Add a MuteByEnvVars example to show how #175/#176 could be done.

examples/mute-by-envvars-stream.js

@@ -0,0 +1,108 @@
+/*
+ * Example of a MuteByEnvVars Bunyan stream to mute log records matching some
+ * envvars. I.e. as a way to do:
+ *      https://github.com/trentm/node-bunyan/issues/175
+ *      https://github.com/trentm/node-bunyan/pull/176
+ * outside of core.
+ *
+ * Usage:
+ *  $ node mute-by-envvars-stream.js
+ *  {"name":"mute-by-envvars-stream",...,"msg":"hi raw stream"}
+ *  {"name":"mute-by-envvars-stream",...,"foo":"bar","msg":"added \"foo\" key"}
+ *
+ *  $ BUNYAN_MUTE_foo=bar node mute-by-envvars-stream.js
+ *  {"name":"mute-by-envvars-stream",...,"msg":"hi raw stream"}
+ *
+ * Dev Notes:
+ * - This currently treats all 'BUNYAN_MUTE_foo=bar' envvar values as strings.
+ *   That might not be desired.
+ * - This is a quick implementation: inefficient and not well tested.
+ * - Granted that Bunyan streams are hard to compose. For example, using
+ *   `MuteByEnvVars` to be a filter before writing logs to a *file* is a pain
+ *   for the file open/close handling. It would be nicer if Bunyan had a
+ *   pipeline of "filters" (more like core node.js streams).
+ */
+
+var bunyan = require('../lib/bunyan');
+
+
+function MuteByEnvVars(opts) {
+    opts = opts || {};
+    this.stream = opts.stream || process.stdout;
+
+    var PREFIX = 'BUNYAN_MUTE_';
+
+    // Process the env once.
+    this.mutes = {};
+    for (k in process.env) {
+        if (k.indexOf(PREFIX) === 0) {
+            this.mutes[k.slice(PREFIX.length)] = process.env[k];
+        }
+    }
+}
+
+/**
+ * Returns the given object's "o" property named by "s" using the dot notation.
+ *
+ * this({ name: { first: "value" } }, name.first) == "value"
+ *
+ * This is a verbatin copy of http://stackoverflow.com/a/6491621/433814
+ *
+ * @param o {object} is an object.
+ * @param s (string} is the string in the "dot" notation.
+ */
+MuteByEnvVars.prototype._objectFromDotNotation = function (o, s) {
+    s = s.replace(/\[(\w+)\]/g, '.$1');  // convert indexes to properties
+    s = s.replace(/^\./, ''); // strip leading dot
+    var a = s.split('.');
+    while (a.length) {
+        var n = a.shift();
+        if (n in o) {
+            o = o[n];
+        } else {
+            return;
+        }
+    }
+    return o;
+}
+
+MuteByEnvVars.prototype.write = function (rec) {
+    if (typeof (rec) !== 'object') {
+        console.error('error: MuteByEnvVars raw stream got a non-object '
+            + 'record: %j', rec);
+        return;
+    }
+
+    var muteRec = false;
+    var keys = Object.keys(this.mutes);
+    for (var i = 0; i < keys.length; i++) {
+        var k = keys[i];
+        var match = this._objectFromDotNotation(rec, k);
+        if (match === this.mutes[k]) {
+            muteRec = true;
+            break;
+        }
+    }
+    if (!muteRec) {
+        this.stream.write(JSON.stringify(rec) + '\n');
+    }
+}
+
+
+
+// ---- example usage of the MuteByEnvVars stream
+
+var log = bunyan.createLogger({
+    name: 'mute-by-envvars-stream',
+    streams: [
+        {
+            level: 'info',
+            stream: new MuteByEnvVars(),
+            type: 'raw'
+        },
+    ]
+});
+
+
+log.info('hi raw stream');
+log.info({foo: 'bar'}, 'added "foo" key');