integrations
diff --git a/‎github/acc_test.go‎
Lines changed: 13 additions & 5 deletions b/‎github/acc_test.go‎
Lines changed: 13 additions & 5 deletions
diff --git a/‎github/config.go‎
Lines changed: 5 additions & 1 deletion b/‎github/config.go‎
Lines changed: 5 additions & 1 deletion
diff --git a/‎github/config_test.go‎
Lines changed: 214 additions & 0 deletions b/‎github/config_test.go‎
Lines changed: 214 additions & 0 deletions
@@ -49,6 +49,9 @@ type testAccConfig struct {
 	testPublicRepository              string
 	testPublicRepositoryOwner         string
 	testPublicReleaseId               int
+	testPublicRelaseAssetId           string
+	testPublicRelaseAssetName         string
+	testPublicReleaseAssetContent     string
 	testPublicTemplateRepository      string
 	testPublicTemplateRepositoryOwner string
 	testGHActionsAppInstallationId    int
@@ -105,11 +108,16 @@ func TestMain(m *testing.M) {
 	}
 
 	config := testAccConfig{
-		baseURL:                           baseURL,
-		authMode:                          authMode,
-		testPublicRepository:              "terraform-provider-github",
-		testPublicRepositoryOwner:         "integrations",
-		testPublicReleaseId:               186531906,
+		baseURL:                   baseURL,
+		authMode:                  authMode,
+		testPublicRepository:      "terraform-provider-github",
+		testPublicRepositoryOwner: "integrations",
+		testPublicReleaseId:       186531906,
+		// The terraform-provider-github_6.4.0_manifest.json asset ID from
+		// https://github.com/integrations/terraform-provider-github/releases/tag/v6.4.0
+		testPublicRelaseAssetId:           "207956097",
+		testPublicRelaseAssetName:         "terraform-provider-github_6.4.0_manifest.json",
+		testPublicReleaseAssetContent:     "{\n  \"version\": 1,\n  \"metadata\": {\n    \"protocol_versions\": [\n      \"5.0\"\n    ]\n  }\n}",
 		testPublicTemplateRepository:      "template-repository",
 		testPublicTemplateRepositoryOwner: "template-repository",
 		testGHActionsAppInstallationId:    15368,
 
@@ -189,7 +189,11 @@ func (injector *previewHeaderInjectorTransport) RoundTrip(req *http.Request) (*h
 		header := req.Header.Get(name)
 		if header == "" {
 			header = value
-		} else {
+			// NOTE: Some API endpoints expect a single Accept: application/octet-stream header.
+			// If one has been set, it's necessary to preserve it as-is, without
+			// appending previewHeaders value.
+			// See https://github.com/google/go-github/pull/3392
+		} else if strings.ToLower(name) != "accept" || header != "application/octet-stream" {
 			header = strings.Join([]string{header, value}, ",")
 		}
 		req.Header.Set(name, header)
 
