fix: use readers over closers in http input

plugins/inputs/http/http.go

@@ -1,9 +1,11 @@
 package http
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"net/http"
 	"os"
 	"strings"
@@ -95,9 +97,6 @@ func (h *HTTP) gatherURL(
 	if err != nil {
 		return err
 	}
-	if body != nil {
-		defer body.Close()
-	}
 
 	request, err := http.NewRequest(h.Method, url, body)
 	if err != nil {
@@ -175,7 +174,7 @@ func (h *HTTP) gatherURL(
 	return nil
 }
 
-func makeRequestBodyReader(contentEncoding, body string) (io.ReadCloser, error) {
+func makeRequestBodyReader(contentEncoding, body string) (io.Reader, error) {
 	if body == "" {
 		return nil, nil
 	}
@@ -186,10 +185,14 @@ func makeRequestBodyReader(contentEncoding, body string) (io.ReadCloser, error)
 		if err != nil {
 			return nil, err
 		}
-		return rc, nil
+		data, err := ioutil.ReadAll(rc)
+		if err != nil {
+			return nil, err
+		}
+		return bytes.NewReader(data), nil
 	}
 
-	return io.NopCloser(reader), nil
+	return reader, nil
 }
 
 func init() {

plugins/inputs/http/http_test.go

@@ -94,6 +94,40 @@ func TestHTTPHeaders(t *testing.T) {
 	require.NoError(t, acc.GatherError(plugin.Gather))
 }
 
+func TestHTTPContentLengthHeader(t *testing.T) {
+	fakeServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/endpoint" {
+			if r.Header.Get("Content-Length") != "" {
+				_, _ = w.Write([]byte(simpleJSON))
+			} else {
+				w.WriteHeader(http.StatusForbidden)
+			}
+		} else {
+			w.WriteHeader(http.StatusNotFound)
+		}
+	}))
+	defer fakeServer.Close()
+
+	address := fakeServer.URL + "/endpoint"
+	plugin := &httpplugin.HTTP{
+		URLs:    []string{address},
+		Headers: map[string]string{},
+		Body:    "{}",
+		Log:     testutil.Logger{},
+	}
+
+	plugin.SetParserFunc(func() (telegraf.Parser, error) {
+		return parsers.NewParser(&parsers.Config{
+			DataFormat: "json",
+			MetricName: "metricName",
+		})
+	})
+
+	var acc testutil.Accumulator
+	require.NoError(t, plugin.Init())
+	require.NoError(t, acc.GatherError(plugin.Gather))
+}
+
 func TestInvalidStatusCode(t *testing.T) {
 	fakeServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusNotFound)