fix: handle changes/<change>/patch JSON marshalling error

changes_revision.go

@@ -2,6 +2,7 @@ package gerrit
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"net/url"
 )
@@ -140,6 +141,35 @@ type PatchOptions struct {
 	Path string `url:"path,omitempty"`
 }
 
+// StringPointerWriter is a new type based on *string.
+// We would like it to implement Writer interface so that we can avoid
+// unmarshalling of non JSON responses by Client.Do
+type StringPointerWriter struct {
+	Target *string
+}
+
+func NewStringPointerWriter(target *string) (*StringPointerWriter, error) {
+	if target == nil {
+		return nil, errors.New("StringPointerWriter: target *string cannot be nil")
+	}
+	return &StringPointerWriter{Target: target}, nil
+}
+
+// Write implements the io.Writer interface for *StringPointerWriter.
+func (spw *StringPointerWriter) Write(p []byte) (n int, err error) {
+	// Check if the StringPointerWriter pointer itself is nil, or if its Target is nil.
+	if spw == nil || spw.Target == nil {
+		return 0, errors.New("StringPointerWriter: receiver or target *string is nil, cannot write")
+	}
+
+	// *(spw.Target) gives us the actual string value.
+	// We append the new data (converted from []byte to string) to it.
+	*(spw.Target) = *(spw.Target) + string(p)
+
+	// Return the number of bytes written and no error.
+	return len(p), nil
+}
+
 // GetDiff gets the diff of a file from a certain revision.
 //
 // Gerrit API docs: https://gerrit-review.googlesource.com/Documentation/rest-api-changes.html#get-diff
@@ -445,8 +475,17 @@ func (s *ChangesService) GetPatch(ctx context.Context, changeID, revisionID stri
 		return nil, nil, err
 	}
 
-	v := new(string)
-	resp, err := s.client.Do(req, v)
+	strVal := ""
+	var v *string = &strVal
+
+	// Create an instance of our writer struct since the /patch endpoint
+	// returns a base64 encoded string which cannot be marshalled as JSON.
+	stringWriter, err := NewStringPointerWriter(v)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	resp, err := s.client.Do(req, stringWriter)
 	if err != nil {
 		return nil, resp, err
 	}

changes_revision_test.go

@@ -2,6 +2,7 @@ package gerrit_test
 
 import (
 	"context"
+	"encoding/base64"
 	"fmt"
 	"net/http"
 	"net/http/httptest"
@@ -82,3 +83,41 @@ func TestChangesService_ListFilesReviewed(t *testing.T) {
 		t.Errorf("client.Changes.ListFilesReviewed:\ngot:  %q\nwant: %q", got, want)
 	}
 }
+
+func TestChangesService_GetPatch(t *testing.T) {
+	rawPatch := `diff --git a/COMMIT_MSG b/COMMIT_MSG
+index 123..456 100644
+--- a/COMMIT_MSG
++++ b/COMMIT_MSG
+@@ -1,1 +1,1 @@
+-Old subject
++New subject for A
+diff --git a/fileA.txt b/fileA.txt
+new file mode 100644
+index 0000000..abc 100644
+--- /dev/null
++++ b/fileA.txt
+@@ -0,0 +1 @@
++Content for A
+`
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if got, want := r.URL.String(), "/changes/123/revisions/456/patch"; got != want {
+			t.Errorf("request URL:\ngot:  %q\nwant: %q", got, want)
+		}
+		encodedPatchContent := base64.StdEncoding.EncodeToString(
+			[]byte(rawPatch))
+		fmt.Fprint(w, encodedPatchContent)
+	}))
+	defer ts.Close()
+
+	ctx := context.Background()
+	client := newClient(ctx, t, ts)
+	got, _, err := client.Changes.GetPatch(ctx, "123", "456", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := base64.StdEncoding.EncodeToString([]byte(rawPatch))
+	if !reflect.DeepEqual(*got, want) {
+		t.Errorf("client.Changes.GetPatch:\ngot:  %q\nwant: %q", *got, want)
+	}
+}