Git aliases for better Gerrit usage

What is Gerrit?Gerrit is a web application for code review and git project management. You push commit to specific ref in Gerrit and your collaborators could comment your code, give you a score (-2, -1, 0, 1, 2) or merge it with specific branch. Gerrit…

What is Gerrit?

Gerrit is a web application for code review and git project management. You push commit to specific ref in Gerrit and your collaborators could comment your code, give you a score (-2, -1, 0, 1, 2) or merge it with specific branch. Gerrit generates also events, so yout CI server (for example Jenkins) could start build based on this commit and give the positive score if build is green or negative if it fails.

Pushing commits to gerrit

If you want to push commit to gerrit, then commit has to have generated Change-Id, which is uniq review identifier. You do not need to generate Change-Id on your own, because you could install pre-commit hook from Gerrit:
gitdir=$(git rev-parse --git-dir); scp -p -P <GERRIT_PORT> <GERRIT_SSH>:hooks/commit-msg ${gitdir}/hooks/
Of course, you have to set GERRIT_PORT and GERRIT_SSH to point to yout Gerrit.
To push a commit for review you should use command:
git push origin HEAD:refs/for/<BRANCH_NAME>
It means that your current HEAD should be pushed to remote reference on origin (if Gerrit remote repository is named as origin). BRANCH_NAME is the remote branch with which your code will be compared and to which your commit should be merged (if it pass review).
You often push to master so there is alias to push as review for master in alias section in ~/.gitconfig (globally) or .git/config (only in current repository):
[alias]
  ...
  push-for-review = push origin HEAD:refs/for/master
  ...

To execute it just type:

git push-for-review

If I want to push as review to another branch then I use another alias:

[alias]
  ...
  push-for-review-branch = !git push origin HEAD:refs/for/$1
  ...

and branch name could be pass as argument from command line:

git push-for-review-branch <BRANCH_NAME>

Pushing drafts

If you think that your commit is not ready to merge with remote branch, but you want to share it or just have it in remote repository, you could push it to draft reference. Draft on gerrit is available only for you and other users which are invited by you. Draft could be pushed via command:
git push origin HEAD:refs/drafts/<BRANCH_NAME>
Branch name must be given, because draft could be published and then merged, so branch have to be known before.
There also are simple aliases, which could be used in the same way as during push for review:
[alias]
  ...
  push-as-draft = push origin HEAD:refs/drafts/master
  push-as-draft-branch = !git push origin HEAD:refs/drafts/$1
  ...

Invite for review

After pushing for review or draft you could invite user or group, then they will be notified by Gerrit about new change. To invite from command line there should be added four aliases:
[alias]
  ...
  gerrit-remote = "!sh -c \"git remote -v | grep push | grep ssh | grep gerrit | head -1 | awk '{print $2}' | cut -d'/' -f3\""
  gerrit-host = "!sh -c \"git gerrit-remote | cut -d':' -f1\""
  gerrit-port = "!sh -c \"git gerrit-remote | cut -d':' -f2\""
  gerrit-invite = "!sh -c \"ssh -p git gerrit-port git gerrit-host 'gerrit set-reviewers --add' $1 git log | grep Change-Id | head -1 | tr -d ' ' | cut -d':' -f2\""
  ...

First alias selects remote repository which contains gerrit in name or url, could be used to push via ssh and extracts url to this repository.

Second and third alias uses the first to extract host and port from repository url. It is necessary for executing remote command via ssh.

The last alias extract Change-Id from HEAD and add user or group given form command line. Example usage:

git gerrit-invite <USER_OR_GROUP>

Summary

Gerrit is a great tool for git management and code reviewing, but it is difficult to type all references by memory. Git aliases described here are great support and simplify Gerrit usage.
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Clojure web development – state of the art

It’s now more than a year that I’m getting familiar with Clojure and the more I dive into it, the more it becomes the language. Once you defeat the “parentheses fear”, everything else just makes the difference: tooling, community, good engineering practices. So it’s now time for me to convince others. In this post I’ll try to walktrough a simple web application from scratch to show key tools and libraries used to develop with Clojure in late 2015.

Note for Clojurians: This material is rather elementary and may be useful for you if you already know Clojure a bit but never did anything bigger than hello world application.

Note for Java developers: This material shows how to replace Spring, Angular, grunt, live-reload with a bunch of Clojure tools and libraries and a bit of code.

The repo with final code and individual steps is here.

Bootstrap

I think all agreed that component is the industry standard for managing lifecycle of Clojure applications. If you are a Java developer you may think of it as a Spring (DI) replacement - you declare dependencies between “components” which are resolved on “system” startup. So you just say “my component needs a repository/database pool” and component library “injects” it for you.

To keep things simple I like to start with duct web app template. It’s a nice starter component application following the 12-factor philosophy. So let’s start with it:

lein new duct clojure-web-app +example

The +example parameter tells duct to create an example endpoint with HTTP routes - this would be helpful. To finish bootstraping run lein setup inside clojure-web-app directory.

