Implement fastly.env.get as a way to read environment variables (#50)

C@E [exposes various pieces of information about the service and host as environment variables](https://developer.fastly.com/reference/compute/ecp-env/). This patch adds an official way to read those variables.

The patch also removes the previous, undocumented way this information was exposed, as more discussion lead to the consensus that this approach makes more sense.

Author: tschneidereit

c-dependencies/js-compute-runtime/js-compute-builtins.cpp

@@ -424,6 +424,35 @@ namespace Logger {
   }
 }
 
+namespace Env {
+  bool env_get(JSContext* cx, unsigned argc, Value* vp) {
+    CallArgs args = CallArgsFromVp(argc, vp);
+    if (!args.requireAtLeast(cx, "fastly.env.get", 1))
+      return false;
+
+    size_t var_name_len;
+    UniqueChars var_name_chars = encode(cx, args[0], &var_name_len);
+    if (!var_name_chars) {
+      return false;
+    }
+    RootedString env_var(cx, JS_NewStringCopyZ(cx, getenv(var_name_chars.get())));
+    if (!env_var) return false;
+
+    args.rval().setString(env_var);
+    return true;
+  }
+
+  const JSFunctionSpec methods[] = {
+    JS_FN("get", env_get, 1, 0),
+  JS_FS_END};
+
+  JSObject* create(JSContext* cx) {
+    RootedObject env(cx, JS_NewPlainObject(cx));
+    if (!env || !JS_DefineFunctions(cx, env, methods)) return nullptr;
+    return env;
+  }
+}
+
 namespace URL {
   bool is_instance(JS::Value);
   JSObject* create(JSContext* cx, SpecString url_str, const JSUrl* base = nullptr);
@@ -436,6 +465,11 @@ namespace Fastly {
 
   static bool debug_logging_enabled = false;
 
+  static PersistentRooted<JSObject*> env;
+
+  static PersistentRooted<JSObject*> baseURL;
+  static PersistentRooted<JSString*> defaultBackend;
+
   bool dump(JSContext* cx, unsigned argc, Value* vp) {
     CallArgs args = CallArgsFromVp(argc, vp);
     if (!args.requireAtLeast(cx, __func__, 1))
@@ -543,8 +577,11 @@ namespace Fastly {
     JS_FS_END
   };
 
-  static PersistentRooted<JSObject*> baseURL;
-  static PersistentRooted<JSString*> defaultBackend;
+  bool env_get(JSContext* cx, unsigned argc, Value* vp) {
+    CallArgs args = CallArgsFromVp(argc, vp);
+    args.rval().setObject(*env);
+    return true;
+  }
 
   bool baseURL_get(JSContext* cx, unsigned argc, Value* vp) {
     CallArgs args = CallArgsFromVp(argc, vp);
@@ -587,6 +624,7 @@ namespace Fastly {
   }
 
   const JSPropertySpec properties[] = {
+    JS_PSG("env", env_get, JSPROP_ENUMERATE),
     JS_PSGS("baseURL", baseURL_get, baseURL_set, JSPROP_ENUMERATE),
     JS_PSGS("defaultBackend", defaultBackend_get, defaultBackend_set, JSPROP_ENUMERATE),
   JS_PS_END};
@@ -595,7 +633,10 @@ namespace Fastly {
     RootedObject fastly(cx, JS_NewPlainObject(cx));
     if (!fastly) return false;
 
+    env.init(cx, Env::create(cx));
+    if (!env) return false;
     baseURL.init(cx);
+    defaultBackend.init(cx);
 
     if (!JS_DefineProperty(cx, global, "fastly", fastly, 0)) return false;
     return JS_DefineFunctions(cx, fastly, methods) &&
@@ -3157,56 +3198,6 @@ namespace ClientInfo {
   }
 }
 
