Provide uri_arg_ when radixtree_uri_with_parameter

Add the prefix `uri_arg_` to the APISIX `ctx.var` allowing a APISIX configured to use the `radixtree_uri_with_parameter` router to access `opts.matched`.
This allows the usage of the matches inside for example the `proxy_rewrite` plugin.

Also see https://github.com/api7/lua-resty-radixtree/#parameters-in-path

apisix/core/ctx.lua

@@ -274,6 +274,11 @@ do
                     end
                 end
 
+            elseif core_str.has_prefix(key, "uri_arg_") then
+                if t._ctx.curr_req_matched then
+                    val = t._ctx.curr_req_matched[(sub_str(key, 9))]
+                end
+
             elseif core_str.has_prefix(key, "http_") then
                 key = key:lower()
                 key = re_gsub(key, "-", "_", "jo")

t/core/ctx_with_params.t

@@ -0,0 +1,106 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+use t::APISIX 'no_plan';
+
+repeat_each(1);
+no_long_string();
+no_root_location();
+no_shuffle();
+
+our $yaml_config = <<_EOC_;
+apisix:
+    router:
+        http: 'radixtree_uri_with_parameter'
+_EOC_
+
+add_block_preprocessor(sub {
+    my ($block) = @_;
+
+    if (!$block->yaml_config) {
+        $block->set_value("yaml_config", $yaml_config);
+    }
+});
+
+run_tests;
+
+__DATA__
+
+=== TEST 1: sanity
+--- config
+    location /t {
+        content_by_lua_block {
+            local core = require("apisix.core")
+            local ctx = {}
+            core.ctx.set_vars_meta(ctx)
+
+            ngx.say("remote_addr: ", ctx.var["remote_addr"])
+            ngx.say("server_port: ", ctx.var["server_port"])
+        }
+    }
+--- request
+GET /t
+--- response_body
+remote_addr: 127.0.0.1
+server_port: 1984
+
+
+=== TEST 1: add route and get `uri_arg_`
+--- config
+    location /t {
+        content_by_lua_block {
+            local t = require("lib.test_admin").test
+            local code, body = t('/apisix/admin/routes/1',
+                ngx.HTTP_PUT,
+                [[{
+                    "methods": ["GET"],
+                    "plugins": {
+                        "serverless-pre-function": {
+                            "phase": "access",
+                            "functions" : ["return function() ngx.log(ngx.INFO, \"uri_arg_path: \", ngx.ctx.api_ctx.var.uri_arg_path) end"]
+                        }
+                    },
+                    "upstream": {
+                        "type": "roundrobin",
+                        "nodes": {
+                            "127.0.0.1:1980": 1
+                        }
+                    },
+                    "uri": "/:path"
+                }]]
+                )
+
+            if code >= 300 then
+                ngx.status = code
+            end
+            ngx.say(body)
+        }
+    }
+--- request
+GET /t
+--- response_body
+passed
+
+
+
+=== TEST 8: `uri_arg_path` exist
+--- request
+GET /hello
+--- response_body
+hello world
+--- error_log
+uri_arg_path: hello
+