In the previous tutorial we completed the job of integrating the client-side validators for the Shopping Calculator input fields into the corresponding WUI in such a way that the user will be notified with the corresponding help messages when she enters invalid values in the form itself.

Introduction

As you remember, the injected validators have been implemented by using a forked version of the valip validation library done by Chas Emerick. That library was in turn a forked version of the valip library originally created by James Reeves and it was aimed at making the original library as portable as possible between Clojure and ClojureScript. When Chas Emerick forked the valip original library in 2012, Reader Conditionals did not exist. At those time you had two alternatives to make your code portable from CLJ to CLJS, namely:

• the crossover features by the cljsbuild plugin;
• the cljx plugin by Kevin Lynagh.

The problem with those alternatives is that they are now both deprecated in favor of the much easier, more powerful and flexible Reader Conditionals extension we cited above.

When I recently decided to switch this series of tutorials on CLJS from the leiningen build tool to the boot one, I realized that I could exploit that decision to accommodate the valip portable library to the new CLJ/CLJS Reader Conditional extension as well.

This tutorial is a kind of a walk-through of that migration experience and has to be intended as an effort to stimulate CLJ/CLJS newbies to start learning that pair of programming languages while doing, namely while being collaborative with the maintainers of CLJ/CLJS libraries. Most of the time the migration path needed to make a CLJ library portable on CLJS via Reader Conditionals is not as hard as you may think.

Livin' on the edge

When you start using a library implemented by others, you can easily end up with few misunderstandings of its use or even with same unexpected issues. In these cases, the first thing you should do is to browse and read its documentation. As you know, one problem with open source software regards the corresponding documentation which is frequently minimal, if not absent, outdated or requiring a level of comprehension of details which as newbie we still have to grasp.

Likely, most of the CLJ/CLJS open source libraries are hosted on github which offers an amazing support for collaboration and social coding. Even if few CLJ/CLJS libraries have extensive documentation and/or an associated mailing-list for submitting doubts and questions, every CLJ/CLJS library hosted on github is supported by complex, although easy-to-use, issue and version control management systems. Those two systems help a lot in managing almost any distributed and remote collaboration requirements.

The Valip Library

As said, the main purpose of Chas Emerick while forking the original valip library was to make it portable from CLJ to CLJS. Consequently, it should be very easy to adopt the Reader Conditionals extension, because most of the porting works should already be done by Chas Emerick himself.

Fork, clone and branch

The first step is to fork the library from github and then create a local clone of the fork in your computer.

git clone https://github.com/<your_github_name>/valip.git
Cloning into 'valip'...
remote: Counting objects: 309, done.
remote: Total 309 (delta 0), reused 0 (delta 0), pack-reused 309
Receiving objects: 100% (309/309), 36.37 KiB | 0 bytes/s, done.
Resolving deltas: 100% (101/101), done.
Checking connectivity... done.

Now add to your cloned repository the remote address of the original valip library

cd valip
git remote add upstream https://github.com/cemerick/valip.git
git remote -v
origin	https://github.com/magomimmo/valip.git (fetch)
origin	https://github.com/magomimmo/valip.git (push)
upstream	https://github.com/cemerick/valip.git (fetch)
upstream	https://github.com/cemerick/valip.git (push)

NOTE 1: in github parlance the original repository you fork is named upstream.

Finally, make a new branch to keep your work separated from the master branch

git checkout -b reader-conditionals
Switched to a new branch 'reader-conditionals'

and you're ready to start collaborating.

Look at the build file

When I want to grasp an initial understanding of a new CLJ/CLJS library, the very first thing I do, aside from reading the corresponding README.md file when available, is to take a look at its build file. As most CLJ/CLJS libraries, valip, being based on the leiningen build tool, uses a project.clj build file:

(defproject com.cemerick/valip "0.3.2"
  :description "Functional validation library for Clojure and ClojureScript, forked from https://github.com/weavejester/valip"
  :url "http://github.com/cemerick/valip"
  :dependencies [[org.clojure/clojure "1.4.0"]])

A pretty minimal build file in this case. As you can see, valip depends on CLJ 1.4.0 release. To be able to use the Reader Conditionals extension, the very first thing to be updated is the CLJ dependency: from 1.4.0 to 1.7.0 (in a very short time the clojure-dev team will deliver the 1.8.0 release):

(defproject com.cemerick/valip "0.3.2"
  :description "Functional validation library for Clojure and ClojureScript, forked from https://github.com/weavejester/valip"
  :url "http://github.com/cemerick/valip"
  :dependencies [[org.clojure/clojure "1.8.0"]])

NOTE 1: this tutorial uses the leiningen build tool. You need to install it by following these very easy instructions.

leiningen has a lot of sane defaults for its build directives. For example, if you do not specify a :source-paths directive, it assumes src as default. If you do not specify a :target-path directive, it assume target directory as default and if you do not specify a :test-paths it will assume the test directory as default and so on. That's why the project.clj is so concise.

Directory layout

The second thing I generally look at is the layout of the project directory:

tree
.
├── README.md
├── project.clj
├── src
│   ├── cljs
│   │   └── reader.clj
│   └── valip
│       ├── core.clj
│       ├── java
│       │   └── predicates.clj
│       ├── js
│       │   └── predicates.cljs
│       ├── predicates
│       │   └── def.clj
│       └── predicates.clj
└── test
    └── valip
        └── test
            ├── core.clj
            └── predicates.clj

9 directories, 10 files

As you see the source files are confined in the src directory, while the test source files are confined in the test directory, mimicking the layout of the src directory. Nothing new, even coming from a boot background. As you'll later discover, you can use exactly the same directory arrangement regardless of the build tool you are going to use for the project itself.

Migration preparation

To prepare a library originally implemented for CLJ only to cover CLJS via the Reader Conditionals extension, there are a few steps you should follow:

• update the CLJ dependency to the 1.8.0 release, because the Reader Conditionals extension was introduced in that release on (we already did this);
• identify all the functions that are JVM specific, these can't target CLJS;
• identify all the macros defined in the library, because CLJS's macros must be defined in a different compilation stage from the one where they are consumed.

