The initial response is an “Access Denied” page and that’s all we can get when running Chrome in headless mode. This doesn’t happen at all in headed mode. When troubleshooting it’s important to identify what we know and what we don’t know. Without this step it’s impossible to pursue a course of action that targets the unknown and isn’t redundant. This may sound basic but, unless you understand why, it’s non-intuitive how to get there. Troubleshooting is sometimes seen as running through a checklist but that only works if you have encountered the problem before. What do we know? We know that the browser made a single request and we received a response that already said access denied. The original page wasn’t rendered and the browser made no other requests. This means that a server somewhere made a call based strictly on what we sent for that first request and our block has nothing to do with page content. That rules out troubleshooting anything after the page render and limits our scope to the request alone. The request itself is a bunch of bits and bytes sent over the internet and accepted by a server. Comparing HTTP Request headersīecause there is (supposed to be) little difference between Chrome when run in headless vs headed mode it’s a reasonable assumption that the core network stack is the same and there are no differences in how the browser transmits requests at the packet level. This points us to the content of the request alone. We can use a service that echos back our HTTP requests to inspect the differences between a request made from headless and headed Chrome. The following script uses to get a JSON response that represents the request the server received. The header for headed Chrome is mostly the same minus the “Headless”. ![]() The User-Agent has long been a basic, naive way of blocking unwanted traffic. This is a good first place to start to see if we get what we need.īlocking on User-Agent is naive and rarely used as a countermeasure nowadays because of how simple it is to bypass. It actually provides more value to a website to not block with it and use it to identify unwanted traffic because visibility is better than being blind. The solution is as easy as changing the User-Agent header which you can override on a page-by-page level with the method tUserAgent(). You can set the user agent to headed Chrome which, at the time of this writing, is “Mozilla/5.0 (Macintosh Intel Mac OS X 10_14_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/.75 Safari/537.36”. That’s why the method of troubleshooting is more important than the solution. These sorts of hurdles pop up all the time when trying to automate websites and, often times, you’re not going to find clean googlable answers so you’ll need to figure out how to solve it yourself.I’m sure that everyone who has ever tried to upload a sketch from the Arduino IDE has seen this error message: avrdude: ser_open(): can't open device "\\.\COM4": Access is denied. The number of the serial port can be different, but the error is the same.īasically (in simplified form) this error means that the USB port is in use by another application in your computer, so the Arduino IDE cannot use it to upload your sketch. It is important to understand that this error has nothing to do with Arduino, the access to the serial ports are controlled by the operating system. Tip #1: Check your port in Device Manager #MEGASYNC LOGIN ACCESS DENIED SERIAL# Note the number of the port (in my case COM4): Open Device Manager and check that your IoT device appears in the Ports (COM & LPT) section. Tip #2: Check your port in the Arduino IDE The Arduino IDE is quite good to detect connected devices, but in case you have multiple devices connected at the same time this is definitely worth to check: Open Arduino IDE and check in the Tools –> Port menu that you are trying to upload to the port you have seen in the Device Manager. Try to close any programs that may use this port. ![]() #MEGASYNC LOGIN ACCESS DENIED MAC OS X#.
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