failed the gzip class in server school.
What HTTP response code should be returned? I would say 415 Unsupported Media Type but it's not the entity's Content-Type that is the problem -- it's the encoding of the otherwise supported entity body.
Which is more appropriate: 415? 400? Perhaps a custom response code?
Addendum: I have, of course, thoroughly checked rfc2616. If the answer is there I may need some new corrective eyewear, but I don't believe that it is.
Update:
This has nothing to do with sending a response that might be unacceptable to a client. The problem is that the client is sending the server what may or may not be a valid media type in an encoding the server cannot understand (as per the Content-Encoding header the client packaged with the request message).
It's an edge-case and wouldn't be encountered when dealing with browser user-agents, but it could crop up in REST APIs accepting entity bodies to create/modify resources.
As i'm reading it, 415 Unsupported Media Type sounds like the most appropriate.
From RFC 2616:
10.4.16 415 Unsupported Media Type
The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.
Yeah, the text part says "media type" rather than "encoding", but the actual description doesn't include any mention of that distinction.
The new hotness, RFC 7231, is even explicit about it:
6.5.13. 415 Unsupported Media Type
The 415 (Unsupported Media Type) status code indicates that the
origin server is refusing to service the request because the payload
is in a format not supported by this method on the target resource.
The format problem might be due to the request's indicated
Content-Type or Content-Encoding, or as a result of inspecting the
data directly.
They should make that the final question on Who Wants To Be a Millionaire!
Well the browser made a request that the server cannot service because the information the client provided is in a format that cannot be handled by the server. However, this isn't the server's fault for not supporting the data the client provided, it's the client's fault for not listening to the server's Acccept-* headers and providing data in an inappropriate encoding. That would make it a Client Error (400 series error code).
My first instinct is 400 Bad Request is the appropriate response in this case.
405 Method Not Allowed isn't right because it refers to the HTTP verb being one that isn't allowed.
406 Not Acceptable looks like it might have promise, but it refers to the server being unable to provide data to the client that satisfies the Accept-* request headers that it sent. This doesn't seem like it would fit your case.
412 Precondition Failed is rather vaguely defined. It might be appropriate, but I wouldn't bet on it.
415 Unsupported Media Type isn't right because it's not the data type that's being rejected, it's the encoding format.
After that we get into the realm of non-standard response codes.
422 Unprocessable Entity describes a response that should be returned if the request was well-formed but if it was semantically incorrect in some way. This seems like a good fit, but it's a WebDAV extension to HTTP and not standard.
Given the above, I'd personally opt for 400 Bad Request. If any other HTTP experts have a better candidate though, I'd listen to them instead. ;)
UPDATE: I'd previously been referencing the HTTP statuses from their page on Wikipedia. Whilst the information there seems to be accurate, it's also less than thorough. Looking at the specs from W3C gives a lot more information on HTTP 406, and it's leading me to think that 406 might be the right code after all.
10.4.7 406 Not Acceptable
The resource identified by the request is only capable of generating
response entities which have content characteristics not acceptable
according to the accept headers sent in the request.
Unless it was a HEAD request, the response SHOULD include an entity
containing a list of available entity characteristics and location(s)
from which the user or user agent can choose the one most appropriate.
The entity format is specified by the media type given in the
Content-Type header field. Depending upon the format and the
capabilities of the user agent, selection of the most appropriate
choice MAY be performed automatically. However, this specification
does not define any standard for such automatic selection.
Note: HTTP/1.1 servers are allowed to return responses which are
not acceptable according to the accept headers sent in the
request. In some cases, this may even be preferable to sending a
406 response. User agents are encouraged to inspect the headers of
an incoming response to determine if it is acceptable.
If the response could be unacceptable, a user agent SHOULD temporarily
stop receipt of more data and query the user for a decision on further
actions.
While it does mention the Content-Type header explicitly, the wording mentions "entity characteristics", which you could read as covering stuff like GZIP versus DEFLATE compression.
One thing worth noting is that the spec says that it may be appropriate to just send the data as is, along with the headers to tell the client what format it's in and what encoding it uses, and just leave it for the client to sort out. So if the client sends a header indicating it accepts GZIP compression, but the server can only generate a response with DEFLATE, then sending that along with headers saying it's DEFLATE should be okay (depending on the context).
Client: Give me a GZIPPED page.
Server: Sorry, no can do. I can DEFLATE pack it for you. Here's the DEFLATE packed page. Is that okay for you?
Client: Welllll... I didn't really want DEFLATE, but I can decode it okay so I'll take it.
(or)
Client: I think I'll have to clear that with my user. Hold on.