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I'm confused with Status Code 304 "The HTTP 304 Not Modified client redirection response code indicates that there is no need to retransmit the requested resources", what does retransmit the requested resources refers to?
Context:
I'm using JSON SERVER to mock the back-end
Every time I request for the url the first time, it would be okay (200)
The following requests would result to status 304
The description of HTTP 304 sounds very vague to me, why would it say there's no need to retransmit the requested resources when I didn't cache the data originated from db.json in the first place.
Client code:
fetch(`http://localhost:4000/profiles`)
.then(res => res.json())
.then(data => setProfiles(data));
Server log:
GET /profiles 200 1.970ms - - # The first request is status 200
GET /profiles 304 2.609ms - - # The subsequent requests are status 304
GET /profiles 304 2.951ms - -
GET /profiles 304 2.903ms - -
# ...
To rephrase "the HTTP 304 Not Modified client redirection response code indicates that there is no need to retransmit the requested resources":
You request a resource (the data from /profiles) once, and the server sends you that data with a 200 OK status. Now when you request the same resource (/profiles) and its data hasn't changed from the first request, the server will respond with a 304 Not Modified since it assumes you already have the data — it hasn't been modified since the request that was 200 OK.
You say you didn't cache the data in the first request but the server is assuming you would (like the MDN docs for 304 Not Modified say, "It is an implicit redirection to a cached resource") and is trying to save resources.
You'll have to determine if it's best in your specific situation to
cache the first response,
read a possible Expires header and only rerequest after that moment in time, or
possibly omit an If-None-Match ETag header as to tell the server that you don't have a cached version of the resource to use
Related
I am designing a ReST API which follows the basic CRUD pattern.
My API can receive a request to update a resource which may take a short time to process. Ideally I would like to inform clients that a new version is about to be available and that there is some uncertainty over when the version I have cached actually expires.
So the process I intend to use something like this (improvements welcome):
client: GET /some/item
myapi: 200 OK
last-modified: time-stamp-of-v1
etag: some-hash-relating-to-v1-of-my-item-in-this-format
content: json or whatever
data/for/some/item/v1...
client: PUT /some/item
if-match: some-hash-relating-to-v1-of-my-item-in-this-format
content: json or whatever
data/for/some/item/v2...
myapi: 202 ACCEPTED,
content: json or whatever
time-accepted: time-stamp-after-v1-but-before-v2
your item will be at /some/item
here is a URI /some/taskid to track progress
while upload is pending:
client: GET /some/item
myapi: 200 OK
some/item ...
last-modified: time-stamp-of-v1
etag: some-hash-relating-to-v1-of-my-item-in-this-format
>>>> expires: time-stamp-after-v1-but-before-v2 <<<
>>>> warning: 110 Response is stale <<<<
content: json or whatever
data/for/some/item/v1...
client: GET /some/task/id
myapi: 200 OK
content: json or whatever
time-accepted: time-stamp-after-v1-but-before-v2
your item will be at /some/item
status/of/upload/v2...
after task completed:
client: GET /some/item
myapi: 200 OKAY
some/item/v2 ...
last-modified: time-stamp-of-v2
etag: some-hash-relating-to-v2-of-my-item-in-this-format
content: json or whatever
data/for/some/item/v2...
client: GET /some/task/id
myapi: 303 SEE OTHER
look-here: /some/item
If you are a proxy and know know your content is stale you can put "warning: 110 - response is stale" in the header.
However, in this case the data is not actually invalid yet.
I would like to say that I can guarantee it is valid up until the time I received and passed on the upload request (time-stamp-after-v1-but-before-v2 or later as if I am in contact with the upload server). It hasn't really expired at the time I receive the upload request. I just expect its going to.
(In fact if the request fails it might not be updated at all).
Now the default choice is just to serve the old content and let the client catch up on its own. This has high latency. If possible, I would like to do better.
For example, if the client knows the document is about to expire it could poll more often or it could try to upgrade the connection to a web-socket and get sent an update the moment I get it (would that still count as ReST?)
There is another case where using expired data must be avoided at all costs. For that scenario I think I want to tell the client that the resource is temporarily unavailable. Using the warning and expires fields as I have above seems correct there. Though it might be better to send a 503 with a suitable retry-after header.
