binder: make binding to Map work better with string destinations

[aldas]

Relates to #2552 and #988

Difference from previous implementations is that in case we are binding to unsupported Map we ended in with panic. Now we skip binding (params/query/header) and try other sources (ala body)

package main

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

func main() {
	e := echo.New()
	e.Use(middleware.Logger())
	e.Use(middleware.Recover())

	// test: `curl -XPOST --header "Content-Type: application/json" -d '{"module1": "2", "module2": "3"}' http://127.0.0.1:8080/test/string/1`
	// output old: {"id":"1","module1":"2","module2":"3"}
	// output new: {"id":"1","module1":"2","module2":"3"}
	e.POST("/test/string/:id", func(c echo.Context) error {
		p := map[string]string{}
		if err := c.Bind(&p); err != nil {
			return err
		}
		return c.JSON(http.StatusOK, p)
	})

	// test: `curl -XPOST --header "Content-Type: application/json" -d '{"module1": 2, "module2": 3}' http://127.0.0.1:8080/test/int/1`
	// output old: {"message":"Internal Server Error"}
	// output new: {"module1":"2","module2":"3"}
	e.POST("/test/int/:id", func(c echo.Context) error {
		p := map[string]int{}
		if err := c.Bind(&p); err != nil {
			return err
		}
		return c.JSON(http.StatusOK, p)
	})

	e.Start("127.0.0.1:8080")
}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (584cb85) 92.89% compared to head (aea150e) 93.02%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2554      +/-   ##
==========================================
+ Coverage   92.89%   93.02%   +0.12%     
==========================================
  Files          39       39              
  Lines        4658     4673      +15     
==========================================
+ Hits         4327     4347      +20     
+ Misses        240      236       -4     
+ Partials       91       90       -1     

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[astromechza]

Thanks @aldas, this looks much more robust than before 👍

[georgmu]

There is still an issue when having code like this:

var params map[string]any
c.Bind(&params)

This works for JSON body, but fails for path params (since params is nil).

A small addition helps to solve this (this is the same that the JSON decoder does):

--- a/bind.go
+++ b/bind.go
@@ -138,6 +138,9 @@ func (b *DefaultBinder) bindData(destination interface{}, data map[string][]stri
        // You are better off binding to struct but there are user who want this map feature. Source of data for these cases are:
        // params,query,header,form as these sources produce string values, most of the time slice of strings, actually.
        if typ.Kind() == reflect.Map && typ.Key().Kind() == reflect.String {
+               if val.IsNil() {
+                       val.Set(reflect.MakeMap(typ))
+               }
                k := typ.Elem().Kind()
                isElemInterface := k == reflect.Interface
                isElemString := k == reflect.String

I can prepare a merge request (including a test case) for this.

[dakhtarovpx]

Hello there!

Thank you for your PR.

I'd like to ask: when do you plan to release this PR? v4.11.4 is the latest version, and it still doesn't work at the moment.

[aldas]

I do not know at the moment. Meanwhile use:

p := map[string]string{}
if err := c.Bind(&p); err != nil {