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+// Copyright 2015 CoreOS, Inc.
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+//
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+// Licensed under the Apache License, Version 2.0 (the "License");
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+// you may not use this file except in compliance with the License.
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+// You may obtain a copy of the License at
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+//
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+// http://www.apache.org/licenses/LICENSE-2.0
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+//
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+// Unless required by applicable law or agreed to in writing, software
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+// distributed under the License is distributed on an "AS IS" BASIS,
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+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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+// See the License for the specific language governing permissions and
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+// limitations under the License.
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+
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+// Package journal provides write bindings to the systemd journal
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+package journal
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+
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+import (
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+ "bytes"
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+ "encoding/binary"
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+ "errors"
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+ "fmt"
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+ "io"
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+ "io/ioutil"
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+ "net"
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+ "os"
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+ "strconv"
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+ "strings"
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+ "syscall"
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+)
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+
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+// Priority of a journal message
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+type Priority int
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+
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+const (
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+ PriEmerg Priority = iota
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+ PriAlert
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+ PriCrit
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+ PriErr
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+ PriWarning
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+ PriNotice
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+ PriInfo
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+ PriDebug
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+)
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+
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+var conn net.Conn
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+
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+func init() {
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+ var err error
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+ conn, err = net.Dial("unixgram", "/run/systemd/journal/socket")
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+ if err != nil {
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+ conn = nil
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+ }
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+}
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+
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+// Enabled returns true iff the systemd journal is available for logging
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+func Enabled() bool {
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+ return conn != nil
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+}
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+
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+// Send a message to the systemd journal. vars is a map of journald fields to
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+// values. Fields must be composed of uppercase letters, numbers, and
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+// underscores, but must not start with an underscore. Within these
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+// restrictions, any arbitrary field name may be used. Some names have special
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+// significance: see the journalctl documentation
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+// (http://www.freedesktop.org/software/systemd/man/systemd.journal-fields.html)
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+// for more details. vars may be nil.
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+func Send(message string, priority Priority, vars map[string]string) error {
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+ if conn == nil {
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+ return journalError("could not connect to journald socket")
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+ }
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+
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+ data := new(bytes.Buffer)
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+ appendVariable(data, "PRIORITY", strconv.Itoa(int(priority)))
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+ appendVariable(data, "MESSAGE", message)
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+ for k, v := range vars {
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+ appendVariable(data, k, v)
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+ }
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+
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+ _, err := io.Copy(conn, data)
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+ if err != nil && isSocketSpaceError(err) {
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+ file, err := tempFd()
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+ if err != nil {
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+ return journalError(err.Error())
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+ }
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+ _, err = io.Copy(file, data)
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+ if err != nil {
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+ return journalError(err.Error())
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+ }
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+
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+ rights := syscall.UnixRights(int(file.Fd()))
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+
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+ /* this connection should always be a UnixConn, but better safe than sorry */
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+ unixConn, ok := conn.(*net.UnixConn)
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+ if !ok {
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+ return journalError("can't send file through non-Unix connection")
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+ }
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+ unixConn.WriteMsgUnix([]byte{}, rights, nil)
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+ } else if err != nil {
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+ return journalError(err.Error())
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+ }
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+ return nil
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+}
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+
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+func appendVariable(w io.Writer, name, value string) {
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+ if !validVarName(name) {
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+ journalError("variable name contains invalid character, ignoring")
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+ }
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+ if strings.ContainsRune(value, '\n') {
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+ /* When the value contains a newline, we write:
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+ * - the variable name, followed by a newline
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+ * - the size (in 64bit little endian format)
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+ * - the data, followed by a newline
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+ */
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+ fmt.Fprintln(w, name)
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+ binary.Write(w, binary.LittleEndian, uint64(len(value)))
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+ fmt.Fprintln(w, value)
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+ } else {
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+ /* just write the variable and value all on one line */
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+ fmt.Fprintf(w, "%s=%s\n", name, value)
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+ }
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+}
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+
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+func validVarName(name string) bool {
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+ /* The variable name must be in uppercase and consist only of characters,
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+ * numbers and underscores, and may not begin with an underscore. (from the docs)
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+ */
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+
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+ valid := name[0] != '_'
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+ for _, c := range name {
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+ valid = valid && ('A' <= c && c <= 'Z') || ('0' <= c && c <= '9') || c == '_'
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+ }
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+ return valid
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+}
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+
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+func isSocketSpaceError(err error) bool {
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+ opErr, ok := err.(*net.OpError)
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+ if !ok {
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+ return false
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+ }
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+
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+ sysErr, ok := opErr.Err.(syscall.Errno)
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+ if !ok {
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+ return false
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+ }
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+
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+ return sysErr == syscall.EMSGSIZE || sysErr == syscall.ENOBUFS
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+}
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+
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+func tempFd() (*os.File, error) {
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+ file, err := ioutil.TempFile("/dev/shm/", "journal.XXXXX")
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+ if err != nil {
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+ return nil, err
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+ }
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+ syscall.Unlink(file.Name())
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+ if err != nil {
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+ return nil, err
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+ }
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+ return file, nil
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+}
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+
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+func journalError(s string) error {
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+ s = "journal error: " + s
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+ fmt.Fprintln(os.Stderr, s)
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+ return errors.New(s)
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+}
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Xiang Li