Golang gin receives json data and images

php editor Baicao introduces to you how to receive JSON data and images in the Golang gin framework. During the development process, we often need to process JSON data and image files passed from the front end. Golang's gin framework provides simple and easy-to-use methods to receive and process this data. Through the introduction of this article, you will learn how to use structures in the gin framework to receive JSON data and how to process uploaded image files. Let’s explore together!

Question content

I have the code for the request handler:

func (h *handlers) updateprofile() gin.handlerfunc {
    type request struct {
        username    string `json:"username" binding:"required,min=4,max=20"`
        description string `json:"description" binding:"required,max=100"`
    }

    return func(c *gin.context) {
        var updaterequest request

        if err := c.bindjson(&updaterequest); err != nil {
            var validationerrors validator.validationerrors

            if errors.as(err, &validationerrors) {
                validateerrors := base.bindingerror(validationerrors)
                c.abortwithstatusjson(http.statusbadrequest, gin.h{"error": validateerrors})
            } else {
                c.abortwitherror(http.statusbadrequest, err)
            }

            return
        }

        avatar, err := c.formfile("avatar")
        if err != nil {
            c.abortwithstatusjson(http.statusbadrequest, gin.h{
                "error": "image not contains in request",
            })
            return
        }

        log.print(avatar)

        if avatar.size > 3<<20 { // if avatar size more than 3mb
            c.abortwithstatusjson(http.statusbadrequest, gin.h{
                "error": "image is too large",
            })
            return
        }

        file, err := avatar.open()
        if err != nil {
            c.abortwitherror(http.statusinternalservererror, err)
        }

        session := sessions.default(c)
        id := session.get("sessionid")
        log.printf("id type: %t", id)

        err = h.userservice.updateprofile(fmt.sprintf("%v", id), file, updaterequest.username, updaterequest.description)
        if err != nil {
            c.abortwithstatusjson(http.statusbadrequest, gin.h{})
            return
        }

        c.indentedjson(http.statusnocontent, gin.h{"message": "succesfull update"})
    }
}

I unit tested this handler:

func testuser_updateprofile(t *testing.t) {
    type testcase struct {
        name               string
        image              io.reader
        username           string
        description        string
        expectedstatuscode int
    }

    router := gin.default()

    memstore := memstore.newstore([]byte("secret"))
    router.use(sessions.sessions("session", memstore))

    usergroup := router.group("user")
    repo := user.newmemory()
    service := userservice.new(repo)
    userhandlers.register(usergroup, service)

    testimage := make([]byte, 100)
    rand.read(testimage)
    image := bytes.newreader(testimage)

    testcases := []testcase{
        {
            name:               "request with image",
            image:              image,
            username:           "bobik",
            description:        "wanna be sharik",
            expectedstatuscode: http.statusnocontent,
        },
        {
            name:               "request without image",
            image:              nil,
            username:           "sharik",
            description:        "wanna be bobik",
            expectedstatuscode: http.statusnocontent,
        },
    }

    for _, tc := range testcases {
        t.run(tc.name, func(t *testing.t) {
            body := &bytes.buffer{}
            writer := multipart.newwriter(body)

            imagewriter, err := writer.createformfile("avatar", "test_avatar.jpg")
            if err != nil {
                t.fatal(err)
            }

            if _, err := io.copy(imagewriter, image); err != nil {
                t.fatal(err)
            }

            data := map[string]interface{}{
                "username":    tc.username,
                "description": tc.description,
            }
            jsondata, err := json.marshal(data)
            if err != nil {
                t.fatal(err)
            }

            jsonwriter, err := writer.createformfield("json")
            if err != nil {
                t.fatal(err)
            }

            if _, err := jsonwriter.write(jsondata); err != nil {
                t.fatal(err)
            }

            writer.close()

            // creating request
            req := httptest.newrequest(
                http.methodpost,
                "http://localhost:8080/user/account/updateprofile",
                body,
            )
            req.header.set("content-type", writer.formdatacontenttype())
            log.print(req)

            w := httptest.newrecorder()
            router.servehttp(w, req)

            assert.equal(t, tc.expectedstatuscode, w.result().statuscode)
        })
    }
}

The following error occurred during the test: Error #01: Invalid character '-' in numeric literal

This is the request body (I print it using log.print(req)):

&{POST http://localhost:8080/user/account/updateprofile HTTP/1.1 1 1 map[Content-Type:[multipart/form-data; boundary=30b24345de9d8d83ecbdd146262d86894c45b4f3485e4615553621fd2035]] {--30b24345de9d8d83ecbdd146262d86894c45b4f3485e4615553621fd2035
Content-Disposition: form-data; name="avatar"; filename="test_avatar.jpg"
Content-Type: application/octet-stream


--30b24345de9d8d83ecbdd146262d86894c45b4f3485e4615553621fd2035
Content-Disposition: form-data; name="json"

{"description":"wanna be bobik","username":"sharik"}
--30b24345de9d8d83ecbdd146262d86894c45b4f3485e4615553621fd2035--
} <nil> 414 [] false localhost:8080 map[] map[] <nil> map[] 192.0.2.1:1234 http://localhost:8080/user/account/updateprofile <nil> <nil> <nil> <nil>}

First, I have only string as json data and convert it to bytes. When the error occurred, I converted the json data using json.marshal without success. I want to parse json data using c.bind and given image using c.formfile, is this possible?

renew. I replaced the code to get the avatar first and then get the json through the bind structure. Now I have eof error.

