我今天一直在用PowerShell制作多部分HTTP POST。希望下面的代码对你有帮助。

• PowerShell本身 * 无法 * 执行多部分表单上传。
• 关于它的样本也不多。我基于this和this构建了代码。
• 当然，Invoke-RestMethod需要PowerShell 3.0，但上面后面的链接中的代码显示了如何直接使用.NET进行HTTP POST，允许您在Windows XP中运行此功能。

祝你好运！请告诉我你是否让它工作了。

function Send-Results {
    param (
        [parameter(Mandatory=$True,Position=1)] [ValidateScript({ Test-Path -PathType Leaf $_ })] [String] $ResultFilePath,
        [parameter(Mandatory=$True,Position=2)] [System.URI] $ResultURL
    )
    $fileBin = [IO.File]::ReadAllBytes($ResultFilePath)
    $computer= $env:COMPUTERNAME

    # Convert byte-array to string (without changing anything)
    #
    $enc = [System.Text.Encoding]::GetEncoding("iso-8859-1")
    $fileEnc = $enc.GetString($fileBin)

    <#
    # PowerShell does not (yet) have built-in support for making 'multipart' (i.e. binary file upload compatible)
    # form uploads. So we have to craft one...
    #
    # This is doing similar to: 
    # $ curl -i -F "file=@file.any" -F "computer=MYPC" http://url
    #
    # Boundary is anything that is guaranteed not to exist in the sent data (i.e. string long enough)
    #    
    # Note: The protocol is very precise about getting the number of line feeds correct (both CRLF or LF work).
    #>
    $boundary = [System.Guid]::NewGuid().ToString()    # 

    $LF = "`n"
    $bodyLines = (
        "--$boundary",
        "Content-Disposition: form-data; name=`"file`"$LF",   # filename= is optional
        $fileEnc,
        "--$boundary",
        "Content-Disposition: form-data; name=`"computer`"$LF",
        $computer,
        "--$boundary--$LF"
        ) -join $LF

    try {
        # Returns the response gotten from the server (we pass it on).
        #
        Invoke-RestMethod -Uri $URL -Method Post -ContentType "multipart/form-data; boundary=`"$boundary`"" -TimeoutSec 20 -Body $bodyLines
    }
    catch [System.Net.WebException] {
        Write-Error( "FAILED to reach '$URL': $_" )
        throw $_
    }
}

这件事一直困扰着我，还没有找到一个满意的解决办法。虽然这里提出的要点可以做yob，它是不有效的情况下，大文件的传输。我写了一篇博客文章，提出了一个解决方案，基于.NET 4.5中的HttpClient类。如果这对你来说不是问题，你可以在下面的地址http://blog.majcica.com/2016/01/13/powershell-tips-and-tricks-multipartform-data-requests/检查我的解决方案
编辑：

function Invoke-MultipartFormDataUpload
{
    [CmdletBinding()]
    PARAM
    (
        [string][parameter(Mandatory = $true)][ValidateNotNullOrEmpty()]$InFile,
        [string]$ContentType,
        [Uri][parameter(Mandatory = $true)][ValidateNotNullOrEmpty()]$Uri,
        [System.Management.Automation.PSCredential]$Credential
    )
    BEGIN
    {
        if (-not (Test-Path $InFile))
        {
            $errorMessage = ("File {0} missing or unable to read." -f $InFile)
            $exception =  New-Object System.Exception $errorMessage
            $errorRecord = New-Object System.Management.Automation.ErrorRecord $exception, 'MultipartFormDataUpload', ([System.Management.Automation.ErrorCategory]::InvalidArgument), $InFile
            $PSCmdlet.ThrowTerminatingError($errorRecord)
        }

        if (-not $ContentType)
        {
            Add-Type -AssemblyName System.Web

            $mimeType = [System.Web.MimeMapping]::GetMimeMapping($InFile)

            if ($mimeType)
            {
                $ContentType = $mimeType
            }
            else
            {
                $ContentType = "application/octet-stream"
            }
        }
    }
    PROCESS
    {
        Add-Type -AssemblyName System.Net.Http