Valip current state

With valip we're in a good position. Indeed, its directory layout already partially fits with the above preparation, because Chas Emerick's goal was to make valip portable on JSVM (JavaScript Virtual Machine) either via the :crossover feature of the lein-cljsbuild plugin or via the lein-cljx plugin.

Let's explore the current directory layout of the valip library:

• all the functions specific to the JVM are confined in the predicates.clj source file hosted in the src/valip/java directory;
• all the functions specific to the JSVM (JavaScript Virtual Machine) are confined in the predicates.cljs source file hosted in the src/valip/js directory;
• all the functions which are agnostic from the hosting platform are confined in the core.clj and predicates.clj source files living in the src/valip directory;
• all the macros are confined in the def.clj source file are hosted in the src/valip/predicates directory.

So far, so good. But what does it mean that the reader.clj source file is hosted in the src/cljs directory?

A smart trick by a smart guy

As said, the :source-paths directive of the project.clj file is set by default to src. By knowing the way CLJ maps namespace segments to file pathnames, there is a smell of something strange going on in that src/cljs/reader.clj source file. Let's take a look at the it:

(ns cljs.reader
  "A dummy namespace, allowing valip.predicates to :require cljs.reader even in Clojure,
so as to allow portable usage of `read-string`."
  (:refer-clojure :exclude (read-string)))

(def read-string clojure.core/read-string)

Ahah! This is were the smart trick lurks. Chas Emerick defined a dummy cljs.reader namespace mimicking the predefined CLJS cljs.reader namespace. This dummy namespace aliases the read-string from the clojure.core namespace in such a way that the cljs.reader can be required even when valip runs on a JVM.

To see how this dummy namespace is used, let's take a look at the valip.predicates namespace declaration from the predicates.clj file hosted in the src/valip directory:

(ns valip.predicates
  "Predicates useful for validating input strings, such as ones from HTML forms.
All predicates in this namespace are considered portable between different
Clojure implementations."
  (:require [clojure.string :as str]
            [cljs.reader :refer [read-string]])
  (:refer-clojure :exclude [read-string]))

The read-string function is first referred from the cljs.reader namespace we just saw above. Then, to prevent a symbol collision with the read-string symbol from the clojure.core namespace, it's excluded from being interned in the valip.predicates namespace. This has to do with one of the differences between CLJ and CLJS, namely:

• The CLJS read and read-string symbols are defined in the cljs.reader namespace, while the corresponding CLJ symbols are defined in the clojure.core namespace.

This incidental complexity was needed because the Reader Conditionals were not available at the time of writing the valip library. As we'll see later, even if the dummy namespace seems to be a very smart trick, it is also affected by a subtle and serious security issue.

Steps

As we learned few tutorials ago, the Reader Conditionals extension offers the #? reader macro to dynamically differentiate at compile-time the forms to be evaluated depending on the features of the hosting platform. At the moment we are interested in two features:

• :clj is available when CLJ compiles on a JVM;
• :cljs is available when CLJ compiles on a JSVM.

With the Reader Conditionals machinery in our hands we can proceed with the next steps, namely:

1. get rid of the above smart and dangerous trick, by deleting the src/cljs directory and the reader.clj file as well;
2. change the file extension of the predicates.clj and core.clj source files hosted in the src/valip directory from .clj to .cljc;
3. move the specific JVM symbols' definitions from the predicates.clj source file hosted in the src/valip/java directory to the above predicates.cljc source file;
4. move the specific JSVM symbols' definitions from the predicates.cljs source file to the above predicates.cljc source file;
5. use the #? reader macro to differentiate the namespaces' requirements in the valip.core and valip.predicates namespaces declaration, depending on the feature made available by the hosting platform at compile-time;
6. use the #? reader macro to differentiate the symbols' definitions in the valip.predicates namespace as well;
7. use the #? reader macro to differentiate the namespaces' requirements and the symbols' definitions for the unit tests as well;
8. delete the original src/valip/java/predicates.clj and src/valip/js/predicates.cljs source files, because we absorbed their content in the predicates.cljc source file.

Not such a big deal, right? Wrong!

The valip project.clj build file is for CLJ only. If we want to be able to compile and test the migrated valip library on CLJS, we need to add both the lein-cljsbuild and the lein-doo plugins.

Moreover, unless you had the chance to read the first edition of this series or you already know about the leiningen build tool, those things will be new to you and the signal/noise ratio of the final project.clj build file is going to be much worse when compared with the project.clj we started from.

But don't worry! We're not going to complicate the project.clj file with cljsbuild to make valip compliant with the Reader Conditionals extension, we'll continue to use boot.

Execution

In the following paragraphs we're going to execute step by step the above plan.

Step 1

As said, we first have to delete the src/cljs directory and the contained reader.clj file as well, because we do not need the Chas Emerick trick anymore:

cd /path/to/valip
rm -rf src/cljs

Step 2

We now need to rename the predicates.clj and core.clj source files hosted in the src/valip directory respectively to predicates.cljc and core.cljc:

mv src/valip/predicates.clj src/valip/predicates.cljc
mv src/valip/core.clj src/valip/core.cljc

These files contains all the symbols' definitions that are already portable between CLJ and CLJS. Obviously we have to update their namespace declarations as well, but we'll take care of this later.

Step 3

Next, we have to move the definitions specific for the JVM into the above predicates.cljc source file. Open the predicates.clj source file hosted in the src/valip/java directory, copy all the symbols' definitions and append them in the predicates.cljc source file.

While you are at it, introduce the #? reader macro to inform the compiler that these definition are specific for the JVM platform. This way you're partially anticipating Step 6:

;;; above the rest of the file
#?(:clj (defn url?
          "Returns true if the string is a valid URL."
          [s]
          (try
            (let [uri (URI. s)]
              (and (seq (.getScheme uri))
                   (seq (.getSchemeSpecificPart uri))
                   (re-find #"//" s)
                   true))
            (catch URISyntaxException _ false))))

#?(:clj (defn- dns-lookup [^String hostname ^String type]
          (let [params {"java.naming.factory.initial"
                        "com.sun.jndi.dns.DnsContextFactory"}]
            (try
              (.. (InitialDirContext. (Hashtable. params))
                  (getAttributes hostname (into-array [type]))
                  (get type))
              (catch NamingException _
                nil)))))

#?(:clj (defpredicate valid-email-domain?
          "Returns true if the domain of the supplied email address has a MX DNS entry."
          [email]
          [email-address?]
          (if-let [domain (second (re-matches #".*@(.*)" email))]
            (boolean (dns-lookup domain "MX")))))

NOTE 2: note that we removed the valip.predicates alias (i.e., preds) in the valid-email-domain definition because we moved the definition itself in that namespace.

