Powershell: How can I POST excel (.xlsx) files in a multipart/form-data request?

Question

I'm trying to POST some data to an Express server using Multer as the file upload middleware.

The request includes a few text fields, an API (.yaml) file and an.xlsx file. I can successfully post the.yaml file and the text fields, but not the excel file.

Below is how I have constructed the multipart/form-data call:

# ----- BUILD & EXECUTE API CALL ------

# Set up the boundary, separator and file encoding to use
$boundary = [System.Guid]::NewGuid().ToString() 
$LF = "`r`n"
$enc = [System.Text.Encoding]::GetEncoding("iso-8859-1")

# Get the filename of the .yaml file
$apiFileName = Split-Path $apiFilePath -leaf

# Encode the .yaml file contents
$apiDefBin = [IO.File]::ReadAllBytes("$apiFilePath")
$apiDefEnc = $enc.GetString($apiDefBin)

# Get the filename of the .xlsx file
$excelFileName = Split-Path $excelFilePath -leaf

# Encode the .xlsx file contents
$excelBin = [IO.File]::ReadAllBytes("$excelFilePath")
$excelEnc = $enc.GetString($excelBin)

# Build the body of the multipart request
$bodyLines = (
  "--$boundary",
  'Content-Disposition: form-data; name="textField"',
  '',
  "$textField",
  "--$boundary",
  "Content-Disposition: form-data; name=`"apiDef`"; filename=`"$apiFileName`"",
  'Content-Type: application/octet-stream',
  $apiDefEnc,
  "--$boundary--",
  "Content-Disposition: form-data; name=`"excelFile`"; filename=`"$excelFileName`"",
  'Content-Type: application/octet-stream',
  $excelFileEnc,
  "--$boundary--"
) -join $LF

# Execute the call
Invoke-WebRequest $url `
  -Verbose `
  -Method Post `
  -TimeoutSec 60 `
  -ContentType "multipart/form-data; boundary=$boundary" `
  -Body $bodylines

The request seems successful:

I am printing req.body and req.files on the server, to see what was posted:

{ textField: 'some text here' }
{ apiDef:
   [ { fieldname: 'apiDef',
       originalname: 'api-def.yaml',
       encoding: '7bit',
       mimetype: 'application/octet-stream',
       destination: 'temp',
       filename: 'api-def.yaml',
       path: 'temp\\api-def.yaml',
       size: 2276 } ] }

So the.yaml file is successfully posted, as is the text field. However, the excel file is not sent.

I have tried changing the content-type, and researched if there is another encoding I should be using, but to no avail.

Is what I'm trying to do possible? What am I doing wrong?

Answer 1

Try taking the two dashes out after the boundary in the line above just before the upload of the xlsx file?

$apiDefEnc, "--$boundary--", <------ THIS BIT "Content-Disposition: form-data; name= "excelFile "; filename= "$excelFileName "", 'Content-Type: application/octet-stream',