Solution

tl;dr

We can define a structure to receive json data and image files at the same time (note the field labels):

var updaterequest struct {
    avatar *multipart.fileheader `form:"avatar" binding:"required"`
    user   struct {
        username    string `json:"username" binding:"required,min=4,max=20"`
        description string `json:"description" binding:"required,max=100"`
    } `form:"user" binding:"required"`
}

// c.shouldbind will choose binding.formmultipart based on the content-type header.
// we call c.shouldbindwith to make it explicitly.
if err := c.shouldbindwith(&updaterequest, binding.formmultipart); err != nil {
    _ = c.abortwitherror(http.statusbadrequest, err)
    return
}

Can

gin automatically parse other content types in multipart/form-data?

For example, xml or yaml.

The current gin (@1.9.0) does not automatically parse xml or yaml in multipart/form-data. json We're lucky, because gin happens to use json.unmarshal to parse form field values ​​when the target field is a struct or map. See binding.setwithpropertype.

We can parse them ourselves like this (updaterequest.event is the string value in the form):

var event struct {
    at     time.time `xml:"time" binding:"required"`
    player string    `xml:"player" binding:"required"`
    action string    `xml:"action" binding:"required"`
}

if err := binding.xml.bindbody([]byte(updaterequest.event), &event); err != nil {
    _ = c.abortwitherror(http.statusbadrequest, err)
    return
}

(not to be confused with yaml in the application/xml request or xml in the application/x-yaml request. This is only required if the xml content or the yaml content is in a multipart/form-data request) .

other

1. c.bindjson cannot be used to read json from multipart/form-data because it assumes the request body starts with valid json. But it starts with a boundary that looks like --30b24345d.... That's why it fails with the error message invalid character '-' in numeric literal.
2. Calling c.bindjson after c.formfile("avatar") will not work because calling c.formfile will cause the entire request body to be Read. And there is nothing readable after c.bindjson. That's why you see the eof error.

Demo in a single executable file

This is the complete demo. Run ./... -v -count 1: using

go test

package m

import (
    "bytes"
    "crypto/rand"
    "fmt"
    "io"
    "mime/multipart"
    "net/http"
    "net/http/httptest"
    "testing"
    "time"

    "github.com/gin-gonic/gin"
    "github.com/gin-gonic/gin/binding"
    "github.com/stretchr/testify/assert"
)

func handle(c *gin.Context) {
    var updateRequest struct {
        Avatar *multipart.FileHeader `form:"avatar" binding:"required"`
        User   struct {
            Username    string `json:"username" binding:"required,min=4,max=20"`
            Description string `json:"description" binding:"required,max=100"`
        } `form:"user" binding:"required"`
        Event string `form:"event" binding:"required"`
    }

    // c.ShouldBind will choose binding.FormMultipart based on the Content-Type header.
    // We call c.ShouldBindWith to make it explicitly.
    if err := c.ShouldBindWith(&updateRequest, binding.FormMultipart); err != nil {
        _ = c.AbortWithError(http.StatusBadRequest, err)
        return
    }
    fmt.Printf("%#v\n", updateRequest)

    var event struct {
        At     time.Time `xml:"time" binding:"required"`
        Player string    `xml:"player" binding:"required"`
        Action string    `xml:"action" binding:"required"`
    }

    if err := binding.XML.BindBody([]byte(updateRequest.Event), &event); err != nil {
        _ = c.AbortWithError(http.StatusBadRequest, err)
        return
    }

    fmt.Printf("%#v\n", event)
}

func TestMultipartForm(t *testing.T) {
    testImage := make([]byte, 100)

    if _, err := rand.Read(testImage); err != nil {
        t.Fatal(err)
    }
    image := bytes.NewReader(testImage)

    body := &bytes.Buffer{}
    writer := multipart.NewWriter(body)

    imageWriter, err := writer.CreateFormFile("avatar", "test_avatar.jpg")
    if err != nil {
        t.Fatal(err)
    }

    if _, err := io.Copy(imageWriter, image); err != nil {
        t.Fatal(err)
    }

    if err := writer.WriteField("user", `{"username":"bobik","description":"wanna be sharik"}`); err != nil {
        t.Fatal(err)
    }

    xmlBody := `<?xml version="1.0" encoding="UTF-8"?>
<root>
   <time>2023-02-14T19:04:12Z</time>
   <player>playerOne</player>
   <action>strike (miss)</action>
</root>`
    if err := writer.WriteField("event", xmlBody); err != nil {
        t.Fatal(err)
    }

    writer.Close()

    req := httptest.NewRequest(
        http.MethodPost,
        "http://localhost:8080/update",
        body,
    )
    req.Header.Set("Content-Type", writer.FormDataContentType())
    fmt.Printf("%v\n", req)

    w := httptest.NewRecorder()
    c, engine := gin.CreateTestContext(w)
    engine.POST("/update", handle)
    c.Request = req
    engine.HandleContext(c)

    assert.Equal(t, 200, w.Result().StatusCode)
}

Thank you for reading!

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