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libcurl is a cross-platform multi-protocol network transfer library. It is widely used both as a stand-alone command-line utility and as a standard or optional library for many programming languages and development environments.

RB-libcURL is a libcurl binding for Realbasic and Xojo ("classic" framework) projects. Library binaries for various platforms are available, or can be built from source.

The minimum supported libcURL version is 7.15.2. The recommended minimum version is 7.33.0. Versions prior to 7.33.0 will function with degraded features, but versions prior to 7.15.2 will not function properly at all. The minimum supported Xojo version is RS2010R4.


This example performs a synchronous HTTP GET request on the calling thread. More examples.

  Dim curl As New cURLClient
  If curl.Get("") Then 
      Dim page As String = curl.GetDownloadedData()
  End If


†= feature might not be available at run-time due to a build-time decision of the installed version of libcURL


It is strongly recommended that you familiarize yourself with libcURL, as this project preserves the semantics of libcURL's API in an object-oriented, Xojo-flavored wrapper.

For a simplified client interface that is appropriate for most types of transfers, you should use the cURLClient class. Refer to the examples below for demonstrations of cURLClient.

For more thorough documentation of individual classes and methods refer to the wiki.

Each libcURL handle or handle equivalent is managed by an object class. These handle-managing classes all descend from a common ancestor, the abstract cURLHandle class.

libcURL uses several different handle types or equivalents:

Handle Type Object Class Comment
curl_easy EasyHandle A persistent collection of sockets, caches, and options which together will be used when libcURL is told to perform a transfer.
curl_multi MultiHandle A set of one or more curl_easy handles whose transfers will be performed simultaneously.
curl_share ShareHandle A set of one or more curl_easy handles that will share SSL session data, DNS caches, and/or HTTP cookies.
slist ListPtr A linked list of string values.
form MultipartForm An HTTP form which libcURL will encode as multipart/form-data.
mime MIMEMessage A MIME message (HTTP form, email message, etc.) (libcURL 7.56.0 or later)
url URLParser An interface to libcurl's URL parser (libcURL 7.62.0 or later)

Every transfer is associated with an EasyHandle. After creating a new EasyHandle instance, you can set various options for the handle by calling the SetOption method with the desired cURL option number and its new value. Options will persist until they are overwritten or reset.

Once all the desired options have been set (e.g. URL, port, username and/or password, cookies, etc.) you are ready to begin the transfer. Depending on your specific requirements, you can do it in one of several ways.

You may call EasyHandle.Perform directly. However, this is a blocking call; not merely synchronous: the entire application blocks for the duration of the transfer. As such, it is useful only in single-threaded console applications.

To perform one or more transfers in a non-blocking manner use the MultiHandle class. The MultiHandle class represents a curl_multi handle (AKA a "stack"). Add the EasyHandle to the multi stack and then call MultiHandle.Perform (or MultiHandle.PerformOnce on a RB/Xojo thread.)

How to incorporate libcURL into your Realbasic/Xojo project

Import the libcURL module

  1. Download the RB-libcURL project either in ZIP archive format or by cloning the repository with your Git client.
  2. Open the RB-libcURL project in REALstudio or Xojo. Open your project in a separate window.
  3. Copy the libcURL module and the DEFAULT_CA_INFO_PEM file into your project and save.

Ensure the libcURL shared library is installed

libcURL is installed by default on most Unix-like operating systems, including OS X and most Linux distributions.

Windows does not have it installed by default, you will need to ship all the necessary DLLs with your application. You can use pre-built DLLs available here, or you can build them yourself from source.

Depending on compile-time options, you may need to include additional DLLs for other libraries like OpenSSL or ZLib. Newly added features like HTTP/2 support may require building the latest version from source with special build flags and additional libraries. Review the libcURL documentation for the feature you're interested in.

RB-libcURL will raise a PlatformNotSupportedException when used if all required DLLs/SOs/DyLibs are not available at runtime.


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