go 46 lines · 8 steps

Handling multi-file uploads in Gin

A Gin handler parses a multipart form, validates each file's size, saves them to disk, and reports what landed.

Explained by highlit
Gin Intermediate file-upload multipart validation http-handler error-handling
1func UploadFiles(c *gin.Context) {
2 form, err := c.MultipartForm()
3 if err != nil {
4 c.JSON(http.StatusBadRequest, gin.H{"error": "invalid multipart form"})
5 return
6 }
7 
8 files := form.File["documents"]
9 if len(files) == 0 {
10 c.JSON(http.StatusBadRequest, gin.H{"error": "no files provided"})
11 return
12 }
13 
14 const maxSize = 10 << 20
15 uploaded := make([]gin.H, 0, len(files))
16 
17 for _, file := range files {
18 if file.Size > maxSize {
19 c.JSON(http.StatusRequestEntityTooLarge, gin.H{
20 "error": fmt.Sprintf("%s exceeds the 10MB limit", file.Filename),
21 })
22 return
23 }
24 
25 name := fmt.Sprintf("%d-%s", time.Now().UnixNano(), filepath.Base(file.Filename))
26 dst := filepath.Join("uploads", name)
27 
28 if err := c.SaveUploadedFile(file, dst); err != nil {
29 c.JSON(http.StatusInternalServerError, gin.H{
30 "error": fmt.Sprintf("failed to save %s", file.Filename),
31 })
32 return
33 }
34 
35 uploaded = append(uploaded, gin.H{
36 "original": file.Filename,
37 "stored": name,
38 "size": file.Size,
39 })
40 }
41 
42 c.JSON(http.StatusCreated, gin.H{
43 "count": len(uploaded),
44 "files": uploaded,
45 })
46}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Validate the whole request shape before touching any file so bad requests fail fast with clear status codes.
  2. 2Renaming uploads with a timestamp and filepath.Base prevents collisions and strips client-supplied path components.
  3. 3Accumulating results in a slice lets you return a single structured summary after all files succeed.

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