koa-neo4j

koa-neo4j is a framework for creating RESTful web servers. It's been built on top of the widely adapted Koa library and the NoSQL graph database technology of Neo4j. koa-neo4j enables one to create web servers scalable both in terms of code complexity and horizontal growth in deployment.

Table of contents

1. Introduction
2. Install
3. Usage
   • Defining an API
   • Authentication
   • Lifecycle hooks
     • check lifecycle
     • preProcess lifecycle
     • execution lifecycle
     • postProcess lifecycle
     • postServe lifecycle
   • Procedures
4. License

Introduction

Choosing a NoSQL graph database for persistence is wise for a number of reasons. While Neo4j provides the DB infrastructure for such choice, applications using Neo4j normally conduct queries directly from the client side, which might not be the best option:

• Database is exposed to the client, unless some explicit security mechanism is in place; one can see the innards of the database by View page source
• There is no one server to rule them all, queries are strings, scattered around different clients (web, mobile, etc.)
• Third-party developers might not be familiar with Cypher

koa-neo4j addresses all of the above issues:

• Stands as a middle layer between clients and the database
• Gives structure to your server's logic in form of a file-based project; finally a home for Cypher! All of the clients can then talk to an instance of this server
• Converts Cypher files to REST routes, a cross-platform web standard that developers are familiar with, it does so on top of the widely-adapted koa server, ripe for further customization

In addition, it comes with goodies:

• Hassle-free authentication and non-opinionated user management, you describe (in Cypher) how your users and roles are stored, the framework provides authentication and role-based access management
• Lifecycle hooks, enabling one to tweak incoming and outgoing data based on one's needs, allowing utilisation of the full power of nodejs and javascript ecosystem in the process
• Procedures as a means for creating reusable blocks of backend code

Install

npm install koa-neo4j --save

Usage

To get started quickly you can clone koa-neo4j-starter-kit

var KoaNeo4jApp = require('koa-neo4j');

var app = new KoaNeo4jApp({
    // Neo4j config objects, mandatory
    neo4j: {
        boltUrl: 'bolt://localhost',
        user: 'neo4j',
        password: '<YOUR_NEO4J_PASSWORD>'
    },

    // Authentication config object, optional
    // authentication: {...} // explained below

    // APIs config object, optional (same effect could be achieved later by app.defineAPI)
    apis: [
        {
            method: 'GET',
            route: '/authors',
            cypherQueryFile: './cypher/authors.cyp'
        },
        {
            method: 'GET',
            route: '/articles/:skip/:limit',
            cypherQueryFile: './cypher/articles.cyp'
        }
    ],

    // Koa middlewares could be injected and will be loaded before api invoked,e.g:a koa static file serving middleware as following
    middleware:[convert(staticFile('./public'))]
});

app.listen(3000, function() {
    console.log('App listening on port 3000.');
});

Defining an API

An API is defined by at least three keys:

method, specifies the request type (GET|POST|PUT|DEL)

route, the path to this API (e.g. the first API defined in apis above becomes http://localhost:3000/authors)

cypherQueryFile, path to the corresponding .cyp file

Optionally you can specify roles whom can access this route with allowedRoles and also lifecycle hooks.

As an example:

app.defineAPI({
    // allowedRoles: ['admin', 'author']    // roles are case insensitive
    method: 'POST',
    route: '/create-article',
    cypherQueryFile: './cypher/create_article.cyp'
});

And then in ./cypher/create_article.cyp:

CREATE (a:Article {
    title: $title,
    author: $author,
    created_at: timestapm()
})
RETURN a

Cypher queries accept parameters via the $ syntax.

These parameters are matched by query parameters /articles?title=Hello&author=World or route parameters (e.g. if route was defined as /create-article/:author/:title then /create-article/World/Hello)

In addition, any data accompanied by the request will also be passed to the Cypher query, retaining the variable names, so for example:

curl --data "title=The%20Capital%20T%20Truth&author=David%20Foster%20Wallace" localhost:3000/create-article

becomes a POST request, {"title": "The Capital T Truth", "author": "David Foster Wallace"} will be passed to ./cypher/create_article.cyp which refers to these parameters as $title and $author

In case of encountering same variable names, priority is applied: request data > route params > query params

Authentication

Authentication is facilitated through JSON web token, all it takes to have authentication in your app is to supplement Authentication config object either with authentication key when initiating the app instance or in configureAuthentication method:

app.configureAuthentication({
    // route, mandatory.
    route: '/auth',

    // secret, mandatory. This is the key that JWT uses to encode objects, best practice is to use a
    // long and random password-like string
    secret: 'secret',

