Mount Arc in Echo

Your service already uses Echo and you want Arc’s commands and queries beside your Echo routes. Echo v5’s Any route matches every method, including QUERY, so one wildcard route hands Arc everything your own routes do not claim.

Delegate to Arc

Build and start Arc first. This code is compiled and tested in the recipes module:

// NewEcho returns an Echo instance that serves host routes and forwards every
// other request, unchanged, to the started Arc application.
func NewEcho(app http.Handler) *echo.Echo {
    e := echo.New()
    e.GET("/healthz", func(c *echo.Context) error {
        return c.NoContent(http.StatusNoContent)
    })
    // Echo v5's Any matches every method, including QUERY.
    e.Any("/*", echo.WrapHandler(app))
    return e
}

Method-specific Echo routes, such as GET /healthz, take precedence over the Any route. Echo passes the original request to Arc, so Arc’s routes, empty 404/405 responses and Allow headers reach the client unchanged.

Echo v4 is different

The recipe targets Echo v5 (github.com/labstack/echo/v5). Echo v4’s Any registers a fixed method list; check whether your version includes QUERY and register it explicitly with Add if not. The recipe module does not test v4.

What the recipe proves

The test serves the instance over real HTTP with Echo v5.4.0 and checks command execution, /validate without execution, GET and QUERY argument binding, HEAD, Arc’s empty 404/405, and that cancelling the client request cancels the query’s context. Direct SSE flushes two ordered results, direct WebSocket upgrades and sends two results, and disconnect and application shutdown join the source. Correlation IDs and QUERY’s no-store survive the host. It does not cover other Echo versions, hub multiplexing or Echo middleware you add.

Identity and lifecycle

Use an Arc authentication handler such as the JWT bearer recipe, or authentication.HostPrincipal() after your host has installed a verified Arc principal. Your host owns the listener and timeouts. Initiate server.Shutdown and app.Shutdown together, then join both with fresh bounded cleanup budgets, as in the coordinated shutdown helper. Waiting for HTTP drain first stalls active SSE handlers until the deadline; Arc must cancel their observations while HTTP drains. The Echo tests exercise this sequence with an active SSE stream. See hosting and the HTTP contract.