So the question is: how should I reply to a GET while the upload of a new version is pending?
In anticipation of answers along the lines of use a messaging framework like AMQP or zeroMQ instead for low latency, I should point out this API is acting as a AMQP gateway/proxy for clients unwilling to use AMQP directly. Information on using webhooks or websockets would be still be interesting.
Some related useful content is:
How to proper design a restful API to invalidate a cache?
https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
HTTP status code for temporarily unavailable pages
http://www.albertoleal.me/posts/how-to-prevent-race-conditions-in-restful-apis.html
(the etag prevents races from simultaneously uploads)
Tl;Dr;
While upload is pending send:
client: GET /some/item
myapi: 200 OK
some/item ...
last-modified: time-stamp-of-v1
etag: some-hash-relating-to-v1-of-my-item-in-this-format
expires: time-stamp-after-v1-but-before-v2
stale-while-revalidate: 100
warning: 110 Response is stale
content: json or whatever
data/for/some/item/v1...
At first sight it looks like using Warning is not correct. See https://www.rfc-editor.org/rfc/rfc7234#section-5.5.0
In this case the server is acting as a proxy (though not an HTTP proxy).
It is not disconnected from AMQP and "A proxy MUST NOT send stale responses" unless it is disconnected.
This is annoying as it looked like the right thing to do here.
4.2.4. Serving Stale Responses
A "stale" response is one that either has explicit expiry
information or is allowed to have heuristic expiry calculated, but
is not fresh according to the calculations in Section 4.2.
A cache MUST NOT generate a stale response if it is prohibited by
an explicit in-protocol directive (e.g., by a "no-store" or
"no-cache" cache directive, a "must-revalidate"
cache-response-directive, or an applicable "s-maxage" or
"proxy-revalidate" cache-response-directive; see Section 5.2.2).
**> A cache MUST NOT send stale responses unless it is disconnected
(i.e., it cannot contact the origin server or otherwise find a
forward path) or doing so is explicitly allowed (e.g., by the
max-stale request directive; see Section 5.2.1).**
A cache SHOULD generate a Warning header field with the 110
warn-code (see Section 5.5.1) in stale responses. Likewise, a
cache SHOULD generate a 112 warn-code (see Section 5.5.3) in stale
responses if the cache is disconnected.
A cache SHOULD NOT generate a new Warning header field when
forwarding a response that does not have an Age header field, even if
the response is already stale. A cache need not validate a response
that merely became stale in transit.
Also
4.4. Invalidation
Because unsafe request methods (Section 4.2.1 of [RFC7231]) such as
PUT, POST or DELETE have the potential for changing state on the
origin server, intervening caches can use them to keep their contents
up to date.
**> A cache MUST invalidate the effective Request URI (Section 5.5 of
[RFC7230]) as well as the URI(s) in the Location and Content-Location
response header fields (if present) when a non-error status code is
received in response to an unsafe request method.**
However a warning is required if stale-while-revalidate is used (see https://www.rfc-editor.org/rfc/rfc5861)
The stale-while-revalidate Cache-Control Extension
When present in an HTTP response, the stale-while-revalidate Cache-
Control extension indicates that caches MAY serve the response in
which it appears after it becomes stale, up to the indicated number
of seconds.
stale-while-revalidate = "stale-while-revalidate" "=" delta-seconds
If a cached response is served stale due to the presence of this
extension, the cache SHOULD attempt to revalidate it while still
serving stale responses (i.e., without blocking).
I thought this was unclear so I submitted an errata. This was rejected (though at the time of writing its still showing as reported) on the grounds that the cache control extensions in rfc5861 override the MUST NOT in rfc7234 ("doing so is explicitly allowed" see above).
It is okay to use expires but its not very helpful as it doesn't imply anything.
5.3. Expires
The "Expires" header field gives the date/time after which the
response is considered stale. See Section 4.2 for further discussion
of the freshness model.
**> The presence of an Expires field does not imply that the original
resource will change or cease to exist at, before, or after that
time.**
We have an endpoint which when you post create a new version of resource and returns a 201 and the location of the newly created resource. It determines the new version number based on a comparison of the current version and the version being posted (using a semver like ruleset).
