How to escape an Invoke-Webrequest in Powershell

Question

I have a network device with a status page accessible by a Java applet. Using Fiddler I was able to find an http feed of the status, but the page has a constant refresh. (Firefox displays the page but keeps refreshing, Chrome sees it as an extension-less file and tries to save it but never finishes as there is always more data.)

The status page uses NTLM authentication so I though I would use an Invoke-Webrequest. The following code logs in and starts downloading the page but as its a constant data stream never finishes:

$url = "http://xxx.xxx.xxx.xxx/api/notify"
$user = "user"
$pass= "password"
$secpasswd = ConvertTo-SecureString $pass -AsPlainText -Force
$credential = New-Object System.Management.Automation.PSCredential($user, $secpasswd)
$data = Invoke-restmethod $url -Credential $credential

Is there a way to escape from an Invoke-Webrequest after receiving a certain number of characters? Or is there a better way to do this?

If you want to get just the page's contents use the parameter -UseBasicParsing. — Keith Hill, Aug 03 '15 at 20:19

Alexander Obersht · Accepted Answer · 2015-08-05T23:19:09.970

I don't think it's doable with Invoke-WebRequest, but you could use .NET WebRequest and StreamReader classes instead. Example:

$sUri = "http://www.w3.org" # Replace with your URI
$sEncoding = "utf-8"
$iCharactersToRead = 1000 # How many characters we want to read
$sAuthType = "NTLM"
$sUserName = "username"
$sPassword = "password"

# Creating a new HttpWebRequest object.
[System.Net.HttpWebRequest]$oHttpWebRequest = [System.Net.WebRequest]::Create($sUri)
# This may be superflous if your HTTP server doesn't use compression.
$oHttpWebRequest.AutomaticDecompression = `
        ([System.Net.DecompressionMethods]::Deflate `
    -bor [System.Net.DecompressionMethods]::GZip)

# Since you have NTLM auth, you need to add a credential.
$oCredential = New-Object -TypeName System.Net.NetworkCredential($sUserName, $sPassword)
$oCredentialCache = New-Object -TypeName System.Net.CredentialCache
$oCredentialCache.Add($sUri, "NTLM", $oCredential)
$oHttpWebRequest.Credentials = $oCredentialCache

# Creating a StreamReader object that will read the response stream.
$oResponseStream = $oHttpWebRequest.GetResponse().GetResponseStream()
$oContentReader = New-Object -TypeName System.IO.StreamReader($oResponseStream,
    [System.Text.Encoding]::GetEncoding($sEncoding), $true)

# Trying to read the specified number of characters from the stream.
$sContent = [String]::Empty
try {
    for ($i = 0; $i -lt $iCharactersToRead; $i++) { 
        $sContent += [Char]$oContentReader.Read() 
    } 
}
finally {
    $oContentReader.Close()
}

Instead of utf-8 you may need to specify another encoding name, depending on which encoding your HTTP server uses. See Encoding.WebName reference for more details.

Alexander, thank you! It worked! All I had to do was modify the authentication slightly to log into the device. — Tom Wiebe, Aug 05 '15 at 19:40

How to escape an Invoke-Webrequest in Powershell

1 Answers1