        $httpClientHandler = New-Object System.Net.Http.HttpClientHandler

        if ($Credential)
        {
            $networkCredential = New-Object System.Net.NetworkCredential @($Credential.UserName, $Credential.Password)
            $httpClientHandler.Credentials = $networkCredential
        }

        $httpClient = New-Object System.Net.Http.Httpclient $httpClientHandler

        $packageFileStream = New-Object System.IO.FileStream @($InFile, [System.IO.FileMode]::Open)

        $contentDispositionHeaderValue = New-Object System.Net.Http.Headers.ContentDispositionHeaderValue "form-data"
        $contentDispositionHeaderValue.Name = "fileData"
        $contentDispositionHeaderValue.FileName = (Split-Path $InFile -leaf)

        $streamContent = New-Object System.Net.Http.StreamContent $packageFileStream
        $streamContent.Headers.ContentDisposition = $contentDispositionHeaderValue
        $streamContent.Headers.ContentType = New-Object System.Net.Http.Headers.MediaTypeHeaderValue $ContentType

        $content = New-Object System.Net.Http.MultipartFormDataContent
        $content.Add($streamContent)

        try
        {
            $response = $httpClient.PostAsync($Uri, $content).Result

            if (!$response.IsSuccessStatusCode)
            {
                $responseBody = $response.Content.ReadAsStringAsync().Result
                $errorMessage = "Status code {0}. Reason {1}. Server reported the following message: {2}." -f $response.StatusCode, $response.ReasonPhrase, $responseBody

                throw [System.Net.Http.HttpRequestException] $errorMessage
            }

            $responseBody = [xml]$response.Content.ReadAsStringAsync().Result

            return $responseBody
        }
        catch [Exception]
        {
            $PSCmdlet.ThrowTerminatingError($_)
        }
        finally
        {
            if($null -ne $httpClient)
            {
                $httpClient.Dispose()
            }

            if($null -ne $response)
            {
                $response.Dispose()
            }
        }
    }
    END { }
}

干杯

在研究了multipart/form-data是如何构建的之后，我找到了解决问题的方法。很多帮助都是以http://www.paraesthesia.com/archive/2009/12/16/posting-multipartform-data-using-.net-webrequest.aspx的形式出现的。
然后，解决方案是根据该约定手动构建请求的主体。我已经离开了像正确的内容长度等细节。
以下是我现在使用的一个摘录：

$path = "/Some/path/to/data/"

    $boundary_id = Get-Date -Format yyyyMMddhhmmssfffffff
    $boundary = "------------------------------" + $boundary_id

    $url = "http://..."
    [System.Net.HttpWebRequest] $req = [System.Net.WebRequest]::create($url)
    $req.Method = "POST"
    $req.ContentType = "multipart/form-data; boundary=$boundary"
    $ContentLength = 0
    $req.TimeOut = 50000

    $reqst = $req.getRequestStream()

    <#
    Any time you write a file to the request stream (for upload), you'll write:
        Two dashes.
        Your boundary.
        One CRLF (\r\n).
        A content-disposition header that tells the name of the form field corresponding to the file and the name of the file. That looks like:
        Content-Disposition: form-data; name="yourformfieldname"; filename="somefile.jpg" 
        One CRLF.
        A content-type header that says what the MIME type of the file is. That looks like:
        Content-Type: image/jpg
        Two CRLFs.
        The entire contents of the file, byte for byte. It's OK to include binary content here. Don't base-64 encode it or anything, just stream it on in.
        One CRLF.
    #>

    <# Upload #1: XFA #> 
    $xfabuffer = [System.IO.File]::ReadAllBytes("$path\P7-T.xml")

    <# part-header #>
    $header = "--$boundary`r`nContent-Disposition: form-data; name=`"xfa`"; filename=`"xfa`"`r`nContent-Type: text/xml`r`n`r`n"
    $buffer = [Text.Encoding]::ascii.getbytes($header)        
    $reqst.write($buffer, 0, $buffer.length)
    $ContentLength = $ContentLength + $buffer.length

    <# part-data #>
    $reqst.write($xfabuffer, 0, $xfabuffer.length)
    $ContentLength = $ContentLength + $xfabuffer.length

