sub_try_request.md

Try a REST request and get new token if needed

Rather than each time requesting a new bearer token it is better to first try whether the old token is still valid. If not, enter the sub which retrieves a new token and retry the call. To do so, you need

• a sub with the logic to get the token
• put the REST-calls for data inside a DO-UNTIL loop

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Sub to get a new token

SUB CheckIfSuccessful(vErr)
   // Sub is testing if there was an Error with previous statement
   
   SET ErrorMode = 1; // break if there's an error
   IF vErr = 0 THEN
   	LET vSuccessful = 1;
   ELSEIF vErr = 12 THEN
       TRACE Token seems to be invalid. Get new token ...;
       
       LIB CONNECT TO 'REST POST Request';
       Authentication:
       SQL SELECT 
           "access_token",
           "token_type",
           "expires_in",
           "expiration_time",
           "error_message"
       FROM JSON (wrap on) "root"
       WITH CONNECTION (
           URL "$(vBaseAPIurl)/api/Authentication"
           ,QUERY "username" "#####"
           ,QUERY "password" "#####"
       ); 
       
       LET vToken = FieldValue('access_token', 1);
       DROP TABLE Authentication;
       TRACE New Token is $(vToken);	
   ELSE
      	LET vErr = Num(vErr) & ' (' & Text(vErr) & ')';
       TRACE Error $(vErr); 
       EXIT SCRIPT;
   END IF
END SUB

Try and repeat logic to retrieve data

// First call of REST API is put in a do-until loop with error handling, so if the 
// REST call was unsuccessful, a new token is requested and the call is repeated once again.

SET ErrorMode = 0;  // ignore if there's an error. The sub CheckIfSuccessful will reset to 1
DO
   // your REST select-data command goes in here 
   LIB CONNECT TO 'REST GET Request';

   RestConnectorMasterTable:
   SQL SELECT 
       ...
   FROM JSON (wrap on) "root"
   WITH CONNECTION (
       URL "$(vBaseAPIurl)/api/endpoint"
       ,HTTPHEADER "Authorization" "Bearer $(vToken)"
       ...
   );     

   CALL CheckIfSuccessful(ScriptError);
LOOP UNTIL vSuccessful;