feat(config): stream type for bunyan config

docs/example-config.yml

@@ -0,0 +1,5 @@
+data:
+  logger:
+    level: debug
+    name: salty-dog
+    stream: !stream stderr

src/config/index.ts

@@ -7,6 +7,7 @@ import { promisify } from 'util';
 import { envType } from 'src/config/type/Env';
 import { includeSchema, includeType } from 'src/config/type/Include';
 import { regexpType } from 'src/config/type/Regexp';
+import { streamType } from 'src/config/type/Stream';
 import { NotFoundError } from 'src/error/NotFoundError';
 
 export const CONFIG_ENV = 'SALTY_HOME';
@@ -14,6 +15,7 @@ export const CONFIG_SCHEMA = Schema.create([DEFAULT_SAFE_SCHEMA], [
   envType,
   includeType,
   regexpType,
+  streamType,
 ]);
 
 includeSchema.schema = CONFIG_SCHEMA;

src/config/type/Stream.ts

@@ -0,0 +1,23 @@
+import { Type as YamlType } from 'js-yaml';
+
+import { NotFoundError } from 'src/error/NotFoundError';
+
+const ALLOWED_STREAMS = new Set([
+  'stdout',
+  'stderr',
+]);
+
+export const streamType = new YamlType('!stream', {
+  kind: 'scalar',
+  resolve(name: string) {
+    if (ALLOWED_STREAMS.has(name) && Reflect.has(process, name)) {
+      return true;
+    } else {
+      throw new NotFoundError(`process stream not found: ${name}`);
+    }
+  },
+  construct(name: string) {
+    return Reflect.get(process, name);
+  },
+});
+