    <# part-separator "One CRLF" #>
    $terminal = "`r`n"
    $buffer = [Text.Encoding]::ascii.getbytes($terminal)        
    $reqst.write($buffer, 0, $buffer.length)
    $ContentLength = $ContentLength + $buffer.length

    <# Upload #1: PDF template #>
    $pdfbuffer = [System.IO.File]::ReadAllBytes("$path\P7-T.pdf")

    <# part-header #>
    $header = "--$boundary`r`nContent-Disposition: form-data; name=`"pdf`"; filename=`"pdf`"`r`nContent-Type: application/pdf`r`n`r`n"
    $buffer = [Text.Encoding]::ascii.getbytes($header)        
    $reqst.write($buffer, 0, $buffer.length)
    $ContentLength = $ContentLength + $buffer.length

    <# part-data #>
    $reqst.write($pdfbuffer, 0, $pdfbuffer.length)
    $ContentLength = $ContentLength + $pdfbuffer.length

    <# part-separator "One CRLF" #>
    $terminal = "`r`n"
    $buffer = [Text.Encoding]::ascii.getbytes($terminal)        
    $reqst.write($buffer, 0, $buffer.length)
    $ContentLength = $ContentLength + $buffer.length

    <#
    At the end of your request, after writing all of your fields and files to the request, you'll write:

    Two dashes.
    Your boundary.
    Two more dashes.
    #>
    $terminal = "--$boundary--"
    $buffer = [Text.Encoding]::ascii.getbytes($terminal)        
    $reqst.write($buffer, 0, $buffer.length)
    $ContentLength = $ContentLength + $buffer.length

    $reqst.flush()
    $reqst.close()

    # Dump request to console
    #$req

    [net.httpWebResponse] $res = $req.getResponse()

    # Dump result to console
    #$res

    # Dump result-body to filesystem
<#    
    $resst = $res.getResponseStream()
    $sr = New-Object IO.StreamReader($resst)
    $result = $sr.ReadToEnd()
    $res.close()
#>

    $null = New-Item -ItemType Directory -Force -Path "$path\result"
    $target = "$path\result\P7-T.pdf"

    # Create a stream to write to the file system.
    $targetfile = [System.IO.File]::Create($target)

    # Create the buffer for copying data.
    $buffer = New-Object Byte[] 1024

    # Get a reference to the response stream (System.IO.Stream).
    $resst = $res.GetResponseStream()

    # In an iteration...
    Do {
        # ...attemt to read one kilobyte of data from the web response stream.
        $read = $resst.Read($buffer, 0, $buffer.Length)

        # Write the just-read bytes to the target file.
        $targetfile.Write($buffer, 0, $read)

        # Iterate while there's still data on the web response stream.
    } While ($read -gt 0)

    # Close the stream.
    $resst.Close()
    $resst.Dispose()

    # Flush and close the writer.
    $targetfile.Flush()
    $targetfile.Close()
    $targetfile.Dispose()

我已经将@akauppi的答案重新混合到一个更通用的解决方案中，一个cmdlet：

• 可以从Get-ChildItem获取管道输入以上传文件
• 将URL作为位置参数
• 将字典作为位置参数，并将其作为附加表单数据发送
• 接受（可选）-Credential参数
• 接受一个（可选）-FilesKey参数来指定文件上载部分的formdata键
• 支持-WhatIf
• 具有-Verbose日志记录
• 如果出现错误，则退出并返回错误

可以这样称呼：

$url ="http://localhost:12345/home/upload"
$form = @{ description = "Test 123." }
$pwd = ConvertTo-SecureString "s3cr3t" -AsPlainText -Force
$creds = New-Object System.Management.Automation.PSCredential ("john", $pwd)

Get-ChildItem *.txt | Send-MultiPartFormToApi $url $form $creds -Verbose -WhatIf

下面是完整cmdlet的代码：

function Send-MultiPartFormToApi {
    # Attribution: [@akauppi's post](https://stackoverflow.com/a/25083745/419956)
    # Remixed in: [@jeroen's post](https://stackoverflow.com/a/41343705/419956)
    [CmdletBinding(SupportsShouldProcess = $true)] 
    param (
        [Parameter(Position = 0)]
        [string]
        $Uri,

