feat: adds support for nginx variables in service_name param

apisix/core/utils.lua

@@ -337,6 +337,24 @@ do
     end
 end
 -- Resolve ngx.var in the given string
+-- @function core.utils.resolve_var
+-- @tparam string tpl The template string to resolve variables in
+-- @tparam table ctx The context table containing variables
+-- @tparam function escaper Optional function to escape resolved values
+-- @treturn string The resolved string
+-- @treturn string|nil Error message if any
+-- @treturn number Number of variables replaced
+-- @usage
+-- local utils = require("apisix.core.utils")
+--
+-- -- Usage examples:
+-- local res = utils.resolve_var("$host", ctx.var)     -- "example.com"
+-- local res = utils.resolve_var("${host}", ctx.var)   -- "example.com"
+-- local res = utils.resolve_var("TMP_${VAR1}_${VAR2}", ctx.var) -- "TMP_value1_value2"
+-- local res = utils.resolve_var("\\$host", ctx.var)   -- "$host"
+--
+-- -- Usage in APISIX context:
+-- local service_name = utils.resolve_var(up_conf.service_name, api_ctx.var)
 _M.resolve_var = resolve_var
 
 
@@ -461,5 +479,4 @@ function _M.check_tls_bool(fields, conf, plugin_name)
     end
 end
 
-
 return _M

apisix/upstream.lua

@@ -297,7 +297,12 @@ function _M.set_by_route(route, api_ctx)
             return 503, err
         end
 
-        local new_nodes, err = dis.nodes(up_conf.service_name, up_conf.discovery_args)
+        local service_name, err = core.utils.resolve_var(up_conf.service_name, api_ctx.var)
+        if not service_name or service_name == "" then
+            return 503, "resolve_var resolves to empty string: " .. (err or "nil")
+        end
+
+        local new_nodes, err = dis.nodes(service_name, up_conf.discovery_args)
         if not new_nodes then
             return HTTP_CODE_UPSTREAM_UNAVAILABLE, "no valid upstream node: " .. (err or "nil")
         end