codeartifact: normalize Cargo metadata accepts

internal/strategy/codeartifact.go

@@ -303,7 +303,7 @@ func (c *CodeArtifact) do(r *http.Request, token string) (*http.Response, error)
 	}
 	copyHeaders(upstream.Header, codeArtifactRequestHeaders(r.Header))
 	if shouldRewriteCodeArtifactMetadata(target.Path) {
-		stripCodeArtifactMetadataRequestHeaders(upstream.Header)
+		normalizeCodeArtifactMetadataRequestHeaders(upstream.Header, target.Path)
 	}
 	setCodeArtifactAuthorization(upstream, token)
 
@@ -389,7 +389,7 @@ func (c *CodeArtifact) followCrossOriginRedirect(
 	}
 	copyHeaders(redirected.Header, codeArtifactRequestHeaders(r.Header))
 	if rewriteMetadata {
-		stripCodeArtifactMetadataRequestHeaders(redirected.Header)
+		normalizeCodeArtifactMetadataRequestHeaders(redirected.Header, c.originURL(r).Path)
 	}
 
 	resp, err := c.client.Do(redirected)

internal/strategy/codeartifact_metadata.go

@@ -41,7 +41,7 @@ func codeArtifactPackageFormat(path string) string {
 	return parts[0]
 }
 
-func stripCodeArtifactMetadataRequestHeaders(headers http.Header) {
+func normalizeCodeArtifactMetadataRequestHeaders(headers http.Header, path string) {
 	for _, name := range []string{
 		"Accept-Encoding",
 		"If-Match",
@@ -53,6 +53,9 @@ func stripCodeArtifactMetadataRequestHeaders(headers http.Header) {
 	} {
 		headers.Del(name)
 	}
+	if codeArtifactPackageFormat(path) == codeArtifactCargoFormat {
+		headers.Set("Accept", "application/json")
+	}
 }
 
 func isCodeArtifactJSONResponse(path string, headers http.Header) bool {

internal/strategy/codeartifact_metadata_test.go

@@ -15,11 +15,13 @@ import (
 
 func TestCodeArtifactRewritesPackageMetadata(t *testing.T) {
 	tests := []struct {
-		name        string
-		path        string
-		contentType string
-		body        func(string) string
-		want        func(string) string
+		name             string
+		path             string
+		contentType      string
+		requestAccept    string
+		wantOriginAccept string
+		body             func(string) string
+		want             func(string) string
 	}{
 		{
 			name: "npm tarball URL",
@@ -32,9 +34,11 @@ func TestCodeArtifactRewritesPackageMetadata(t *testing.T) {
 			},
 		},
 		{
-			name:        "Cargo download template and anonymous access",
-			path:        "/cargo/repository/config.json",
-			contentType: "application/octet-stream",
+			name:             "Cargo download template and anonymous access",
+			path:             "/cargo/repository/config.json",
+			contentType:      "application/octet-stream",
+			requestAccept:    "text/plain",
+			wantOriginAccept: "application/json",
 			body: func(origin string) string {
 				return `{"dl":"` + origin + `/cargo/repository/crates/{crate}/{version}","api":"` + origin + `/cargo/repository/-","auth-required":true}`
 			},
@@ -91,6 +95,9 @@ func TestCodeArtifactRewritesPackageMetadata(t *testing.T) {
 			originURL = originServer.URL
 			proxyURL := "https://cachew.example.com/" + originServer.Listener.Addr().String()
 			req := httptest.NewRequest(http.MethodGet, codeArtifactPath(originServer, test.path), nil).WithContext(ctx)
+			if test.requestAccept != "" {
+				req.Header.Set("Accept", test.requestAccept)
+			}
 			req.Header.Set("Accept-Encoding", "gzip")
 			req.Header.Set("If-None-Match", `"old-metadata"`)
 			req.Header.Set("Range", "bytes=0-10")
@@ -107,6 +114,7 @@ func TestCodeArtifactRewritesPackageMetadata(t *testing.T) {
 			mu.Lock()
 			headers := observedHeaders.Clone()
 			mu.Unlock()
+			assert.Equal(t, test.wantOriginAccept, headers.Get("Accept"))
 			assert.Equal(t, "", headers.Get("Accept-Encoding"))
 			assert.Equal(t, "", headers.Get("If-None-Match"))
 			assert.Equal(t, "", headers.Get("Range"))
@@ -197,6 +205,7 @@ func TestCodeArtifactRejectsUnsafePackageMetadata(t *testing.T) {
 
 func TestCodeArtifactRewritesRedirectedCargoMetadata(t *testing.T) {
 	type observedHeaders struct {
+		accept         string
 		acceptEncoding string
 		ifNoneMatch    string
 		rangeHeader    string
@@ -205,6 +214,7 @@ func TestCodeArtifactRewritesRedirectedCargoMetadata(t *testing.T) {
 	var originURL string
 	download := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		observed = observedHeaders{
+			accept:         r.Header.Get("Accept"),
 			acceptEncoding: r.Header.Get("Accept-Encoding"),
 			ifNoneMatch:    r.Header.Get("If-None-Match"),
 			rangeHeader:    r.Header.Get("Range"),
@@ -228,6 +238,7 @@ func TestCodeArtifactRewritesRedirectedCargoMetadata(t *testing.T) {
 	transport.DisableCompression = true
 	strategy.client.Transport = transport
 	req := httptest.NewRequest(http.MethodGet, codeArtifactPath(originServer, "/cargo/repository/config.json"), nil).WithContext(ctx)
+	req.Header.Set("Accept", "text/plain")
 	req.Header.Set("Accept-Encoding", "gzip")
 	req.Header.Set("If-None-Match", `"metadata"`)
 	req.Header.Set("Range", "bytes=0-10")
@@ -238,7 +249,7 @@ func TestCodeArtifactRewritesRedirectedCargoMetadata(t *testing.T) {
 	assert.Equal(t, http.StatusOK, w.Code)
 	proxyURL := "https://cachew.example.com/" + originServer.Listener.Addr().String()
 	assertJSONEqual(t, `{"dl":"`+proxyURL+`/cargo/repository/crates/{crate}/{version}","auth-required":false}`, w.Body.String())
-	assert.Equal(t, observedHeaders{}, observed)
+	assert.Equal(t, observedHeaders{accept: "application/json"}, observed)
 }
 
 func TestCodeArtifactValidatesProxyBaseURL(t *testing.T) {