Expand dotenv references for Elysia backend

apps/backend/src/index.ts

@@ -1,4 +1,5 @@
 import "@/polyfills";
+import "./server/env-expand";
 import "@/instrument";
 import { app } from "./server/app";
 

apps/backend/src/server/env-expand.ts

@@ -0,0 +1,36 @@
+/* eslint-disable no-restricted-syntax -- This bootstrap normalizes process.env before getEnvVariable reads it. */
+
+const envReferencePattern = /\$\{([A-Za-z_][A-Za-z0-9_]*)(?::-(.*?))?\}|\$([A-Za-z_][A-Za-z0-9_]*)/g;
+
+function expandEnvValue(value: string): string {
+  return value.replace(envReferencePattern, (_match, bracedName: string | undefined, defaultValue: string | undefined, bareName: string | undefined) => {
+    const name = bracedName ?? bareName;
+    if (name == null) {
+      return "";
+    }
+    const referencedValue = process.env[name];
+    if (bracedName != null && defaultValue != null && (referencedValue == null || referencedValue === "")) {
+      return defaultValue;
+    }
+    return referencedValue ?? "";
+  });
+}
+
+for (let iteration = 0; iteration < 10; iteration++) {
+  let changed = false;
+  for (const [key, value] of Object.entries(process.env)) {
+    if (value == null || !envReferencePattern.test(value)) {
+      envReferencePattern.lastIndex = 0;
+      continue;
+    }
+    envReferencePattern.lastIndex = 0;
+    const expandedValue = expandEnvValue(value);
+    if (expandedValue !== value) {
+      process.env[key] = expandedValue;
+      changed = true;
+    }
+  }
+  if (!changed) {
+    break;
+  }
+}

apps/backend/src/server/server.ts

@@ -1,4 +1,5 @@
 import "@/polyfills";
+import "./env-expand";
 import "@/instrument";
 import { getEnvVariable } from "@hexclave/shared/dist/utils/env";
 import { app } from "./app";