Web applications can acquire real-time information from the DataHub Web Server using two methods:
HTTP requests to ASP documents are used to poll data relatively infrequently.
WebSocket connections are used to acquire real-time data at high speed with low latency
An ASP document is a primarily static document with script snippets embedded within it using a special syntax:
<%= expression
%> (With an = sign) Evaluates the expression and
inserts the result as a string into the output document, replacing
all characters from the opening <%= to the
closing %>. The expression is not a complete
statement and must not end with a semicolon character or other
statement completion syntax. For example, 3 + 2
is an expression. x = 3 + 2; is a
statement.
<% statement or fragment
%> (Without an = sign) Evaluates the statements
within the delimiters, and deletes all characters in the output
document from the opening <% to the closing
%>. The code within the delimiters does
not need to be a complete statement. A single statement could be
split across multiple occurrences of the <%
%> pair. This allows you to, for example, create a
loop that mixes literal text with computed values by breaking the
opening and closing braces of the loop body across multiple
<% %> regions. The concatenation of all
statements and statement fragments must form a syntactically correct
script.
All other characters All characters, including white space, not contained within
<%= %> or <%
%> pairs are treated as literal text and simply
copied to the output document.
When an ASP document is evaluated, all code within the special delimiters is evaluated to construct the output document. This document is then returned to the originator of the HTTP request.
ASP scripts run in the same global context as all other Gamma scripts, meaning that they have full access to other functions and scripts you define. It also means that a long-running script within an ASP page will delay other scripts. It is a good idea to keep the run-time of ASP scripts low.
The resulting output from an ASP document does not need to be valid HTML. It could be JSON, XML, plain text, or any text format that the client application requires.
Place your ASP documents in the folder
{config}\WebContent or one of its sub-folders, where
{config} indicates the folder containing your DataHub
instance configuration, and WebContent will be treated as the
root of the HTML file system.
ASP documents must be named with a .asp extension.