Logging server for in-app purchase's server to server notification on google app script

iap_gas_server.js

function doGet(e) {
  var row = defineRow(e);
  var cell = getCell(row);
  return ContentService.createTextOutput(cell).setMimeType(ContentService.MimeType.JSON);
}

function doPost(e) {
  if (e == null || e.postData == null || e.postData.contents == null) { return; }

  var body = e.postData.contents;
  var json = JSON.parse(body);
  var columns = [];
  var headers = getHeaders()
  for (i in headers){
    var header = headers[i];
    var column = "";
    switch(header) {
      case "date":
        column = new Date();
        break;
      case "json":
        if(json['environment'] == 'PROD') {
          break;
        }
        column = body;
        break;
      case "次回更新":
        var transaction = latestTransaction(json);
        var expMs = parseInt(transaction["expires_date_ms"]);
        var expiresDate = new Date(expMs);
        var expStr = expiresDate.toLocaleDateString('ja-JP') + " " + expiresDate.toLocaleTimeString('ja-JP');
        column = expStr;
        break;
      case "original_transaction_id":
        var transaction = latestTransaction(json);
        var oid = transaction["original_transaction_id"];
        column = oid;
        break;
      default:
        column = parse(json, header);
        break;
    }
    columns.push(column);
  }
  getSheet().appendRow(columns);
}

/** PRIVATE */

function getCell(row) {
  var values = getSheet().getDataRange().getValues();
  var column = findHeader("json");
  return values[row][column].trim();
}

function defineRow(e) {
  if(e.parameter == undefined || e.parameter.row == undefined) {
    return getSheet().getLastRow() - 1;
  }
  var row = parseInt(e.parameter.row);
  return row;
}

function getHeaders() {
  var sheet = getSheet();
  return sheet.getRange(1,1,1,sheet.getLastColumn()).getValues()[0];
}

function findHeader(key) {
  return getHeaders().indexOf(key);
}

function getSheet() {
  return SpreadsheetApp.getActive().getSheetByName("receiver"); 
}

function parse(json, header) {
  var keys = header.split(".").reverse();
  var key = keys.pop();
  var value = json[key];
  while(key && value) {
    key = keys.pop();
    if(key) {
      value = value[key];
    }
  }
  return stringify(value);
}

function stringify(value) {
    if(typeof(value) === 'string') {
        return value;
      } else {
        return JSON.stringify(value);
      }
}

function latestTransaction(json) {
    var product = parse(json, "auto_renew_product_id");
    var transactions = json["unified_receipt"]["latest_receipt_info"];
    var transaction = transactions.find(function(t) { return t["product_id"] == product });
    return transaction
}

/* TEST */
function doTest() {
  var row = defineRow({});
  var cell = getCell(row);
  return cell
}

This is a sample log of our sandbox app's server to server notification.