fix: HTTP/1.1 requests with truncated kernel versions

[Sobuno]

Overview

This PR fixes a bug where requests cannot be sent over HTTP/1.1 if the HostOs header's value starts or ends with whitespace.

HTTP/2 is not affected by this bug as the underlying h2 package trims the whitespace itself.

This fixes #1087.

Notes

Leading and trailing whitespace in any request header value will prevent requests from being sent when using HTTP 1.1 as h11 package's normalize_and_validate function (https://github.com/python-hyper/h11/blob/62c5068c971579d61fa1b55373390e12f25fd856/h11/_headers.py#L152) validates the header using a regex that explicitly disallows trailing whitespace. h2, used for HTTP 2 traffic, trims the values itself.

The HostOs header can end up with leading whitespace if platform.system() returns an empty string (which per Python's documentation is possible: "An empty string is returned if the value cannot be determined.")

The HostOs header can end up with trailing whitespace in two cases:

• If platform.version() returns an empty string (which per Python's documentation is possible: "An empty string is returned if the value cannot be determined.")
• If platform.version() returns a string that ends with a whitespace character.

The latter case can happen on e.g. a Linux platform where platform.version() usually returns the kernel version. The uname struct fields are 65 characters (as seen here: https://github.com/torvalds/linux/blob/9154c4af7829b6f82712b4d1a2a720adddacdb8d/include/uapi/linux/utsname.h#L25) - A kernel version longer than 65 characters may end up being with a whitespace as the last character.

Testing Instructions

• Use a kernel version that ends in a whitespace (e.g. some of the triple-digit Ubuntu backported HWE kernels will end up cutting off the timestamp at a whitespace)
• Connect to Microsoft Graph while Microsoft Graph cannot establish an HTTP/2 connection for some reason
• See that a request is made - Without this fix, h11 would give an Invalid header value error

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Sobuno]

(I experienced this issue today as https://graph.microsoft.com seemingly stopped allowing HTTP/2 traffic, causing the package to fall back to the h11 package's validation mechanism instead.)