core/http/middleware/baseurl.go

package middleware

import (
	"strings"

	"github.com/labstack/echo/v4"
)

// BaseURL returns the base URL for the given HTTP request context.
// It takes into account that the app may be exposed by a reverse-proxy under a different protocol, host and path.
// The returned URL is guaranteed to end with `/`.
// The method should be used in conjunction with the StripPathPrefix middleware.
func BaseURL(c echo.Context) string {
	path := c.Path()
	origPath := c.Request().URL.Path

	// Check if StripPathPrefix middleware stored the original path
	if storedPath, ok := c.Get("_original_path").(string); ok && storedPath != "" {
		origPath = storedPath
	}

	// Check X-Forwarded-Proto for scheme
	scheme := "http"
	if c.Request().Header.Get("X-Forwarded-Proto") == "https" {
		scheme = "https"
	} else if c.Request().TLS != nil {
		scheme = "https"
	}

	// Check X-Forwarded-Host for host
	host := c.Request().Host
	if forwardedHost := c.Request().Header.Get("X-Forwarded-Host"); forwardedHost != "" {
		host = forwardedHost
	}

	if path != origPath && strings.HasSuffix(origPath, path) && len(path) > 0 {
		prefixLen := len(origPath) - len(path)
		if prefixLen > 0 && prefixLen <= len(origPath) {
			pathPrefix := origPath[:prefixLen]
			if !strings.HasSuffix(pathPrefix, "/") {
				pathPrefix += "/"
			}
			return scheme + "://" + host + pathPrefix
		}
	}

	return scheme + "://" + host + "/"
}