Exhaust every request body before closing it (#5166) (#5479)

From the documentation:
> The default HTTP client's Transport may not
> reuse HTTP/1.x "keep-alive" TCP connections if the Body is
> not read to completion and closed.

This effectively enable keep-alive for the fixed requests.

Signed-off-by: Romain Baugue <romain.baugue@elwinar.com>

discovery/marathon/marathon.go

@@ -17,6 +17,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"math/rand"
 	"net"
@@ -306,7 +307,10 @@ func fetchApps(ctx context.Context, client *http.Client, url string) (*appList,
 	if err != nil {
 		return nil, err
 	}
-	defer resp.Body.Close()
+	defer func() {
+		io.Copy(ioutil.Discard, resp.Body)
+		resp.Body.Close()
+	}()
 
 	if (resp.StatusCode < 200) || (resp.StatusCode >= 300) {
 		return nil, errors.Errorf("non 2xx status '%v' response during marathon service discovery", resp.StatusCode)

documentation/examples/custom-sd/adapter-usage/main.go

@@ -17,6 +17,8 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"io"
+	"io/ioutil"
 	"net"
 	"net/http"
 	"os"
@@ -98,7 +100,10 @@ func (d *discovery) parseServiceNodes(resp *http.Response, name string) (*target
 	}
 
 	dec := json.NewDecoder(resp.Body)
-	defer resp.Body.Close()
+	defer func() {
+		io.Copy(ioutil.Discard, resp.Body)
+		resp.Body.Close()
+	}()
 	err := dec.Decode(&nodes)
 
 	if err != nil {

documentation/examples/remote_storage/remote_storage_adapter/opentsdb/client.go

@@ -17,6 +17,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"io"
 	"io/ioutil"
 	"math"
 	"net/http"
@@ -114,7 +115,10 @@ func (c *Client) Write(samples model.Samples) error {
 	if err != nil {
 		return err
 	}
-	defer resp.Body.Close()
+	defer func() {
+		io.Copy(ioutil.Discard, resp.Body)
+		resp.Body.Close()
+	}()
 
 	// API returns status code 204 for successful writes.
 	// http://opentsdb.net/docs/build/html/api_http/put.html

notifier/notifier.go

@@ -19,6 +19,8 @@ import (
 	"crypto/md5"
 	"encoding/json"
 	"fmt"
+	"io"
+	"io/ioutil"
 	"net"
 	"net/http"
 	"net/url"
@@ -508,7 +510,10 @@ func (n *Manager) sendOne(ctx context.Context, c *http.Client, url string, b []b
 	if err != nil {
 		return err
 	}
-	defer resp.Body.Close()
+	defer func() {
+		io.Copy(ioutil.Discard, resp.Body)
+		resp.Body.Close()
+	}()
 
 	// Any HTTP status 2xx is OK.
 	if resp.StatusCode/100 != 2 {

notifier/notifier_test.go

@@ -14,6 +14,7 @@
 package notifier
 
 import (
+	"bytes"
 	"context"
 	"crypto/md5"
 	"encoding/json"
@@ -224,7 +225,7 @@ func TestCustomDo(t *testing.T) {
 			testutil.Equals(t, testURL, req.URL.String())
 
 			return &http.Response{
-				Body: ioutil.NopCloser(nil),
+				Body: ioutil.NopCloser(bytes.NewBuffer(nil)),
 			}, nil
 		},
 	}, nil)

scrape/scrape.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"math"
 	"net/http"
 	"sync"
@@ -543,7 +544,10 @@ func (s *targetScraper) scrape(ctx context.Context, w io.Writer) (string, error)
 	if err != nil {
 		return "", err
 	}
-	defer resp.Body.Close()
+	defer func() {
+		io.Copy(ioutil.Discard, resp.Body)
+		resp.Body.Close()
+	}()
 
 	if resp.StatusCode != http.StatusOK {
 		return "", errors.Errorf("server returned HTTP status %s", resp.Status)

storage/remote/client.go

@@ -95,7 +95,10 @@ func (c *Client) Store(ctx context.Context, req []byte) error {
 		// recoverable.
 		return recoverableError{err}
 	}
-	defer httpResp.Body.Close()
+	defer func() {
+		io.Copy(ioutil.Discard, httpResp.Body)
+		httpResp.Body.Close()
+	}()
 
 	if httpResp.StatusCode/100 != 2 {
 		scanner := bufio.NewScanner(io.LimitReader(httpResp.Body, maxErrMsgLen))
@@ -148,7 +151,10 @@ func (c *Client) Read(ctx context.Context, query *prompb.Query) (*prompb.QueryRe
 	if err != nil {
 		return nil, errors.Wrap(err, "error sending request")
 	}
-	defer httpResp.Body.Close()
+	defer func() {
+		io.Copy(ioutil.Discard, httpResp.Body)
+		httpResp.Body.Close()
+	}()
 	if httpResp.StatusCode/100 != 2 {
 		return nil, errors.Errorf("server returned HTTP status %s", httpResp.Status)
 	}