Rewrite middleware in v4.1.16 no longer supports matching beginning of path

[chlindell]

Issue Description

Rewrite middleware was changed in v4.1.16 here:
5428358

After this change it seems it's not possible to explicitly match beginning of path anymore.

• Is there some way to get the old behavior or let the users write proper regexps? (besides rewriting the rewrite middleware)
• https://github.com/labstack/echo/blob/master/middleware/rewrite.go#L62 is adding end-of-line but not beginning-of-line. Is that intentional?

Checklist

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

Expected behaviour

Before we were using this:

	// Rewrite requests without version to use v1
	e.Pre(echomiddleware.Rewrite(map[string]string{
		"^/abc/*": "/v1/abc/$1",
	}))

where ^ is regexp for beginning of string.

Some examples before and what they got mapped to:

/abc/test -> /v1/abc/test
/v1/abc/test  (same, no rewrite)
/v2/abc/test (same, no rewrite)

Actual behaviour

The new versions re-formats the beginning of line character using regexp.QuoteMeta so it can't be used anymore. Rewrite will change ANY "version prefix" to v1 if removing "^", not just ones without it, e.g.:

/abc/test -> /v1/abc/test
/v2/abc/test -> /v1/abc/test
/not/like/this/abc/test -> /v1/abc/test

which is not what we intended and breaks backwards compatibility.

Steps to reproduce

Working code to debug

package main

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

func main() {
	e := echo.New()
	// Rewrite requests without version to use v1.
	// This worked on v4.1.13 but now nothing matches until removing the ^ here.
	// However, that makes it match in the middle of strings.
	e.Pre(echomiddleware.Rewrite(map[string]string{
		"^/abc/*": "/v1/abc/$1",
	}))

	group := e.Group("")
	group.Use(echomiddleware.Logger())
	group.Any("/v1/abc/test", func(c echo.Context) error {
		return c.String(http.StatusOK, "Route: /v1/abc/test")
	})

	e.Logger.Fatal(e.StartServer(e.Server))
}

Version/commit

[stale]

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