PaymentsAPI

PaymentsAPI provides a simple payments RESTful API based on HTTP server implemented in Go (and gokit.io) that deals with Json format files to provide CRUD functionality against a Postgresql database. I used Gokit to help in separating implementation concerns by employing an onion layered model, where at the very core we have our use cases or business domain (source code dependencies can only point inward) and then wrapping that with other functionality layers.

Here are the main requirements on which the design is based:

• Fetching a single payment resource
• Creating, updating and deleting a payment resource
• Listing a collection of payment resources (here is what a list of payments might look like )
• Persisting resource state (to a database)

Design

The prototype can arguably be devided in the following components:

• The HTTP server and router. This is where the HTTP server is launched and managed and the routing for the various endpoints is provided.

• The gokit wrapper. Gokit is used in order to implement a decorator pattern where concerns such as logging, monitoring, transport, circuit breaking are separated and do not introduce any dependencies in the core functionality code.

• The core Payments Service functionality This is where the core logic resides. The CRUD functionality and database model are managed and implemented at this level.

• The Postgres database layer that employs Gorm to talk to Postgres Gorm is used to facilitate the HTTP server's interaction with the Postgresql database. Since this is a fin-tech application where a delicate balance between data integrity and reliability on one hand and high performance and scalability on the other, needs to be achieved the design decision was to employ a typical sql-type database (for structured data) such as Postgres as it also guarantees ACID operations.

A few opensource frameworks and libraries were used in the implementation of this project:

• Gokit - separation of concerns for designing microservices
• Gorm - layer that facilitates interaction with the DB from Go
• Gorilla/Mux - for http routing
• Viper - for reading configuration files
• A few libraries dedicated to testing scenarios such as Assert, Mock and GoMocket.

More details about design choices can be found in the design doc.

cUrl commands to use as client

This design did not address implementing a client to run against the API. In development cUrl commands were used to run against the server as can be seen below:

• View payments:

$ curl "http://localhost:8080/v1/payments/"

[]

• Add a payment based on the payment1.json file:

$ curl -X POST --data-binary @payment1.json "http://localhost:8080/v1/payments/"

{"created_id":"2e1f6c5d-3965-489e-a156-6f0e7d482c9e"}

• List payment with id = 2e1f6c5d-3965-489e-a156-6f0e7d482c9e:

curl "http://localhost:8080/v1/payments/2e1f6c5d-3965-489e-a156-6f0e7d482c9e"

{"id":"2e1f6c5d-3965-489e-a156-6f0e7d482c9e","type":"Payment","version":0,"organisation_id":"743d5b63-8e6f-432e-a8fa-c5d8d2ee5fcb","attributes":{"amount":"130.21","beneficiary_party":{"account_number":"31926819","bank_id":"403000","bank_id_code":"GBDSC","account_name":"W Owens","account_number_code":"BBAN","address":"1 The Beneficiary Localtown SE2","name":"Wilfred Jeremiah Owens","account_type":0},"charges_information":{"bearer_code":"SHAR","sender_charges":[{"amount":"5.00","currency":"GBP"},{"amount":"10.00","currency":"USD"}],"receiver_charges_amount":"1.00","receiver_charges_currency":"USD"},"currency":"GBP","debtor_party":{"account_number":"GB29XABC10161234567801","bank_id":"203301","bank_id_code":"GBDSC","account_name":"EJ Brown Black","account_number_code":"IBAN","address":"10 Debtor Crescent Sourcetown NE1","name":"Emelia Jane Brown"},"end_to_end_reference":"Wil piano Jan","fx":{"contract_reference":"FX123","exchange_rate":"2.00000","original_amount":"200.42","original_currency":"USD"},"numeric_reference":"1002001","payment_id":"123456789012345678","payment_purpose":"Paying for goods/services","payment_scheme":"FPS","payment_type":"Credit","processing_date":"2017-01-18","reference":"Payment for Em's piano lessons","scheme_payment_sub_type":"InternetBanking","scheme_payment_type":"ImmediatePayment","sponsor_party":{"account_number":"56781234","bank_id":"123123","bank_id_code":"GBDSC"}}}

• Update payment with id: 2e1f6c5d-3965-489e-a156-6f0e7d482c9e, based on the payment information from payment0.json

$ curl -X PUT --data-binary @payment0.json "http://localhost:8080/v1/payments/2e1f6c5d-3965-489e-a156-6f0e7d482c9e" 

{"updated_id":"2e1f6c5d-3965-489e-a156-6f0e7d482c9e"}

• List payment with id = 2e1f6c5d-3965-489e-a156-6f0e7d482c9e to see that information has been updated:

$ curl "http://localhost:8080/v1/payment/2e1f6c5d-3965-489e-a156-6f0e7d482c9e"