Step 4

You should now do the same thing with the predicates.cljs currently living in the valip.js directory. While you're there, take advantage of the opportunity of adding the CLJS url? definition inside the #? reader macro already used for the CLJ url? definition as follows:

#?(:clj (defn url?
          "Returns true if the string is a valid URL."
          [s]
          (try
            (let [uri (URI. s)]
              (and (seq (.getScheme uri))
                   (seq (.getSchemeSpecificPart uri))
                   (re-find #"//" s)
                   true))
            (catch URISyntaxException _ false)))
   :cljs (defn url?
           [s]
           (let [uri (-> s goog.Uri/parse)]
             (and (seq (.getScheme uri))
                  (seq (.getSchemeSpecificPart uri))
                  (re-find #"//" s)))))

As you see, you're conditionally defining the url? symbol depending on the feature of the platform at compile-time, being it JVM or JSVM.

Step 5

The next step is the most tedious one. You have to update the valip.core and valip.predicates namespaces' declarations to accommodate the different CLJ and CLJS namespaces' requirements. Lets first review all those namespaces' declarations.

(ns valip.core
  "Functional validations.")

Here there is really nothing to be done. Go on by reviewing and comparing the original JVM and JSVM specific namespaces' declarations with the valip.predicates one:

(ns valip.java.predicates
  "Useful validation predicates implemented for JVM Clojure."
  (:require [valip.predicates :as preds]
            [valip.predicates.def :refer (defpredicate)])
  (:import
    (java.net URI URISyntaxException)
    java.util.Hashtable
    javax.naming.NamingException
    javax.naming.directory.InitialDirContext))

(ns valip.js.predicates
  "Useful validation predicates implemented for ClojureScript using the Google Closure libraries
where necessary."
  (:import goog.Uri))

(ns valip.predicates
  "Predicates useful for validating input strings, such as ones from HTML forms.
All predicates in this namespace are considered portable between different
Clojure implementations."
  (:require [clojure.string :as str]
            [cljs.reader :refer [read-string]])
  (:refer-clojure :exclude [read-string]))

Never read from untrusted source

First we have to make a short digression about the security issue we talked about above:

Never use clojure.core/read and clojure.core/read-string functions when dealing with untrusted sources in CLJ.

That said, cljs.reader/read and cljs.reader/read-string are unaffected by the same security issues, because they adopted the same approach used to implement clojure.edn/read and clojure.edn/read-string which can read data structures, but are not able to evaluate them.

All that to say that in the valip.predicates namespace declaration we have to differentiate the reader namespace requirement between CLJ and CLJS.

Following is the valip.predicates namespace declaration incorporating the above solution for the cited security issue and any other specific namespace declaration specific for the two considered platforms (i.e., JVM and JSVM):

(ns valip.predicates
  "Predicates useful for validating input strings, such as ones from HTML forms."
  #?(:clj (:require [clojure.string :as str]
                    [clojure.edn :refer [read-string]]
                    [valip.predicates.def :refer [defpredicate]])
     :cljs (:require [clojure.string :as str]
                     [cljs.reader :refer [read-string]]))
  #?(:clj (:refer-clojure :exclude [read-string])
     :cljs (:require-macros [valip.predicates.def :refer [defpredicate]]))
  #?(:clj (:import (java.net URI URISyntaxException)
                   java.util.Hashtable
                   javax.naming.NamingException
                   javax.naming.directory.InitialDirContext)
     :cljs (:import goog.Uri)))

To make the code more readable, we adopted an expanded declaration form. If you want to make the declaration more compact you could use this smart trick.

Step 6

We already differentiated any platform specific symbol definition in the valip.predicates namespace while we pasted those symbols during the execution of the Step 3. So there is nothing else left to be done in this step.

Step 7

We now have to deal with the valip unit tests confined in the src/test directory. Mutatis mutandis, we have to replicate the above Step 2, Step 4 and Step 5 to the content of the test/valip/test directory:

Let's start by updating the files extensions:

mv test/valip/test/core.clj test/valip/test/core.cljc
mv test/valip/test/predicates.clj test/valip/test/predicates.cljc

Then open the two files and update their namespaces declarations and symbols definitions as follows:

;;; core.cljc
(ns valip.test.core
  #?(:clj (:require [valip.core :refer [validation-on validate]]
                    [clojure.test :refer [deftest is]])
     :cljs (:require [valip.core :refer [validation-on validate]]
                     [cljs.test :refer-macros [deftest is]])))

As in the previous cases, you could make the :require more compact by using the same cited trick.

(ns valip.test.predicates
  #?(:cljs (:require [valip.predicates :refer [present?
                                               matches
                                               max-length
                                               min-length
                                               email-address?
                                               digits?
                                               integer-string?
                                               decimal-string?
                                               gt
                                               gte
                                               lt
                                               lte
                                               over
                                               under
                                               at-most
                                               at-least
                                               between
                                               url?]]
                     [cljs.test :refer-macros [deftest is]])
     :clj (:use valip.predicates clojure.test)))

;;; some tests following...

#?(:clj (deftest test-valid-email-domain?
          (is (valid-email-domain? "example@google.com"))
          (is (not (valid-email-domain? "foo@example.com")))
          (is (not (valid-email-domain? "foo@google.com.nospam")))
          (is (not (valid-email-domain? "foo")))))

;;; some tests following

NOTE 3: In CLJS, when you want to :use a namespace instead of :require it, you must use the :only form of :use. In those cases I still prefer to use the :refer form of :require.

NOTE 4: the valid-email-domain? predicate and its corresponding test can only be evaluated on the JVM.

