Google App Engine http.DefaultTransport

2014-09-23T10:00:00+00:00

While working on a small project recently that utilizes Go and Google’s App Engine, I ran into the following error:

http.DefaultTransport and http.DefaultClient are not available in App Engine. See https://developers.google.com/appengine/docs/go/urlfetch/overview

Google suggests using the "appengine/urlfetch" package to make requests, but this is not ideal. You are now at the mercy of that implementation and the possibility of being behind the standard version. Additionally, you lose the ability to make requests via third-party packages.

You can work around this by assigning a transport from that package:

client := &http.Client{
    Transport: &urlfetch.Transport{Context: ctx},
}

If you’re using an external package, you can do the same thing as long as you can pass the transport in. I recently used this with tweetlib:

transport := &tweetlib.Transport{
    Config:    tweetlibConfig,
    Token:     token,
    Transport: &urlfetch.Transport{Context: ctx},
}

If the package you’re using doesn’t expose the transport, you’ll need to fork the project and hopefully your patch will be accepted.

I recommend reading the documentation for urlfetch and net/http to better understand how they work.

JavaScript automation in OS X Yosemite

2014-09-09T10:00:00+00:00

In Mac OS X Yosemite, the automation tools incorporate a new scripting language: JavaScript. Since I use some AppleScript with Alfred for resizing windows, I decided to give it a try.

Here is the original:

tell application "Finder"
    set b to bounds of window of desktop
    set width to item 3 of b
    set height to item 4 of b
end tell
 
set name to name of ¬
  (info for (path to frontmost application))

set q to "{query}" --- the query variable from Alfred
 
tell application name
    activate
    if q is "f" then
        set nb to ¬
          {0, 0, width, height}
    else if q is "m" then
        set nb to ¬
          {width/8, height/8, width/1.125, height/1.125}
    else if q is "tr" then
        set nb to {width/2, 0, width, height/2}
    else if q is "tl" then
        set nb to {0, 0, width/2, height/2}
    else if q is "th" then
        set nb to {0, 0, width, height/2}
    else if q is "r" then
        set nb to {width/2, 0, width, height}
    else if q is "l" then
        set nb to {0, 0, width/2, height}
    else if q is "br" then
        set nb to {width/2, height/2, width, height}
    else if q is "bl" then
        set nb to {0, height/2, width/2, height}
    else if q is "bh" then
        set nb to {0, height/2, width, height}
    else if q is "h" then
        set nb to {width/4, 0, width/1.25, height}
    end if
end tell

set bounds of first window to nb

And here is the same script rewritten in JavaScript:

finder = Application("Finder")
bounds = finder.desktop.window.bounds()
width = bounds["width"]
height = bounds["height"]
query = "{query}" // the query variable from Alfred

boundsMap = {
  "f":  {"x":0, "y":0, "width":width, "height":height},
  "m":  {"x":width/8, "y":height/8, 
         "width":width/1.3, "height":height/1.3},
  "tr": {"x":width/2, "y":0, "width":width, "height":height/2},
  "tl": {"x":0, "y":0, "width":width/2, "height":height/2},
  "th": {"x":0, "y":0, "width":width, "height":height/2},
  "r":  {"x":width/2, "y":0, "width":width/2, "height":height},
  "l":  {"x":0, "y":0, "width":width/2, "height":height},
  "br": {"x":width/2, "y":height/2, "width":width, "height":height},
  "bl": {"x":0, "y":height/2, "width":width/2, "height":height},
  "bh": {"x":0, "y":height/2, "width":width, "height":height/2},
  "h":  {"x":width/4, "y":0, "width":width/2, "height":height},
}

SystemEvents = Application("System Events")
appName = SystemEvents.processes.whose({ frontmost: true })[0].name()
app = Application(appName)
app.windows[0].bounds = boundsMap[query]

There are a couple things to note here. First, the JavaScript used is not standard. Some syntax is not required (var, ;), while other syntax and globals are built into the language: .whose({ frontmost: true }, console.log, $, etc. The API for interacting with objects is also different from traditional JavaScript. For example, properties are accessed like methods, e.g. .name(), while setters still use the = assignment. Element arrays are an exception—they can be accessed like regular javascript properties (Mail.windows), but also have syntactic sugar as well: Mail.windows.byName('New Message') or Mail.windows.byId(412). There is a global object called ObjectSpecifier which identifies an object or property’s class: ObjectSpecifier.classOf(Mail.inbox).

The script performs the exact same function, but the JavaScript is easier to read and understand, in my opinion. I believe there are two reasons for this: the syntax is clear and the use of a data structure is intuitive. With AppleScript, it took me some time to peruse the documentation to even understand how to create a hash/map as a comparison.

I’m interested in seeing whether this becomes the preferred option for automation in Mac OS or if it is just an alternative. For now you can learn more about JavaScript automation in Yosemite at the current (and so far, only) documentation.

Robby Colvin

Google App Engine http.DefaultTransport

JavaScript automation in OS X Yosemite