httq

Middleware for bridging HTTP and AMQP

Installation

npm install httq

Prequisits

• RabbitMQ
• Familiarity with Rascal

Usage

Step 1 - Plug httq into an express app

var httq = require('httq')
var async = require('async')
var rascal = require('rascal')
var express = require('express')
var bodyParser = require('body-parser')
var config = require('./config.json')
 
var rascalConfig = rascal.withDefaultConfig(config.rascal)
 
rascal.createBroker(rascalConfig, function(err, broker) {
 
    if (err) bail(err)
 
    var app = express()
    app.use(bodyParser.json())
    httq.init(broker, config.httq.book_loan_v1, function(err, httqs) {
        if (err) bail(err)
        app.post('/api/library/v1/books/:isbn/loans', httqs.book_loan_v1)
        app.listen(3000)
    })
 
    console.log('Try: curl -H "Content-Type: application/json" -X POST http://localhost:3000/api/library/v1/books/978-0132350884/loans -d \'{"member": "6545345"}\'')
 
    function bail(err) {
        console.error(err.message)
        process.exit(1)
    }
})

Step 2 - Configure httq and rascal

{
    "httq": {
        "routes": {
            "book_loan_v1": {
                "methods": ["post"],
                "pattern": "/api/library/v1/books/:isbn/loans",
                "sequence": ["requestToTemplateVars", "requestPathToRoutingKey", "requestToMessage", "fireAndForget"],
                "warez": {
                    "requestPathToRoutingKey": {
                        "options": {
                            "method": {
                                "suffix": true,
                                "mapping": {
                                    "POST": "created"
                                }
                            }
                        }
                    },
                    "fireAndForget": {
                        "options": {
                            "publication": "p1"
                        }
                    }
                }
            }
        }
    },
    "rascal": {
        "vhosts": {
            "/": {
                "namespace": true,
                "exchanges": {
                    "e1": {}
                },
                "queues": {
                    "q1": {}
                },
                "bindings": {
                    "b1": {
                        "source": "e1",
                        "destination": "q1",
                        "bindingKey": "api.library.v1.#.loans.created"
                    }
                }
            }
        },
        "publications": {
            "p1": {
                "exchange": "e1"
            }
        },
        "subscriptions": {
            "s1": {
                "queue": "q1"
            }
        }
    }
}

Step 3 - Start the app and send it an HTTP request

$ node server.js &
$ curl -H "Content-Type: application/json" -X POST -d '{"member":"6545345"}' http://localhost:3000/api/library/v1/books/978-0132350884/loans
{"txid":"c09f94a4-f152-46d5-8266-39505bb446a1"}

Step 4 - Check your broker for the message.

It should look something like this:

{
  "fields": {
    "consumerTag": "amq.ctag-Nw13m2-6DntZKTS1PhK5gg",
    "deliveryTag": 1,
    "redelivered": false,
    "exchange": "e1",
    "routingKey": "api.library.v1.books.978-0132350884.loans.created"
  },
  "properties": {
    "contentType": "application/json",
    "headers": {
      "httq": {
        "method": "POST",
        "url": "/api/library/v1/books/978-0132350884/loans",
        "query": {},
        "headers": {
          "user-agent": "curl/7.30.0",
          "host": "localhost:3000",
          "accept": "*/*",
          "content-type": "application/json",
          "content-length": "20"
        },
        "params": {
          "isbn": "978-0132350884"
        }
      }
    },
    "deliveryMode": 2,
    "messageId": "c09f94a4-f152-46d5-8266-39505bb446a1"
  },
  "content": {
    "member": "6545345"
  }
}

Middleware

httq middleware needs to be initialised for each route in your express application, by passing httq.init with a broker, configuration, ctx (optional), and callback. The init method will build a chain of middleware in the order defined by the sequence attribute. If you need to pass paramters to a specific middleware then specifiy it in the warez block.

{
    "sequence": ["requestToTemplateVars", "requestPathToRoutingKey", "requestToMessage", "fireAndForget"],
    "warez": {
        "requestPathToRoutingKey": {
            "options": {
                "method": {
                    "suffix": true,
                    "mapping": {
                        "POST": "created"
                    }
                }
            }
        },
        "fireAndForget": {
            "options": {
                "publication": "p1"
            }
        }
    }
}

Each middleware in the chain should export a single function that expects the config, context and callback. It should return the a function with typical express middleware signature. If you want a middleware to appear twice just relist it in the sequence. If you want the two instances to have different parameters, give it a unique name and specify the 'type' parameter.

