dotcloud/docker

// Package export implements a serializer for the systemd Journal Export Format
// as documented at https://systemd.io/JOURNAL_EXPORT_FORMATS/
package export // import "github.com/docker/docker/daemon/logger/journald/internal/export"

import (
    "encoding/binary"
    "fmt"
    "io"
    "unicode/utf8"
)

// Returns whether s can be serialized as a field value "as they are" without
// the special binary safe serialization.
func isSerializableAsIs(s string) bool {
    if !utf8.ValidString(s) {
        return false
    }
    for _, c := range s {
        if c < ' ' && c != '\t' {
            return false
        }
    }
    return true
}

// WriteField writes the field serialized to Journal Export format to w.
//
// The variable name must consist only of uppercase characters, numbers and
// underscores. No validation or sanitization is performed.
func WriteField(w io.Writer, variable, value string) error {
    if isSerializableAsIs(value) {
        _, err := fmt.Fprintf(w, "%s=%s\n", variable, value)
        return err
    }

    if _, err := fmt.Fprintln(w, variable); err != nil {
        return err
    }
    if err := binary.Write(w, binary.LittleEndian, uint64(len(value))); err != nil {
        return err
    }
    _, err := fmt.Fprintln(w, value)
    return err
}

// WriteEndOfEntry terminates the journal entry.
func WriteEndOfEntry(w io.Writer) error {
    _, err := fmt.Fprintln(w)
    return err
}