    // userCypherQueryFile, mandatory. This cypher query is invoked with `$username` and is expected to return
    // a single object at least containing two keys: `{id: <user_id>, password: <user_password_or_hash>}`
    // the returned `id` would later be passed to get roles of this user
    userCypherQueryFile: './cypher/user.cyp',

    // rolesCypherQueryFile, optional. Invoked with `$id` returned from userCypherQueryFile, this query is
    // expected to return a list of strings describing roles of this user, you can do all sorts of traversals
    // that cypher allows to generate this list. Defaults to labels of the node matching the id:
    // `MATCH (user) WHERE id(user) = $id RETURN {roles: labels(user)}`
    // rolesCypherQueryFile: './cypher/roles.cyp'
});

And your desired $username to user mapping in userCypherQueryFile:

// Takes $username and returns a user object with at least 'id' and 'password'
MATCH (author:Author)-[:HAS]->(account:UserAccount)
WHERE account.user_name = $username
RETURN {id: id(author), password: account.password_hash}

When authentication is configured, you can access it by sending a POST request to the route you specified. Pass a JSON object to e.g. /auth in the following form:

{
  "username": "<user_name>",
  "password": "<user_password_or_hash>",
  "remember": true
}

Note that if you don't set "remember": true, the generated token expires in an hour.

Returned object contains a token which should be supplemented as Authorization header in subsequent calls to routes that have allowedRoles protection.

In addition, a user object is returned that matches the object returned by userCypherQueryFile except for the password key, which is deleted (so that security won't be compromised should clients decide to save this object) and roles key, which is the object returned by rolesCypherQueryFile.

When a request to a route guarded by allowedRoles is received, the request either does not have an Authorization header set, in which case the server responds with a 401: Unauthorized error, or the Authorization header is present. In case of a valid header (not expired or manipulated), the request goes through and the user object would be attached to the Koa context and made available to lifecycle hooks as ctx.user.

Lifecycle hooks

A lifecycle hook is a single function or a group of functions invoked at a certain phase in request-to-response cycle. It helps with shaping the data according to one's needs. Further, the framework comes with a number of built-in hook functions, ready to be dropped in their corresponding lifecycle.

A hook function takes the form of a normal JavaScript function, with arguments consistent with the lifecycle in which it'd be deployed. If an array of functions is submitted for a lifecycle, each function in the array is executed, sequentially, and the returned object from the function would be passed as the first argument of the next function.

app.defineAPI({
    // ...
    preProcess: [
        function(params, ctx) {
            // do something with params and/or ctx
            return {modified: 'params'};
        },  //     ‾‾‾‾‾‾‾‾‾‾|‾‾‾‾‾‾‾‾‾
        //                   |
        //         ↓‾‾‾‾‾‾‾‾‾‾
        function(params, ctx) {
            params.again = 'modified';
            // params now is: {modified: 'params', again: 'modified'}
            return params;
        },  //     ‾‾|‾‾‾
        //           |
        //           ↓
        function(params, ctx) {
            params.and = 'again';
            // params now is: {modified: 'params', again: 'modified', and: 'again'}
            return params;
        },
        //      ... this can continue ...
    ],
    // ...
});

ProTip: if returned value in a hook function is a Promise or an array containing any Promises, first argument of the next function would be the resolved value or an array with all it's elements resolved, respectively.

check lifecycle

Hook function signature: (params[, ctx]) -> :boolean

This lifecycle is the first one that a request goes through. It is useful for scenarios where you want to check the parameters or the user before commencing. A false return value produces an error in check lifecycle error.

// Example:
app.defineAPI({
    // ...
    check: function(params, ctx) {
        // check user has enough money
        return params.amount < getBalance(ctx.user.id);
    },
    // ...
});

// Default:
check: function (params) {
  // Always passes
  return true;
}

check built-in hook functions: import/require from koa-neo4j/check (DOCS)

preProcess lifecycle

Hook function signature: (params[, ctx]) -> params

Using this lifecycle, one can adjust parameters before sending them to Cypher. Parsing strings is a usual suspect, the framework comes with many built-in parse functions for this lifecycle.

// Example:
var parseFloats = require('koa-neo4j/preprocess').parseFloats;

app.defineAPI({
    // ...
    preProcess: [ 
        // parse params.amount as float
        parseFloats('amount'),

        function(params) {
            // give 10% discount
            params.amount = params.amount * 0.9;
            return params;
        },
        // ...
    ],
    // ...
});

// Default:
preProcess: function (params) {
  // Returns `params` unchanged
  return params;
}

preProcess built-in hook functions: import/require from koa-neo4j/preprocess (DOCS)

execution lifecycle

Execution happens between preProcess and postProcess, takes params as input and generates result. Currently there are 4 types of execution, if all were present in an API or Procedure definition, priority is applied:

params.result > params.cypher > cypherQueryFile

ProTip: key would be consumed as a result of any params.<key> execution, meaning that the key reference in params would be deleted in subsequent references to params.

