How to upload object attachments from SFDC to an external source.

gistfile1.cls

/*
TODO: 
- Handle 404s / other errors
- Handle invalid Attachment ids
- 

*/

class testUploadAttachment {
  @future(callout=true)
  public static HttpResponse remoteAttachmentUpload(Id attachment_id, String remote_url) {
      Http conn = new Http();
      Attachment attachment_obj = [Select Id, Name, ParentId, Body from Attachment where Id =: attachment_id];

      HttpRequest req = new HttpRequest();
      req.setEndpoint(remote_url);
    	req.setMethod('POST');
    	req.setHeader('Content-Type','application/x-www-form-urlencoded');        
    	req.setBody('attachmentId=' + attachment_obj.Id + 
      	'&Title=' + attachment_obj.Name + 
      	'&parentId=' + attachment_obj.ParentId + 
      	'&Body=' + EncodingUtil.base64Encode(attachment_obj.Body));

      HttpResponse res = conn.send(req);
      return res;
  }
}