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// SPDX-License-Identifier: Unlicense OR MIT
package log
/*
#cgo LDFLAGS: -llog
#include <stdlib.h>
#include <android/log.h>
*/
import "C"
import (
"bufio"
"log"
"os"
"runtime"
"syscall"
"unsafe"
)
// 1024 is the truncation limit from android/log.h, plus a \n.
const logLineLimit = 1024
var logTag = C.CString(appID)
func init() {
// Android's logcat already includes timestamps.
log.SetFlags(log.Flags() &^ log.LstdFlags)
log.SetOutput(new(androidLogWriter))
// Redirect stdout and stderr to the Android logger.
logFd(os.Stdout.Fd())
logFd(os.Stderr.Fd())
}
type androidLogWriter struct {
// buf has room for the maximum log line, plus a terminating '\0'.
buf [logLineLimit + 1]byte
}
func (w *androidLogWriter) Write(data []byte) (int, error) {
// Truncate the buffer, leaving space for the '\0'.
if max := len(w.buf) - 1; len(data) > max {
data = data[:max]
}
buf := w.buf[:len(data)+1]
copy(buf, data)
// Terminating '\0'.
buf[len(data)] = 0
C.__android_log_write(C.ANDROID_LOG_INFO, logTag, (*C.char)(unsafe.Pointer(&buf[0])))
return len(data), nil
}
func logFd(fd uintptr) {
r, w, err := os.Pipe()
if err != nil {
panic(err)
}
if err := syscall.Dup3(int(w.Fd()), int(fd), syscall.O_CLOEXEC); err != nil {
panic(err)
}
go func() {
lineBuf := bufio.NewReaderSize(r, logLineLimit)
// The buffer to pass to C, including the terminating '\0'.
buf := make([]byte, lineBuf.Size()+1)
cbuf := (*C.char)(unsafe.Pointer(&buf[0]))
for {
line, _, err := lineBuf.ReadLine()
if err != nil {
break
}
copy(buf, line)
buf[len(line)] = 0
C.__android_log_write(C.ANDROID_LOG_INFO, logTag, cbuf)
}
// The garbage collector doesn't know that w's fd was dup'ed.
// Avoid finalizing w, and thereby avoid its finalizer closing its fd.
runtime.KeepAlive(w)
}()
}
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