A daemon written in V (vlang/veb), designed and intended to be run as a microservice,
implementing a special Customers API prototype with a smart yet simplified data scheme
Rationale: This project is a direct V port of the earlier developed Customers API Lite microservice prototype, written in Java using Spring Boot framework, and tailored to be run as a microservice in a Docker container. The following description of the underlying architecture and logics has been taken from here almost as is, without any principal modifications or adjustment.
This repo is dedicated to develop a microservice that implements a prototype of REST API service for ordinary Customers operations like adding/retrieving a Customer to/from the database, also doing the same ops with Contacts (phone or email) which belong to a Customer account.
The data scheme chosen is very simplified and consisted of only three SQL database tables, but that's quite sufficient because the service operates on only two entities: a Customer and a Contact (phone or email). And a set of these operations is limited to the following ones:
- Create a new customer (put customer data to the database).
- Create a new contact for a given customer (put a contact regarding a given customer to the database).
- Retrieve from the database and list all customer profiles.
- Retrieve profile details for a given customer from the database.
- Retrieve from the database and list all contacts associated with a given customer.
- Retrieve from the database and list all contacts of a given type associated with a given customer.
As it is clearly seen, there are no mutating, usually expected operations like update or delete an entity and that's made intentionally.
The microservice incorporates the SQLite database as its persistent store. It is located in the data/db/ directory as an XZ-compressed database file with minimal initial data — actually having two Customers and by six Contacts for each Customer. The database file is automatically decompressed during build process of the microservice and ready to use as is even when containerized with Docker.
Generally speaking, this project might be explored as a PoC (proof of concept) on how to amalgamate V REST API service backed by SQLite database, running standalone as a conventional daemon in host or VM environment, or in a containerized form as usually widely adopted nowadays.
Surely, one may consider this project to be suitable for a wide variety of applied areas and may use this prototype as: (1) a template for building similar microservices, (2) for evolving it to make something more universal, or (3) to simply explore it and take out some snippets and techniques from it for educational purposes, etc.
The microservice might be built and run successfully under Ubuntu Server (Ubuntu 24.04.2 LTS x86-64) and Arch Linux (both proven). — First install the necessary dependencies (build-essential, tcc, libsqlite3-dev, docker.io):
- In Ubuntu Server:
$ sudo apt-get update && \
sudo apt-get install build-essential tcc libsqlite3-dev docker.io -y
...
- In Arch Linux:
$ sudo pacman -Syu base-devel tcc sqlite docker
...
The V distribution can be installed differently for these Linux distros:
- In Ubuntu Server:
$ curl -LOk https://github.com/vlang/v/releases/latest/download/v_linux.zip
...
$
$ unzip v_linux.zip
...
Then it needs to add V to the PATH environment variable to make it accessible system-wide — edit the .profile config so that it will contain reference to the v/ directory, something like the following (and do relogin after that):
$ cat .profile
...
PATH="$HOME/bin:$HOME/.local/bin:$HOME/v:$PATH"
...
- In Arch Linux — from the AUR (Arch User Repository) since it is not yet added to the official Arch Linux repositories. For that to be done, simply download a snapshot of the V AUR-package, unpack it and do build/install it system-wide:
$ mkdir -p aur/build && cd aur/build/
$ curl -LOk https://aur.archlinux.org/cgit/aur.git/snapshot/vlang.tar.gz
...
$
$ tar -xvf vlang.tar.gz
...
$
$ cd vlang/ && makepkg -sirc
...
Then V can be invoked from anywhere just like system default C compiler:
$ v --version
V 0.4.9 a59ebea
Since V is still in beta state and changing continuously, this project is currently developing using the version (and the last build commit) of V given above, from 3rd of March, 2025.
The microservice is utilizing a third-party module vseryakov.syslog to be able to log messages to the Unix syslog facility, so it needs to install this module prior building the microservice:
$ v install vseryakov.syslog
Scanning `vseryakov.syslog`...
Installing `vseryakov.syslog`...
Installed `vseryakov.syslog` in ~/.vmodules/vseryakov/syslog .