If the version you post is identical to the existing version then no version number is updated. What should we return in this case?
We could just return a 201 even though we have not technically created anything.
I don't want to return a 409 as its not really a conflict, like when you post something with the same id. If you posted the same thing when the existing version was slightly different then you would happily get a 201.
We could just return a 200, but then that would seem weird, and increases the response codes that the users have to deal with
Does the idempotency of the 201 response matter?
Any better suggestions?
How about 303 - See Other? Seems to fit. I draw your attention to this sentence
from the spec at https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource.
That sounds like what you want to do to me. Here's the rest of it.
10.3.4 303 See Other
The response to the request can be found under a different URI and SHOULD be retrieved using a GET method on that resource. This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource. The new URI is not a substitute reference for the originally requested resource. The 303 response MUST NOT be cached, but the response to the second (redirected) request might be cacheable.
The different URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
Note: Many pre-HTTP/1.1 user agents do not understand the 303
status. When interoperability with such clients is a concern, the
302 status code may be used instead, since most user agents react
to a 302 response as described here for 303
I am a bit puzzled by the other answers as some get it almost right. So, let's clear up things a bit. If all requests are indeed performed with the POST method, in the context of ReSTfulness, they are supposed to modify state on the target server. Otherwise, the meaning of POST is a bit relaxed as you can see in RFC 7231, sec. 4.3.3.
Since the intent of the requests is to create a new version of a resource, they have failed if a version with the given presentation already exists. This would disqualify any 2xx-class response codes. From section 6.3:
The 2xx (Successful) class of status code indicates that the client's request was successfully received, understood, and accepted.
If you absolutely wanted to, you could go for 202/Accepted, which "is intentionally noncommittal." This is a bit of a stretch, though, as this status code is intended for queued processing. I would advise against it.
The 204/No Content code suggested by others is a bit of a poor choice. It were absolutely correct if you POSTed to the resource you were updating, though.
As the result is neither informational (1xx) nor a fault by the server (5xx). Let us have a look at the 3xx class first. From section 6.4:
The 3xx (Redirection) class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request.
One of the most prominent one here would be 304/Not Modified. While sounding like a perfect fit, this code is unfortunately not applicable here. It can only be returned in response to conditional GET or HEAD requests.
302/Found may sound like the next best fit. However, this code is intended for temporary redirects, which is in all likelyhood not what you want.
As has been suggested here, 303/See Other is indeed a good choice:
The 303 (See Other) status code indicates that the server is redirecting the user agent to a different resource [...] which is intended to provide an indirect response to the original request.
[...]
This status code is applicable to any HTTP method. It is primarily used to allow the output of a POST action to redirect the user agent to a selected resource
All other 3xx codes are dealing with various forms of redirects that hardly relate to the situation here.
A final look, 4xx-class of status codes. From RFC 7231, sec. 6.5:
The 4xx (Client Error) class of status code indicates that the client seems to have erred. Except when responding to a HEAD request, the server SHOULD send a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method.
Very few of these are actually deeling with the request body. Two of those who do would stand out here: One is 400/Bad Request, which is by design overly broad. It is - if you will - a catch-all solution. However, this would imply that the request body is malformed (as in syntactically incorrect) in some way, which is probably not the case.
More interesting is 409/Conflict. From the RFC (emphasis mine):
The 409 (Conflict) status code indicates that the request could not be completed due to a conflict with the current state of the target resource.
The wording of the definition places this code close to the PUT method, but is not exclusive. To reiterate the definition of the 4xx codes:
These status codes are applicable to any request method.
422/Unprocessable Entity is a contender, but it implies a semantic error, which really isn't the case here.
Ultimately (drumroll) the final piece of the puzzle could be found in section 4.3.3:
If the result of processing a POST would be equivalent to a representation of an existing resource, an origin server MAY redirect the user agent to that resource by sending a 303 (See Other) response with the existing resource's identifier in the Location field.
Note the "MAY." So you can really choose between 303 and 409. I feel 409 were the better fit, as clearly an earlier request introduced a state that is incompatible with the current one. OTOH, 303 may be the politer way to go and is closer to the standard. Either way, as a consumer of your API, I would really like to know if my requests failed. And be it by not having any effect whatsoever.