Step 8

We can now get rid of the original source files containing platform specific predicates, because they have been completely absorbed in the predicates.cljc file:

rm -rf src/valip/java
rm -rf src/valip/js

We end up with the following directory layout:

tree
.
├── README.md
├── project.clj
├── src
│   └── valip
│       ├── core.cljc
│       ├── predicates
│       │   └── def.clj
│       └── predicates.cljc
└── test
    └── valip
        └── test
            ├── core.cljc
            └── predicates.cljc

6 directories, 7 files

As you see the only surviving pure CLJ file is def.clj, which is the one containing the macro definitions.

Those steps represent the easiest part of making the valip validation library compliant with the Reader Conditionals extension. If we want to stay with the leiningen build tool, we should now attempt the difficult ones:

• the addition of the lein-cljsbuild plugin to the project.clj;
• the execution of the tests on the JSVM platform.

Before digging in that new sea, take the opportunity to see if we're able to run the newly updated valip library in CLJ.

Run and test in CLJ

The only thing we need to do for running and testing the updated CLJ version of the valip library is to update its project.clj build file by upgrading the pinned CLJ release in the :dependencies section - we already did this at the beginning of the tutorial:

(defproject com.cemerick/valip "0.3.2"
  :description "Functional validation library for Clojure and ClojureScript, forked from https://github.com/weavejester/valip"
  :url "http://github.com/cemerick/valip"
  :dependencies [[org.clojure/clojure "1.8.0"]])

You're now ready to run the CLJ tests by launching the lein test task as follows:

cd /path/to/valip
lein test

lein test valip.test.core

lein test valip.test.predicates

Ran 21 tests containing 78 assertions.
0 failures, 0 errors.

Nice work. All the unit tests assertions passed. Let's now see if we can use the valip library from the lein based repl task:

cd /path/to/valip
lein repl
nREPL server started on port 49762 on host 127.0.0.1 - nrepl://127.0.0.1:49762
REPL-y 0.3.7, nREPL 0.2.10
Clojure 1.8.0
Java HotSpot(TM) 64-Bit Server VM 1.8.0_66-b17
    Docs: (doc function-name-here)
          (find-doc "part-of-name-here")
  Source: (source function-name-here)
 Javadoc: (javadoc java-object-or-class-here)
    Exit: Control+D or (exit) or (quit)
 Results: Stored in vars *1, *2, *3, an exception in *e

user=>

user=> (require '[valip.predicates :as v])
nil

user=> (v/present? nil)
false

user=> (v/present? "")
false

user=> (v/present? " ")
false

user=> (v/present? "foo")
true

Good. Are not you curious about the predicates that have been defined within the #? reader macro? Let's evaluate them at the REPL:

user=> (v/url? "http://www.google.com")
true

user=> (v/valid-email-domain? "me@me.com")
true

user=> (v/valid-email-domain? "me@googlenospam.com")
false

user=> (v/url? "www.google.com")
nil

As you know, when evaluated in boolean context, nil is like false. I would prefer that the last expression return false, but I can live with it.

Digression about corner cases

One of the few tests I like to write are the ones testing corner cases. If we want to be serious about functional programming, we should never forget that a function is a relation between a set of inputs and a set of permissible outputs with the property that each input is related to exactly one output. The corner cases are where the things became interesting.

Just to make an example, evaluate the following expression at the REPL:

(+ 1)
1

But what about the following?

(+)
0

This corner case is interesting. In mathematics, the element 0 is the identity element (or neutral element) for the + operation.

Let's try with the multiplication:

user=> (* 10)
10

user=> (*)
1

As you see the identity element for the multiplication is the element 1. On the contrary, subtraction and division do not have an identity element, as you can verify by yourself:

user=> (-)

ArityException Wrong number of args (0) passed to: core/-  clojure.lang.AFn.throwArity (AFn.java:429)

user=> (/)

ArityException Wrong number of args (0) passed to: core//  clojure.lang.AFn.throwArity (AFn.java:429)

Do you see how important is to test the corner cases? Let's now see how valip behaves on corner cases. We already met one of them:

(v/present? nil)
false

This corner cases does not regard the arities of the function but the function's domain/co-domain.

Let's now test other corner cases of the functions/predicates defined by the valip library.

user=> ((v/matches #"...") "foo")
true
user=> ((v/matches #"...") "")
false
user=> ((v/matches #"...") nil)

NullPointerException   java.util.regex.Matcher.getTextLength (Matcher.java:1283)
user=>

That's bad. The present? predicate is defined for the nil element, while the function returned by the matches HOF function is not, as you can verify from it's source code:

(source v/matches)
(defn matches
  "Creates a predicate that returns true if the supplied regular expression
  matches its argument."
  [re]
  (fn [s] (boolean (re-matches re s))))
nil

Let's go on with few other functions/predicates corner cases:

user=> (v/email-address? nil)

NullPointerException   java.util.regex.Matcher.getTextLength (Matcher.java:1283)

user=> (v/integer-string? nil)

NullPointerException   java.util.regex.Matcher.getTextLength (Matcher.java:1283)

user=> (v/decimal-string? nil)

NullPointerException   java.util.regex.Matcher.getTextLength (Matcher.java:1283)

user=> (v/digits? nil)

NullPointerException   java.util.regex.Matcher.getTextLength (Matcher.java:1283)

user=> (v/alphanumeric? nil)

NullPointerException   java.util.regex.Matcher.getTextLength (Matcher.java:1283)

Oh my God. They all raised a null pointer exception with the nil corner cases. I'm not saying they should not. I'm saying that once you decided your library behaves in some way, for example not considering that nil element as member of a function, you should uniformly stay with this decision, and valip does not.

Do you want to see other misalignment? Evaluate a couple of valip HOF functions returning predicates?

user=> ((v/min-length 5) nil)
false
user=> ((v/max-length 5) nil)
true

I don't know about you, but I can't accept such a misaligned behaviors, because I'm sure they're going to later generate bugs that will be difficult to catch.

Now exit the REPL, because it's time to start a TDD session to fix the original valip library.

Enter boot

Even if we could update the project.clj by adding to it the lein-auto plugin, we prefer to switch to boot, because we already know everything about creating a build.boot build file to support TDD.