Build the microservice using the V frontend:
$ if [ ! -d bin ]; then \
mkdir bin; \
fi && \
v -prod -o bin/api-lited . && \
if [ -f data/db/customers-api-lite.db.xz ]; then \
unxz data/db/customers-api-lite.db.xz; \
fi
Or build the microservice using GNU Make (optional, but for convenience — it covers the same V frontend build workflow under the hood):
$ make clean
...
$ make all # <== Building the daemon.
...
Build a Docker image for the microservice:
$ # Pull the Ubuntu LTS image first, if not already there:
$ sudo docker pull ubuntu:latest
...
$ # Then build the microservice image:
$ sudo docker build -tcustomersapi/api-lite-v .
...
Run the microservice using its executable directly, built previously by the V frontend or GNU Make's all target:
$ ./bin/api-lited; echo $?
...
To run the microservice as a true daemon, i.e. in the background, redirecting all the console output to /dev/null, the following form of invocation of its executable can be used:
$ ./bin/api-lited > /dev/null 2>&1 &
...
Note: This will suppress all the console output only; logging to a logfile and to the Unix syslog will remain unchanged.
Run a Docker image of the microservice, deleting all stopped containers prior to that (if any):
$ sudo docker rm `sudo docker ps -aq`; \
export PORT=8765 && sudo docker run -dp${PORT}:${PORT} --name api-lite-v customersapi/api-lite-v; echo $?
...
The following is not necessary but might be considered somewhat interesting — to look up into the running container, and check out that the microservice's daemon executable, config, logfile, and accompanied SQLite database are at their expected places and in effect:
$ sudo docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
<container_id> customersapi/api-lite-v "bin/api-lited" About a minute ago Up About a minute 0.0.0.0:8765->8765/tcp, :::8765->8765/tcp api-lite-v
$
$ sudo docker exec -it api-lite-v bash; echo $?
daemon@<container_id>:/var/tmp/api-lite$
daemon@<container_id>:/var/tmp/api-lite$ uname -a
Linux <container_id> 6.8.0-53-generic #55-Ubuntu SMP PREEMPT_DYNAMIC Fri Jan 17 15:37:52 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
daemon@<container_id>:/var/tmp/api-lite$
daemon@<container_id>:/var/tmp/api-lite$ ls -al
total 36
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:50 .
drwxrwxrwt 1 root root 4096 Mar 7 19:20 ..
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:20 bin
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:20 data
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:20 etc
drwxr-xr-x 2 daemon daemon 4096 Mar 7 19:50 log_
daemon@<container_id>:/var/tmp/api-lite$
daemon@<container_id>:/var/tmp/api-lite$ ls -al bin/ data/db/ etc/ log_/
bin/:
total 1244
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:20 .
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:50 ..
-rwxrwxr-x 1 daemon daemon 1258216 Mar 7 19:10 api-lited
data/db/:
total 40
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:20 .
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:20 ..
-rw-rw-r-- 1 daemon daemon 24576 Mar 7 19:10 customers-api-lite.db
etc/:
total 16
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:20 .
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:50 ..
-rw-rw-r-- 1 daemon daemon 797 Mar 7 19:10 settings.conf
log_/:
total 16
drwxr-xr-x 2 daemon daemon 4096 Mar 7 19:50 .
drwxr-xr-x 1 daemon daemon 4096 Mar 7 19:50 ..
-rw-r--r-- 1 daemon daemon 176 Mar 7 19:50 customers-api-lite.log
daemon@<container_id>:/var/tmp/api-lite$
daemon@<container_id>:/var/tmp/api-lite$ ldd bin/api-lited
linux-vdso.so.1 (0x00007ffed47e1000)
libsqlite3.so.0 => /lib/x86_64-linux-gnu/libsqlite3.so.0 (0x00007546dfb91000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007546df97f000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007546df896000)
/lib64/ld-linux-x86-64.so.2 (0x00007546dfe5b000)
daemon@<container_id>:/var/tmp/api-lite$
daemon@<container_id>:/var/tmp/api-lite$ netstat -plunt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp6 0 0 :::8765 :::* LISTEN 1/bin/api-lited
daemon@<container_id>:/var/tmp/api-lite$
daemon@<container_id>:/var/tmp/api-lite$ ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
daemon 1 0.0 0.5 28068 9344 ? Ssl 19:50 0:00 bin/api-lited
daemon 8 0.0 0.2 4588 3840 pts/0 Ss 19:55 0:00 bash
daemon 25 0.0 0.2 7888 3968 pts/0 R+ 20:00 0:00 ps aux
daemon@<container_id>:/var/tmp/api-lite$
daemon@<container_id>:/var/tmp/api-lite$ exit # Or simply <Ctrl-D>.
