Gulter is a Go HTTP middleware designed to simplify the process of uploading files
for your web apps. It follows the standard
http.Handler
and http.HandlerFunc
interfaces so you can
always use with any of framework or the standard library router.
Multiple files per form field are already supported
Name and idea was gotten from the insanely popular multer package in NodeJS that does the same.
go get -u -v github.com/adelowo/gulter
Assuming you have a HTML form like this:
<form action="/" method="post" enctype="multipart/form-data">
<input type="file" name="form-field-1" />
<input type="file" name="form-field-2" />
</form>
To create a new Gulter instance, you can do something like this:
handler, _ := gulter.New(
gulter.WithMaxFileSize(10<<20),
gulter.WithValidationFunc(
gulter.ChainValidators(gulter.MimeTypeValidator("image/jpeg", "image/png"),
func(f gulter.File) error {
// Your own custom validation function on the file here
// Else you can really just drop the ChainValidators and use only the MimeTypeValidator or just
// one custom validator alone
return nil
})),
gulter.WithStorage(s3Store),
)
The handler
is really just a HTTP middleware with the following signature
Upload(keys ...string) func(next http.Handler) http.Handler
. keys
here
are the input names from the HTML form, so you can chain this into almost any HTTP
router.
package main
import (
"fmt"
"net/http"
"github.com/adelowo/gulter"
"github.com/adelowo/gulter/storage"
)
func main() {
s3Store, err := storage.NewS3FromEnvironment(storage.S3Options{
Bucket: "std-router",
})
if err != nil {
panic(err.Error())
}
handler, err := gulter.New(
gulter.WithMaxFileSize(10<<20),
gulter.WithStorage(s3Store),
)
mux := http.NewServeMux()
// upload all files with the "name" and "lanre" fields on this route
mux.Handle("/", handler.Upload("name", "lanre")(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
fmt.Println("Uploaded file")
// return all uploaded files
f, err := gulter.FilesFromContext(r)
if err != nil {
fmt.Println(err)
return
}
// return uploaded files with the form field "lanre"
ff, err := gulter.FilesFromContextWithKey(r, "lanre")
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("%+v", ff)
for _, v := range f {
fmt.Printf("%+v", v)
fmt.Println()
}
})))
http.ListenAndServe(":3300", mux)
s3Store, err := storage.NewS3FromEnvironment(storage.S3Options{
Bucket: "chi-router",
})
if err != nil {
panic(err.Error())
}
handler := gulter.New(
gulter.WithMaxFileSize(10<<20),
gulter.WithValidationFunc(gulter.ChainValidators(gulter.MimeTypeValidator("image/jpeg", "image/png"))),
gulter.WithStorage(s3Store),
)
router := chi.NewMux()
// upload all files in the form fields called "form-field-1" and "form-field-2"
router.With(handler.Upload("form-field-1", "form-field-2")).Post("/", func(w http.ResponseWriter, r *http.Request) {
fmt.Println("Uploaded file")
f, err := gulter.FilesFromContext(r)
if err != nil {
fmt.Println(err)
return
}
ff, err := gulter.FilesFromContextWithKey(r, "form-field-1") // or form-field-2
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("%+v", ff)
for _, v := range f {
fmt.Printf("%+v", v)
fmt.Println()
}
})
While this middleware automatically uploads your files, sometimes you need details about the uploaded file to show to the user, this could be making up the image url or path to the image. To get that in your HTTP handler, you can use either:
FilesFromContextWithKey
: retrieve a named input uploaded file.FilesFromContext
: retrieve all uploaded files
Gulter also ships with two storage implementations at the moment:
S3Store
: supports S3 or any compatible service like Minio,R2 & othersDiskStore
: uses a local filesystem backed store to upload filesCloudinaryStore
: uploads file to cloudinary
Sometimes, the keys you have configured the middleware might get dropped from the
frontend for some reason, ideally the middleware fails if it cannot find a
configured key in the request. To disable this behavior and ignore the missing
key, you can make use of the WithIgnoreNonExistentKey(true)
option to prevent the
middleware from causing an error when such keys do not exists
Since Gulter is a middleware that runs, it returns an error to the client if found,
this might not match your existing structure, so to configure the response, use the
WithErrorResponseHandler
. The default is shown below and can be used as a template
to define yours.
errHandler ErrResponseHandler = func(err error) http.HandlerFunc {
return func(w http.ResponseWriter, _ *http.Request) {
w.Header().Set("Content-Type", "application/json")
w.WriteHeader(http.StatusInternalServerError)
fmt.Fprintf(w, `{"message" : "could not upload file", "error" : %s}`, err.Error())
}
}
Sometimes, you could have some custom logic to validate uploads, in this example below, we limit the size of the upload based on the mimeypes of the uploaded files
var customValidator gulter.ValidationFunc = func(f gulter.File) error {
switch f.MimeType {
case "image/png":
if f.Size > 4096 {
return errors.New("file size too large")
}
return nil
case "application/pdf":
if f.Size > (1024 * 10) {
return errors.New("file size too large")
}
return nil
default:
return nil
}
}