If nothing has been created by the operation, 201 is not suitable for that:
6.3.2. 201 Created
The 201 (Created) status code indicates that the request has been fulfilled and has resulted in one or more new resources being created. [...]
See below some options you could consider if the operation succeeds:
6.3.1. 200 OK
The 200 (OK) status code indicates that the request has succeeded. The payload sent in a 200 response depends on the request method. For the methods defined by this specification, the intended meaning of the payload can be summarized as:
[...]
POST: a representation of the status of, or results obtained from, the action;
[...]
Aside from responses to CONNECT, a 200 response always has a payload, though an origin server MAY generate a payload body of zero length. If no payload is desired, an origin server ought to send 204 (No Content) instead. [...]
6.3.5. 204 No Content
The 204 (No Content) status code indicates that the server has successfully fulfilled the request and that there is no additional content to send in the response payload body. [...]
If the operation fails:
6.5.1. 400 Bad Request
The 400 (Bad Request) status code indicates that the server cannot will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).
11.2. 422 Unprocessable Entity
The 422 (Unprocessable Entity) status code means the server understands the content type of the request entity (hence a 415 (Unsupported Media Type) status code is inappropriate), and the syntax of the request entity is correct (thus a 400 (Bad Request) status code is inappropriate) but was unable to process the contained instructions. For example, this error condition may occur if an XML request body contains well-formed (i.e., syntactically correct), but semantically erroneous, XML instructions.
A 201 Created should be used whenever you creating a new resource without doubt.
As defined in HTTP Method Definitions RFC, either200 Ok or 204 No Contentis an appropriate response if the operation does not create a new resource depending on the response body content.
The action performed by the POST method might not result in a resource
that can be identified by a URI. In this case, either 200 (OK) or 204
(No Content) is the appropriate response status, depending on whether
or not the response includes an entity that describes the result.
If a resource has been created on the origin server, the response
SHOULD be 201 (Created) and contain an entity which describes the
status of the request and refers to the new resource, and a Location
header (see section 14.30).
Now, coming back to your original question about what to use when the operation is successful and there is nothing to return, you should use 204 No Content. This status code is specifically meant for scenarios where the requested operation is successfully completed but there is no additional relevant information that the server can provide.
The 204 (No Content) status code indicates that the server has successfully fulfilled the request and that there is no additional content to send in the response payload body.
I don't think that for this case the idempotency is an issue, because the state of the system is not the same as it was in the inicial request, because the entity now exists, so you can respond with a different code.
200 should be fine, but it is a little weird as you said.
I have never use this, but I read that for some case you should redirect with a 302, to make a get for other resource, in this case I think this apply, return a 302 and make a get pointing for the old semver, assuming that you have a get endpoint for this entity.
If the POST'd resource has the same version number, but different data, then a 409 would be fitting. But if the data is the same as what's already stored, then a 409 might not be required. Through process of elimination I would say 200 OK would be fine.
We could just return a 200, but then that would seem weird, and increases the response codes that the users have to deal with
If this is a costly concern, consider eliminating the 201, not the 200. The fact of the matter is that for any decently complex service there may be at some point a situation where a 20X (where X is not 0) is applicable. So does that mean we code with each of the 20X responses in mind and spend time checking if our services has situations where 20X is preferred over 200? I suspect not. So unless there is a specific reason to respond with a 20X, for example to deal with a specific use case, then just use 200 and reduce the amount of coding and documenting required. I suspect for most scenarios, the calling client does not care.
Ultimately, the correct answer probably depends on whatever client is consuming your API. If you are building the client too, you could do whatever you prefer... (Just don't get too crazy.)
Assuming you are writing the API and client:
My opinion/suggestion is...
If there IS a new version number: The 201 HTTP status code would fit will.
If there is NOT a new version number: The 200 or 204 HTTP status code would fit well.
If there is no benefit to the client knowing the version number has changed or is the same: Send the 200 HTTP status code.
If you don't control the client consuming your API: Obviously defer to what they expect.
You may also wish review all of the HTTP Status Codes in the HTTP RFC spec. The above status codes also link directly to the relevant section.