exit
0
The microservice exposes six REST API endpoints to web clients. They are all intended to deal with customer entities and/or contact entities that belong to customer profiles. The following table displays their syntax:
| No. | Endpoint name | Request method and REST URI | Request body |
|---|---|---|---|
| 1 | Create customer | PUT /v1/customers |
{"name":"{customer_name}"} |
| 2 | Create contact | PUT /v1/customers/contacts |
{"customer_id":"{customer_id}","contact":"{customer_contact}"} |
| 3 | List customers | GET /v1/customers |
– |
| 4 | Retrieve customer | GET /v1/customers/{customer_id} |
– |
| 5 | List contacts for a given customer | GET /v1/customers/{customer_id}/contacts |
– |
| 6 | List contacts of a given type for a given customer | GET /v1/customers/{customer_id}/contacts/{contact_type} |
– |
- The
{customer_name}placeholder is a string — it usually means the full name given to a newly created customer. - The
{customer_id}placeholder is a decimal positive integer number, greater than0. - The
{customer_contact}placeholder is a string — it denotes a newly created customer contact (phone or email). - The
{contact_type}placeholder is a string and can take one of two possible values, case-insensitive:phoneoremail.
The following command-line snippets display the exact usage for these endpoints (the cURL utility is used as an example to access them)^:
- Create customer
$ curl -vXPUT http://localhost:8765/v1/customers \
-H 'content-type: application/json' \
-d '{"name":"Jamison Palmer"}'
...
> PUT /v1/customers HTTP/1.1
...
> content-type: application/json
> Content-Length: 25
...
< HTTP/1.1 201 Created
< Location: /v1/customers/3
< Content-Type: application/json
< Content-Length: 32
< Server: veb
...
{"id":3,"name":"Jamison Palmer"}
- Create contact
$ curl -vXPUT http://localhost:8765/v1/customers/contacts \
-H 'content-type: application/json' \
-d '{"customer_id":"3","contact":"+12197654320"}'
...
> PUT /v1/customers/contacts HTTP/1.1
...
> content-type: application/json
> Content-Length: 44
...
< HTTP/1.1 201 Created
< Location: /v1/customers/3/contacts/phone
< Content-Type: application/json
< Content-Length: 26
< Server: veb
...
{"contact":"+12197654320"}
Or create email contact:
$ curl -vXPUT http://localhost:8765/v1/customers/contacts \
-H 'content-type: application/json' \
-d '{"customer_id":"3","contact":"[email protected]"}'
...
> PUT /v1/customers/contacts HTTP/1.1
...
> content-type: application/json
> Content-Length: 58
...
< HTTP/1.1 201 Created
< Location: /v1/customers/3/contacts/email
< Content-Type: application/json
< Content-Length: 40
< Server: veb
...
{"contact":"[email protected]"}
- List customers
$ curl -v http://localhost:8765/v1/customers
...
> GET /v1/customers HTTP/1.1
...
< HTTP/1.1 200 OK
< Content-Type: application/json
< Content-Length: 136
< Server: veb
...
[{"id":1,"name":"Jammy Jellyfish"},{"id":2,"name":"Noble Numbat"},{"id":3,"name":"Jamison Palmer"},{"id":4,"name":"Sarah Kitteringham"}]
- Retrieve customer
$ curl -v http://localhost:8765/v1/customers/3
...
> GET /v1/customers/3 HTTP/1.1
...
< HTTP/1.1 200 OK
< Content-Type: application/json
< Content-Length: 32
< Server: veb
...
{"id":3,"name":"Jamison Palmer"}
- List contacts for a given customer
$ curl -v http://localhost:8765/v1/customers/3/contacts
...
> GET /v1/customers/3/contacts HTTP/1.1
...
< HTTP/1.1 200 OK
< Content-Type: application/json
< Content-Length: 186
< Server: veb
...
