Naveen Sampath | 04696f7 | 2022-06-13 15:19:14 +0530 | [diff] [blame] | 1 | // Copyright 2015 CoreOS, Inc. |
| 2 | // |
| 3 | // Licensed under the Apache License, Version 2.0 (the "License"); |
| 4 | // you may not use this file except in compliance with the License. |
| 5 | // You may obtain a copy of the License at |
| 6 | // |
| 7 | // http://www.apache.org/licenses/LICENSE-2.0 |
| 8 | // |
| 9 | // Unless required by applicable law or agreed to in writing, software |
| 10 | // distributed under the License is distributed on an "AS IS" BASIS, |
| 11 | // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 12 | // See the License for the specific language governing permissions and |
| 13 | // limitations under the License. |
| 14 | |
| 15 | // Package journal provides write bindings to the local systemd journal. |
| 16 | // It is implemented in pure Go and connects to the journal directly over its |
| 17 | // unix socket. |
| 18 | // |
| 19 | // To read from the journal, see the "sdjournal" package, which wraps the |
| 20 | // sd-journal a C API. |
| 21 | // |
| 22 | // http://www.freedesktop.org/software/systemd/man/systemd-journald.service.html |
| 23 | package journal |
| 24 | |
| 25 | import ( |
| 26 | "bytes" |
| 27 | "encoding/binary" |
| 28 | "errors" |
| 29 | "fmt" |
| 30 | "io" |
| 31 | "io/ioutil" |
| 32 | "net" |
| 33 | "os" |
| 34 | "strconv" |
| 35 | "strings" |
| 36 | "sync" |
| 37 | "sync/atomic" |
| 38 | "syscall" |
| 39 | "unsafe" |
| 40 | ) |
| 41 | |
| 42 | // Priority of a journal message |
| 43 | type Priority int |
| 44 | |
| 45 | const ( |
| 46 | PriEmerg Priority = iota |
| 47 | PriAlert |
| 48 | PriCrit |
| 49 | PriErr |
| 50 | PriWarning |
| 51 | PriNotice |
| 52 | PriInfo |
| 53 | PriDebug |
| 54 | ) |
| 55 | |
| 56 | var ( |
| 57 | // This can be overridden at build-time: |
| 58 | // https://github.com/golang/go/wiki/GcToolchainTricks#including-build-information-in-the-executable |
| 59 | journalSocket = "/run/systemd/journal/socket" |
| 60 | |
| 61 | // unixConnPtr atomically holds the local unconnected Unix-domain socket. |
| 62 | // Concrete safe pointer type: *net.UnixConn |
| 63 | unixConnPtr unsafe.Pointer |
| 64 | // onceConn ensures that unixConnPtr is initialized exactly once. |
| 65 | onceConn sync.Once |
| 66 | ) |
| 67 | |
| 68 | func init() { |
| 69 | onceConn.Do(initConn) |
| 70 | } |
| 71 | |
| 72 | // Enabled checks whether the local systemd journal is available for logging. |
| 73 | func Enabled() bool { |
| 74 | onceConn.Do(initConn) |
| 75 | |
| 76 | if (*net.UnixConn)(atomic.LoadPointer(&unixConnPtr)) == nil { |
| 77 | return false |
| 78 | } |
| 79 | |
| 80 | if _, err := net.Dial("unixgram", journalSocket); err != nil { |
| 81 | return false |
| 82 | } |
| 83 | |
| 84 | return true |
| 85 | } |
| 86 | |
| 87 | // Send a message to the local systemd journal. vars is a map of journald |
| 88 | // fields to values. Fields must be composed of uppercase letters, numbers, |
| 89 | // and underscores, but must not start with an underscore. Within these |
| 90 | // restrictions, any arbitrary field name may be used. Some names have special |
| 91 | // significance: see the journalctl documentation |
| 92 | // (http://www.freedesktop.org/software/systemd/man/systemd.journal-fields.html) |
| 93 | // for more details. vars may be nil. |
| 94 | func Send(message string, priority Priority, vars map[string]string) error { |
| 95 | conn := (*net.UnixConn)(atomic.LoadPointer(&unixConnPtr)) |
| 96 | if conn == nil { |
| 97 | return errors.New("could not initialize socket to journald") |
| 98 | } |
| 99 | |
| 100 | socketAddr := &net.UnixAddr{ |
| 101 | Name: journalSocket, |
| 102 | Net: "unixgram", |
| 103 | } |
| 104 | |
| 105 | data := new(bytes.Buffer) |
| 106 | appendVariable(data, "PRIORITY", strconv.Itoa(int(priority))) |
| 107 | appendVariable(data, "MESSAGE", message) |
| 108 | for k, v := range vars { |
| 109 | appendVariable(data, k, v) |
| 110 | } |
| 111 | |
| 112 | _, _, err := conn.WriteMsgUnix(data.Bytes(), nil, socketAddr) |