201 : when new version is created
202 : when existing version is updated
204 : when request is accepted but no processing is done
by def, 204 = No Content
The server has fulfilled the request but does not need to return an
entity-body, and might want to return updated metainformation. The
response MAY include new or updated metainformation in the form of
entity-headers, which if present SHOULD be associated with the
requested variant.
If the client is a user agent, it SHOULD NOT change its document view
from that which caused the request to be sent. This response is
primarily intended to allow input for actions to take place without
causing a change to the user agent's active document view, although
any new or updated metainformation SHOULD be applied to the document
currently in the user agent's active view.
The 204 response MUST NOT include a message-body, and thus is always
terminated by the first empty line after the header fields.
So its slight tangential to your needs but I think its the best fit.
I have 2 resources User and Album. A user has a list of albums. To get albums there are 2 REST API.
user/{userId}/albums/{albumId} gets album by albumId. If not found returns 404
user/{userId}/albums gets all albums by userId. In this case, if a user has no albums, what should be the status code 204 or 404?
Is the absence of any album really seen as an error? Assuming the albums are returned as a JSON array, the common response to such a situation would be a HTTP 200 with an empty array as the body.
Returning 404 signals that the resource doesn't exist, kind of saying that it isn't even possible to ask for the list of albums for this particular user. But in fact, it's possible to successfully return the list of albums, it's just that the list is empty. It doesn't seem at all exceptional to me. This is completely in contrast to retrieval of one specific album using an ID that doesn't exist (using your other endpoint); in such a situation a 404 is correct.
While a 204 seems better than a 404, because it at least tells the client that the request was successful but had no content, its intention is not really to be used to signal a "successful absence". Rather, it signals that the resource DOES exist but for some reason the server chose not to include the resource in the response body - for example the purpose of the request could have been to simply pass back some headers to the client.
A 204 can also be used as a response to a POST request where some action was carried out by the server without necessarily creating any new resource (which would have implied a 201 CREATED), or where it's for some other reason not relevant to return any resource.
I think it's clear that what you need is a
GET /user/xxx/albums
HTTP/1.1 200 OK
[]
Here is what the RFC2616 that defines the HTTP protocol says about Status-codes:
The first digit of the Status-Code defines the class of response. The last two digits do not have any categorization role. There are
5 values for the first digit:
- 1xx: Informational - Request received, continuing process
- 2xx: Success - The action was successfully received,
understood, and accepted
- 3xx: Redirection - Further action must be taken in order to
complete the request
- 4xx: Client Error - The request contains bad syntax or cannot
be fulfilled
- 5xx: Server Error - The server failed to fulfill an apparently
valid request
In your case, the request was successful, but there are no albums to show, so you definitely should use a status from the 2xx category.
Here is what the RFC says about the 204 status:
10.2.5 204 No Content
The server has fulfilled the request but does not need to return an
entity-body, and might want to return updated metainformation. The
response MAY include new or updated metainformation in the form of
entity-headers, which if present SHOULD be associated with the
requested variant.
If the client is a user agent, it SHOULD NOT change its document
view from that which caused the request to be sent. This response
is primarily intended to allow input for actions to take place
without causing a change to the user agent's active document view,
although any new or updated metainformation SHOULD be applied to
the document currently in the user agent's active view.
The 204 response MUST NOT include a message-body, and thus is
always terminated by the first empty line after the header fields.
The RFC states that the 204 is primarily intended to allow inputs, so you shouldn't use this one. I would use the 200 in this case.
Error Code 404
The web site hosting server will typically generate a "404 Not Found" web page when a user attempts to follow a broken or dead link.
Return Code 204
The server has fulfilled the request but does not need to return an entity-body.
Conclusion
You obviously need to return a 204 status code. If you use the 404 one, the user may be disturbed. More, you use 404 when the targeted album doesn't exist. Using 404 for both 1 and 2 is illogical.
When you ask for a specific resource, say a user, and the user doesn't exist, then you should return 404. For example, you have an API to retrieve a user using the following URL:
https://yourdomain.com/api/users/:userid
and a request is made to retrieve user 1234, that doesn't exist, then you should return 404. In this case, the client requested a resource that doesn't exist.
https://yourdomain.com/api/users/1234
404
Now suppose you have an api that returns all users in the system using the following url:
https://yourdomain.com/api/users
If there are no users in the system, then, in this case, you should return 204.