Let's create the boot.properties file:

cd /path/to/valip
boot -V > boot.properties

If you open it you'll see:

#http://boot-clj.com
#Fri Mar 03 15:11:25 CET 2017
BOOT_CLOJURE_NAME=org.clojure/clojure
BOOT_CLOJURE_VERSION=1.8.0
BOOT_VERSION=2.7.1

Now create the build.boot file for the valip project with the following content:

(set-env!
 :source-paths #{"src"}

 :dependencies '[[org.clojure/clojure "1.8.0"]
                 [adzerk/boot-test "1.2.0"]])

(require '[adzerk.boot-test :refer [test]])

(deftask testing
  []
  (merge-env! :source-paths #{"test"})
  identity)

(deftask clj-tdd
  "Launch a CLJ TDD Environment"
  []
  (comp
   (testing)
   (watch)
   (test :namespaces #{'valip.test.core 'valip.test.predicates})))

Here we set the :source-paths environment variable to the src directory. Then we set the needed dependencies and made the test symbol visible. Next we defined two new tasks:

• testing task: to add the test directory to the :source-paths environment variable;
• clj-tdd: to launch a CLJ based TDD session.

TDD session

We're now ready to go. Launch the clj-tdd environment:

cd /path/to/valip
boot clj-tdd

Starting file watcher (CTRL-C to quit)...


Testing valip.test.core

Testing valip.test.predicates

Ran 21 tests containing 78 assertions.
0 failures, 0 errors.
Elapsed time: 4.832 sec

All assertions succeeded. This is not a surprise, because we already checked this in the previous lein test session.

Add corner case assertions

Now edit the test/valip/test/predicates.cljc file to start adding the assertions covering the domain corner cases we did not like from the previous lein repl session:

(deftest test-matches
  (is ((matches #"...") "foo"))
  (is (not ((matches #"...") "foobar")))
  (is (not ((matches #"...") nil)))) ; corner case

As soon as you save the file you'll receive the expected error:

Testing valip.test.core

Testing valip.test.predicates

ERROR in (test-matches) (Matcher.java:1283)
expected: (not ((matches #"...") nil))
  actual: java.lang.NullPointerException: null
 at ...

Ran 21 tests containing 79 assertions.
0 failures, 1 errors.
clojure.lang.ExceptionInfo: Some tests failed or errored
    data: {:test 21, :pass 78, :fail 0, :error 1, :type :summary}
    ...
Elapsed time: 0.647 sec

Open the src/valip/predicates.cljs to take a look at the matches function definition:

(defn matches
  "Creates a predicate that returns true if the supplied regular expression
  matches its argument."
  [re]
  (fn [s] (boolean (re-matches re s))))

The java.lang.NullPointerException: null has been raised because we passed the nil value to the anonymous function returned by matches and re-matches does not like it. re-matches expects its argument to be a string.

Now launch the CLJ REPL as usual for playing a little bit with re-matches function:

# from a new terminal
cd /path/to/valip
boot repl
nREPL server started on port 50035 on host 127.0.0.1 - nrepl://127.0.0.1:50035
REPL-y 0.3.7, nREPL 0.2.12
Clojure 1.8.0
Java HotSpot(TM) 64-Bit Server VM 1.8.0_66-b17
        Exit: Control+D or (exit) or (quit)
    Commands: (user/help)
        Docs: (doc function-name-here)
              (find-doc "part-of-name-here")
Find by Name: (find-name "part-of-name-here")
      Source: (source function-name-here)
     Javadoc: (javadoc java-object-or-class-here)
    Examples from clojuredocs.org: [clojuredocs or cdoc]
              (user/clojuredocs name-here)
              (user/clojuredocs "ns-here" "name-here")
boot.user=>

boot.user=> (re-matches #"..." nil)

java.lang.NullPointerException:

Ok. Let's see if we pass it a void string "" instead of the nil value.

boot.user=> (re-matches #"..." "")
nil

Could we transform nil into ""? Sure. Use the str function:

boot.user=> (str nil)
""

We can now go back to the predicates.cljc file to fix the bug:

(defn matches
  "Creates a predicate that returns true if the supplied regular expression
  matches its argument."
  [re]
  (fn [s] (boolean (re-matches re (str s))))) ;; wrap s within str

As soon as you save the file clj-tdd re-executes the tests and returns success:

Testing valip.test.core

Testing valip.test.predicates

Ran 21 tests containing 79 assertions.
0 failures, 0 errors.
Elapsed time: 0.656 sec

While we are there, let's add the ((matches #"...") "") corner case as well. We already know it will succeed.

(deftest test-matches
  (is (not ((matches #"...") "")))   ; corner case
  (is (not ((matches #"...") nil)))  ; corner case
  (is ((matches #"...") "foo"))
  (is (not ((matches #"...") "foobar"))))

Testing valip.test.core

Testing valip.test.predicates

Ran 21 tests containing 80 assertions.
0 failures, 0 errors.
Elapsed time: 0.561 sec

Extend the coverage

If you consider that all valip functions/predicates receive strings as arguments to be evaluated, we already have a hint to extend the current valip test assertions to cover and fix the nil corner cases in the corresponding source code: just wrap any string argument within a str function.

(deftest test-max-length
  (is ((max-length 5) ""))       ; corner case
  (is ((max-length 5) nil))
  (is ((max-length 5) "hello"))  ; corner case
  (is ((max-length 5) "hi"))
  (is (not ((max-length 5) "hello world"))))

While extending the tests assertions, you'll note that the test-max-length has bee defined two times with a different body. Something that the CLJ compiler was not able to catch. The second occurrence had to be renamed has test-min-length:

(deftest test-min-length
  (is (not ((min-length 5) "")))    ; corner case
  (is (not ((min-length 5) nil)))   ; corner case
  (is ((min-length 5) "hello"))
  (is ((min-length 5) "hello world"))
  (is (not ((min-length 5) "hi"))))

The next failure you'll met will be with the test-email-address? predicate:

(deftest test-email-address?
  (is (not (email-address? "")))    ; corner case
  (is (not (email-address? nil)))   ; corner case
  (is (email-address? "foo@example.com"))
  (is (email-address? "foo+bar@example.com"))
  (is (email-address? "foo-bar@example.com"))
  (is (email-address? "foo.bar@example.com"))
  (is (email-address? "foo@example.co.uk"))
  (is (not (email-address? "foo")))
  (is (not (email-address? "foo@bar")))
  (is (not (email-address? "foo bar@example.com")))
  (is (not (email-address? "foo@foo_bar.com"))))

