Add an example showing how to use raw streams for #130

examples/specific-level-streams.js

@@ -0,0 +1,77 @@
+#!/usr/bin/env node
+/**
+ * <https://github.com/trentm/node-bunyan/issues/130> was a request to have
+ * bunyan core support logging some levels to one stream and others to another,
+ * *not* limited by bunyan's current support that a stream `level` implies
+ * "that level and higher".
+ *
+ * Let's do that with a custom raw stream.
+ */
+
+var bunyan = require('../lib/bunyan'),
+    safeCycles = bunyan.safeCycles;
+var fs = require('fs');
+
+/**
+ * Use case #1: cli tool that outputs errors on stderr and everything else on
+ * stdout.
+ *
+ * First make a raw bunyan stream (i.e. an object with a `.write(rec)`).
+ */
+function SpecificLevelStream(levels, stream) {
+    var self = this;
+    this.levels = {};
+    levels.forEach(function (lvl) {
+        self.levels[bunyan.resolveLevel(lvl)] = true;
+    });
+    this.stream = stream;
+}
+SpecificLevelStream.prototype.write = function (rec) {
+    if (this.levels[rec.level] !== undefined) {
+        var str = JSON.stringify(rec, safeCycles()) + '\n';
+        this.stream.write(str);
+    }
+}
+
+var log1 = bunyan.createLogger({
+    name: 'use-case-1',
+    streams: [{
+        level: 'trace',
+        type: 'raw',
+        stream: new SpecificLevelStream(
+            ['trace', 'debug', 'info', 'warn'],
+            process.stdout)
+    },{
+        level: 'error',
+        type: 'raw',
+        stream: new SpecificLevelStream(
+            ['error'],
+            process.stderr)
+    }]
+});
+
+log1.info('hi at info level (this should be on stdout)');
+log1.error('alert alert (this should be on stderr)');
+
+
+/**
+ * Use case #2: nginx-style logger that separates error- and access-logs
+ */
+var log2 = bunyan.createLogger({
+    name: 'use-case-2',
+    streams: [{
+        level: 'info',
+        type: 'raw',
+        stream: new SpecificLevelStream(
+            ['info'],
+            fs.createWriteStream('specific-level-stream-http.log',
+                {flags: 'a', encoding: 'utf8'}))
+    },{
+        level: 'warn',
+        path: 'specific-level-stream-http.err.log'
+    }
+  ]
+});
+
+log2.info('200 GET /blah');
+log2.error('500 GET /boom');