How to use Fiddler to modify the status code in an HTTP response

fiddlerhttphttp-status-codeshttpresponse

I need to test some client application code I've written to test its' handling of various status codes returned in an HTTP response from a web server.

I have Fiddler 2 (Web Debugging Proxy) installed and I believe there's a way to modify responses using this application, but I'm struggling to find out how. This would be the most convenient way, as it would allow me to leave both client and server code unmodified.

Can anyone assist as I'd like to intercept the HTTP response being sent from server to client and modify the status code before it reaches the client?

Any advice would be much appreciated.

Best Answer

Ok, so I assume that you're already able to monitor your client/server traffic. What you want to do is set a breakpoint on the response then fiddle with it before sending it on to the client.

Here are a couple of different ways to do that:

Rules > Automatic Breakpoints > After Responses
In the quickexec box (the black box at the bottom) type "bpafter yourpage.svc". Now Fiddler will stop at a breakpoint before all requests to any URL that contains "yourpage.svc". Type "bpafter" with no parameters to clear the breakpoint.
Programmatically tamper with the response using FiddlerScript. The best documentation for FiddlerScript is on the official site: http://www.fiddler2.com/Fiddler/dev/

Once you've got a response stopped at the breakpoint, just double click it to open it in the inspectors. You've got a couple of options now:

Right next to the green Run to Completion button (which you click to send the response) there's a dropdown that lets you choose some default response types.
Or, on the Headers inspector, change the response code & message in the textbox at the top.
Or, click the "Raw" inspector and mess with the raw response to do arbitrary things to it. Also a good way to see what your client does when it gets a malformed response, which you'll probably test accidentally :)

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Python – How to download a file over HTTP

One more, using urlretrieve:

import urllib
urllib.urlretrieve("http://www.example.com/songs/mp3.mp3", "mp3.mp3")

(for Python 3+ use import urllib.request and urllib.request.urlretrieve)

Yet another one, with a "progressbar"

import urllib2

url = "http://download.thinkbroadband.com/10MB.zip"

file_name = url.split('/')[-1]
u = urllib2.urlopen(url)
f = open(file_name, 'wb')
meta = u.info()
file_size = int(meta.getheaders("Content-Length")[0])
print "Downloading: %s Bytes: %s" % (file_name, file_size)

file_size_dl = 0
block_sz = 8192
while True:
    buffer = u.read(block_sz)
    if not buffer:
        break

    file_size_dl += len(buffer)
    f.write(buffer)
    status = r"%10d  [%3.2f%%]" % (file_size_dl, file_size_dl * 100. / file_size)
    status = status + chr(8)*(len(status)+1)
    print status,

f.close()

HTTP status code for update and delete

For a PUT request: HTTP 200 or HTTP 204 should imply "resource updated successfully".

For a DELETE request: HTTP 200 or HTTP 204 should imply "resource deleted successfully". HTTP 202 can also be returned which would imply that the instruction was accepted by the server and the "resource was marked for deletion".

PUT

If an existing resource is modified, either the 200 (OK) or 204 (No Content) response codes SHOULD be sent to indicate successful completion of the request.

DELETE

A successful response SHOULD be 200 (OK) if the response includes an entity describing the status, 202 (Accepted) if the action has not yet been enacted, or 204 (No Content) if the action has been enacted but the response does not include an entity.

Source: W3.org: HTTP/1.1 Method Definitions

HTTP 200 OK: Standard response for successful HTTP requests. The actual response will depend on the request method used.

HTTP 204 No Content: The server successfully processed the request, but is not returning any content

Source: List of HTTP status codes: 2xx Success

Best Answer

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