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.

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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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