{"id":"2e1f6c5d-3965-489e-a156-6f0e7d482c9e","type":"Payment","version":0,"organisation_id":"743d5b63-8e6f-432e-a8fa-c5d8d2ee5fcb","attributes":{"amount":"100.21","beneficiary_party":{"account_number":"31926819","bank_id":"403000","bank_id_code":"GBDSC","account_name":"W Owens","account_number_code":"BBAN","address":"1 The Beneficiary Localtown SE2","name":"Wilfred Jeremiah Owens","account_type":0},"charges_information":{"bearer_code":"SHAR","sender_charges":[{"amount":"5.00","currency":"GBP"},{"amount":"10.00","currency":"USD"}],"receiver_charges_amount":"1.00","receiver_charges_currency":"USD"},"currency":"GBP","debtor_party":{"account_number":"GB29XABC10161234567801","bank_id":"203301","bank_id_code":"GBDSC","account_name":"EJ Brown Black","account_number_code":"IBAN","address":"10 Debtor Crescent Sourcetown NE1","name":"Emelia Jane Brown"},"end_to_end_reference":"Wil piano Jan","fx":{"contract_reference":"FX123","exchange_rate":"2.00000","original_amount":"200.42","original_currency":"USD"},"numeric_reference":"1002001","payment_id":"123456789012345678","payment_purpose":"Paying for goods/services","payment_scheme":"FPS","payment_type":"Credit","processing_date":"2017-01-18","reference":"Payment for Em's piano lessons","scheme_payment_sub_type":"InternetBanking","scheme_payment_type":"ImmediatePayment","sponsor_party":{"account_number":"56781234","bank_id":"123123","bank_id_code":"GBDSC"}}}

• Add a new payment based on information contained in payment0.json

$ curl -X POST --data-binary @payment1.json "http://localhost:8080/v1/payments/"

{"created_id":"d0f2bc35-7778-4e0a-a285-0618545c438f"}

• List all payments to see that the newly created payment (id = d0f2bc35-7778-4e0a-a285-0618545c438f) has been added to the payments list

$ curl "http://localhost:8080/v1/payments/"

[{"id":"2e1f6c5d-3965-489e-a156-6f0e7d482c9e","type":"Payment","version":0,"organisation_id":"743d5b63-8e6f-432e-a8fa-c5d8d2ee5fcb","attributes":{"amount":"100.21","beneficiary_party":{"account_number":"31926819","bank_id":"403000","bank_id_code":"GBDSC","account_name":"W Owens","account_number_code":"BBAN","address":"1 The Beneficiary Localtown SE2","name":"Wilfred Jeremiah Owens","account_type":0},"charges_information":{"bearer_code":"SHAR","sender_charges":[{"amount":"5.00","currency":"GBP"},{"amount":"10.00","currency":"USD"}],"receiver_charges_amount":"1.00","receiver_charges_currency":"USD"},"currency":"GBP","debtor_party":{"account_number":"GB29XABC10161234567801","bank_id":"203301","bank_id_code":"GBDSC","account_name":"EJ Brown Black","account_number_code":"IBAN","address":"10 Debtor Crescent Sourcetown NE1","name":"Emelia Jane Brown"},"end_to_end_reference":"Wil piano Jan","fx":{"contract_reference":"FX123","exchange_rate":"2.00000","original_amount":"200.42","original_currency":"USD"},"numeric_reference":"1002001","payment_id":"123456789012345678","payment_purpose":"Paying for goods/services","payment_scheme":"FPS","payment_type":"Credit","processing_date":"2017-01-18","reference":"Payment for Em's piano lessons","scheme_payment_sub_type":"InternetBanking","scheme_payment_type":"ImmediatePayment","sponsor_party":{"account_number":"56781234","bank_id":"123123","bank_id_code":"GBDSC"}}},
{"id":"d0f2bc35-7778-4e0a-a285-0618545c438f","type":"Payment","version":0,"organisation_id":"743d5b63-8e6f-432e-a8fa-c5d8d2ee5fcb","attributes":{"amount":"130.21","beneficiary_party":{"account_number":"31926819","bank_id":"403000","bank_id_code":"GBDSC","account_name":"W Owens","account_number_code":"BBAN","address":"1 The Beneficiary Localtown SE2","name":"Wilfred Jeremiah Owens","account_type":0},"charges_information":{"bearer_code":"SHAR","sender_charges":[{"amount":"5.00","currency":"GBP"},{"amount":"10.00","currency":"USD"}],"receiver_charges_amount":"1.00","receiver_charges_currency":"USD"},"currency":"GBP","debtor_party":{"account_number":"GB29XABC10161234567801","bank_id":"203301","bank_id_code":"GBDSC","account_name":"EJ Brown Black","account_number_code":"IBAN","address":"10 Debtor Crescent Sourcetown NE1","name":"Emelia Jane Brown"},"end_to_end_reference":"Wil piano Jan","fx":{"contract_reference":"FX123","exchange_rate":"2.00000","original_amount":"200.42","original_currency":"USD"},"numeric_reference":"1002001","payment_id":"123456789012345678","payment_purpose":"Paying for goods/services","payment_scheme":"FPS","payment_type":"Credit","processing_date":"2017-01-18","reference":"Payment for Em's piano lessons","scheme_payment_sub_type":"InternetBanking","scheme_payment_type":"ImmediatePayment","sponsor_party":{"account_number":"56781234","bank_id":"123123","bank_id_code":"GBDSC"}}}]

