An error occurred when the url variable parameter was used with c.bind(slice)

[elissa2333]

Issue Description

An error occurred when the url variable parameter was used with c.bind(slice)

Checklist

• Dependencies installed
• No typos
• Searched existing issues and docs

Expected behaviour

The binding result is consistent with the fixed url

Actual behaviour

raise error： binding element must be a struct

Steps to reproduce

pass: curl -X POST -H "Content-Type: application/json" -d '[{"id":2333}]' localhost:1323/a
fail: curl -X POST -H "Content-Type: application/json" -d '[{"id":2333}]' localhost:1323/b

Working code to debug

package main

import (
	"github.com/labstack/echo/v4"
	"net/http"
)

type Test struct {
	ID int `json:"id"`
}

func main() {
	e := echo.New()

	e.POST("/a", handle)

	// :name = b
	e.POST("/:name", handle) // -> error: binding element must be a struct
	e.Logger.Fatal(e.Start(":1323"))
}

func handle(c echo.Context) error {
	var m []*Test
	if err := c.Bind(&m); err != nil {
		return c.JSON(http.StatusBadRequest, echo.Map{"error": err})
	}

	return c.JSON(http.StatusOK, m)
}

Version/commit

github.com/labstack/echo/v4 v4.1.17

[elissa2333]

The echo version returns to 4.0.0 and works normally

[rdiek]

fixed this problem for me:

git diff bind.go
diff --git a/bind.go b/bind.go
index f891474..9b94326 100644
--- a/bind.go
+++ b/bind.go
@@ -90,6 +90,10 @@ func (b *DefaultBinder) bindData(ptr interface{}, data map[string][]string, tag
        typ := reflect.TypeOf(ptr).Elem()
        val := reflect.ValueOf(ptr).Elem()

+       // Slice (dont work in it)
+       if typ.Kind() == reflect.Slice {
+               return nil
+       }
        // Map
        if typ.Kind() == reflect.Map {
                for k, v := range data {

[elissa2333]

Thank you

[aldas]

Can confirm that this bug is in v4.1.17

import (
	"github.com/labstack/echo/v4"
	"log"
	"net/http"
	"net/http/httptest"
	"strings"
	"testing"
)

type Element struct {
	ID int `json:"id"`
}

func TestExample(t *testing.T) {
	e := echo.New()
	req := httptest.NewRequest(http.MethodGet, "/api/endpoint?lang=en", strings.NewReader(`[{"id": 1}]`))
	req.Header.Set(echo.HeaderContentType, echo.MIMEApplicationJSON)
	rec := httptest.NewRecorder()
	c :=  e.NewContext(req, rec)

	err := handle(c)
	if err != nil {
		t.Fatal(err)
	}
	response := string(rec.Body.Bytes())
	if strings.Contains(response, "binding element must be a struct"){
		t.Fatal(response)
	}
}

func handle(c echo.Context) error {
	var payload []Element
	if err := c.Bind(&payload); err != nil {
		return c.JSON(http.StatusBadRequest, echo.Map{"error": err})
	}

	return c.JSON(http.StatusOK, payload)
}

Result:

=== RUN   TestExample
2020/10/27 10:53:59 en
    test_test.go:31: {"error":{"message":"binding element must be a struct"}}
        
--- FAIL: TestExample (0.00s)
FAIL

Process finished with exit code 1

@lammel could you have a look?

[aldas]

@elissa2333 could you reopen this issue?

[lammel]

I think there is a similar issue open concering struct binding.