No check of length of parameter values

[linux019]

Issue Description

Checklist

• [x] Dependencies installed
• [x] No typos
• [x] Searched existing issues and docs

Working code to debug

package main

import (
	"fmt"
	"github.com/labstack/echo"
)

func main() {
	e := echo.New()
	ctx := e.NewContext(nil, nil)
	ctx.SetParamNames("a")
	fmt.Println(ctx.ParamValues())
}

Version/commit

https://github.com/labstack/echo/blob/fc4b1c0a830f194bf6334d2b3e61d92cccebb2be/context.go#L316 - missing check

[lammel]

This should be fixed with PR #1535

[stevenvegt]

It seems the split between the names, values and the maxIndex is still causing problems.

I encountered problems before as described in this issue https://github.com/labstack/echo/issues/1258

This is my middleware:

// DecodeURIPath is a echo middleware that decodes path parameters
func DecodeURIPath(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		newValues := make([]string, len(c.ParamValues()))
		for i, value := range c.ParamValues() {
			path, err := url.PathUnescape(value)
			if err != nil {
				path = value
			}
			newValues[i] = path
		}
		c.SetParamValues(newValues...)
		return next(c)
	}
}

During execution maxParam is 1, pnames empty and pvalues contains 1 entry with value "".

However, c.ParamValues() returns nothing because instead of the maxParam, it uses the length of pnames: https://github.com/labstack/echo/pull/1535/files#diff-05a3aa0ab9e5687ff167e0ef3ae4c5a6R316

After calling SetParamValues(newValues...) pvalues becomes an empty arrray. But remember, the maxParam is still set to 1.

Then the during the next request Reset https://github.com/labstack/echo/blob/master/context.go#L636 still uses this value to iterate over the pvalues and causes an

echo: http: panic serving 127.0.0.1:55010: runtime error: index out of range [0] with length 0

[stevenvegt]

FYI: adding the line:

c.SetParamNames(c.ParamNames()...)

Seems to fix my problem by resetting the maxParam value.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stevenvegt]

A comment just to annoy out stale-bot and giving the echo team a bit of extra time to look at this problem :)

[lammel]

We had the same issues in our tests where we are using ctx.Reset() which caused the index out of range panic on access to pvalues:

panic: runtime error: index out of range [0] with length 0 [recovered]

We are using a simple workaround in our test helpers now. Calling ctx.SetParamNames("") and ctx.SetParamValues("") before Reset() of the context ensure the length is set properly.

Example:

// Workaround required for echo v4.1.17, see GitHub #1531
h.Ctx.SetParamNames("")
h.Ctx.SetParamValues("")
h.Ctx.Reset(req, rec)

I will try to work out a PR to cleanup the param value handling and avoid the current pitfalls

[lammel]

PR #1659 has been merged addressing the symptoms so echo should not panic anymore.