httpcaddyfile: New handle_path directive (#3281)

* caddyconfig: WIP implementation of handle_path

* caddyconfig: Complete the implementation - h.NewRoute was key

* caddyconfig: Add handle_path integration test

* caddyhttp: Use the path matcher as-is, strip the trailing *, update test

modules/caddyhttp/rewrite/caddyfile.go

@@ -15,9 +15,12 @@
 package rewrite
 
 import (
+	"encoding/json"
 	"strconv"
 	"strings"
 
+	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/caddyconfig"
 	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
 	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
 )
@@ -25,6 +28,7 @@ import (
 func init() {
 	httpcaddyfile.RegisterHandlerDirective("rewrite", parseCaddyfileRewrite)
 	httpcaddyfile.RegisterHandlerDirective("uri", parseCaddyfileURI)
+	httpcaddyfile.RegisterDirective("handle_path", parseCaddyfileHandlePath)
 }
 
 // parseCaddyfileRewrite sets up a basic rewrite handler from Caddyfile tokens. Syntax:
@@ -110,3 +114,73 @@ func parseCaddyfileURI(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, err
 	}
 	return rewr, nil
 }
+
+// parseCaddyfileHandlePath parses the handle_path directive. Syntax:
+//
+//     handle_path [<matcher>] {
+//         <directives...>
+//     }
+//
+// Only path matchers (with a `/` prefix) are supported as this is a shortcut
+// for the handle directive with a strip_prefix rewrite.
+func parseCaddyfileHandlePath(h httpcaddyfile.Helper) ([]httpcaddyfile.ConfigValue, error) {
+	if !h.Next() {
+		return nil, h.ArgErr()
+	}
+	if !h.NextArg() {
+		return nil, h.ArgErr()
+	}
+
+	// read the prefix to strip
+	path := h.Val()
+	if !strings.HasPrefix(path, "/") {
+		return nil, h.Errf("path matcher must begin with '/', got %s", path)
+	}
+
+	// we only want to strip what comes before the '/' if
+	// the user specified it (e.g. /api/* should only strip /api)
+	var stripPath string
+	if strings.HasSuffix(path, "/*") {
+		stripPath = path[:len(path)-2]
+	} else if strings.HasSuffix(path, "*") {
+		stripPath = path[:len(path)-1]
+	} else {
+		stripPath = path
+	}
+
+	// the ParseSegmentAsSubroute function expects the cursor
+	// to be at the token just before the block opening,
+	// so we need to rewind because we already read past it
+	h.Reset()
+	h.Next()
+
+	// parse the block contents as a subroute handler
+	handler, err := httpcaddyfile.ParseSegmentAsSubroute(h)
+	if err != nil {
+		return nil, err
+	}
+	subroute, ok := handler.(*caddyhttp.Subroute)
+	if !ok {
+		return nil, h.Errf("segment was not parsed as a subroute")
+	}
+
+	// make a matcher on the path and everything below it
+	pathMatcher := caddy.ModuleMap{
+		"path": h.JSON(caddyhttp.MatchPath{path}),
+	}
+
+	// build a route with a rewrite handler to strip the path prefix
+	route := caddyhttp.Route{
+		HandlersRaw: []json.RawMessage{
+			caddyconfig.JSONModuleObject(Rewrite{
+				StripPathPrefix: stripPath,
+			}, "handler", "rewrite", nil),
+		},
+	}
+
+	// prepend the route to the subroute
+	subroute.Routes = append([]caddyhttp.Route{route}, subroute.Routes...)
+
+	// build and return a route from the subroute
+	return h.NewRoute(pathMatcher, subroute), nil
+}