        [Parameter(Position = 1)]
        [HashTable]
        $FormEntries,

        [Parameter(Position = 2, Mandatory = $false)]
        [System.Management.Automation.Credential()]
        [System.Management.Automation.PSCredential]
        $Credential,

        [Parameter(
            ParameterSetName = "FilePath",
            Mandatory = $true,
            ValueFromPipeline = $true,
            ValueFromPipelineByPropertyName = $true
        )]
        [Alias("Path")]
        [string[]]
        $FilePath,

        [Parameter()]
        [string]
        $FilesKey = "files"
    );

    begin {
        $LF = "`n"
        $boundary = [System.Guid]::NewGuid().ToString()

        Write-Verbose "Setting up body with boundary $boundary"

        $bodyArray = @()

        foreach ($key in $FormEntries.Keys) {
            $bodyArray += "--$boundary"
            $bodyArray += "Content-Disposition: form-data; name=`"$key`""
            $bodyArray += ""
            $bodyArray += $FormEntries.Item($key)
        }

        Write-Verbose "------ Composed multipart form (excl files) -----"
        Write-Verbose ""
        foreach($x in $bodyArray) { Write-Verbose "> $x"; }
        Write-Verbose ""
        Write-Verbose "------ ------------------------------------ -----"

        $i = 0
    }

    process {
        $fileName = (Split-Path -Path $FilePath -Leaf)

        Write-Verbose "Processing $fileName"

        $fileBytes = [IO.File]::ReadAllBytes($FilePath)
        $fileDataAsString = ([System.Text.Encoding]::GetEncoding("iso-8859-1")).GetString($fileBytes)

        $bodyArray += "--$boundary"
        $bodyArray += "Content-Disposition: form-data; name=`"$FilesKey[$i]`"; filename=`"$fileName`""
        $bodyArray += "Content-Type: application/x-msdownload"
        $bodyArray += ""
        $bodyArray += $fileDataAsString

        $i += 1
    }

    end {
        Write-Verbose "Finalizing and invoking rest method after adding $i file(s)."

        if ($i -eq 0) { throw "No files were provided from pipeline." }

        $bodyArray += "--$boundary--"

        $bodyLines = $bodyArray -join $LF

        # $bodyLines | Out-File data.txt # Uncomment for extra debugging...

        try {
            if (!$WhatIfPreference) {
                Invoke-RestMethod `
                    -Uri $Uri `
                    -Method Post `
                    -ContentType "multipart/form-data; boundary=`"$boundary`"" `
                    -Credential $Credential `
                    -Body $bodyLines
            } else {
                Write-Host "WHAT IF: Would've posted to $Uri body of length " + $bodyLines.Length
            }
        } catch [Exception] {
            throw $_ # Terminate CmdLet on this situation.
        }

        Write-Verbose "Finished!"
    }
}

-Form 选项

Power Shell 7.2+为多部分/表单数据添加了一个整洁的功能。从MS学习示例6：

$Uri = 'https://api.contoso.com/v2/profile'
$Form = @{
firstName  = 'John'
lastName   = 'Doe'
email      = 'john.doe@contoso.com'
avatar     = Get-Item -Path 'c:\Pictures\jdoe.png'
birthday   = '1980-10-15'
hobbies    = 'Hiking','Fishing','Jogging'
}
$Result = Invoke-WebRequest -Uri $Uri -Method Post -Form $Form

但这个功能也有一些缺点。对我来说，缺乏一个选项来控制文件的MIME类型使它毫无用处。我必须以application/pdf的格式发送PDF，但PS将以octet-stream的格式发送。

使用.NET的灵活脚本

受MS Learn Example 5和各种问题中的答案的启发，我使用.NET类制作了自己的Power Shell脚本。我认为这是一个非常灵活和强大的脚本：

#
# Assembles a POST WebRequest
# 

Add-Type -AssemblyName System.Net.Http, System.Collections

$url = "http://localhost:14783"

