PowerShell: Investigate possible BUG Invoke-WebRequest content type charset

@mklement0 Yes exactly, I’ll edit the initial post to make it clearer

@CarloToso,

Based on my summary of what I think the issue is, and your confirmation of it as correct, I’m confused by the following sentence in the initial post:

The charset in the headers should be ignored and default to UTF8

To reconfirm: It should not be ignored, and should instead be honored, just like it already is for -ContentType, correct?

Proceeding on the assumption that my summary is correct:

A simple, setup-free way to verify that -ContentType is honored, but an equivalent Content-Type header field is not is via https://httpbin.org/post, which simply echoes the body back to you:

• Given that UTF-8 is JSON’s default, and that PowerShell now uses UTF-8 encoding by the default for a [string]-based -Body argument with content type application/json, the following works as expected:

# Output: [pscustomobject] @{ foo = 'sß' }
(Invoke-RestMethod https://httpbin.org/post -Body '{ "foo": "sß" }' -Method POST -ContentType application/json).json

• If you send the wrong encoding, which PowerShell applies due to the charset attribute in the -ContentType argument, the .json property value is empty (the attribute is ignored by https://httpbin.org/post, in line with the application/json media-type definition):

# NO output, because the effectively ISO-8859-1-encoded body cannot be decoded *as UTF8* by https://httpbin.org/post
(Invoke-RestMethod https://httpbin.org/post -Body '{ "foo": "sß" }' -Method POST -ContentType 'application/json; charset=iso-8859-1').json

• Trying to make the same intentional mistake with an equivalent Content-Type header field does NOT provoke the symptom, which implies that the charset attribute was ignored by PowerShell, and that UTF-8 was sent:

# !! Output: [pscustomobject] @{ foo = 'sß' } - despite the attempt to send broken encoding
# !! PowerShell *ignored* the 'charset' attribute.
(Invoke-RestMethod https://httpbin.org/post -Body '{ "foo": "sß" }' -Method POST -Headers @{ 
  'Content-Type' = 'application/json; charset=iso-8859-1' 
}).json

@CarloToso, you’re right - I misread the source code; I’ve edited my previous comment to remove the mistaken interpretation.