[{"contact":"+12197654320"},{"contact":"+12197654321"},{"contact":"+12197654322"},{"contact":"[email protected]"},{"contact":"[email protected]"},{"contact":"[email protected]"}]
- List contacts of a given type for a given customer
$ curl -v http://localhost:8765/v1/customers/3/contacts/phone
...
> GET /v1/customers/3/contacts/phone HTTP/1.1
...
< HTTP/1.1 200 OK
< Content-Type: application/json
< Content-Length: 82
< Server: veb
...
[{"contact":"+12197654320"},{"contact":"+12197654321"},{"contact":"+12197654322"}]
Or list email contacts:
$ curl -v http://localhost:8765/v1/customers/3/contacts/email
...
> GET /v1/customers/3/contacts/email HTTP/1.1
...
< HTTP/1.1 200 OK
< Content-Type: application/json
< Content-Length: 105
< Server: veb
...
[{"contact":"[email protected]"},{"contact":"[email protected]"},{"contact":"[email protected]"}]
^ The given names in customer accounts and in email contacts (in samples above) are for demonstrational purposes only. They have nothing common WRT any actual, ever really encountered names elsewhere.
The microservice has the ability to log messages to a logfile and to the Unix syslog facility. To enable debug logging, the debug.enabled setting in the microservice main config file etc/settings.conf should be set to true before starting up the microservice. When running under Ubuntu Server or Arch Linux (not in a Docker container), logs can be seen and analyzed in an ordinary fashion, by tailing the log_/customers-api-lite.log logfile:
$ tail -f log_/customers-api-lite.log
...
[2025-03-07][20:10:10] [DEBUG] [Customers API Lite]
[2025-03-07][20:10:10] [DEBUG] [sqlite.DB{ conn: 5885185ffea8 }]
[2025-03-07][20:10:10] [INFO ] Server started on port 8765
[2025-03-07][20:13:00] [DEBUG] [PUT]
[2025-03-07][20:13:00] [DEBUG] [Saturday Sunday]
[2025-03-07][20:13:00] [DEBUG] [5|Saturday Sunday]
[2025-03-07][20:15:00] [DEBUG] [PUT]
[2025-03-07][20:15:00] [DEBUG] customer_id=5
[2025-03-07][20:15:00] [DEBUG] [[email protected]]
[2025-03-07][20:15:00] [DEBUG] [email|[email protected]]
[2025-03-07][20:15:50] [DEBUG] [GET]
[2025-03-07][20:15:50] [DEBUG] customer_id=5
[2025-03-07][20:15:50] [DEBUG] [5|Saturday Sunday]
[2025-03-07][20:17:00] [DEBUG] [GET]
[2025-03-07][20:17:00] [DEBUG] customer_id=5 | contact_type=email
[2025-03-07][20:17:00] [DEBUG] [[email protected]]
Messages registered by the Unix system logger can be seen and analyzed using the journalctl utility:
$ journalctl -f
...
