Console Transport

The console transport writes log entries to os.Stdout (info, debug, trace) or os.Stderr (warn, error, fatal) as plain text: the message followed by logfmt-style key=value pairs. One line per entry, no colors, no JSON.

For human-readable dev output, prefer Pretty

The console transport is intentionally minimal. For day-to-day local development you almost certainly want the Pretty Transport: it provides color-coded levels, themes, and three view modes that make multi-field logs easy to scan. Pick console only when you specifically need a no-color, no-JSON, logfmt-style writer (e.g. CI logs that humans grep, fixture generation, deliberate plain output).

For production logging, use the structured transport or one of the logger wrappers.

go get go.loglayer.dev/transports/console

Basic Usage

import (
    "go.loglayer.dev"
    "go.loglayer.dev/transports/console"
)

log := loglayer.New(loglayer.Config{
    Transport: console.New(console.Config{}),
})

log.Info("hello world")
log.WithMetadata(loglayer.Metadata{"id": 42, "user": "alice"}).Info("logged in")

hello world
logged in id=42 user=alice

Output Routing

By default:

• Debug, Info → os.Stdout
• Warn, Error, Fatal → os.Stderr

Set Writer to override and send everything to a single writer (useful in tests or when redirecting output):

console.New(console.Config{Writer: &buf})

Config

type Config struct {
    transport.BaseConfig

    MessageField string // when set, emit one structured object per entry
    DateField    string // include timestamp under this key
    LevelField   string // include level under this key

    DateFn   func() string                              // override default ISO-8601 timestamp
    LevelFn  func(loglayer.LogLevel) string             // override level string
    MessageFn func(loglayer.TransportParams) string     // format the entire message
    Stringify bool                                       // JSON-encode the structured object

    Writer io.Writer
}

Logfmt Rendering

Fields and metadata render as key=value pairs after the message, in sorted-by-key order:

log.WithFields(loglayer.Fields{"requestId": "abc"}).
    WithMetadata(loglayer.Metadata{"status": 200, "bytes": 1024}).
    Info("request served")
// "request served bytes=1024 requestId=abc status=200"

Values render based on type:

• Strings: bare when safe, quoted when they contain spaces, =, ", \, or control characters. \", \\, \n, \r, \t are escaped inside quotes.
• Numbers and bools: rendered directly (id=42, enabled=true).
• time.Time: RFC3339Nano (ts=2026-04-26T12:00:00Z).
• error: the result of Error(), quoted if needed.
• Anything else (maps, structs, slices): JSON-encoded and treated as a quoted string (obj="{\"a\":1}").

Keys are sorted to keep output stable across runs (Go map iteration is non-deterministic).

Level / Timestamp

By default the line is just message + fields. Add a level or timestamp via LevelField / DateField:

console.New(console.Config{
    DateField:  "ts",
    LevelField: "level",
})

log.Info("served")
// "served level=info ts=2026-04-26T12:00:00Z"

Override the value formatters with LevelFn / DateFn:

console.New(console.Config{
    LevelField: "lvl",
    LevelFn:    func(l loglayer.LogLevel) string { return strings.ToUpper(l.String()) },
    DateField:  "ts",
    DateFn:     func() string { return time.Now().Format(time.RFC822) },
})

Single-Object Output (MessageField)

Setting MessageField switches the transport into structured-object mode. Instead of msg key=value..., it builds one map containing the message + data + (optionally) timestamp/level fields, and prints just that:

console.New(console.Config{
    MessageField: "msg",
    DateField:    "ts",
    LevelField:   "level",
})

log.Info("structured")
// map[level:info msg:structured ts:2026-04-26T...]

Add Stringify: true to JSON-encode the object instead:

console.New(console.Config{MessageField: "msg", Stringify: true})
log.Info("json out")
// {"msg":"json out"}

If you only want JSON output, prefer the structured transport; it's purpose-built for that.

Custom Message Function

MessageFn replaces the default message-then-logfmt assembly with a single string of your choice. It receives the full TransportParams so you can format based on the level, fields, or anything else.

console.New(console.Config{
    MessageFn: func(p loglayer.TransportParams) string {
        return fmt.Sprintf("[%s] %s", p.LogLevel, strings.Join(stringifyMessages(p.Messages), " | "))
    },
})

When MessageFn is set, the logfmt tail still appends after its return value (use it for header formatting, not full takeover).

Metadata Handling

Map metadata is merged into the same data bag as fields and errors. Struct metadata is JSON-roundtripped into root fields before logfmt rendering. See Metadata for the design.

Threat Model: Plaintext (Not for Pipelines)

User message strings are sanitized for control characters before output (CR, LF, ESC, Unicode bidi controls, zero-width joiners; see sanitize.Message). Field and metadata string values are quoted and \n / \r / \t are escaped, so user-controlled string fields can't forge log lines. Non-string values pass through their typed renderer (numbers, bools, JSON encoding for nested), which doesn't introduce control characters.

If your service has untrusted input flowing into a logged field and the resulting log lines are read by a parser sensitive to subtle escape variations, use structured instead. Structured emits JSON; encoding/json applies a strict, well-specified escaping. Console (like pretty) is for the developer's terminal during local dev.

Fatal Behavior

This transport writes fatal entries normally; whether the process actually exits is the core's decision via Config.DisableFatalExit (default: exit). See Fatal Exits the Process.