-namespace ServiceInfo {
-  namespace Slots { enum {
-    Count
-  };};
-
-  static constexpr char ENV_CACHE_GENERATION[] = "FASTLY_CACHE_GENERATION";
-  static constexpr char ENV_CUSTOMER_ID[] = "FASTLY_CUSTOMER_ID";
-  static constexpr char ENV_HOSTNAME[] = "FASTLY_HOSTNAME";
-  static constexpr char ENV_POP[] = "FASTLY_POP";
-  static constexpr char ENV_REGION[] = "FASTLY_REGION";
-  static constexpr char ENV_SERVICE_ID[] = "FASTLY_SERVICE_ID";
-  static constexpr char ENV_SERVICE_VERSION[] = "FASTLY_SERVICE_VERSION";
-  static constexpr char ENV_TRACE_ID[] = "FASTLY_TRACE_ID";
-
-  const unsigned ctor_length = 0;
-
-  bool check_receiver(JSContext* cx, HandleObject self, const char* method_name);
-
-  template<const char* var_name>
-  bool env_var_get(JSContext* cx, unsigned argc, Value* vp) {
-    METHOD_HEADER(0)
-
-    RootedString env_var(cx, JS_NewStringCopyZ(cx, getenv(var_name)));
-    if (!env_var) return false;
-
-    args.rval().setString(env_var);
-    return true;
-  }
-
-  const JSFunctionSpec methods[] = {
-  JS_FS_END};
-
-  const JSPropertySpec properties[] = {
-    JS_PSG("cacheGeneration", env_var_get<ENV_CACHE_GENERATION>, 0),
-    JS_PSG("customerId", env_var_get<ENV_CUSTOMER_ID>, 0),
-    JS_PSG("hostname", env_var_get<ENV_HOSTNAME>, 0),
-    JS_PSG("pop", env_var_get<ENV_POP>, 0),
-    JS_PSG("region", env_var_get<ENV_REGION>, 0),
-    JS_PSG("serviceId", env_var_get<ENV_SERVICE_ID>, 0),
-    JS_PSG("serviceVersion", env_var_get<ENV_SERVICE_VERSION>, 0),
-    JS_PSG("traceId", env_var_get<ENV_TRACE_ID>, 0),
-  JS_PS_END};
-
-  CLASS_BOILERPLATE_NO_CTOR(ServiceInfo)
-
-  JSObject* create(JSContext* cx) {
-    return JS_NewObjectWithGivenProto(cx, &class_, proto_obj);
-  }
-}
-
 
 namespace FetchEvent {
   namespace Slots { enum {
@@ -3216,7 +3207,6 @@ namespace FetchEvent {
     PendingPromiseCount,
     DecPendingPromiseCountFunc,
     ClientInfo,
-    ServiceInfo,
     Count
   };};
 
@@ -3272,22 +3262,6 @@ static PersistentRooted<JSObject*> INSTANCE;
     return true;
   }
 
-  bool service_get(JSContext* cx, unsigned argc, Value* vp) {
-    METHOD_HEADER(0)
-    RootedValue serviceInfo(cx, JS::GetReservedSlot(self, Slots::ServiceInfo));
-
-    if (serviceInfo.isUndefined()) {
-      RootedObject obj(cx, ServiceInfo::create(cx));
-      if (!obj)
-        return false;
-      serviceInfo.setObject(*obj);
-      JS::SetReservedSlot(self, Slots::ServiceInfo, serviceInfo);
-    }
-
-    args.rval().set(serviceInfo);
-    return true;
-  }
-
   static JSObject* prepare_downstream_request(JSContext* cx) {
       return Request::create(cx, RequestHandle { INVALID_HANDLE },
                              BodyHandle { INVALID_HANDLE }, true);
@@ -3682,7 +3656,6 @@ static PersistentRooted<JSObject*> INSTANCE;
 
   const JSPropertySpec properties[] = {
     JS_PSG("client", client_get, 0),
-    JS_PSG("service", service_get, 0),
     JS_PSG("request", request_get, 0),
   JS_PS_END};