[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Andrei Kulakov]

Andrei Kulakov  added the comment:

I've tried it with flask_client_long_headers.py , but I get the same output as 
I've gotten before with flask_client.py .

Can you try it on a few different systems?

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Bhushan Shelke]

Bhushan Shelke  added the comment:

Attaching screenshot of TCP dump captured via wireshark
Packet-2

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Added file: https://bugs.python.org/file49678/packet-2.PNG

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Bhushan Shelke]

Bhushan Shelke  added the comment:

Also attaching screenshot of TCP dump captured via wireshark
Packet-1

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Added file: https://bugs.python.org/file49677/packet-1.PNG

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Bhushan Shelke]

Bhushan Shelke  added the comment:

Hmm... intriguing... I just downloaded the files, an executed again, following 
is response

Server
```127.0.0.1 - - [14/Dec/2020 13:07:34] "{}POST 
http://localhost:6000/getResponse HTTP/1.1" 405 -```

Client
```py flask_client.py
b'\n405 Method 
Not Allowed\nMethod Not Allowed\nThe method is not allowed 
for the requested URL.\n'

```

Since my theory is based on - body being appended sent fist before header in 
TCP packet. I just uploaded a file(flask_client_long_headers.py) having long 
header values. Could you please use this and check if you can reproduce it now. 
Also please suggest me any other alternative through which I could send more 
relevant information.

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Added file: https://bugs.python.org/file49676/flask_client_long_headers.py

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Andrei Kulakov]

Andrei Kulakov  added the comment:

I cannot reproduce with 3.9.0, using attached files -- I do not get either 400 
or 405; I get "None received" message:

```python3 flask_client.py  

  
--INS--
b'"None received"\n'

```

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nosy: +andrei.avk

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Bhushan Shelke]

Bhushan Shelke  added the comment:

Any update on this? Did the files I submitted help in reproducing/identifying 
the issue?

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Bhushan Shelke]

Bhushan Shelke  added the comment:

I had uploaded one file(simple_flask.py) to be used as server to the ticket 
when I created the ticket. Since ticket allows only one file upload, I'd pasted 
relevant code in ticket itself. I've now uploaded the client python 
file(flask_client.py) to ticket which should help you reproduce this. This is 
not using any third party library.

Also regarding content-length - It was part triaging I was doing, I continue to 
get the issue even if I remove that header completely. You can notice in sample 
client program that I have attached.

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Added file: https://bugs.python.org/file49623/flask_client.py

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Christian Heimes]

Christian Heimes  added the comment:

I also noticed that you are passing an explicit content length. 
{'Content-Length' : '0'} is wrong for a POST payload of "{}" with standard 
transfer encoding. It should be len("{}") == 2.

A zero content length only valid for chunked transfer encoding, which either 
requires header {"transfer-encoding": "chunked"} or encode_chunked=True.

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Christian Heimes]

Christian Heimes  added the comment:

So far we don't even know for sure if there is a bug in Python's http module. 
It would be helpful if you could provide a reproducer that does not use any 3rd 
party code like requests.

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Bhushan Shelke]

Bhushan Shelke  added the comment:

Any tentative Date for fix to be generally available?

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Bhushan Shelke]

Bhushan Shelke  added the comment:

I have looked at requests lib code. As far as I could understand following is 
the flow of packages used in this case -

request "uses->" urllib3 "uses->" http

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Ronald Oussoren]

Ronald Oussoren  added the comment:

Please check with the requests project as well, I'm not sure how much of the 
stdlib HTTP client is used by requests.

This issue can stay open because the issue is reproducible using the stdlib.

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Bhushan Shelke]

Bhushan Shelke  added the comment:

Yes Ronald I am using requests library however I tried HTTPSConnection class 
from http.client package as well getting same error, may be because cause is in 
the core http library itself

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Ronald Oussoren]

Ronald Oussoren  added the comment:

Are you using the requests library (https://requests.readthedocs.io/en/master/)?

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Bhushan Shelke]

Change by Bhushan Shelke :


--
components: +Library (Lib)

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[issue42417] Empty body {} in POST requests leads to 405 Method not allowed error

[Bhushan Shelke]

New submission from Bhushan Shelke :

I have a Tomcat+Java based server exposing REST APIs. I am writing a client in 
python to consume those APIs. Everything is fine until I send empty body in 
POST request. It is a valid use case for us. If I send empty body I get 400 bad 
request error - Invalid character found in method name [{}POST]. HTTP method 
names must be tokens. If I send empty request from POSTMAN or Java or CURL it 
works fine, problem is only when I used python as a client. 

If I use python based server (attached a simple server program for same) then I 
get 405 Method not allowed instead of 400 that I get using java based server.

Server code is Following is python snippet -

json_object={}
header = {'alias': 'A', 'Content-Type' : 'application/json', 'Content-Length' : 
'0'} 
resp = requests.post(url, auth=(username, password), headers=header, 
json=json_object) 
I tried using data as well instead of json param to send payload with not much 
of success.

I captured the wireshark dumps to undertand it further and found that, the 
request tomcat received is not as per RFC2616 
(https://www.w3.org/Protocols/rfc2616/rfc2616-sec5.html). Especially the part - 
Request-Line = Method SP Request-URI SP HTTP-Version CRLF Because I could see 
in from wireshark dumps it looked like - {}POST MY-APP-URI HTTP/1.1

As we can see the empty body is getting prefixed with http-method, hence tomcat 
reports that as an error. I then looked at python http library code -client.py. 
Following are relevant details -

File - client.py

Method - _send_output (starting at line # 1001) - It first sends the header at 
line #1010 and then the body somewhere down in the code. I thought(I could be 
wrong here) perhaps in this case header is way longer 310 bytes than body 2 
bytes, so by the time complete header is sent on wire body is pushed and hence 
TCP frames are order in such a way that body appears first. To corroborate this 
I added a delay of 1 second just after sending header line#1011 and bingo, the 
error disappeared and it started working fine. Not sure if this is completely 
correct analysis, but can someone in the know can confirm or let me know how to 
fix this.

--
components: Windows
files: sample_flask.py
messages: 381470
nosy: bhushan.shelke, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: Empty body {} in POST requests leads to 405 Method not allowed error
type: behavior
versions: Python 3.9
Added file: https://bugs.python.org/file49609/sample_flask.py

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