Proxy vs Firewall

I got asked the question recently, “What is the difference between a proxy and a firewall?”

I’ll paraphrase my simple analogy in response:

If you think of a firewall as a telephone, you can think of a proxy as a telephone operator.

As analogous to a firewall, you can think of calling the server via telephone, and then speaking directly to the server in order to make a request, and the server responds to you directly.  The telephone might have some rules built in to it, about who you are allowed to call, and when (these are the firewall rules).

Extending this analogy, a proxy is like a telephone operator.  Rather than make a request to the server directly, you are only allowed to call the operator.  The operator receives your entire request, and then makes a separate call to the server.  After passing the request to the server, the operator then receives the entire response from the server, and passes the response to you.

Now, imagine that the operator must consult a long list of rules to see if your request is valid before passing it to the server, and also must compare the server response to another long list of rules to ensure that it’s valid before passing the response back to you.  This is known as filtering.

Shortcut:  Pinch to Zoom in Android Emulator

Also, pinch to zoom with one finger in Android

This is known to work with Android Marshmallow.  I have not tried this with other versions, but I have tried it on Bluestacks emulator as well as physical devices.

Problem:  Can’t Pinch to Zoom in Android Emulator

When you do Android development, running an emulator is a necessity.  In the emulator, the mouse simulates a touch event.  Unfortunately, using only a mouse, you can’t “pinch to zoom” in or out.  Although some laptop panels and computer monitors support touch input, this is expensive, and not a guaranteed solution.

Solution: Tap then Drag

Remember that the left mouse button simulates a virtual finger touching the display…

• Tap:  Click the mouse button (quickly press, then release the left mouse button)
• Drag:  Press the left mouse button and hold it down.  Move the mouse to a desired location, then release the left mouse button.

In quick succession, Tap, then Drag

Zoom Out

Starting at the bottom-middle of the display, tap, then drag up to the upper-right.

Zoom Out: Tap on the bottom-middle (A) then quickly touch and drag (B) from the bottom-middle to the upper-right.

Zoom In

Starting at the upper-right of the display, tap, then drag down to the bottom-middle.

Zoom In: Tap on the upper-left (C) then quickly touch and drag (D) from the upper-left to the bottom-middle

Caveats

• This is known to work with applications that let you pan in both directions, such as Google Maps
• Although this effect seems to be built in to the OS, it might be difficult to trigger this effect in applications that explicitly scroll in one direction (such as vertical only).
• This approach might not work with applications that implement their own custom multi-touch logic.