Use the gin.CreateTestContext in test, could not get the param in the route.

[Hanaasagi]

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Description

#2755 only fixes the slice bounds out of range panic. Route params are not be handled correctly in test context. I can explain what happened.

When call CreateTestContext, it will call New function to create a Engine. The maxParams will be the default value 0.

gin/test_helpers.go

Lines 9 to 16 in 9c27053

	// CreateTestContext returns a fresh engine and context for testing purposes
	func CreateTestContext(w http.ResponseWriter) (c *Context, r *Engine) {
	r = New()
	c = r.allocateContext()
	c.reset()
	c.writermem.reset(w)
	return
	}

Then allocateContext init the Params. The cap and len are both 0. params is the reference of Params.

gin/gin.go

Lines 202 to 205 in 9c27053

	func (engine *Engine) allocateContext() *Context {
	v := make(Params, 0, engine.maxParams)
	return &Context{engine: engine, params: &v}
	}

Even if we add a route, it only incrs the maxParams value, it has not effect on the Context we created by CreateTestContext before. The condition will always be false.

gin/tree.go

Lines 462 to 479 in 9c27053

	if params != nil && cap(*params) > 0 {
	if value.params == nil {
	value.params = params
	}
	// Expand slice within preallocated capacity
	i := len(*value.params)
	*value.params = (*value.params)[:i+1]
	val := path[:end]
	if unescape {
	if v, err := url.QueryUnescape(val); err == nil {
	val = v
	}
	}
	(*value.params)[i] = Param{
	Key: n.path[1:],
	Value: val,
	}
	}

How to reproduce

package main

import (
	"fmt"
	"net/http"
	"net/http/httptest"

	"github.com/gin-gonic/gin"
)

func main() {
	w := httptest.NewRecorder()
	ctx, engine := gin.CreateTestContext(w)
	engine.GET("/hello/:name", func(ctx *gin.Context) {
		fmt.Printf("Param name is %s\n", ctx.Param("name"))
		ctx.String(http.StatusOK, "Hello %s", ctx.Param("name"))
	})
	var err error
	ctx.Request, err = http.NewRequest(http.MethodGet, "/hello/world", nil)
	if err != nil {
		panic(err)
	}
	engine.HandleContext(ctx)
}

Expectations

Get following output after running the code.

[GIN-debug] GET    /hello/:name              --> main.main.func1 (1 handlers)
Param name is world

Actual result

[GIN-debug] GET    /hello/:name              --> main.main.func1 (1 handlers)
Param name is 

ctx.Param("name") returns a empty string.

Environment

• go version: go version go1.16 darwin/amd64
• gin version (or commit ref): v1.7.2-0.20210704023713-9c27053243cb
• operating system: macOs Big Sur 11.4, Darwin Kernel Version 20.5.0

[Hanaasagi]

One way to fix this problem is check the cap of params everytime when we use.

[Hanaasagi]

Hello, Any thoughts on this?

[RoCry]

Hello, Any thoughts on this?

@Hanaasagi We met the same issue and fixed it #2803, please feel free to leave suggestions.

[alochym01]

@Hanaasagi i have same issue, is there any work around
#2833

[jlaneve]

Here's a workaround for now:

gin.SetMode(gin.TestMode)

w := httptest.NewRecorder()
c, _ := gin.CreateTestContext(w)

c.Params = []gin.Param{gin.Param{Key: "k", Value: "v"}}

foo(c)

if w.Code != 200 {
    b, _ := ioutil.ReadAll(w.Body)
    t.Error(w.Code, string(b))
}

[appleboy]

fixed in #2803 and released in v1.8.2