{
    "sequence": ["logStart", "logEnd"],
    "warez": {
        "logStart": {
            "type": "logger",
            "options": {
                "message": "start"
            }
        },
        "logEnd": {
            "type": "logger",
            "options": {
                "message": "end"
            }
        }
    }
}

module.exports = function(config, ctx, next) {
    // ...
    next(null, function(req, res, next) {
        // ...
    })
}

Provided Middleware

requestToTemplateVars

Extracts variables from the request and stores them in req.httq.templateVars, e.g.

{
    templateVars: {
        method: "POST",
        url: "/api/library/v1/books/978-0132350884/loans",
        params: {
            isbn: "978-0132350884"
        },
        headers: {
            user-agent: "curl/7.30.0",
            host: "localhost:3000",
            accept: "*/*",
            content-type: "application/json",
            content-length: "20"
        }
        query: {
        }
    }
}
These are typically usd when generating the routing key and message published to your AMQP broker.
 
#### requestToRoutingKey
Generates a routing key from the request by passing the templateVars through a hogan template. The routing key is stored in req.httq.message.routingKey
```json
{
    "requestToRoutingKey": {
        "options": {
            "template": "library.v2.books.loans.{{request.method}}"
        }
    }
}

You can map the request method to something more meaningful

{
    "requestToRoutingKey": {
        "options": {
            "template": "library.v2.books.loans.{{request.method}}"
            "method": {
                "mapping": {
                    "POST": "created"
                }
            }
        }
    }
}

requestPathToRoutingKey

Generates a routing key from the request by replacing slashes with full stops. The routing key is stored in req.httq.message.routingKey. No parameters are required but you may optionall include the request method.

{
    "requestPathToRoutingKey": {
        "options": {
            "method": {
                "prefix": true,
                "mapping": {
                    "POST": "created"
                }
            }
        }
    }
}

requestToMessage

Generates AMQP message headers and content from the request. This is stored in req.httq.message.headers and req.httq.message.content. You can see an example of the generated message in step 4.

requestToMessageContent

Generates AMQP message content from the request. A json document reprsenting the full request (url, params, headers, query parameters and body) is stored in req.httq.message.content

requestToSchemaUrl

Generates a schema url from the request by passing the templateVars through a hogan template. The routing key is stored in req.httq.message.schema

httpSourcedJsonValidator

Validates the message against a JSON schema downloaded using http. The validator uses tv4 and tv4-formats. The schema url must be set it req.httq.message.schema and will be downloaded and cached (along with any referenced schemas) in during the request flow. If a schema cannot be downloaded the middleware responds with 500. If validation succeeds the message will be decorated with an httq header giving the uri of the schema that the message was validated against. If validation fails, httq will respond with 400 'Bad Request' and a json document describing the errors, e.g.

[
    {
        "message": "Missing required property: id",
        "params": {
            "key": "id"
        },
        "code": 302,
        "dataPath": "",
        "schemaPath": "/required/0",
        "subErrors": null,
        "name": "ValidationError"
    },
    {
        "message": "Missing required property: type",
        "params": {
            "key": "type"
        },
        "code": 302,
        "dataPath": "",
        "schemaPath": "/required/1",
        "subErrors": null,
        "name": "ValidationError"
    }
]

s3SourcedJsonValidator

Validates the message against a JSON schema from S3. The validator uses tv4 and tv4-formats. The schema url must be set it req.httq.message.schema and will be downloaded and cached (along with any referenced schemas) in during the request flow. If a schema cannot be downloaded the middleware responds with 500. If validation succeeds the message will be decorated with an httq header giving the uri of the schema that the message was validated against. If validation fails, httq will respond with 400 'Bad Request' and a json document describing the errors as specified above.

The s3SourcedJsonValidator requires the following configuration

{
    "s3": {
        "bucket": "s3-bucket-name",
        "region": "aws-region"
    }
}

filesystemSourcedJsonValidator

Validates the message against a JSON schema from the file system. The validator uses tv4 and tv4-formats. The schema url must be set it req.httq.message.schema and will be loaded and cached (along with any referenced schemas) in during the request flow. If a schema cannot be read the middleware responds with 500. If validation succeeds the message will be decorated with an httq header giving the uri of the schema that the message was validated against. If validation fails, httq will respond with 400 'Bad Request' and a json document describing the errors as specified above.

fireAndForget

Publishes the AMQP message to a Rascal publication using the routing key defined in the context. If successful the middleware will return 202 "Accepted" and a transaction id corresponding to the message id

{"txid":"c09f94a4-f152-46d5-8266-39505bb446a1"}

Custom Middlware

You can override the httq middleware or add your own by initialising the ctx "warez" attribute, e.g.

var customFireAndForget = require('./lib/customFireAndForget')
var extraMiddleware = require('./lib/extraMiddleware')
 
httq.init(broker, config.httq.book_loan_v1, {
    warez: {
        fireAndForget: customFireAndForget,
        extraMiddleware: extraMiddleware
    }
}, function(err, httqs) {
    //...
})