go 42 lines · 7 steps

Validated signup handler in Gin

A Gin endpoint that binds JSON, returns precise validation errors, and maps store failures to the right HTTP status.

Explained by highlit
Gin Intermediate request validation error handling http status codes struct tags
1package handlers
2 
3type SignupRequest struct {
4 Email string `json:"email" binding:"required,email"`
5 Password string `json:"password" binding:"required,min=8,max=72"`
6 ConfirmPassword string `json:"confirm_password" binding:"required,eqfield=Password"`
7 DisplayName string `json:"display_name" binding:"required,min=2,max=50"`
8 AcceptTerms bool `json:"accept_terms" binding:"required"`
9}
10 
11func (h *AuthHandler) Signup(c *gin.Context) {
12 var req SignupRequest
13 if err := c.ShouldBindJSON(&req); err != nil {
14 var ve validator.ValidationErrors
15 if errors.As(err, &ve) {
16 fields := make(map[string]string, len(ve))
17 for _, fe := range ve {
18 fields[fe.Field()] = fe.Tag()
19 }
20 c.JSON(http.StatusBadRequest, gin.H{"error": "validation_failed", "fields": fields})
21 return
22 }
23 c.JSON(http.StatusBadRequest, gin.H{"error": "invalid request body"})
24 return
25 }
26 
27 user, err := h.users.Create(c.Request.Context(), req.Email, req.Password, req.DisplayName)
28 if errors.Is(err, store.ErrEmailTaken) {
29 c.JSON(http.StatusConflict, gin.H{"error": "email already registered"})
30 return
31 }
32 if err != nil {
33 c.JSON(http.StatusInternalServerError, gin.H{"error": "could not create account"})
34 return
35 }
36 
37 c.JSON(http.StatusCreated, gin.H{
38 "id": user.ID,
39 "email": user.Email,
40 "display_name": user.DisplayName,
41 })
42}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Declarative `binding` tags push input validation out of handler logic and into the struct definition.
  2. 2Inspecting error types with `errors.As` and `errors.Is` lets one handler return distinct responses for distinct failures.
  3. 3Returning a curated response struct keeps internal fields like password hashes from leaking to clients.

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