CODEWITHSUNDEEP
google-apps-script
M14d3n
M14d3n

Reputation: 6296

UrlFetchApp.fetch(url) intermittent "Unexpected error"

In order to check HTTP service status I've wrote script that goes through spreadsheet and for a list of URLs checks if they are Up or Down, script is time driven every five minutes.

I have rare intermittent "Unexpected error" errors from UrlFetchApp.fetch(url) and from time to time there are DNS and Timeout errors that will go away if I repeat request after few seconds.

No few actual questions if someone can help: I've used Utilities.sleep(5000) to pause for 5 seconds, is that OK or there are better ways to wait and try to fetch again after few seconds?

Why do I get "Unexpected error" even if I repeat request after 5 seconds, when script is run again after five minutes there is no "Unexpected error" !?

How could I improve code below?

Actual script:

/* 
Periodically check status of web sites :-)
Google Apps for Busines UrlFetch daily limit is 100.000 requests,

Algorithm
  read site and old status from sheet
  check site and set new status  
  if status changed send email (+sms in future by using twilio)
  update status in spreadsheet

"Site, Status code, Time of last change, Last error description"
*/
function main() {
  var sheet = SpreadsheetApp.getActiveSheet() ;
  var currentRow, oldStatusCode, newStatusCode ;
  var url, response, err, subject, message ; 
  var today = new Date() ;

  currentRow = 2
  while ((url = sheet.getRange(currentRow, 1).getValue()) != "") {
    oldStatusCode = sheet.getRange(currentRow, 2).getValue() ;
    newStatusCode = "Ok"
    subject = "mCheck: " + url + " Up Status Change!" ;  
    message = url + " Up Status Change!" + "\n Time: " + today.toUTCString() ;

    var tries = 3 ; // Check at least three times that status changed and it is not a one time glitch
    do {
      try {
        response = UrlFetchApp.fetch(url) ;
      } catch (err) {
      newStatusCode = "Down"
      sheet.getRange(currentRow, 4).setValue(err.message) ;
      subject = "mCheck: " + url + " Down Status Change!" ;  
      message = url + " Down Status Change!" + "\n Error message: " + err.message + "\n Time: " + today.toUTCString() ;
      if (err.message.indexOf("Unexpected") > -1) { // If UrlFetch failed on Google side just ignore this iteration...
        newStatusCode = oldStatusCode ;
      }
    }
    if (oldStatusCode != newStatusCode) { // In case of status change wait 5 seconds before trying again
      Utilities.sleep(5000) ;
    }
    --tries ;
  } while ((oldStatusCode != newStatusCode) && tries >= 0)

  if (oldStatusCode != newStatusCode) {
    sheet.getRange(currentRow, 2).setValue(newStatusCode) ;
    sheet.getRange(currentRow, 3).setValue(today.toUTCString()) ;
    if (oldStatusCode != "") {
      MailApp.sendEmail(email_to, subject, message) ;
    }
  }
  ++currentRow;
 }

}

Upvotes: 4

Views: 3775

Answers (1)

oshliaer
oshliaer

Reputation: 4979

You may use a muteHttpExceptions parameter for to catch failures. The fetch will not throw an exception if the response code indicates failure, and will instead return the HTTPResponse.

Sample

var params = {muteHttpExceptions:true};
response = UrlFetchApp.fetch(url, params);

And you may use a cURL or analoge for a sheldue.

Sample

cURL. Set this at a sheldue to your operation sistem.

curl -L URL_OF_YOUR_SCRIPT

Add to the script

function doGet(e) {
    var result = {'status': 'ok'};
    try{
        main();
    }catch(err){
        result.['status'] = err;
    }
  return ContentService.createTextOutput(JSON.stringify(result)).setMimeType(ContentService.MimeType.JSON);
 }

You should deploy your script as a Web App for this.

If you'll be use second sample you don't need Utilities.sleep(5000) more.

Best.

Upvotes: 1

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