LoggerEntry

LoggerEntry is a logger with preset fields; passing at least one field returns a new immutable Entry.

Creation

// From a Logger
entry := logger.WithFields(
    dd.String("service", "api"),
    dd.String("env", "prod"),
)

// Via the global Logger
entry := dd.Default().WithFields(
    dd.String("service", "api"),
)

// Single-field shortcut
entry := logger.WithField("request_id", "req-123")

Chained Calls

// Append fields (returns a new Entry; the original is unchanged)
base := logger.WithFields(dd.String("svc", "api"))
enhanced := base.WithFields(dd.String("env", "prod"))

// New fields overwrite same-named old fields
entry := base.WithField("svc", "gateway")  // svc becomes "gateway"

Immutability

When at least one field is passed, WithFields / WithField return a new LoggerEntry; the original Entry is unaffected and safe for concurrent use. Calling WithFields() with no fields is a no-op optimization that returns the original Entry directly.

Logging Methods

All Logger logging methods are also available on the Entry; emitted logs automatically carry the preset fields:

Basic Logs

Method	Description
Debug(args ...any)	Debug level
Info(args ...any)	Info level
Warn(args ...any)	Warn level
Error(args ...any)	Error level
Fatal(args ...any)	Fatal level (by default calls os.Exit(1), deferred functions will not run; customizable via FatalHandler)
Log(level LogLevel, args ...any)	Specified level

Formatted Logs

Method	Description
Debugf(format string, args ...any)	Formatted Debug
Infof(format string, args ...any)	Formatted Info
Warnf(format string, args ...any)	Formatted Warn
Errorf(format string, args ...any)	Formatted Error
Fatalf(format string, args ...any)	Formatted Fatal (by default calls os.Exit(1), deferred functions will not run; customizable via FatalHandler)
Logf(level LogLevel, format string, args ...any)	Formatted, specified level

Structured Logs

Method	Description
DebugWith(msg string, fields ...Field)	Structured Debug (merges preset fields)
InfoWith(msg string, fields ...Field)	Structured Info
WarnWith(msg string, fields ...Field)	Structured Warn
ErrorWith(msg string, fields ...Field)	Structured Error
FatalWith(msg string, fields ...Field)	Structured Fatal (by default calls os.Exit(1), deferred functions will not run; customizable via FatalHandler)
LogWith(level LogLevel, msg string, fields ...Field)	Structured, specified level

Print Methods

Method	Description
Print(args ...any)	Output to the Writer (LevelInfo, includes caller info, subject to security filtering)
Println(args ...any)	Same behavior as Print
Printf(format string, args ...any)	Formatted output (LevelInfo, includes caller info, subject to security filtering)

Field Chaining

Method	Description
WithFields(fields ...Field) *LoggerEntry	Append fields, returns a new Entry
WithField(key string, value any) *LoggerEntry	Add a single field, returns a new Entry

Usage Examples

HTTP Request Logging

func handleRequest(w http.ResponseWriter, r *http.Request) {
    reqLog := logger.WithFields(
        dd.String("method", r.Method),
        dd.String("path", r.URL.Path),
        dd.String("remote", r.RemoteAddr),
    )

    reqLog.Info("request started")

    // Handling logic...

    reqLog.WithField("status", 200).Info("request completed")
}

Service Component Logging

serviceLog := logger.WithFields(
    dd.String("service", "user-service"),
    dd.String("version", "2.1.0"),
)

serviceLog.Info("service started")

dbLog := serviceLog.WithField("component", "database")
dbLog.Info("connected")
dbLog.ErrorWith("query failed", dd.Err(err))

Next Steps

• Logger -- Logger instance methods
• Structured Fields -- Field constructors
• Package Functions -- Global log functions