out_gstdout

README

Example: out_gstdout

The following example code implements a simple output plugin that prints the records to the standard output interface (STDOUT).

Every output plugin go through four callbacks associated to different phases:

Plugin Phase	Callback
Registration	FLBPluginRegister()
Initialization	FLBPluginInit()
Runtime Flush	FLBPluginFlush()
Exit	FLBPluginExit()

Plugin Registration

When Fluent Bit loads a Golang plugin, it lookup and load the registration callback that aims to populate the internal structure with plugin name and description among others:

//export FLBPluginRegister
func FLBPluginRegister(ctx unsafe.Pointer) int {
	return output.FLBPluginRegister(ctx, "gstdout", "Stdout GO!")
}

This function is invoked at start time before any configuration is done inside the engine.

Plugin Initialization

Before the engine starts, it initialize all plugins that were requested to start. Upon initialization a configuration context already exists, so the plugin can ask for configuration parameters or do any other internal checks. E.g:

//export FLBPluginInit
func FLBPluginInit(ctx unsafe.Pointer) int {
	return output.FLB_OK
}

The function must return FLB_OK when it initialized properly or FLB_ERROR if something went wrong. If the plugin reports an error, the engine will not load the instance.

Runtime Flush

Upon flush time, when Fluent Bit want's to flush it buffers, the runtime flush callback will be triggered.

The callback will receive a raw buffer of msgpack data with it proper bytes length and the tag associated.

//export FLBPluginFlush
func FLBPluginFlush(data unsafe.Pointer, length C.int, tag *C.char) int {
    return output.FLB_OK
}

for more details about how to process the incoming msgpack data, refer to the out_gstdout.go file.

When done, there are three returning values available:

Return value	Description
FLB_OK	The data have been processed normally.
FLB_ERROR	An internal error have ocurred, the plugin will not handle the set of records/data again.
FLB_RETRY	A recoverable error have ocurred, the engine can try to flush the records/data later.

Plugin Exit

When Fluent Bit will stop using the instance of the plugin, it will trigger the exit callback. e.g:

//export FLBPluginExit
func FLBPluginExit() int {
	return output.FLB_OK
}