Ok, let’s dive into the code. Component and injection related code should be in system.clj file:

(defn new-system [config]
  (let [config (meta-merge base-config config)]
    (-> (component/system-map
         :app  (handler-component (:app config))
         :http (jetty-server (:http config))
         :example (endpoint-component example-endpoint))
        (component/system-using
         {:http [:app]
          :app  [:example]
          :example []}))))

In the first section you instantiate components without dependencies, which are resolved in the second section. So in this example, “http” component (server) requires “app” (application abstraction), which in turn is injected with “example” (actual routes). If your component needs others, you just can get then by names (precisely: by Clojure keywords).

To start the system you must fire a REPL - interactive environment running within context of your application:

lein repl

After seeing prompt type (go). Application should start, you can visit http://localhost:3000 to see some example page.

A huge benefit of using component approach is that you get fully reloadable application. When you change literally anything - configuration, endpoints, implementation, you can just type (reset) in REPL and your application is up-to-date with the code. It’s a feature of the language, no JRebel, Spring-reloaded needed.

Adding REST endpoint

Ok, in the next step let’s add some basic REST endpoint returning JSON. We need to add 2 dependencies in project.clj file:

:dependencies
 ...
  [ring/ring-json "0.3.1"]
  [cheshire "5.1.1"]

Ring-json adds support for JSON for your routes (in ring it’s called middleware) and cheshire is Clojure JSON parser (like Jackson in Java). Modifying project dependencies if one of the few tasks that require restarting the REPL, so hit CTRL-C and type lein repl again.

To configure JSON middleware we have to add wrap-json-body and wrap-json-response just before wrap-defaults in system.clj:

(:require 
 ...
 [ring.middleware.json :refer [wrap-json-body wrap-json-response]])

(def base-config
   {:app {:middleware [[wrap-not-found :not-found]
                      [wrap-json-body {:keywords? true}]
                      [wrap-json-response]
                      [wrap-defaults :defaults]]

And finally, in endpoint/example.clj we must add some route with JSON response:

(:require 
 ...
 [ring.util.response :refer [response]]))

(defn example-endpoint [config]
  (routes
    (GET "/hello" [] (response {:hello "world"}))
    ...

Reload app with (reset) in REPL and test new route with curl:

curl -v http://localhost:3000/hello

< HTTP/1.1 200 OK
< Date: Tue, 15 Sep 2015 21:17:37 GMT
< Content-Type: application/json; charset=utf-8
< Set-Cookie: ring-session=37c337fb-6bbc-4e65-a060-1997718d03e0;Path=/;HttpOnly
< X-XSS-Protection: 1; mode=block
< X-Frame-Options: SAMEORIGIN
< X-Content-Type-Options: nosniff
< Content-Length: 151
* Server Jetty(9.2.10.v20150310) is not blacklisted
< Server: Jetty(9.2.10.v20150310)
<
* Connection #0 to host localhost left intact
{"hello": "world"}

It works! In case of any problems you can find working version in this commit.

Adding frontend with figwheel

Coding backend in Clojure is great, but what about the frontend? As you may already know, Clojure could be compiled not only to JVM bytecode, but also to Javascript. This may sound familiar if you used e.g. Coffescript. But ClojureScript philosophy is not only to provide some syntax sugar, but improve your development cycle with great tooling and fully interactive development. Let’s see how to achieve it.

The best way to introduce ClojureScript to a project is figweel. First let’s add fighweel plugin and configuration to project.clj:

:plugins
   ...
   [lein-figwheel "0.3.9"]

And cljsbuild configuration:

:cljsbuild
    {:builds [{:id "dev"
               :source-paths ["src-cljs"]
               :figwheel true
               :compiler {:main       "clojure-web-app.core"
                          :asset-path "js/out"
                          :output-to  "resources/public/js/clojure-web-app.js"
                          :output-dir "resources/public/js/out"}}]}

In short this tells ClojureScript compiler to take sources from src-cljs with figweel support and but resulting JavaScript into resources/public/js/clojure-web-app.js file. So we need to include this file in a simple HTML page:

<!DOCTYPE html>
<head>
</head>
<body>
  <div id="main">
  </div>
  <script src="js/clojure-web-app.js" type="text/javascript"></script>
</body>
</html>

To serve this static file we need to change some defaults and add corresponding route. In system.clj change api-defaults to site-defaults both in require section and base-config function. In example.clj add following route:

(GET "/" [] (io/resource "public/index.html")

Again (reset) in REPL window should reload everything.

But where is our ClojureScript source file? Let’s create file core.cljs in src-cljs/clojure-web-app directory:

(ns ^:figwheel-always clojure-web-app.core)

(enable-console-print!)

(println "hello from clojurescript")

Open another terminal and run lein fighweel. It should compile ClojureScript and print ‘Prompt will show when figwheel connects to your application’. Open http://localhost:3000. Fighweel window should prompt:

To quit, type: :cljs/quit
cljs.user=>

Type (js/alert "hello"). Boom! If everything worked you should see and alert in your browser. Open developers console in your browser. You should see hello from clojurescript printed on the console. Change it in core.cljs to (println "fighweel rocks") and save the file. Without reloading the page your should see updated message. Figweel rocks! Again, in case of any problems, refer to this commit.

In the next post I’ll show how to fetch data from MongoDB, serve it with REST to the broser and write ReactJs/Om components to render it. Stay tuned!