Mar 07 23:10:10 <hostname> api-lited[<pid>]: [Customers API Lite]
Mar 07 23:10:10 <hostname> api-lited[<pid>]: [sqlite.DB{ conn: 5885185ffea8 }]
Mar 07 23:10:10 <hostname> api-lited[<pid>]: Server started on port 8765
Mar 07 23:13:00 <hostname> api-lited[<pid>]: [PUT]
Mar 07 23:13:00 <hostname> api-lited[<pid>]: [Saturday Sunday]
Mar 07 23:13:00 <hostname> api-lited[<pid>]: [5|Saturday Sunday]
Mar 07 23:15:00 <hostname> api-lited[<pid>]: [PUT]
Mar 07 23:15:00 <hostname> api-lited[<pid>]: customer_id=5
Mar 07 23:15:00 <hostname> api-lited[<pid>]: [[email protected]]
Mar 07 23:15:00 <hostname> api-lited[<pid>]: [email|[email protected]]
Mar 07 23:15:50 <hostname> api-lited[<pid>]: [GET]
Mar 07 23:15:50 <hostname> api-lited[<pid>]: customer_id=5
Mar 07 23:15:50 <hostname> api-lited[<pid>]: [5|Saturday Sunday]
Mar 07 23:17:00 <hostname> api-lited[<pid>]: [GET]
Mar 07 23:17:00 <hostname> api-lited[<pid>]: customer_id=5 | contact_type=email
Mar 07 23:17:00 <hostname> api-lited[<pid>]: [[email protected]]
Mar 07 23:20:10 <hostname> api-lited[<pid>]: Server stopped
Inside the running container logs might be queried also by tailing the log_/customers-api-lite.log logfile:
daemon@<container_id>:/var/tmp/api-lite$ tail -f log_/customers-api-lite.log
[2025-03-07][20:40:10] [DEBUG] [Customers API Lite]
[2025-03-07][20:40:10] [DEBUG] [sqlite.DB{ conn: 5c709503ad88 }]
[2025-03-07][20:40:10] [INFO ] Server started on port 8765
[2025-03-07][20:45:00] [DEBUG] [PUT]
[2025-03-07][20:45:00] [DEBUG] [Saturday Sunday]
[2025-03-07][20:45:00] [DEBUG] [5|Saturday Sunday]
[2025-03-07][20:47:00] [DEBUG] [PUT]
[2025-03-07][20:47:00] [DEBUG] customer_id=5
[2025-03-07][20:47:00] [DEBUG] [[email protected]]
[2025-03-07][20:47:00] [DEBUG] [email|[email protected]]
[2025-03-07][20:49:00] [DEBUG] [GET]
[2025-03-07][20:49:00] [DEBUG] customer_id=5
[2025-03-07][20:49:00] [DEBUG] [5|Saturday Sunday]
[2025-03-07][20:49:30] [DEBUG] [GET]
[2025-03-07][20:49:30] [DEBUG] customer_id=5 | contact_type=email
[2025-03-07][20:49:30] [DEBUG] [[email protected]]
And of course, Docker itself gives the possibility to read log messages by using the corresponding command for that:
$ sudo docker logs -f api-lite-v
[2025-03-07][20:40:10] [DEBUG] [Customers API Lite]
[2025-03-07][20:40:10] [DEBUG] [sqlite.DB{ conn: 5c709503ad88 }]
[2025-03-07][20:40:10] [INFO ] Server started on port 8765
[2025-03-07][20:45:00] [DEBUG] [PUT]
[2025-03-07][20:45:00] [DEBUG] [Saturday Sunday]
[2025-03-07][20:45:00] [DEBUG] [5|Saturday Sunday]
[2025-03-07][20:47:00] [DEBUG] [PUT]
[2025-03-07][20:47:00] [DEBUG] customer_id=5
[2025-03-07][20:47:00] [DEBUG] [[email protected]]
[2025-03-07][20:47:00] [DEBUG] [email|[email protected]]
[2025-03-07][20:49:00] [DEBUG] [GET]
[2025-03-07][20:49:00] [DEBUG] customer_id=5
[2025-03-07][20:49:00] [DEBUG] [5|Saturday Sunday]
[2025-03-07][20:49:30] [DEBUG] [GET]
[2025-03-07][20:49:30] [DEBUG] customer_id=5 | contact_type=email
[2025-03-07][20:49:30] [DEBUG] [[email protected]]
Server stopped
When the URI path or request body passed in an incoming request contains inappropriate input, the microservice will respond with the HTTP 400 Bad Request status code, including a specific response body in JSON representation which may describe a possible cause of underlying client error, like the following:
$ curl http://localhost:8765/v1/customers/=qwerty4838=-i-.--089asdf..nj524987
{"error":"HTTP 400 Bad Request: Request is malformed. Please check your inputs."}
$
$ curl http://localhost:8765/v1/customers/3..,,7/contacts
{"error":"HTTP 400 Bad Request: Request is malformed. Please check your inputs."}
$
$ curl http://localhost:8765/v1/customers/--089asdf../contacts/email
{"error":"HTTP 400 Bad Request: Request is malformed. Please check your inputs."}
$
$ curl -XPUT http://localhost:8765/v1/customers/contacts \
-H 'content-type: application/json' \
-d '{"customer_id":"3","contact":"12197654320--089asdf../nj524987"}'
{"error":"HTTP 400 Bad Request: Request is malformed. Please check your inputs."}