Package sdlogger is a logger that formats entries as JSON understood by Stackdriver log collectors.

The JSON format is defined by the Google Cloud Logging plugin for fluentd, which is mainly used by Google Kubernetes Engine + Stackdriver stack. See

Though not properly documented, GAE environment also understands subset of this format.



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func Factory

func Factory(w LogEntryWriter, prototype LogEntry, mut LogEntryMutator) func(context.Context) logging.Logger

Factory returns a factory of logger.Logger instances that log to the given LogEntryWriter (usually &Sink{...}) using the LogEntry (if any) as a prototype for log entries.

For each log message, makes a copy of 'prototype', overwrites its Severity, Message, Time and Fields (keeping other fields as they are), calls 'mut' callback (which is allowed to mutate the log entry), and writes the result to LogEntryWriter. This allows to "prepopulate" fields like TraceID or OperationID in all log entries emitted by logging.Logger.

Such factory can be installed in the context via logging.SetFactory.


type CloudErrorsSink

type CloudErrorsSink struct {
	Client *errorreporting.Client
	Out    LogEntryWriter

CloudErrorsSink wraps a LogEntryWriter and an errorreporting.Client.

func (*CloudErrorsSink) Write

func (s *CloudErrorsSink) Write(l *LogEntry)

Write appends a log entry to the given writer and reports the message to the cloud error reporting for the Error severity.

type LogEntry

type LogEntry struct {
	// Severity is a string denoting the logging level of the entry.
	Severity Severity `json:"severity"`
	// Message is a single line human readable string of the log message.
	Message string `json:"message,omitempty"`
	// Timestamp is the unix timestamp of when the entry was produced.
	Timestamp Timestamp `json:"timestamp,omitempty"`
	// TraceID is 32-byte hex string with Stackdriver trace ID.
	TraceID string `json:",omitempty"`
	// TraceSampled is true if this trace will be uploaded to Stackdriver.
	TraceSampled bool `json:",omitempty"`
	// SpanID is a 16-byte hex string with Stackdriver span ID.
	SpanID string `json:",omitempty"`
	// Operation is used to group log lines from a single request together.
	Operation *Operation `json:",omitempty"`
	// RequestInfo is information about the handled HTTP request.
	RequestInfo *RequestInfo `json:"httpRequest,omitempty"`
	// Fields are extra structured data that may be tagged in the log entry.
	Fields logging.Fields `json:"fields,omitempty"`

LogEntry defines a structure of JSON log entries recognized by google-fluentd plugin on GKE.

See for a list of possible magical fields. All other fields are exposed as part of jsonPayload in Stackdriver logs.

type LogEntryMutator

type LogEntryMutator func(context.Context, *LogEntry)

LogEntryMutator may mutate log entries before they are written.

type LogEntryWriter

type LogEntryWriter interface {
	// Write appends a log entry to the output.

LogEntryWriter knows how to write LogEntries to some output.

type Operation

type Operation struct {
	ID string `json:"id"`

Operation is used to group log lines from a single request together.

type RequestInfo

type RequestInfo struct {
	Method       string `json:"requestMethod"` // e.g. "GET"
	URL          string `json:"requestUrl"`    // e.g. "http://host/path"
	Status       int    `json:"status"`        // e.g. 200
	RequestSize  string `json:"requestSize"`   // e.g. "123123"
	ResponseSize string `json:"responseSize"`  // e.g. "2324"
	UserAgent    string `json:"userAgent"`     // e.g. "Mozilla/4.0 ..."
	RemoteIP     string `json:"remoteIp"`      // e.g. ""
	Latency      string `json:"latency"`       // e.g. "3.5s"

RequestInfo contains information about handled HTTP request.

See following definition for all fields we can possibly expose here:

type Severity

type Severity string

Severity is a string denoting the logging level of the entry.

Must be one of the predefined constants, otherwise Stackdriver may not recognize it.

const (
	UnknownSeverity Severity = ""
	DebugSeverity   Severity = "DEBUG"
	InfoSeverity    Severity = "INFO"
	WarningSeverity Severity = "WARNING"
	ErrorSeverity   Severity = "ERROR"

All allowed severities. Using other values results in undefined behavior.

func LevelToSeverity

func LevelToSeverity(l logging.Level) Severity

LevelToSeverity converts logging level to the corresponding severity.

type SeverityTracker

type SeverityTracker struct {
	Out LogEntryWriter
	// contains filtered or unexported fields

SeverityTracker wraps LogEntryWriter and observes severity of messages there.

func (*SeverityTracker) MaxSeverity

func (s *SeverityTracker) MaxSeverity() Severity

MaxSeverity returns maximum severity observed thus far or "".

func (*SeverityTracker) Write

func (s *SeverityTracker) Write(l *LogEntry)

Write is part of LogEntryWriter interface.

type Sink

type Sink struct {
	Out io.Writer
	// contains filtered or unexported fields

Sink takes care of JSON-serializing log entries and synchronizing writes to an io.Writer (usually stdout or stderr).

Implements LogEntryWriter.

Sink can either be used directly for fine-grain control of what is getting logged, or via a logging.Logger for interoperability with most of LUCI code.

There should be at most one Sink instance assigned to a given io.Writer, shared by all Logger instances writing to it. Violating this requirement may cause malformed log lines.

func (*Sink) Write

func (s *Sink) Write(l *LogEntry)

Write appends a log entry to the output by JSON-serializing and writing it.

Panics if the LogEntry can't be serialized (this should not be possible). Ignores errors from io.Writer.

type Timestamp

type Timestamp struct {
	Seconds int64 `json:"seconds"`
	Nanos   int64 `json:"nanos"`

Timestamp represents a unix timestamp.

func ToTimestamp

func ToTimestamp(t time.Time) Timestamp

ToTimestamp converts time.Time to Timestamp.