// Copyright 2016 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/*
Package logging contains a Stackdriver Logging client suitable for writing logs.
For reading logs, and working with sinks, metrics and monitored resources,
see package cloud.google.com/go/logging/logadmin.

This client uses Logging API v2.
See https://cloud.google.com/logging/docs/api/v2/ for an introduction to the API.


Creating a Client

Use a Client to interact with the Stackdriver Logging API.

	// Create a Client
	ctx := context.Background()
	client, err := logging.NewClient(ctx, "my-project")
	if err != nil {
		// TODO: Handle error.
	}


Basic Usage

For most use cases, you'll want to add log entries to a buffer to be periodically
flushed (automatically and asynchronously) to the Stackdriver Logging service.

	// Initialize a logger
	lg := client.Logger("my-log")

	// Add entry to log buffer
	lg.Log(logging.Entry{Payload: "something happened!"})


Closing your Client

You should call Client.Close before your program exits to flush any buffered log entries to the Stackdriver Logging service.

	// Close the client when finished.
	err = client.Close()
	if err != nil {
		// TODO: Handle error.
	}


Synchronous Logging

For critical errors, you may want to send your log entries immediately.
LogSync is slow and will block until the log entry has been sent, so it is
not recommended for normal use.

	err = lg.LogSync(ctx, logging.Entry{Payload: "ALERT! Something critical happened!"})
	if err != nil {
		// TODO: Handle error.
	}


Payloads

An entry payload can be a string, as in the examples above. It can also be any value
that can be marshaled to a JSON object, like a map[string]interface{} or a struct:

	type MyEntry struct {
		Name  string
		Count int
	}
	lg.Log(logging.Entry{Payload: MyEntry{Name: "Bob", Count: 3}})

If you have a []byte of JSON, wrap it in json.RawMessage:

	j := []byte(`{"Name": "Bob", "Count": 3}`)
	lg.Log(logging.Entry{Payload: json.RawMessage(j)})


The Standard Logger

You may want use a standard log.Logger in your program.

	// stdlg is an instance of *log.Logger.
	stdlg := lg.StandardLogger(logging.Info)
	stdlg.Println("some info")


Log Levels

An Entry may have one of a number of severity levels associated with it.

	logging.Entry{
		Payload: "something terrible happened!",
		Severity: logging.Critical,
	}


Viewing Logs

You can view Stackdriver logs for projects at
https://console.cloud.google.com/logs/viewer. Use the dropdown at the top left. When
running from a Google Cloud Platform VM, select "GCE VM Instance". Otherwise, select
"Google Project" and then the project ID. Logs for organizations, folders and billing
accounts can be viewed on the command line with the "gcloud logging read" command.


Grouping Logs by Request

To group all the log entries written during a single HTTP request, create two
Loggers, a "parent" and a "child," with different log IDs. Both should be in the same
project, and have the same MonitoredResource type and labels.

- Parent entries must have HTTPRequest.Request populated. (Strictly speaking, only the URL is necessary.)

- A child entry's timestamp must be within the time interval covered by the parent request. (i.e., before
the parent.Timestamp and after the parent.Timestamp - parent.HTTPRequest.Latency. This assumes the
parent.Timestamp marks the end of the request.)

- The trace field must be populated in all of the entries and match exactly.

You should observe the child log entries grouped under the parent on the console. The
parent entry will not inherit the severity of its children; you must update the
parent severity yourself.
*/
package logging // import "cloud.google.com/go/logging"