cypherQueryFile

Happens if a cypherQueryFile is supplied. Executes the Cypher query contained in the file, passing params along which Cypher can access with the $ syntax.

params.cypher

If you need string manipulation to create your Cypher query, you can do so in preProcess lifecycle by assigning params.cypher to your query. After all preProcess hook functions are executed, framework will see whether params.cypher is defined, and executes it if present. Except for primitive string, params.cypher may also be string array type which contains multiple cypher queries to execute.

params.result

params.result could be set to a value, a Promise or an array containing Promises. result would then be the value, the resolved value of the Promise or an array with all it's elements resolved, respectively. This is useful when one wants the result to come from procedures, since calling a procedure returns a promise:

// Example:
var someProcedure = app.createProcedure({
    // ...
});

app.defineAPI({
    // ...
    preProcess: [
        // ...
        function(params) {
            params.result = [];
            for (var i = 0; i < params.someArray.length; i++)
                params.result.push(someProcedure({someParameter: params.someArray[i]}));
            return params;
        }
    ],
    postProcess: [
        function(result) {
            // `result` is now an array containing resolved values of calls to someProcedure
            return result;
        }
    ]
});

postProcess lifecycle

Hook function signature: (result[, params, ctx]) -> result

This lifecycle takes the result from execution lifecycle and amends further changes to the result before sending it to the client. If params.cypher is array type assigned in execution lifecycle, result will also be an array contains execution results for each cypher query.

// Example:
var fetchOne = require('koa-neo4j/postprocess').fetchOne;

app.defineAPI({
    // ...
    postProcess: [
        fetchOne,
        function(result, params, ctx) {
            return {
                user: ctx.user,
                balance_after: params.balance - result
            };
        },
        // ...
    ],
    // ...
});

// Default:
postProcess: function (result) {
  // serves result of execution lifecycle, unchanged
  return result;
}

postProcess built-in hook functions: import/require from koa-neo4j/postprocess (DOCS)

postServe lifecycle

Hook function signature: (result[, params, ctx]) -> result

Semantics of postServe is identical to postProcess, except that postServe is invoked after the response of the request is sent (served). This lifecycle suits time consuming tasks that are internal to logic and can be carried out after the request is served.

// Default:
postServe: function (result) {
  // Doesn't do anything
  return result;
}

Procedures

Procedures share semantics with APIs, they are defined in the same way that an API is defined, except they don't accept method, route and allowedRoles. You can create idiomatic and reusable blocks of backend code using procedures and built-in lifecycle hook functions:

var parseIds = require('koa-neo4j/preprocess').parseIds;
var parseDates = require('koa-neo4j/preprocess').parseDates;

var logValues = require('koa-neo4j/debug').logValues;

var errorOnEmptyResult = require('koa-neo4j/postprocess').errorOnEmptyResult;
var fetchOne = require('koa-neo4j/postprocess').fetchOne;
var convertToPreProcess = require('koa-neo4j/postprocess').convertToPreProcess;

var articlesAfterDate = app.createProcedure({
    // Providing a name facilitates debugging
    name: 'articlesAfterDate',
    preProcess: [
        parseIds('author_id'),
        parseDates({'timestamp': 'date'}),
        logValues
    ],
    cypherQueryFile: './cypher/articles_after_date.cyp',
    postProcess: [
        logValues,
        errorOnEmptyResult('author not found'), // returns this message with a 404 http code
        fetchOne,
        convertToPreProcess('articles') // assigns params.articles to result of procedure
    ]
});

var blogsAfterDate = app.createProcedure({
    // ...
});

app.defineAPI({
    allowedRoles: ['admin'],
    route: '/author-activity/:author_id/:timestamp',
    preProcess: [
        articlesAfterDate,
        blogsAfterDate,
        function(params) {
            params.result = {
                // params.date is created by parseDates hook function in articlesAfterDate
                interval: `past ${new Date().getDate() - params.date.getDate()} days`,
                articles: params.articles,
                blogs: params.blogs
            };
            return params;
        }
    ]
})

ProTip: procedures created by app.createProcedure are callable and return a promise that resolves to result:

var someProcedure = app.createProcedure({
    // ...
});

someProcedure(params, ctx).then(function(result) {
    console.log(result);
});

Or if you can use async/await:

app.defineAPI({
    preProcess: [
        async params => {
            // ...
            params.someValue = await someProcedure({some: 'parameter'});
            return params;
        },
        // ...
    ],
    // ...
})

ProTip: a defineAPI block can reuse a procedure's body via the procedure key:

app.defineAPI({
    method: 'POST',
    route: '/some-api',
    procedure: someProcedure
});

License

MIT