Go CLI and HTTP API for subnet calculations. Includes a Dockerfile and supports deployment to Cloud Run.

• Live demo of the calculator: https://subnets.web.app

• Go 1.22+
• Optional: Docker (for container builds)
• Optional: gcloud CLI (for Cloud Run deploys)

• CLI (single calculation):

  • cd backend
  • go run . 192.168.1.10/26

• HTTP server (local):

  • cd backend
  • go run . serve :8080
  • Then: curl 'http://localhost:8080/api/subnet?cidr=192.168.1.10/26'

Server respects PORT env (e.g., PORT=8080 go run . serve). If a positional port is provided (e.g., :8080 or 8080), it overrides the env value.

• Endpoint: GET /api/subnet?cidr=<ip/prefix>
• Query params:
  • cidr (required): IPv4 CIDR like 192.168.1.10/26
• Response (JSON):
  • Subnet details: address, prefix, total, subnetMask, wildcardMask, network, firstHost, lastHost, broadcast, usableHosts
  • Lists of possible addresses: networks[], hosts[], broadcasts[] Example:

GET /api/subnet?cidr=192.168.1.10/26
{
  "address": "192.168.1.10",
  "prefix": 26,
  "total": 64,
  "subnetMask": "255.255.255.192",
  "wildcardMask": "0.0.0.63",
  "network": "192.168.1.0",
  "firstHost": "192.168.1.1",
  "lastHost": "192.168.1.62",
  "broadcast": "192.168.1.63",
  "usableHosts": 62,
  "networks": ["192.168.1.0", "192.168.1.64", "…"],
  "hosts": ["192.168.1.1 - 192.168.1.62", "…"],
  "broadcasts": ["192.168.1.63", "192.168.1.127", "…"]
}

Notes:

• Basic CORS is enabled (Access-Control-Allow-Origin: *).

Build a minimal image via multi-stage Dockerfile:

cd backend
docker build -t subnet-api .
docker run --rm -e PORT=8080 -p 8080:8080 subnet-api
# Test
curl 'http://localhost:8080/api/subnet?cidr=192.168.1.10/26'

The image uses a distroless runtime and reads the port from PORT.

Using an already built container image:

gcloud builds submit --tag gcr.io/<PROJECT_ID>/subnet-api ./backend
gcloud run deploy subnet-api \
  --image gcr.io/<PROJECT_ID>/subnet-api \
  --region us-central1 \
  --allow-unauthenticated

Source-based deploy (builds in Cloud Build):

gcloud run deploy subnet-api \
  --source ./backend \
  --region us-central1 \
  --allow-unauthenticated