Let me give my 2 cents on this. I hope you already know the difference between 404 vs 204.
The scenario i would prefer to use each status code are :
404 Status Code
404 means that the Resource not found or doesn't exist or URL is invalid
For example
GET : https://api.myapp.io/product/product_id_123
GET : https://api.myapp.io/image/nokia.jpg
If the single product / resource item doesn't exist in database or in resource folder, that means the resource of this URL is invalid so we have to throw 404 and Search Engines like Google & bing will not going to cache the result and will not retry again the next day for fresh content.
204 Status Code
204 means that the URL is valid and Server has successfully did the execution but it has no data to return.
For example
GET : https://api.myapp.io/product/search?keyword=nokia
If there is no data matched (single or multiple) for the keyword in database to return back the results, then throw 204 because there is no data to return but the URL is still valid and Search Engines like Google & bing will retry again the next day for fresh content because for them it is not invalid url and when you retry the next day there might be some data which matches the query.
I agree with the responses, but I think is 204 or 200, it depends of your response when the album list is empty.
If you will return a empty array, the return it with 200 code, if you prefer to don't return anything, then the right one will be 204. (I prefer a 200 with empty list)
Only use 404 with a resource doesn't existis, if it is a empty list the choose 204 or 200.
Good hacking man!
I have a REST API where the GET request can take 10-20 seconds. So I usually return a 202 code with a location like http://fakeserver/pending/blah where the client can check the status of this request. pending/blah returns a 200 code with "Status: pending" if the request is still pending, and a 303 code when it's done, with a final location for the result: http://fakeserver/finished/blah .
But what if the server crashes during the request processing? Should pending/blah return a 303 code, and then finished/blah returns a 404? How can I alert the client that the resource may be available at a location, but I'm not sure? Assume the requests are persistent, so that when the server reboots, it continues processing the request.
First of all I'll make the state of processed resource an internal field of this resource. This way you can avoid using strange endpoints like: /finished/blah/ or /pending/blah/ and instead of it introduce a single endpoint /resources/blah/ which will among other fields return the state it's currently in.
After changing architecture to the endpoint mentioned above if you ask for blah and server has crashed you can:
return 200 with pending status - client doesn't have necessarily to know about the crash
return 404, simple not found with and extra message that server has crashed.
return 500 and inform the client explicitly what the problem is.
Other useful codes may be also 409 or 503. Returning any 3XX is not a good idea IMO since no redirection applies here. Personally I'd go for 200 or 500(3).
When a client invokes my REST-ful service, it needs to know if the response came back was 'from me' or rather a diagnosis from the containing web server that something awful happened.
One theory is that, if my code is called, it should always return an HTTP OK(=200), and any errors I've got to return should be just represented in the data I return. After all, it's my code that gets the response, not the naked browser.
Somewhat self-evidently, if I'm using REST to generate HTML read directly by a browser, I absolutely must return an error code if there's an error. In the case I care about, it's always Javascript or Java that is interpreting the entrails of the response.
Another possibility is that there is some family of HTTP status codes that I could return with a high confidence that it/they would never be generated by a problem in the surrounding container. Is this the case?
I use the following:
GET
200 OK
400 Bad Request (when input criteria not correct)
POST
202 Accepted (returned by authorization method)
401 Unauthorized (also returned by authorization)
201 Created (when creating a new resource; I also set the location header)
400 Bad Request (when data for creating new entity is invalid or transaction rollback)
PUT
Same as POST
201 Ok
400 Bad Request
DELETE
200 OK
404 Not Found (same as GET)
I would not know how to avoid that some container returns codes like 404.
4xx codes are meant to handle client errors along with possibly some entity that describes the problem in detail (and thus would mean a combination of both of your mentioned approaches). Since REST relies on HTTP and the according semantics of status as well as methods, always returning 200 in any possible case is a violation of this principle in my opinion.
If you for instance have a request such as http://foo.com/bar/123 which represents a bar ressource with id=123 and you return 200 with some content, the client has no chance to figure out if this was the intended response or some sort of error that occured. Therefore one should try to map error conditions to status codes as discussed in REST: Mapping application errors to HTTP Status codes for example.