Add new line protocol parser and serializer, influxdb output (#3924)

plugins/serializers/influx/reader.go

@@ -0,0 +1,58 @@
+package influx
+
+import (
+	"bytes"
+	"io"
+
+	"github.com/influxdata/telegraf"
+)
+
+// reader is an io.Reader for line protocol.
+type reader struct {
+	metrics    []telegraf.Metric
+	serializer *Serializer
+	offset     int
+	buf        *bytes.Buffer
+}
+
+// NewReader creates a new reader over the given metrics.
+func NewReader(metrics []telegraf.Metric, serializer *Serializer) io.Reader {
+	return &reader{
+		metrics:    metrics,
+		serializer: serializer,
+		offset:     0,
+		buf:        bytes.NewBuffer(make([]byte, 0, serializer.maxLineBytes)),
+	}
+}
+
+// SetMetrics changes the metrics to be read.
+func (r *reader) SetMetrics(metrics []telegraf.Metric) {
+	r.metrics = metrics
+	r.offset = 0
+	r.buf.Reset()
+}
+
+// Read reads up to len(p) bytes of the current metric into p, each call will
+// only serialize at most one metric so the number of bytes read may be less
+// than p.  Subsequent calls to Read will read the next metric until all are
+// emitted.  If a metric cannot be serialized, an error will be returned, you
+// may resume with the next metric by calling Read again.  When all metrics
+// are emitted the err is io.EOF.
+func (r *reader) Read(p []byte) (int, error) {
+	if r.buf.Len() > 0 {
+		return r.buf.Read(p)
+	}
+
+	if r.offset >= len(r.metrics) {
+		return 0, io.EOF
+	}
+
+	_, err := r.serializer.Write(r.buf, r.metrics[r.offset])
+	r.offset += 1
+	if err != nil {
+		r.buf.Reset()
+		return 0, err
+	}
+
+	return r.buf.Read(p)
+}