Add output plugins (incl. OpenTelemetry support)

.gitignore

@@ -1,5 +1,5 @@
-build/
 node_modules/
 coverage/
+build/
 .vscode/
 .nyc_output/

docs/advanced-usage/07-output-plugins.md

@@ -0,0 +1,97 @@
+---
+layout: default
+title: Output Plugins
+parent: Advanced Usage
+nav_order: 7
+permalink: /advanced-usage/output-plugins
+---
+
+# Output Plugins
+
+Output plugins define where and how log records are emitted. The library supports multiple active plugins simultaneously and ships with two built-in implementations.
+
+## Plugin Management
+
+Output plugins can be managed at runtime using the following methods:
+
+| Method | Description |
+|---|---|
+| `log.addOutputPlugin(plugin)` | Adds a plugin alongside any existing ones. |
+| `log.setOutputPlugins(...plugins)` | Replaces all existing plugins with the given one(s). |
+| `log.getOutputPlugins()` | Returns the list of currently registered plugins. |
+
+## StdoutOutputPlugin
+
+The default plugin, registered automatically on startup.
+It writes log records to stdout or a configured [sink function](/cf-nodejs-logging-support/advanced-usage/custom-sink-function). 
+It remains active unless explicitly replaced via `setOutputPlugins()`.
+
+## OpenTelemetryLogsOutputPlugin <span class="label label-yellow">Experimental</span>
+
+> **Note:** This plugin relies on [`@opentelemetry/api-logs`](https://www.npmjs.com/package/@opentelemetry/api-logs), which is marked as experimental by the OpenTelemetry project. Therefore consider this plugin experimental as well and be prepared for potential breaking changes in future releases.
+
+Available since version 8.1.0. Emits log records via the [OpenTelemetry Logs API](https://opentelemetry.io/docs/specs/otel/logs/).
+Only message logs are forwarded, whereas request logs are not emitted.
+It requires a configured OTel SDK with a `LoggerProvider` and appropriate exporters, either via the global OTel SDK (e.g. `@opentelemetry/sdk-node`) or passed explicitly to the constructor. 
+The plugin itself does not initialize any OTel SDK components.
+
+### Registering the Plugin
+
+```js
+import log, { OpenTelemetryLogsOutputPlugin } from 'cf-nodejs-logging-support';
+
+// Keep stdout output and also emit via OTel:
+log.addOutputPlugin(new OpenTelemetryLogsOutputPlugin());
+
+// Emit via OTel only:
+log.setOutputPlugins(new OpenTelemetryLogsOutputPlugin());
+```
+
+The constructor accepts the following optional parameters:
+
+| Parameter | Type | Description |
+|---|---|---|
+| `loggerProvider` | `LoggerProvider` | OTel `LoggerProvider` to use. Defaults to the global provider. |
+| `context` | `Context` or `(record) => Context | undefined` | OTel context to attach to emitted log records. Can be a static `Context` or a resolver function that receives the log record and returns a context. |
+
+### Including Fields as Attributes
+
+By default, only custom fields are forwarded as OTel log attributes. This can be changed with `setIncludeFieldsAsAttributes()`:
+
+```js
+import log, { OpenTelemetryLogsOutputPlugin, FieldInclusionMode } from 'cf-nodejs-logging-support';
+
+const plugin = new OpenTelemetryLogsOutputPlugin();
+plugin.setIncludeFieldsAsAttributes(FieldInclusionMode.AllFields);
+
+log.addOutputPlugin(plugin);
+```
+
+| Mode | Description |
+|---|---|
+| `FieldInclusionMode.CustomFieldsOnly` | Only custom fields are added as attributes (default) |
+| `FieldInclusionMode.AllFields` | All log record fields are added as attributes |
+| `FieldInclusionMode.None` | No fields are added as attributes |
+
+### Exception Attributes
+
+When logging an error, the plugin automatically maps error information to the standard OTel exception attributes:
+
+| OTel Attribute | Source |
+|---|---|
+| `exception.type` | Error name |
+| `exception.message` | Error message |
+| `exception.stacktrace` | Stack trace |
+
+### Logging Level Mapping
+
+The plugin maps the library's log levels to OTel severity levels as follows:
+
+| Logging Level | OTel Severity Text | OTel Severity Number |
+|---|---|---|
+| `error` | `ERROR` | 17 |
+| `warn` | `WARN` | 13 |
+| `info` | `INFO` | 9 |
+| `verbose` | `DEBUG2` | 6 |
+| `debug` | `DEBUG` | 5 |
+| `silly` | `TRACE` | 1 |

docs/advanced-usage/07-winston-transport.md → docs/advanced-usage/08-winston-transport.md

@@ -2,7 +2,7 @@
 layout: default
 title: Winston Transport
 parent: Advanced Usage
-nav_order: 7
+nav_order: 8
 permalink: /advanced-usage/winston-transport
 ---
 

docs/index.markdown

@@ -47,9 +47,9 @@ Create child loggers that inherit and extend a logging context, ideal for
 tracing a single request or transaction across multiple modules.
 </div>
 
-<div class="landing-feature">
-<h3>TypeScript ready</h3>
-Full TypeScript typings are included.
+<div class="landing-feature landing-feature-experimental">
+<h3>OpenTelemetry<span class="label label-yellow">Experimental</span></h3>
+Emit logs via the OpenTelemetry Logs API using the <a href="/cf-nodejs-logging-support/advanced-usage/output-plugins">built-in output plugin</a>.
 </div>
 
 <div class="landing-feature">