(VB.NET) Download a File from a SharePoint Documents Library

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This example shows how to use Chilkat's HttpCurl class to download a file from the root of a SharePoint Documents document library. The example demonstrates how HttpCurl automatically resolves the SharePoint site name to a site ID, finds the drive ID for the Documents library, locates the file by name, and then downloads the file content using Microsoft Graph.

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Dim success As Boolean = False

' This example downloads a file named "hamlet.json" from the root of the SharePoint
' Documents document library.
' 
' The example demonstrates how HttpCurl can automatically resolve all of the
' information needed to locate and download a file:
' 
'   site_name            -> site_id
'   site_id              -> document_library_id
'   document_library_id  -> file_id
'   file_id              -> file content
' 
' The application only provides the SharePoint site name and the desired
' filename.  HttpCurl automatically executes the required Microsoft Graph
' requests to obtain the remaining values.

success = False

' --------------------------------------------------------------------------------------------------------
' Before running this example, create an Azure App Registration and grant it
' the Microsoft Graph permissions required to access SharePoint.
' 
' The application will authenticate using OAuth2 Client Credentials.
' See:
' How to Create SharePoint App Registration for OAuth 2.0 Client Credentials
' --------------------------------------------------------------------------------------------------------

' Build a JSON authentication configuration.
' HttpCurl will use this information to automatically obtain OAuth2 access tokens.
Dim jsonAuth As New Chilkat.JsonObject

' Enable secret lookup.
' 
' Instead of hard-coding sensitive values such as the client ID,
' client secret, and token endpoint, secret specification strings
' are used.  Chilkat automatically retrieves the actual values from
' Windows Credential Manager (Windows) or Apple Keychain (macOS).
' 
' See:
' Secret Specification Strings
jsonAuth.EnableSecrets = True

success = jsonAuth.UpdateString("oauth2.client_id","!!sharepoint|oauth2|client_id")
If (success = True) Then
    success = jsonAuth.UpdateString("oauth2.client_secret","!!sharepoint|oauth2|client_secret")
End If

If (success = True) Then
    success = jsonAuth.UpdateString("oauth2.token_endpoint","!!sharepoint|oauth2|token_endpoint")
End If

If (success = False) Then
    Debug.WriteLine(jsonAuth.LastErrorText)
    Exit Sub
End If


' Request Microsoft Graph permissions that were granted to the application.
jsonAuth.UpdateString("oauth2.scope","https://graph.microsoft.com/.default")

' ---------------------------------------------------------------------------------------------------

Dim curl As New Chilkat.HttpCurl

' Associate the OAuth2 configuration with HttpCurl.
' 
' When the request is executed, Chilkat automatically obtains an access token
' if needed and adds the Authorization: Bearer header to the HTTP request.
curl.SetAuth(jsonAuth)

' Define values that are already known.
' 
' These variables are referenced in curl commands using
' {{variable_name}} substitution syntax.
curl.SetVar("sharepoint_hostname","example.sharepoint.com")
curl.SetVar("site_name","test")

' The first step is to obtain the Microsoft Graph site ID.
' 
' The application only knows the SharePoint site name, so define
' a function that can retrieve the site information.
curl.AddFunction("getSite","GET https://graph.microsoft.com/v1.0/sites/root:/sites/{{site_name}}")

' Extract the site's ID and store it in the HttpCurl variable named site_id.
curl.AddOutput("getSite","id","site_id")

' The next step is to find the Documents document library.
' 
' Microsoft Graph refers to document libraries as "drives".
curl.AddFunction("getDrives","GET https://graph.microsoft.com/v1.0/sites/{{site_id}}/drives")

' Search the returned drives for the one named "Documents"
' and save its drive ID in the document_library_id variable.
curl.AddOutput2("getDrives","value","name","Documents",True,"id","document_library_id")

' Now list the contents of the Documents document library.
curl.AddFunction("getFiles","GET https://graph.microsoft.com/v1.0/sites/{{site_id}}/drives/{{document_library_id}}/root/children")

' Search the returned files for an item named "hamlet.json"
' and save its Microsoft Graph item ID in the file_id variable.
curl.AddOutput2("getFiles","value","name","hamlet.json",True,"id","file_id")

' This is the target request.
' 
' GET -L https://graph.microsoft.com/v1.0/drives/{{document_library_id}}/items/{{file_id}}/content
' 
' The /content endpoint returns the actual contents of the file.
' 
' The -L option instructs HttpCurl to follow the redirect returned by
' Microsoft Graph.  The Graph API typically responds with a redirect
' to the actual file download URL.
Dim curlCommand As String = "GET -L https://graph.microsoft.com/v1.0/drives/{{document_library_id}}/items/{{file_id}}/content"

' Execute the request.
' 
' HttpCurl examines the target request and determines that both
' document_library_id and file_id are required.
' 
' To obtain these values, it automatically builds and executes
' the following dependency chain:
' 
'   1) getSite      -> site_id
'   2) getDrives    -> document_library_id
'   3) getFiles     -> file_id
'   4) download     -> file content
' 
' The final response returned by DoYourThing is the downloaded
' file content from the target request.
success = curl.DoYourThing(curlCommand)
If (success = False) Then
    Debug.WriteLine(curl.LastErrorText)
    Exit Sub
End If


' A successful Graph response should return HTTP 200.
' Any other status code typically indicates an authentication,
' permission, site lookup, document library lookup, or file lookup error.
Dim statusCode As Integer = curl.StatusCode
If (statusCode <> 200) Then
    Debug.WriteLine(curl.ResponseBodyStr)
    Debug.WriteLine("status code = " & statusCode)
    Exit Sub
End If


' The response body contains the contents of the downloaded file.
Dim sbFileContents As New Chilkat.StringBuilder
curl.GetResponseSb(sbFileContents)

' Optionally save the downloaded content to a local file.
' 
' The third argument controls whether the file is appended.
' Passing ckfalse causes the file to be overwritten if it already exists.
success = sbFileContents.WriteFile("c:/temp/hamlet.json","utf-8",False)
If (success = False) Then
    Debug.WriteLine(sbFileContents.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Success.")