FFM-11006 Add Connection close header (#141)

* FFM-11006 Add Connection close header

**What**

- Adds a connection close header to the http requests to prevent
  connections being re-used

**Why**

- We were seeing every other POST /metrics request fail with an EOF
  error but when we ran with the debugger this didn't happen. After some
research it seems like this can happen due to the way the http client
tries to re-use connections. Adding this header means we'll close the
connection once the request has completed

**Testing**

- Tested this fix out locally

Co-authored-by: Erdi Rowlands <erdirowlands@gmail.com>

.harness/ffgolangserversdk.yaml

@@ -36,7 +36,7 @@ pipeline:
                   identifier: Submodule_Init
                   spec:
                     connectorRef: DockerHub
-                    image: golang:1.18.6
+                    image: golang:1.19.9
                     shell: Sh
                     command: "mkdir -p ~/.ssh\nssh-keyscan -t rsa github.com >> ~/.ssh/known_hosts\n\ncat <<EOF >> .gitmodules\n[submodule \"tests/ff-test-cases\"]\n\tpath = tests/ff-test-cases\n\turl = https://github.com/drone/ff-test-cases.git\nEOF\n\ngit submodule update --init --recursive"
               - parallel:
@@ -46,7 +46,7 @@ pipeline:
                       identifier: Build_and_Test
                       spec:
                         connectorRef: DockerHub
-                        image: golang:1.18.6
+                        image: golang:1.19.9
                         shell: Sh
                         command: |-
                           go install github.com/jstemmer/go-junit-report@latest

client/client.go

@@ -5,16 +5,17 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"github.com/cenkalti/backoff/v4"
-	"github.com/harness/ff-golang-server-sdk/sdk_codes"
-	"golang.org/x/sync/errgroup"
 	"log"
 	"net/http"
 	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
 
+	"github.com/cenkalti/backoff/v4"
+	"github.com/harness/ff-golang-server-sdk/sdk_codes"
+	"golang.org/x/sync/errgroup"
+
 	"github.com/harness/ff-golang-server-sdk/evaluation"
 	"github.com/harness/ff-golang-server-sdk/logger"
 
@@ -393,14 +394,20 @@ func (c *CfClient) authenticate(ctx context.Context) error {
 	// Use a custom transport which adds headers for tracking usage
 	// The `WithRequestEditorFn` cannot be used for SSE requests, so we need to provide a custom transport to the
 	// http client so that these headers can be added to all requests.
-	getHeadersFn := func() (map[string]string, error) {
-		return map[string]string{
+	getHeadersFn := func(r *http.Request) (map[string]string, error) {
+		headers := map[string]string{
 			"User-Agent":            "GoSDK/" + analyticsservice.SdkVersion,
 			"Harness-SDK-Info":      fmt.Sprintf("Go %s Server", analyticsservice.SdkVersion),
 			"Harness-EnvironmentID": c.environmentID,
-		}, nil
+		}
+
+		if strings.Contains(r.URL.Path, "/metrics") && r.Method == http.MethodPost {
+			headers["Connection"] = "close"
+		}
+
+		return headers, nil
 	}
-	
+
 	// Wrap the httpClient's transport with our own custom transport, which currently just adds extra headers
 	// for analytics purposes.
 	// If the httpClient doesn't have a Transport we can honour, then just use a default transport.

client/transport.go

@@ -3,7 +3,7 @@ package client
 import "net/http"
 
 // HeadersFn is a function type that provides headers dynamically.
-type HeadersFn func() (map[string]string, error)
+type HeadersFn func(r *http.Request) (map[string]string, error)
 
 // customTransport wraps an http.RoundTripper and allows adding headers dynamically. This means we can still use
 // the goretryable-http client's transport, or a user's transport if they've provided their own http client.
@@ -22,7 +22,7 @@ func NewCustomTransport(baseTransport http.RoundTripper, getHeaderFn HeadersFn)
 
 func (t *customTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 	// Retrieve the headers using the provided function.
-	headers, err := t.getHeaders()
+	headers, err := t.getHeaders(req)
 	if err != nil {
 		return nil, err
 	}