Changing Slack CURL call into PowerShell - json

Question

I've in the middle of writing a translation of a working Slack script from Bash to Powershell, and I'm stumbled on what is literally the meat of the problem; how to use Invoke-WebRequest to replace curl.
This is the curl command that works successfully in Bash on *nix systems:
curl \
-X POST \
-H "Content-type: application/json" \
--data "{
\"attachments\":
[
{
\"mrkdwn_in\": [\"text\"],
\"color\": \"$COLOUR\",
\"text\": \"$MESSAGE\",
}
]
}" \
https://hooks.slack.com/services/tokenpart1/tokenpart2
Note the $COLOUR and $MESSAGE variables are derived from elsewhere in the script (not the section I'm having trouble with).
I can't get it to work in PowerShell. My translation so far is:
$Body = #{
"attachments" = "[
{
"mrkdwn_in": ["text"],
"color": "$Colour",
"text": "$Message",
]"
}
$BodyJSON = $Body |convertto-JSON
Invoke-WebRequest -Headers -Method Post -Body "$BodyJSON" -Uri "https://hooks.slack.com/services/tokenpart1/tokenpart2" -ContentType application/json
This results in the following error:
At C:\path-to-file-etc.ps1:53 char:11
+ "mrkdwn_in": ["text"],
+ ~~~~~~~~~~~~~~~~~~~~~
Unexpected token 'mrkdwn_in": ["text"],
"color": "$COLOUR",
"text": "$MESSAGE",
}
]"' in expression or statement.
At C:\path-to-file-etc.ps1:53 char:11
+ "mrkdwn_in": ["text"],
+ ~
The hash literal was incomplete.At
C:\path-to-file-etc.ps1:53 char:11
+ "mrkdwn_in": ["text"],
+ ~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : ParserError: (:) [], ParentContainsErrorRecordEx
ception
+ FullyQualifiedErrorId : UnexpectedToken
Process exited with code 1
Process exited with code 1
Step Notify (PowerShell) failed
I have pretty much zero experience in Powershell. Also because this script has to be able to dropped onto a whole variety of boxes,I won't use any libraries or custom cmdlets or anything like that. Out of box methods or die.

Answer 1

Since you're using ConvertTo-Json anyway, it's simpler to construct the entire input as a (nested) custom object / hashtable, and let ConvertTo-Json handle all JSON formatting:
$Body = [pscustomobject] #{
attachments = , [pscustomobject] #{
mrkdwn_in = , 'text'
color = $Colour
text = $Message
}
}
$BodyJson = $Body | ConvertTo-Json -Depth 3
Note: You could substitute [ordered] for [pscustomobject] to use a hashtable with ordered keys instead; even omitting either would work, though seeing the entries in the resulting JSON in different order may be confusing.
Note the use of ,, the array-construction operator, to ensure that the attachments and mrkdwn_in entries are treated as arrays.
Additionally, since ConvertTo-Json only fully serializes to a default depth of 2 levels, -Depth 3 must be used to ensure that the value of entry mrkdwn_in is serialized as an array.
As for what you tried:
Your immediate problem (in addition to the missing } that Jeff Zeitlin points out in a comment on the question): You've neglected to escape the embedded " chars. in your multi-line string.
Therefore, as documentation topic Get-Help about_Quoting_Rules discusses, you can either use `" to embed double quotes inside "..." or use a here-string (#"<nl>....<n>"#).
Even with the syntax problems fixed, your code wouldn't work as intended, however, because ConvertTo-Json wouldn't preserve the pre-formatted JSON in the attachments entry and instead treat the string value as a string literal that needs escaping; here's a simple example:
#{
foo = "[
1,
2
]"
} | ConvertTo-Json
The above yields:
{
"foo": "[\n 1, \n 2 \n ]"
}