Here is the assertion failure report:

Testing valip.test.core

Testing valip.test.predicates

ERROR in (test-email-address?) (Matcher.java:1283)
expected: (not (email-address? nil))
  actual: java.lang.NullPointerException: null
...
Ran 21 tests containing 86 assertions.
0 failures, 1 errors.
clojure.lang.ExceptionInfo: Some tests failed or errored
    data: {:test 21, :pass 85, :fail 0, :error 1, :type :summary}
...
Elapsed time: 0.609 sec

As said above, to fix the bug we just to need to wrap the passed argument within a str call:

(defn email-address?
  "Returns true if the email address is valid, based on RFC 2822. Email
  addresses containing quotation marks or square brackets are considered
  invalid, as this syntax is not commonly supported in practise. The domain of
  the email address is not checked for validity."
  [email]
  (let [re (str "(?i)[a-z0-9!#$%&'*+/=?^_`{|}~-]+"
                "(?:\\.[a-z0-9!#$%&'*+/=?" "^_`{|}~-]+)*"
                "@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+"
                "[a-z0-9](?:[a-z0-9-]*[a-z0-9])?")]
    (boolean (re-matches (re-pattern re) (str email))))) ; wrap within str

Same thing with the test-url? corner case assertion about nil argument:

(deftest test-url?
  (is (not (url? "")))
  (is (not (url? nil)))
  (is (url? "http://google.com"))
  (is (url? "http://foo"))
  (is (not (url? "foobar"))))

Testing valip.test.core

Testing valip.test.predicates

ERROR in (test-url?) (URI.java:3042)
expected: (not (url? nil))
  actual: java.lang.NullPointerException: null
 at java.net.URI$Parser.parse (URI.java:3042)
    ...
Ran 21 tests containing 87 assertions.
0 failures, 1 errors.
clojure.lang.ExceptionInfo: Some tests failed or errored
    data: {:test 21, :pass 86, :fail 0, :error 1, :type :summary}
...
Elapsed time: 0.572 sec

Again, just wrap the passed string argument within an str call:

#?(:clj (defn url?
          "Returns true if the string is a valid URL."
          [s]
          (try
            (let [uri (URI. (str s))]      ; wrap within str
              (and (seq (.getScheme uri))
                   (seq (.getSchemeSpecificPart uri))
                   (re-find #"//" (str s)) ; wrap within str
                   true))
            (catch URISyntaxException _ false)))
   :cljs (defn url?
           [s]
           (let [uri (-> s goog.Uri/parse)]
             (and (seq (.getScheme uri))
                  (seq (.getSchemeSpecificPart uri))
                  (re-find #"//" s)))))

NOTE 6: at the moment we do not care about the CLJS definition of the url? predicate.

Keep going on with the corner cases coverage. Next stop is test-digit?:

(deftest test-digits?
  (is (not (digits? "")))
  (is (not (digits? nil)))
  (is (digits? "01234"))
  (is (not (digits? "04xa"))))

Same failure, same solution:

(defn decimal-string?
  "Returns true if the string represents a decimal number."
  [s]
  (boolean (re-matches #"\s*[+-]?\d+(\.\d+(M|M|N)?)?\s*" (str s))))

(defn digits?       
  "Returns true if a string consists only of numerical digits."
  [s]
  (boolean (re-matches #"\d+" (str s))))

I know, it's going to be boring, but the happy path assertions are even more boring than those corner cases.

Next stop is test-integer-string?. Same story as above

(deftest test-integer-string?
  (is (not (integer-string? "")))
  (is (not (integer-string? nil)))
  (is (integer-string? "10"))
  (is (integer-string? "-9"))
  (is (integer-string? "0"))
  (is (integer-string? "  8  "))
  (is (not (integer-string? "10,000")))
  (is (not (integer-string? "foo")))
  (is (not (integer-string? "10x")))
  (is (not (integer-string? "1.1"))))

and same fix too:

(defn integer-string?
  "Returns true if the string represents an integer."
  [s]
  (boolean (re-matches #"\s*[+-]?\d+\s*" (str s))))

You'll have to keep going in the same way up to the end of the predicates.cljc testing file and you're done. Your final test report should be something like the following:

Testing valip.test.core

Testing valip.test.predicates

Ran 21 tests containing 90 assertions.
0 failures, 0 errors.
Elapsed time: 0.619 sec

You can now stop the boot process to proceed with the next step.

Choosing among alternatives

The fact the migrated valip library has been successfully tested on CLJ does not mean that it will work on CLJS as well. We should now attempt another boring part: tooling.

As you saw above, it was very easy to run and test the CLJ version of valip library by using a couple of default leiningen tasks (e.g. repl and test).

On the contrary, we switched to boot building tool to easily create test automation (i.e., clj-tdd task).

We have two alternatives to go on with CLJS:

• we could stay with Leiningen, which is the standard build tool used by the clojurians, by adding to it the lein-cljsbuild plugin to compile the CLJS version of the valip library;
• we could switch to boot.

Leiningen was created by Phil Hagelberg in 2009, in the early days of CLJ itself, when CLJS was not even an idea.

Leiningen can be extended via plugins and even offers a template facility which allows to recreate at will a new project based on a templatificated project's structure, no matter how complex it may be. The Leiningen template facility could even be used to create a boot based project.

lein-cljsbuild is a leiningen plugin created at the end of 2011 to manage compilation tasks required by CLJS and its plethora of compilation options. In some way, you could consider cljsbuild as a build tool specialized for CLJS.

cljx is a second leiningen plugin that got a lot of attention when clojurians realized the opportunity of writing portable code able that could run on JVM and JSVM with few platform differences.

Before the advent of the Reader Conditionals extension, these were the two fundamentals tools used to make Clojure(Script) libraries portable on JVM and JSVM. As mentioned already, cljx is now deprecated, but cljsbuild is still the most used building tool for CLJS.

I personally used cljsbuild quite a lot in the past and it saved me many times from headaches. That said, from when I recently started using boot and few of the tasks implemented by the community, I prefer to stay with the boot building tool when I have to deal with CLJS, as this new edition of the modern-cljs series attests.