$Uri = "$url/public/system_under_test.php"

$cookiedomain = "localhost"

# collect the streams here to dispose them at the end
$OpenStreams = [System.Collections.Generic.List[System.IO.FileStream]]::new()

# returns a .NET ByteArrayContent, useful for text, numbers and others
function Get-Text-Part {
    param ( $FieldName, $FieldValue )

    $Header = [System.Net.Http.Headers.ContentDispositionHeaderValue]::new('form-data')
    $Header.Name = $FieldName
    
    $FieldValueAsBytes =[System.Text.Encoding]::UTF8.GetBytes($FieldValue)
    $FieldContent = [System.Net.Http.ByteArrayContent]::new($FieldValueAsBytes)
    $FieldContent.Headers.ContentDisposition = $Header
    
    return $FieldContent
}

# returns a .NET StreamContent object , useful for arbitrary files
function Get-File-Part {
    param ( $FieldName, $FilePath, $MimeType )

    $Header = [System.Net.Http.Headers.ContentDispositionHeaderValue]::new('form-data')
    $Header.Name = $FieldName
    $Header.FileName = Split-Path -leaf $FilePath

    $FileStream = [System.IO.FileStream]::new($FilePath, [System.IO.FileMode]::Open)
    $FileContent = [System.Net.Http.StreamContent]::new($FileStream)

    $OpenStreams.Add($FileStream)

    $FileContent.Headers.ContentDisposition = $Header
    $FileContent.Headers.ContentType = [System.Net.Http.Headers.MediaTypeHeaderValue]::Parse($MimeType)

    return $FileContent
}

$MultipartContent = [System.Net.Http.MultipartFormDataContent]::new()
$MultipartContent.Add((Get-Text-Part -FieldName 'captcha' -FieldValue 'so what'))
$MultipartContent.Add((Get-Text-Part -FieldName 'company' -FieldValue 'ACME'))
$MultipartContent.Add((Get-Text-Part -FieldName 'name' -FieldValue 'Jon Doe'))
$MultipartContent.Add((Get-Text-Part -FieldName 'phone' -FieldValue '123'))

$FullFilePath = Join-Path -Path (Get-Location) -ChildPath 'HelloWorld.pdf'
$MultipartContent.Add((Get-File-Part -FieldName 'pdf1' -FilePath $FullFilePath -MimeType 'application/pdf'))

$FullFilePath = Join-Path -Path (Get-Location) -ChildPath 'myImage.jpg'
$MultipartContent.Add((Get-File-Part -FieldName 'image1' -FilePath $FullFilePath -MimeType 'image/jpeg'))

$session = New-Object Microsoft.PowerShell.Commands.WebRequestSession
$session.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/112.0.0.0 Safari/537.36"
$session.Cookies.Add((New-Object System.Net.Cookie("session name", "m5k4ek685786586997097746av", "/", "$cookiedomain")))

# you probably do not need -WebSession and exhaustive -Headers
Invoke-WebRequest -Uri $Uri -Body $MultipartContent -Method 'POST' -WebSession $session -ContentType 'multipart/form-data;'-Headers @{
"Accept"="text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7"
  "Accept-Encoding"="gzip, deflate, br"
  "Accept-Language"="de-DE,de;q=0.9,en-US;q=0.8,en;q=0.7"
  "Cache-Control"="max-age=0"
  "Origin"="$url"
  "Referer"="$url/public/system_under_test.php"
  "Sec-Fetch-Dest"="document"
  "Sec-Fetch-Mode"="navigate"
  "Sec-Fetch-Site"="same-origin"
  "Sec-Fetch-User"="?1"
  "Upgrade-Insecure-Requests"="1"
  "sec-ch-ua"="`"Chromium`";v=`"112`", `"Google Chrome`";v=`"112`", `"Not:A-Brand`";v=`"99`""
  "sec-ch-ua-mobile"="?0"
  "sec-ch-ua-platform"="`"Windows`""
}

# Dispose streams otherwise they could stay locked
foreach ( $stream in $OpenStreams){
  $stream.Dispose()
}