How to use GET method of Invoke-WebRequest to build a query string

Question

Is there a standard way to make use of Invoke-WebRequest or Invoke-RestMethod in PowerShell to get information from a web page using a query string?

For example, I know that the following when used with a well formed JSON end point will work:

$Parameters = @{
  Name = 'John'
  Children = 'Abe','Karen','Jo'
}
$Result = Invoke-WebRequest -Uri 'http://.....whatever' -Body ( $Parameters | ConvertTo-Json)  -ContentType application/json -Method Get

along with the equivalent Invoke-WebMethod. An important aspect of this is the content type and ConvertTo-JSON which manages the transformation of the parameters specified in the -Body part in to a standard form, including the array aspect of the "Children" field.

What is an equivalent way to do this with a website which uses, say, a comma delimited convention for managing array arguments in the URL or an approach such as "Children[]=Abe&Children[]=Karen&Children=Jo"?

Is there a content type that I'm missing and is there an equivalent ConvertTo-?? that I can use? My guess is that someone has had to do this before.

For context this is an often used way of encoding an array parameter in the URL and is commonly seen in PHP web sites.

passing arrays as url parameter

Edit Removed references to PHP except for specific context and adjusted the title to refer to a query string. The problem is about encoding a query string not PHP per se.

Answer 1

It seems that the server running PHP is irrelevant here. I think you're asking how to send key/value pairs as query string parameters.

Simple Case

If that's the case, you're in luck. Both Invoke-RestMethod and Invoke-WebRequest will take a [hashtable] in the body and construct your query string for you:

$Parameters = @{
    Name = 'John'
    Children = 'Abe','Karen','Jo'
}
Invoke-WebRequest -Uri 'http://www.example.com/somepage.php' -Body $Parameters -Method Get # <-- optional, Get is the default

Passing Complex Objects

Now seeing that the issue is that you want a query string parameter to have multiple values, essentially an array, this rules out the data types you can pass to the body parameter.

So instead, let's build the URI piece by piece first by starting with a [UriBuilder] object and adding on a query string built using an [HttpValueCollection] object (which allows duplicate keys).

$Parameters = [System.Web.HttpUtility]::ParseQueryString([String]::Empty)
$Parameters['Name'] = 'John'
foreach($Child in @('Abe','Karen','Joe')) {
    $Parameters.Add('Children', $Child)
}

$Request = [System.UriBuilder]'http://www.example.com/somepage.php'

$Request.Query = $Parameters.ToString()

Invoke-WebRequest -Uri $Request.Uri -Method Get # <-- optional, Get is the default

Answer 2

The following appears to work reasonably well as a "first cut". Thanks to @briantist for the key point which was to use the .NET HttpValueCollection. It seems we have to "roll our own" way of building the query string.

The below code snip shows a simple way to transform the hash table containing parameters and values in to a well formed query string by simply traversing the hash table. One limitation is that nesting is not permitted (a parameter value cannot be a complex type such as a hash table).

# Setup, parameters is now a PowerShell hash table
# we convert that on the fly to an appropriate URL
$Parameters = @{
    Name = 'John'
    Children = 'Abe','Karen','Jo'
}
$Uri = 'http://example.com/somepage.php'
$AddSquareBracketsToArrayParameters = $true



$HttpValueCollection = [System.Web.HttpUtility]::ParseQueryString([String]::Empty)
foreach ($Item in $Parameters.GetEnumerator()) {
    if ($Item.Value.Count -gt 1) {
        # It is an array, so treat that as a special case.
        foreach ($Value in $Item.Value) {
            # Add each item in the array, optionally mark the name of the parameter
            # to indicate it is an array parameter.
            $ParameterName = $Item.Key
            if ($AddSquareBracketsToArrayParameters) { $ParameterName += '[]' }                 
            $HttpValueCollection.Add($ParameterName, $Value)
        }
    } else {
        # Add the scalar value.
        $HttpValueCollection.Add($Item.Key,$Item.Value)
    }
}
# Build the request and load it with the query string.
$Request  = [System.UriBuilder]($Uri)
$Request.Query = $HttpValueCollection.ToString()

# Now fire off the request.
Invoke-WebRequest -Uri $Request.Uri