functions/SPClientListItemAttachment/New-SPClientListItemAttachment.ps1

#Requires -Version 3.0

# New-SPClientListItemAttachment.ps1
#
# Copyright (c) 2017 karamem0
#
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# in the Software without restriction, including without limitation the rights
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# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# SOFTWARE.

function New-SPClientListItemAttachment {

<#
.SYNOPSIS
  Creates a new attachment.
.PARAMETER ClientContext
  Indicates the client context.
  If not specified, uses default context.
.PARAMETER ParentObject
  Indicates the list item which a attachment to be created.
.PARAMETER ContentPath
  Indicates the content file path.
.PARAMETER ContentStream
  Indicates the content stream.
.PARAMETER FileName
  Indicates the file name.
.PARAMETER Retrievals
  Indicates the data retrieval expression.
#>


    [CmdletBinding(DefaultParameterSetName = 'ContentStream')]
    param (
        [Parameter(Mandatory = $false)]
        [Microsoft.SharePoint.Client.ClientContext]
        $ClientContext = $SPClient.ClientContext,
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [Microsoft.SharePoint.Client.ListItem]
        $ParentObject,
        [Parameter(Mandatory = $true, ParameterSetName = 'ContentStream')]
        [System.IO.Stream]
        $ContentStream,
        [Parameter(Mandatory = $true, ParameterSetName = 'ContentPath')]
        [string]
        $ContentPath,
        [Parameter(Mandatory = $true, ParameterSetName = 'ContentStream')]
        [Parameter(Mandatory = $false, ParameterSetName = 'ContentPath')]
        [string]
        $FileName,
        [Parameter(Mandatory = $false)]
        [string]
        $Retrievals
    )

    process {
        if ($ClientContext -eq $null) {
            throw "Cannot bind argument to parameter 'ClientContext' because it is null."
        }
        $Creation = New-Object Microsoft.SharePoint.Client.AttachmentCreationInformation
        if ($PSCmdlet.ParameterSetName -eq 'ContentStream') {
            $Creation.ContentStream = $ContentStream
            $Creation.FileName = $FileName
        }
        if ($PSCmdlet.ParameterSetName -eq 'ContentPath') {
            if (-not (Test-Path -Path $ContentPath)) {
                throw "Cannot find file '$($ContentPath)'."
            }
            $Creation.ContentStream = [System.IO.File]::OpenRead($ContentPath)
            if ($MyInvocation.BoundParameters.ContainsKey('FileName')) {
                $Creation.FileName = $FileName
            } else {
                $Creation.FileName = [System.IO.Path]::GetFileName($ContentPath)
            }
        }
        $ClientObject = $ParentObject.AttachmentFiles.Add($Creation)
        Invoke-SPClientLoadQuery `
            -ClientContext $ClientContext `
            -ClientObject $ClientObject `
            -Retrievals $Retrievals
        Write-Output $ClientObject
    }

}