fix NewObjectId when running in container (globalsign#33)

Author: funny-falcon-at-joomcode

bson/bson.go

@@ -257,7 +257,7 @@ func readRandomUint32() uint32 {
 // machineId stores machine id generated once and used in subsequent calls
 // to NewObjectId function.
 var machineId = readMachineId()
-var processId = os.Getpid()
+var processId = readProcessId()
 
 // readMachineId generates and returns a machine id.
 // If this function fails to get the hostname it will cause a runtime error.
@@ -278,6 +278,23 @@ func readMachineId() []byte {
 	return id
 }
 
+// readProcessId reads process id.
+// If it is too small, then probably we are running in docker, and pid will be always constant. In this case lets generate it.
+func readProcessId() uint16 {
+	pid := os.Getpid()
+	if pid > 10 {
+		// ok, we are not in docker (I hope so)
+		return uint16(pid)
+	}
+	var buf [2]byte
+	_, err := io.ReadFull(rand.Reader, buf[:])
+	if err != nil {
+		// ough, fallback to pid
+		return uint16(pid)
+	}
+	return uint16(buf[0])<<8 | uint16(buf[1])
+}
+
 // NewObjectId returns a new unique ObjectId.
 func NewObjectId() ObjectId {
 	var b [12]byte