fix: Override headers passed to GQL service (#103)

* fix: Override headers passed to GQL service

* test message

* always override

* tests

* fix tests

do.go

@@ -23,6 +23,8 @@ const (
 	opMutation
 )
 
+const applicationJSON = "application/json"
+
 // Operation is an encapsulation of all of the elements that are used to compose an operation
 // using struct tags. The OperationType field should always be passed by reference in order for
 // the data to be able to be marshaled back into it.
@@ -166,12 +168,15 @@ func (c *Client) do(ctx context.Context, body io.Reader, headers http.Header) (j
 	req.Header = headers
 
 	// The Content-Type of this request will always be application/json as per the GraphQL specification.
-	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Content-Type", applicationJSON)
 
 	// We don't want this header to be set because then we won't get the luxury of the transport automatically
 	// decoding the response body for us, if it is encoded.
 	req.Header.Del("Accept-Encoding")
 
+	// Ensure headers compliance with GQL service expectations
+	headers.Set("Accept", applicationJSON)
+
 	// Do the GraphQL request using the HTTP client that was configured for this GraphQL client.
 	resp, err := c.httpClient.Do(req)
 	if err != nil {

do_test.go

@@ -1,7 +1,9 @@
 package goql
 
 import (
+	"bytes"
 	"context"
+	"encoding/json"
 	"net/http"
 	"testing"
 
@@ -221,3 +223,32 @@ func TestDoStruct(t *testing.T) {
 		t.Run(test.Name, fn)
 	}
 }
+
+func TestDoHeadersOverride(t *testing.T) {
+	ts := graphql_test.NewServer(t, true)
+	t.Cleanup(ts.Close)
+	var buf bytes.Buffer
+	query := "query"
+	if err := json.NewEncoder(&buf).Encode(request{ //nolint:gocritic
+		Query:     query,
+		Variables: nil,
+	}); err != nil {
+		t.Fatalf("error building buffer: %v", err)
+	}
+	headers := http.Header{}
+	client := NewClient(ts.URL, DefaultClientOptions)
+	client.do(context.Background(), &buf, headers)
+	if headers.Get("Accept") != applicationJSON {
+		t.Fatal("Unexpected header Accept")
+	}
+	headers.Set("Accept", "some header")
+	client.do(context.Background(), &buf, headers)
+	if headers.Get("Accept") != applicationJSON {
+		t.Fatal("Unexpected header Accept value")
+	}
+	headers.Set("Accept", applicationJSON)
+	client.do(context.Background(), &buf, headers)
+	if headers.Get("Accept") != applicationJSON {
+		t.Fatal("Unexpected header Accept value")
+	}
+}