@@ -2,6 +2,8 @@ package github
 
 import (
 	"context"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 
 	"github.com/shurcooL/githubv4"
@@ -300,3 +302,215 @@ func TestAccConfigMeta(t *testing.T) {
 		}
 	})
 }
+
+func TestPreviewHeaderInjectorTransport_RoundTrip(t *testing.T) {
+	tests := []struct {
+		name                string
+		previewHeaders      map[string]string
+		existingHeaders     map[string]string
+		expectedHeaders     map[string]string
+		expectRoundTripCall bool
+	}{
+		{
+			name:                "empty preview headers",
+			previewHeaders:      map[string]string{},
+			existingHeaders:     map[string]string{"User-Agent": "test"},
+			expectedHeaders:     map[string]string{"User-Agent": "test"},
+			expectRoundTripCall: true,
+		},
+		{
+			name: "add new preview header",
+			previewHeaders: map[string]string{
+				"Accept": "application/vnd.github.v3+json",
+			},
+			existingHeaders: map[string]string{},
+			expectedHeaders: map[string]string{
+				"Accept": "application/vnd.github.v3+json",
+			},
+			expectRoundTripCall: true,
+		},
+		{
+			name: "append to existing header",
+			previewHeaders: map[string]string{
+				"Accept": "application/vnd.github.preview+json",
+			},
+			existingHeaders: map[string]string{
+				"Accept": "application/json",
+			},
+			expectedHeaders: map[string]string{
+				"Accept": "application/json,application/vnd.github.preview+json",
+			},
+			expectRoundTripCall: true,
+		},
+		{
+			name: "preserve existing Accept application/octet-stream",
+			previewHeaders: map[string]string{
+				"Accept": "application/vnd.github.preview+json",
+			},
+			existingHeaders: map[string]string{
+				"Accept": "application/octet-stream",
+			},
+			expectedHeaders: map[string]string{
+				"Accept": "application/octet-stream",
+			},
+			expectRoundTripCall: true,
+		},
+		{
+			name: "preserve existing accept application/octet-stream (lowercase)",
+			previewHeaders: map[string]string{
+				"accept": "application/vnd.github.preview+json",
+			},
+			existingHeaders: map[string]string{
+				"accept": "application/octet-stream",
+			},
+			expectedHeaders: map[string]string{
+				"Accept": "application/octet-stream",
+			},
+			expectRoundTripCall: true,
+		},
+		{
+			name: "preserve existing Accept application/octet-stream (mixed case)",
+			previewHeaders: map[string]string{
+				"AcCePt": "application/vnd.github.preview+json",
+			},
+			existingHeaders: map[string]string{
+				"Accept": "application/octet-stream",
+			},
+			expectedHeaders: map[string]string{
+				"Accept": "application/octet-stream",
+			},
+			expectRoundTripCall: true,
+		},
+		{
+			name: "multiple preview headers",
+			previewHeaders: map[string]string{
+				"Accept":               "application/vnd.github.v3+json",
+				"X-GitHub-Api-Version": "2022-11-28",
+			},
+			existingHeaders: map[string]string{},
+			expectedHeaders: map[string]string{
+				"Accept":               "application/vnd.github.v3+json",
+				"X-Github-Api-Version": "2022-11-28",
+			},
+			expectRoundTripCall: true,
+		},
+		{
+			name: "append multiple preview headers to existing",
+			previewHeaders: map[string]string{
+				"Accept":               "application/vnd.github.v3+json",
+				"X-GitHub-Api-Version": "2022-11-28",
+			},
+			existingHeaders: map[string]string{
+				"Accept":               "application/json",
+				"X-GitHub-Api-Version": "2021-01-01",
+			},
+			expectedHeaders: map[string]string{
+				"Accept":               "application/json,application/vnd.github.v3+json",
+				"X-Github-Api-Version": "2021-01-01,2022-11-28",
+			},
+			expectRoundTripCall: true,
+		},
+		{
+			name: "non-accept headers always append",
+			previewHeaders: map[string]string{
+				"X-Custom-Header": "preview-value",
+			},
+			existingHeaders: map[string]string{
+				"X-Custom-Header": "application/octet-stream",
+			},
+			expectedHeaders: map[string]string{
+				"X-Custom-Header": "application/octet-stream,preview-value",
+			},
+			expectRoundTripCall: true,
+		},
+		{
+			name: "accept header with different value appends",
+			previewHeaders: map[string]string{
+				"Accept": "application/vnd.github.preview+json",
+			},
+			existingHeaders: map[string]string{
+				"Accept": "application/json",
+			},
+			expectedHeaders: map[string]string{
+				"Accept": "application/json,application/vnd.github.preview+json",
+			},
+			expectRoundTripCall: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Create a mock RoundTripper that records the request
+			var capturedRequest *http.Request
+			mockRT := &mockRoundTripper{
+				roundTripFunc: func(req *http.Request) (*http.Response, error) {
+					capturedRequest = req
+					return &http.Response{
+						StatusCode: http.StatusOK,
+						Body:       http.NoBody,
+					}, nil
+				},
+			}
+
+			injector := &previewHeaderInjectorTransport{
+				rt:             mockRT,
+				previewHeaders: tt.previewHeaders,
+			}
+
+			// Create a test request with existing headers
+			req := httptest.NewRequest(http.MethodGet, "https://api.github.com/test", nil)
+			for name, value := range tt.existingHeaders {
+				req.Header.Set(name, value)
+			}
+
+			// Execute RoundTrip
+			resp, err := injector.RoundTrip(req)
+			// Verify no error
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+
+			// Verify response
+			if resp == nil {
+				t.Fatal("expected non-nil response")
+			}
+
+			// Verify RoundTrip was called on the underlying transport
+			if tt.expectRoundTripCall && capturedRequest == nil {
+				t.Fatal("expected RoundTrip to be called on underlying transport")
+			}
+
+			// Verify headers in the captured request
+			if capturedRequest != nil {
+				for name, expectedValue := range tt.expectedHeaders {
+					actualValue := capturedRequest.Header.Get(name)
+					if actualValue != expectedValue {
+						t.Errorf("header %q: expected %q, got %q", name, expectedValue, actualValue)
+					}
+				}
+
+				// Verify no unexpected headers were added
+				for name := range capturedRequest.Header {
+					if _, exists := tt.expectedHeaders[name]; !exists {
+						// Allow headers that were in existingHeaders but not in expectedHeaders
+						if _, wasExisting := tt.existingHeaders[name]; !wasExisting {
+							t.Errorf("unexpected header %q: %q", name, capturedRequest.Header.Get(name))
+						}
+					}
+				}
+			}
+		})
+	}
+}
+
+// mockRoundTripper is a mock implementation of http.RoundTripper for testing.
+type mockRoundTripper struct {
+	roundTripFunc func(*http.Request) (*http.Response, error)
+}
+
+func (m *mockRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	if m.roundTripFunc != nil {
+		return m.roundTripFunc(req)
+	}
+	return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}, nil
+}