Enough words. Let's get started.

Bootify CLJS valip

To be able to quickly set up a CLJ TDD environment, in the previous paragraph we already created the boot.properties and build.boot files. It is now very easy to update the build.boot file to be able to extend it for covering the CLJS version of valip as well. We start very simply, by just adding the boot-cljs boot task and requiring its main cljs task to run the CLJS compiler.

(set-env!
 ...
 :dependencies '[...
                 [org.clojure/clojurescript "1.9.494"]
                 [adzerk/boot-cljs "1.7.228-2"]])

(require '...
         '[adzerk.boot-cljs :refer [cljs]])

NOTE 7: note that we also added the latest stable CLJS release to the :dependencies section.

Shoot the gun

We are now immediately able to launch the CLJS compilation:

cd /path/to/valip
boot cljs
Writing main.cljs.edn...
Compiling ClojureScript...
• main.js
WARNING: No such namespace: goog.Uri, could not locate goog/Uri.cljs, goog/Uri.cljc, or Closure namespace "" at line 127 src/valip/predicates.cljc
WARNING: Use of undeclared Var goog.Uri/parse at line 127 src/valip/predicates.cljc

Oops. We immediately got a couple of warnings. The first says the CLJS compiler was not able to find the goog.Uri namespace. The second warning says that its parse symbol it is undefined.

Uhm, pretty weird warnings.

Getting rid of warnings

To me, warnings are potential errors and I don't at all like to let them survive to eventually wake me up at night or while I'm on vacation. This to say that we're now going to get rid of them.

First, let's take a look at the predicates.cljc source file starting from its namespace declaration:

(ns valip.predicates
  "Predicates useful for validating input strings, such as ones from HTML forms."
  ...
  #?(:clj (:import (java.net URI URISyntaxException)
                   java.util.Hashtable
                   javax.naming.NamingException
                   javax.naming.directory.InitialDirContext)
     :cljs (:import goog.Uri)))

As you see, in the :cljs condition of the #? reader macro, the namespace declaration :import the Google Closure goog.Uri class as suggested by the corresponding paragraph in the CLJS wiki.

Now proceed to the url? definition:

#?(:clj  (...)
   :cljs (defn url?
           [s]
           (let [uri (-> s goog.Uri/parse)]
             (and (seq (.getScheme uri))
                  (seq (.getSchemeSpecificPart uri))
                  (re-find #"//" s)))))

In the thread first macro expression (-> s goog.Uri/parse), goog.Uri is used as a namespace while calling the parse static function. Moreover, by taking a look at the goog.Uri documentation, you'll note that the getSchemeSpecificPart getter does not exist and it's only available on the Java counterpart.

Considering that url validation is a very complicated topic and would necessitate a URL parser, I would be inclined to remove the current CLJ and CLJS definitions from valip.

That said, just as a matter of explanation on how to remove the above warnings, here is a possible solution:

#?(:clj (...)
   :cljs (defn url?
           [s]
           (let [uri (.parse goog.Uri (str s))]
             (and (seq (.getScheme uri))
                  ;(seq (.getSchemeSpecificPart uri)) ;; commented out
                  (re-find #"//" (str s))))))

As you already know, to invoke a JS method from an object/class we need to prefix it with the dot . interop special form (.method jsObj arg1 ... argn) as above.

But you can even use (. jsObj (method arg1 ... argn)), i.e. the syntactic sugar form:

#?(:clj (...)
   :cljs (defn url?
           [s]
           (let [uri (. goog.Uri (parse (str s)))]
             (and (seq (. uri (getScheme)))
                  ;; (seq (.getSchemeSpecificPart uri))
                  (re-find #"//" (str s))))))

It's not enough? You have a third form too: (jsObj.method arg1 ... argn)

#?(:clj (...)
   :cljs (defn url?
           [s]
           (let [uri (goog.Uri.parse (str s))]
             (and (seq (.getScheme uri))
                  ;; (seq (.getSchemeSpecificPart uri))
                  (re-find #"//" (str s))))))

Are you getting confused? So am I. Because there is even a forth form. It uses :require instead of :import in the namespace declaration and then uses the class as a namespace:

(ns valip.predicates
  "Predicates useful for validating input strings, such as ones from HTML forms."
  #?(:clj (:require [clojure.string :as str]
                    [clojure.edn :refer [read-string]]
                    [valip.predicates.def :refer [defpredicate]])
     :cljs (:require [clojure.string :as str]
                     [cljs.reader :refer [read-string]]
                     [goog.Uri :as guri])) ;; as a namespace
  #?(:clj (:refer-clojure :exclude [read-string])
     :cljs (:require-macros [valip.predicates.def :refer [defpredicate]]))
  #?(:clj (:import (java.net URI URISyntaxException)
                   java.util.Hashtable
                   javax.naming.NamingException
                   javax.naming.directory.InitialDirContext)))

#?(:clj (...)
   :cljs (defn url?
           [s]
           (let [uri (guri/parse (str s))]
             (and (seq (.getScheme uri))
                  ;; (seq (.getSchemeSpecificPart uri))
                  (re-find #"//" (str s))))))

We have to make a choice and we need to be coherent with it, so we don't disorient the readers of our code. But be prepared to read all the other three forms in the wild.

NOTE 8: Shane Kilkelly suggested me to use the third form, (goog.Uri.parse (str s)), because parse is a static method of the goog.Uri class. Instead, she would use the sugared form, like in (. uri (getScheme)), for instance methods. It makes sense to me.

So, make your choice and launch the CLJS compilation again:

boot cljs
Writing main.cljs.edn...
Compiling ClojureScript...
• main.js

Good shot. Note as in the above code we also covered the corner case of nil argument passed to url? as we already did for the CLJ definition of the same function.

CLJS compiler optimizations

Note that in the above boot cljs command we did not specify any options to the cljs task. As you already know from previous tutorials, this is because cljs uses :none as default.