• Delete payment with id = d0f2bc35-7778-4e0a-a285-0618545c438f

$ curl -X DELETE "http://localhost:8080/v1/payments/d0f2bc35-7778-4e0a-a285-0618545c438f"

{"DeletedAt":"2019-04-22T11:45:26.089166Z"}

• List all payments to visually check that the payment with id = d0f2bc35-7778-4e0a-a285-0618545c438f is no longer in the payments list

$ curl "http://localhost:8080/v1/payments/"

[{"id":"2e1f6c5d-3965-489e-a156-6f0e7d482c9e","type":"Payment","version":0,"organisation_id":"743d5b63-8e6f-432e-a8fa-c5d8d2ee5fcb","attributes":{"amount":"100.21","beneficiary_party":{"account_number":"31926819","bank_id":"403000","bank_id_code":"GBDSC","account_name":"W Owens","account_number_code":"BBAN","address":"1 The Beneficiary Localtown SE2","name":"Wilfred Jeremiah Owens","account_type":0},"charges_information":{"bearer_code":"SHAR","sender_charges":[{"amount":"5.00","currency":"GBP"},{"amount":"10.00","currency":"USD"}],"receiver_charges_amount":"1.00","receiver_charges_currency":"USD"},"currency":"GBP","debtor_party":{"account_number":"GB29XABC10161234567801","bank_id":"203301","bank_id_code":"GBDSC","account_name":"EJ Brown Black","account_number_code":"IBAN","address":"10 Debtor Crescent Sourcetown NE1","name":"Emelia Jane Brown"},"end_to_end_reference":"Wil piano Jan","fx":{"contract_reference":"FX123","exchange_rate":"2.00000","original_amount":"200.42","original_currency":"USD"},"numeric_reference":"1002001","payment_id":"123456789012345678","payment_purpose":"Paying for goods/services","payment_scheme":"FPS","payment_type":"Credit","processing_date":"2017-01-18","reference":"Payment for Em's piano lessons","scheme_payment_sub_type":"InternetBanking","scheme_payment_type":"ImmediatePayment","sponsor_party":{"account_number":"56781234","bank_id":"123123","bank_id_code":"GBDSC"}}}]

In the above examples I have used the payment0.json and payment1.json files from the /cmd folder.

Get started with docker

Get the source code:

$ go get -u github.com/vstoianovici/paymentsapi

Build the environment from the docker-compose.yml file in the root (gowebapp and postgresdb will be deployed):

$ docker-compose up -d

By making use of Gorm's automigrate feature the postgresdb will already have a database called Postgres that has the needed empty tables. A summary of the needed tables will look something like this:

At this point one could proceed to running the cUrl commands outlined above against the REST API stack.

Get started with building the Go binary and deploying a postgres DB

Get the source code:

$ go get -u github.com/vstoianovici/paymentsapi

Build the binary by running the following command in the root:

$ make build

If the build succeeds, the resulting binary named "paymentsAPI" should be found in the /cmd directory.

To build the Postgres db as a Docker container run these 2 commands:

docker build -t postgresdb -f ./Dockerfile_postgres .

followed by

docker run --rm --name postgresdb -e POSTGRES_PASSWORD=password -d -p 5432:5432 postgresdb

In case Postgres is installed in any other way other than the ones described above the user needs to manually create a database named Postgres.

Additionally there is a postgresql.toml file contained in /config that is used for configuring the connection between the Go webapp and the Postgres db. The content is pretty self-explanatory:

DRIVER = "postgres"
HOST = "127.0.0.1"
PORT = 5432
USER = "postgres"
PASSWORD = "password"
DBNAME = "postgres"
SSLMODE = "disable"
Timeout = 5

Run the tests:

$ make test

Feel free to explore the Makefile available in the root directory.

Runtime

• Otherwise, once paymentsAPI is built and ready for runtime it can run (/cmd/paymentsAPI) without any parameters (default should be fine) but there is the option of passing in a different port or a different postgres.toml file (skip this step, if you are deploying with docker-compose, and continue to the curl commands bellow):

$ ./paymentsAPI -h
time=2019-04-22T16:29:07.861485Z tag=start msg="created logger"
Usage of ./paymentsAPI:
  -file string
        Path of postgresql config file to be parsed. (default "../config/postgresql.toml")
  -httptest.serve string
        if non-empty, httptest.NewServer serves on this address and blocks
  -port int
        Port on which the server will listen and serve. (default 8080)

• Once the server is running you can run the previously portrayed cUrl commands.

Build your own paymentsAPI

Anybody can use this resource as a library to create their own implementation of the paymentsAPI as long as they mimic what is being done in /cmd/main.go

For the future, a nice feature to implement would be a gRPC endpoint in addition to the Json over HTTP REST API so that the wallet can be a service in a microservice architecture solution.

Contribute

Contributions to this project are welcome, though please file an issue before starting work on anything major. The next step in the evolution of this product would be a gRPC Transport wrapper to allow for optimum inter-process communication

License

The MIT License (MIT) - see the LICENSE file for more details