Think of your backend as layers with different responsibilities:

HTTP request
   ↓
HANDLER      → HTTP things (JSON, status codes)
   ↓
SERVICE      → business meaning (rules, validations)
   ↓
REPOSITORY   →database talking (SQL)
   ↓
DATABASE

Now the golden rule :

❗ Errors move UPWARD

❗ Meaning is added as they move up

Let’s follow ONE request end-to-end

Example request

POST /websites
{
  "name": "Google",
  "url": "<https://google.com>"
}

1. Handler layer (entry point)

What the handler does (ONLY this):

• Parse HTTP request
• Call service
• Convert result into HTTP response

func(h *WebsiteHandler) CreateWebsite(c *gin.Context) {

Step 1: Parse JSON

var req dto.CreateWebsiteRequest

if err := c.ShouldBindJSON(&req); err !=nil {

• This error is HTTP-level
• It means “client sent bad JSON”

So the handler immediately responds:

c.JSON(http.StatusBadRequest, response.APIResponse{
    Success:false,
    Error:"invalid request body",
})
return