Let's now see if valip compiles with whitespace, simple and advanced options as well:

boot cljs -O whitespace
Writing main.cljs.edn...
Compiling ClojureScript...
• main.js

boot cljs -O simple
Writing main.cljs.edn...
Compiling ClojureScript...
• main.js

boot cljs -O advanced
Writing main.cljs.edn...
Compiling ClojureScript...
• main.js

So far, so good. Let's move on to the CLJS test task.

cljs-tdd

We already ran the clj-tdd environment in a previous paragraph. Let's update the build.boot build file to be able to launch a cljs-tdd environment as well. As usual, to use a new boot task we have to add it to the :dependencies environment variable of the build.boot boot file and require its main namespace to make the task visible to boot itself.

(set-env!
 ...

 :dependencies '[...
                 [crisptrutski/boot-cljs-test "0.3.0"]
                 [doo "0.1.7"] ; used by boot-cljs-test
                 ])

(require '...
         '[crisptrutski.boot-cljs-test :refer [test-cljs]])
...

(deftask cljs-tdd
  "Launch a CLJ TDD Environment"
  []
  (comp
   (testing)
   (watch)
   (test-cljs :namespaces #{'valip.test.core 'valip.test.predicates})))

NOTE 9: We added the doo library to the dependencies because it is used by this version of boot-cljs-test. You could not add it, but you'll see the message Adding: ([doo "0.1.7"]) to :dependencies printed on the console when you run the cljs test.

You can now safely launch the cljs-tdd newly defined task as follows.

boot cljs-tdd
Adding: ([doo "0.1.7"]) to :dependencies

Starting file watcher (CTRL-C to quit)...

Compiling ClojureScript...
• cljs_test/generated_test_suite.js

;; ======================================================================
;; Testing with Phantom:


Testing valip.test.core

Testing valip.test.predicates

Ran 20 tests containing 86 assertions.
0 failures, 0 errors.
Elapsed time: 15.061 sec

Nice. But considering that we are dealing with a portable library, we'd like to run the CLJ and CLJS tests all together, as we already did for the modern-cljs project. That's very easy too. Substitute the previously defined clj-tdd and cljs-tdd tasks with the following tdd new task definition

(deftask tdd
  "Launch a CLJ TDD Environment"
  []
  (comp
   (testing)
   (watch)
   (test-cljs :namespaces #{'valip.test.core 'valip.test.predicates})
   (test :namespaces #{'valip.test.core 'valip.test.predicates})))

and launch it:

Starting file watcher (CTRL-C to quit)...

Compiling ClojureScript...
• cljs_test/generated_test_suite.js

;; ======================================================================
;; Testing with Phantom:


Testing valip.test.core

Testing valip.test.predicates

Ran 20 tests containing 86 assertions.
0 failures, 0 errors.

Testing valip.test.core

Testing valip.test.predicates

Ran 21 tests containing 90 assertions.
0 failures, 0 errors.
Elapsed time: 21.285 sec

Ok. We're done

What's next

We reached our first objective of making the valip library compliant with the Reader Conditionals extension. During the process, we were also able to solve few problems affecting the original valip library:

• the potential security issue created by the use of the clojure.core/read-string function;
• the uncovered corner cases;
• the bug in the url? predicate defined in the context of CLJS.

That said, we still have work to do, namely:

• locally install the updated valip library to test it in the context of a project;
• publish the valip library to clojars to make it available to whomever will be interested.

In this tutorial we're going to explain the first item only. We'll deal with publishing in a further tutorial.

Locally install valip

To quickly finish with this tutorial, we're going to locally install the updated version of valip by using the lein install task.

First we have to update the project.clj build file as follows:

(defproject org.clojars.magomimmo/valip "0.4.0-SNAPSHOT"
  :description "Functional validation library for Clojure and ClojureScript.
                Forked from https://github.com/cemerick/valip"
  :url "http://github.com/magomimmo/valip"
  :dependencies [[org.clojure/clojure "1.7.0"]]
  :clean-targets ^{:protect false} ["resources" "dev-resources" :target-path])

Note that I changed the groupId/artifactID identifier from com.cemerick/valip "0.3.2" to org.clojars.magomimmo/valip "0.4.0-SNAPSHOT". In a later tutorial I'll be more detailed about artifact identifier. Note also that in the above identifier you should substitute magomimmo with your github name.

NOTE 10: I also added the :clean-targets directive of lein.

Now locally install the updated valip library as follows:

cd /path/to/valip
lein install

The lein install task generates the org.clojars.<your_github_name>/valip "0.4.0-SNAPSHOT" artifact in the target directory:

tree target
target
├── classes
│   └── META-INF
│       └── maven
│           └── org.clojars.magomimmo
│               └── valip
│                   └── pom.properties
├── stale
│   └── extract-native.dependencies
└── valip-0.4.0-SNAPSHOT.jar

6 directories, 3 files

and then it locally installs the artifact itself in your local maven repository, overwriting any that wwere already installed:

tree ~/.m2/repository/org/clojars/<your_github_name>/valip
├── 0.4.0-SNAPSHOT
│   ├── _maven.repositories
│   ├── maven-metadata-local.xml
│   ├── valip-0.4.0-SNAPSHOT.jar
│   └── valip-0.4.0-SNAPSHOT.pom
└── maven-metadata-local.xml

1 directory, 5 files

Test valip in a project context

You are now ready to test the portable valip validation library in the context of the modern-cljs project.

First, clone the modern-cljs project in a temporary directory and checkout the latest tutorial branch as follows:

cd /path/to/tmp
git clone https://github.com/magomimmo/modern-cljs.git
cd modern-cljs
git checkout se-tutorial-18

Then edit the build.boot file by substituting the valip dependency with the new updated version:

(set-env!
 ...

 :dependencies '[
                 ...
                 [org.clojars.<your_github_name>/valip "0.4.0-SNAPSHOT"]
                 ...
                 ])

Start TDD

Start the TDD environment

boot tdd
...
Elapsed time: 26.573 sec

and visit the Shopping Calculator URL to play with the Shopping Calculator. Everything should still work as at the end of the Tutorial 18.

You can now stop the boot process.

Next Step - Tutorial 20 House Keeping

In the next tutorial will guide you step by step in publishing the updated version of valip using boot to the notorious clojars community repository.

License

Copyright © Mimmo Cosenza, 2012-15. Released under the Eclipse Public License, the same as Clojure.