go 47 lines · 7 steps

Handling multipart profile uploads in Gin

A Gin handler binds a multipart form, validates and stores an uploaded avatar, then persists the profile.

Explained by highlit
Gin Intermediate form binding file upload validation multipart error handling
1package handlers
2 
3import (
4 "fmt"
5 "net/http"
6 "path/filepath"
7 "time"
8 
9 "github.com/gin-gonic/gin"
10 "github.com/google/uuid"
11)
12 
13type ProfileForm struct {
14 Name string `form:"name" binding:"required"`
15 Bio string `form:"bio" binding:"max=500"`
16 Birthday time.Time `form:"birthday" time_format:"2006-01-02"`
17 Tags []string `form:"tags"`
18 Avatar *multipart.FileHeader `form:"avatar" binding:"required"`
19}
20 
21func UpdateProfile(c *gin.Context) {
22 var form ProfileForm
23 if err := c.ShouldBind(&form); err != nil {
24 c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
25 return
26 }
27 
28 if form.Avatar.Size > 5<<20 {
29 c.JSON(http.StatusRequestEntityTooLarge, gin.H{"error": "avatar exceeds 5MB"})
30 return
31 }
32 
33 filename := fmt.Sprintf("%s%s", uuid.NewString(), filepath.Ext(form.Avatar.Filename))
34 dst := filepath.Join("uploads", "avatars", filename)
35 if err := c.SaveUploadedFile(form.Avatar, dst); err != nil {
36 c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to store avatar"})
37 return
38 }
39 
40 userID := c.GetString("userID")
41 if err := profiles.Update(c, userID, form.Name, form.Bio, form.Birthday, form.Tags, dst); err != nil {
42 c.JSON(http.StatusInternalServerError, gin.H{"error": "could not update profile"})
43 return
44 }
45 
46 c.JSON(http.StatusOK, gin.H{"name": form.Name, "avatar": dst})
47}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Struct tags let Gin bind and validate multipart fields declaratively before any handler logic runs.
  2. 2Generating a random filename with the original extension avoids collisions and path-injection from user input.
  3. 3Guarding each fallible step with an early JSON response keeps the happy path flat and readable.

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