PowerShell and Twilio: SMS

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Twilio is a cloud based messaging service; it can do everything from sending SMS’s, to being the basis of an entirely cloud based virtual call centre.  It’s pretty powerful stuff.

My requirements are fairly basic though, I just want to be able to send SMS’s from a PowerShell script to engineers to alert them when things go wrong.  The first thing to do is head over to Twilio and set yourself a test account up, which is free, and will allow you to send messages to yourself.

All interaction with Twilio is via their REST API and the first method I have to interact with it is using the official Twilio C# DLLs, the instructions to download are here. Once you have the DLLs, pop them in the same directory as the script you are going to be running and here’s a function to make use of them along with a sample call:

function invoke-twilioSMS
(
    [Parameter(Mandatory=$true)][String]$AccountSid,
    [Parameter(Mandatory=$true)][String]$message,
    [Parameter(Mandatory=$true)][String]$fromTel,
    [Parameter(Mandatory=$true)][String]$toTel,
    [Parameter(Mandatory=$true)][String]$authToken,
    [Parameter(Mandatory=$true)][String]$dllPath
)
{
    Add-Type -path "$dllPath\RestSharp.dll"
    Add-Type -path "$dllPath\Twilio.Api.dll"
    
    $twilio = new-object Twilio.TwilioRestClient($AccountSid,$authToken)
    $msg = $twilio.SendSmsMessage($fromTel, $toTel, $message)
}

invoke-twilioSMS -AccountSid "<AccountSid>" `
    -authToken "<authToken>" -message "<message>" `
    -fromTel "<fromTel"> -toTel "<toTel>" `
    -dllPath "<scriptPath>"

The problem with this method is that it’s awkward to get hold of the DLLs, and I find there is something clunky about having to use DLLs to call a REST API.  So in method 2, I make use of the Invoke-RestMethod (which arrived in PowerShell 3.0) to talk to the REST API directly.

function invoke-twilioRESTSMS
(
    [Parameter(Mandatory=$true)][String]$AccountSid,
    [Parameter(Mandatory=$true)][String]$message,
    [Parameter(Mandatory=$true)][String]$fromTel,
    [Parameter(Mandatory=$true)][String]$toTel,
    [Parameter(Mandatory=$true)][String]$authToken
)
{
    # Build a URI
    $URI = "https://api.twilio.com/2010-04-01/Accounts/$AccountSid/SMS/Messages.json"

    # encode authorization header
    $secureAuthToken = ConvertTo-SecureString $authToken -AsPlainText -Force
    $credential = New-Object System.Management.Automation.PSCredential($AccountSid,$secureAuthToken) 
    
    # content
    $postData = "From=$fromTel&To=$toTel&Body=$message"
    
    # Fire Request
    $msg = Invoke-RestMethod -Uri $URI -Body $postData -Credential $credential -Method "POST" -ContentType "application/x-www-form-urlencoded" 
}

invoke-twilioRESTSMS -AccountSid "<AccountSid>" `
    -authToken "<authToken>" -message "<message>" `
    -fromTel "<fromTel"> -toTel "<toTel>"

Method 2 is my preferred why of doing things for something as simple as sending a SMS.

There is still one further way to send a message using PowerShell and Twilio, and this addresses those who are using PowerShell 2.0, so can’t use Invoke-RestMethod, and don’t want to use the DLLs; we can still build a request from scratch using the System.Net.WebRequest object:

function post-twilioSMS
(
    [Parameter(Mandatory=$true)][String]$AccountSid,
    [Parameter(Mandatory=$true)][String]$message,
    [Parameter(Mandatory=$true)][String]$fromTel,
    [Parameter(Mandatory=$true)][String]$toTel,
    [Parameter(Mandatory=$true)][String]$authToken
)
{
    # Build a URI
    $URI = "https://api.twilio.com/2010-04-01/Accounts/$AccountSid/SMS/Messages.json"
    $requestUri = new-object Uri ($URI)

    # Create the request and specify attributes of the request.
    $request = [System.Net.WebRequest]::Create($requestUri)
    
    # encode authorization header
    $authText = $AccountSid + ":" + $authToken
    $authUTF8  = [System.Text.Encoding]::UTF8.GetBytes($authText)
    $auth64 = [System.Convert]::ToBase64String($authUTF8)
    
    # Define the requred headers
    $request.Method = "POST"
    $request.Headers.Add("Authorization: Basic $auth64");
    $request.Accept = "application/json, application/xml, text/json, text/x-json, text/javascript, text/xml"
    $request.ContentType = "application/x-www-form-urlencoded"
    
    # content
    $fromTel     = [System.Web.HttpUtility]::UrlEncode($fromTel)
    $toTel         = [System.Web.HttpUtility]::UrlEncode($toTel)
    $message     = [System.Web.HttpUtility]::UrlEncode($message)
    $postData = "From=$fromTel&To=$toTel&Body=$message"
    
    $request.ContentLength = $postData.Length

    # Stream Bytes
    $postBytes = [System.Text.Encoding]::ascii.GetBytes($postData)
    $requestStream = $request.GetRequestStream()
    $requestStream.Write($postBytes, 0,$postBytes.length)
    $requestStream.flush() 
    $requestStream.Close()
    
    # Fire Request
    $response = $request.GetResponse()
    
    # Output Response
    $responseStream = $response.GetResponseStream()
    $responseReader = New-Object System.IO.StreamReader $responseStream

    $returnedResponse = $responseReader.ReadToEnd() 
    $response.close()
}

post-twilioSMS -AccountSid "<AccountSid>" `
    -authToken "<authToken>" -message "<message>" `
    -fromTel "<fromTel"> -toTel "<toTel>" `
    -dllPath "<scriptPath>"

Method 3 works just fine, its lacks the simplicity of Method 2, but it does give you very granular control over what the Web Request is doing; which I have found very useful when working with other REST API’s which aren’t quite as well behaved as Twilio.

THIS POSTING AND CODE RELATED TO IT ARE PROVIDED “AS IS” AND INFERS NO WARRANTIES OR RIGHTS, USE AT YOUR OWN RISK

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