/usr/share/gocode/src/github.com/hashicorp/serf/command/agent/log_writer.go is in golang-github-hashicorp-serf-dev 0.7.0~ds1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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import (
"sync"
)
// LogHandler interface is used for clients that want to subscribe
// to logs, for example to stream them over an IPC mechanism
type LogHandler interface {
HandleLog(string)
}
// logWriter implements io.Writer so it can be used as a log sink.
// It maintains a circular buffer of logs, and a set of handlers to
// which it can stream the logs to.
type logWriter struct {
sync.Mutex
logs []string
index int
handlers map[LogHandler]struct{}
}
// NewLogWriter creates a logWriter with the given buffer capacity
func NewLogWriter(buf int) *logWriter {
return &logWriter{
logs: make([]string, buf),
index: 0,
handlers: make(map[LogHandler]struct{}),
}
}
// RegisterHandler adds a log handler to receive logs, and sends
// the last buffered logs to the handler
func (l *logWriter) RegisterHandler(lh LogHandler) {
l.Lock()
defer l.Unlock()
// Do nothing if already registered
if _, ok := l.handlers[lh]; ok {
return
}
// Register
l.handlers[lh] = struct{}{}
// Send the old logs
if l.logs[l.index] != "" {
for i := l.index; i < len(l.logs); i++ {
lh.HandleLog(l.logs[i])
}
}
for i := 0; i < l.index; i++ {
lh.HandleLog(l.logs[i])
}
}
// DeregisterHandler removes a LogHandler and prevents more invocations
func (l *logWriter) DeregisterHandler(lh LogHandler) {
l.Lock()
defer l.Unlock()
delete(l.handlers, lh)
}
// Write is used to accumulate new logs
func (l *logWriter) Write(p []byte) (n int, err error) {
l.Lock()
defer l.Unlock()
// Strip off newlines at the end if there are any since we store
// individual log lines in the agent.
n = len(p)
if p[n-1] == '\n' {
p = p[:n-1]
}
l.logs[l.index] = string(p)
l.index = (l.index + 1) % len(l.logs)
for lh, _ := range l.handlers {
lh.HandleLog(string(p))
}
return
}
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