fix(standalone): resolve env var references in config pushed via Admin API

In standalone mode, the file-based config path resolves ${{VAR}} / $ENV://
references in config_yaml.parse(), but config pushed through the Admin API
(`PUT /apisix/admin/configs`) is JSON-decoded straight into _update_config
and bypassed that step, so the references were kept literal.

Resolve them in the Admin API update path before applying the config, so
both standalone config sources behave consistently. Adds a test that pushes
a route whose proxy-rewrite uri uses a ${{VAR:=default}} reference and
verifies the gateway resolves it.

Author: AlinsRan

apisix/admin/standalone.lua

@@ -28,6 +28,7 @@ local events       = require("apisix.events")
 local core         = require("apisix.core")
 local config_yaml  = require("apisix.core.config_yaml")
 local config_validate = require("apisix.admin.config_validate")
+local file         = require("apisix.cli.file")
 
 local ALL_RESOURCE_KEYS = config_validate.get_all_resource_keys()
 
@@ -327,6 +328,16 @@ function _M.init_worker()
         -- this table is generated by json decode, so there is no need to clone it
         config[METADATA_LAST_MODIFIED] = nil
         config[METADATA_DIGEST] = nil
+
+        -- resolve ${{VAR}} / $ENV:// references in the config pushed via the
+        -- Admin API. The file-based standalone path resolves these in
+        -- config_yaml.parse(), but the Admin API path decodes JSON straight
+        -- into _update_config and would otherwise keep them literal.
+        local ok, err = file.resolve_conf_var(config)
+        if not ok then
+            core.log.error("failed to resolve variables in config: ", err)
+            return
+        end
         config_yaml._update_config(config)
     end
     events:register(update_config, EVENT_UPDATE, EVENT_UPDATE)

t/admin/standalone.spec.ts

@@ -944,4 +944,37 @@ describe('Validate API - Standalone', () => {
       });
     });
   });
+
+  describe('Variable resolution', () => {
+    it('resolves ${{VAR}} references in config pushed via the Admin API', async () => {
+      mockDigest += 1;
+      const config = {
+        routes: [
+          {
+            id: 'r_var',
+            uri: '/r_var',
+            upstream: {
+              nodes: { '127.0.0.1:1980': 1 },
+              type: 'roundrobin',
+            },
+            // The proxy-rewrite uri uses a ${{VAR:=default}} reference. The
+            // gateway must resolve it to the default ("/hello"); if it were
+            // left literal, the upstream would receive "${{...}}" instead of
+            // "/hello" and would not return the hello body.
+            plugins: {
+              'proxy-rewrite': { uri: '${{STANDALONE_ENV_TEST:=/hello}}' },
+            },
+          },
+        ],
+      };
+      const putResp = await client.put(ENDPOINT, config, {
+        headers: { [HEADER_DIGEST]: mockDigest },
+      });
+      expect(putResp.status).toEqual(202);
+
+      const resp = await client.get('/r_var');
+      expect(resp.status).toEqual(200);
+      expect(resp.data).toEqual('hello world\n');
+    });
+  });
 });