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How to use HTTP Action in PowerAutomate to upload a file to a Slack channel using the Slack API "files.upload"

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Posted on by dennyregehr

I want to get a PDF attachment from my Inbox when an email arrives (I figured that out), then upload that PDF to a Slack channel using Slack's API call "files.upload". I'm having trouble with the "file" property on their API. I have figured out everything else.

My process:

when email arrives, loop through attachments
when PDF is found, create file in my OneDrive
get File Content from new file in OneDrive
use HTTP action to post to https://slack.com/api/files.upload setting properties:
1. channels
2. filename
3. file

Outgoing payload to Slack:

{
 "uri": "https://slack.com/api/files.upload",
 "method": "POST",
 "headers": {
 "Authorization": "*sanitized*"
 },
 "body": {
 "$content-type": "multipart/form-data",
 "$multipart": [
 {
 "headers": {
 "Content-Disposition": "form-data; name=\"channels\""
 },
 "body": "C05TDD9KG0K"
 },
 {
 "headers": {
 "Content-Disposition": "form-data; name=\"file\";",
 "Content-Transfer-Encoding": "binary"
 },
 "body": "%PDF-1.7\r\n%\uFFFD\uFFFD\uFFFD\uFFFD\r\n1 0 obj\r\n\u003C\u003C/Type/Catalog/Pages ...
 },
 {
 "headers": {
 "Content-Disposition": "form-data; name=\"filename\""
 },
 "body": "Microsoft Security Slate - September 14 2023.pdf"
 }
 ]
 }
}

Return message from Slack:

{
 "ok": false,
 "error": "no_file_data"
}

Seems like I'm just missing the correct formatting of the file contents for the API's "file" property. Anybody else tackled this one? Thanks in advance!

-Denny

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sandeepstw 312 Moderator on at

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Hi There,

For Slack's files.upload API, when dealing with the file parameter, you need to ensure you're sending the actual binary data of the file, not its string representation. The file property should contain the actual binary data of the file. You should not include headers like "%PDF-1.7" within the payload directly. Use "Body" from OneDrive's "Get File Content" Directly: When you use the "Get File Content" action from OneDrive, it returns the binary data of the file. Directly use this output as the body for the file property in your multipart form data.
Multipart formatting should be as follows:

{
"uri": "https://slack.com/api/files.upload",
"method": "POST",
"headers": {
"Authorization": "*sanitized*"
},
"body": {
"$content-type": "multipart/form-data",
"$multipart": [
{
"headers": {
"Content-Disposition": "form-data; name=\"channels\""
},
"body": "C05TDD9KG0K"
},
{
"headers": {
"Content-Disposition": "form-data; name=\"file\";",
"Content-Type": "application/pdf",
"Content-Transfer-Encoding": "binary"
},
"body": "@{outputs('Get_file_content')}"
},
{
"headers": {
"Content-Disposition": "form-data; name=\"filename\""
},
"body": "Microsoft Security Slate - September 14 2023.pdf"
}
]
}
}
In the file section, the "body": "@{outputs('Get_file_content')}" will insert the binary content from your OneDrive action directly.

Please give kudos and mark as solution if it helps.

Thanks,
Sandeep Mishra

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dennyregehr 4 on at

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I tried using "body": "@{outputs('Get_file_content')}" and it sent this to Slack (didn't work):
{ "headers": { "Content-Disposition": "form-data; name=\"file\"", "Content-Type": "application/pdf", "Content-Transfer-Encoding": "binary" }, "body": { "statusCode": 200, "headers": { "Cache-Control": "no-cache", "Pragma": "no-cache", "Accept-Ranges": "bytes", "ETag": "\"{C77A4E8D-9869-4E14-909A-9018BDED3EEB},11\"", "Location": "https://flow-apim-msmanaged-na-eastus2-01.azure-apim.net/apim/onedriveforbusiness/shared-onedriveforbu-1ecbaf4b-5c2b-4f85-97b6-9c226e55656a/datasets/default/files/b%2521OTSjq6HeeUqmD9fPRcR6kbpZwJS5h0VPnWagYVlbQ59vXaY6s362Qb57TnyNEy5H.01FABHFFMNJZ5MO2MYCRHJBGUQDC662PXL/content?inferContentType=True", "x-ms-request-id": "5383aefa-ea0d-4d9a-804c-3ab91b5f6515", "X-AspNet-Version": "4.0.30319", "X-Powered-By": "ASP.NET", "Timing-Allow-Origin": "*", "x-ms-apihub-cached-response": "false", "x-ms-apihub-obo": "false", "Date": "Fri, 22 Sep 2023 16:49:14 GMT", "Content-Length": "206987", "Content-Type": "application/pdf", "Expires": "-1", "Content-Disposition": "attachment; filename=\"Microsoft Security Slate - September 21, 2023.pdf\"" }, "body": { "$content-type": "application/pdf", "$content": "JVBERi0xLjcNCiW1tbW1DQoxIDAg..." } } }

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dennyregehr 4 on at

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I have found a workaround: Slack API supports sending binary content as parameter named "content" as an alternative to "file". I am having success with the content parameter. I was hoping to get the "file" parameter working instead since that works when using curl. If anyone can help me get this "file" parameter working, please reach out.
Thanks,
Denny

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miinn 2 on at

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get File Content from new file in OneDrive
use HTTP action to post to https://slack.com/api/files.upload
I want to upload files to the slack channel using the method above.
Please help me to put the right value in the photo.
I have token and channel id values.
Please........

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Rolson1 45 on at

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Did you ever figure this out?

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