| 113 | if err == nil { |
| 114 | return nil |
| 115 | } |
| 116 | if !isSocketSpaceError(err) { |
| 117 | return err |
| 118 | } |
| 119 | |
| 120 | // Large log entry, send it via tempfile and ancillary-fd. |
| 121 | file, err := tempFd() |
| 122 | if err != nil { |
| 123 | return err |
| 124 | } |
| 125 | defer file.Close() |
| 126 | _, err = io.Copy(file, data) |
| 127 | if err != nil { |
| 128 | return err |
| 129 | } |
| 130 | rights := syscall.UnixRights(int(file.Fd())) |
| 131 | _, _, err = conn.WriteMsgUnix([]byte{}, rights, socketAddr) |
| 132 | if err != nil { |
| 133 | return err |
| 134 | } |
| 135 | |
| 136 | return nil |
| 137 | } |
| 138 | |
| 139 | // Print prints a message to the local systemd journal using Send(). |
| 140 | func Print(priority Priority, format string, a ...interface{}) error { |
| 141 | return Send(fmt.Sprintf(format, a...), priority, nil) |
| 142 | } |
| 143 | |
| 144 | func appendVariable(w io.Writer, name, value string) { |
| 145 | if err := validVarName(name); err != nil { |
| 146 | fmt.Fprintf(os.Stderr, "variable name %s contains invalid character, ignoring\n", name) |
| 147 | } |
| 148 | if strings.ContainsRune(value, '\n') { |
| 149 | /* When the value contains a newline, we write: |
| 150 | * - the variable name, followed by a newline |
| 151 | * - the size (in 64bit little endian format) |
| 152 | * - the data, followed by a newline |
| 153 | */ |
| 154 | fmt.Fprintln(w, name) |
| 155 | binary.Write(w, binary.LittleEndian, uint64(len(value))) |
| 156 | fmt.Fprintln(w, value) |
| 157 | } else { |
| 158 | /* just write the variable and value all on one line */ |
| 159 | fmt.Fprintf(w, "%s=%s\n", name, value) |
| 160 | } |
| 161 | } |
| 162 | |
| 163 | // validVarName validates a variable name to make sure journald will accept it. |
| 164 | // The variable name must be in uppercase and consist only of characters, |
| 165 | // numbers and underscores, and may not begin with an underscore: |
| 166 | // https://www.freedesktop.org/software/systemd/man/sd_journal_print.html |
| 167 | func validVarName(name string) error { |
| 168 | if name == "" { |
| 169 | return errors.New("Empty variable name") |
| 170 | } else if name[0] == '_' { |
| 171 | return errors.New("Variable name begins with an underscore") |
| 172 | } |
| 173 | |
| 174 | for _, c := range name { |
| 175 | if !(('A' <= c && c <= 'Z') || ('0' <= c && c <= '9') || c == '_') { |
| 176 | return errors.New("Variable name contains invalid characters") |
| 177 | } |
| 178 | } |
| 179 | return nil |
| 180 | } |
| 181 | |
| 182 | // isSocketSpaceError checks whether the error is signaling |
| 183 | // an "overlarge message" condition. |
| 184 | func isSocketSpaceError(err error) bool { |
| 185 | opErr, ok := err.(*net.OpError) |
| 186 | if !ok || opErr == nil { |
| 187 | return false |
| 188 | } |
| 189 | |
| 190 | sysErr, ok := opErr.Err.(*os.SyscallError) |
| 191 | if !ok || sysErr == nil { |
| 192 | return false |
| 193 | } |
| 194 | |
| 195 | return sysErr.Err == syscall.EMSGSIZE || sysErr.Err == syscall.ENOBUFS |
| 196 | } |
| 197 | |
| 198 | // tempFd creates a temporary, unlinked file under `/dev/shm`. |
| 199 | func tempFd() (*os.File, error) { |
| 200 | file, err := ioutil.TempFile("/dev/shm/", "journal.XXXXX") |
| 201 | if err != nil { |
| 202 | return nil, err |
| 203 | } |
| 204 | err = syscall.Unlink(file.Name()) |
| 205 | if err != nil { |
| 206 | return nil, err |
| 207 | } |
| 208 | return file, nil |
| 209 | } |
| 210 | |
| 211 | // initConn initializes the global `unixConnPtr` socket. |
| 212 | // It is meant to be called exactly once, at program startup. |
| 213 | func initConn() { |
| 214 | autobind, err := net.ResolveUnixAddr("unixgram", "") |
| 215 | if err != nil { |
| 216 | return |
| 217 | } |
| 218 | |
| 219 | sock, err := net.ListenUnixgram("unixgram", autobind) |
| 220 | if err != nil { |
| 221 | return |
| 222 | } |
| 223 | |
| 224 | atomic.StorePointer(&unixConnPtr, unsafe.Pointer(sock)) |
| 225 | } |