Add commit diff download helper

Co-Authored-By: Virgil <virgil@lethean.io>

commits.go

@@ -53,6 +53,12 @@ func (s *CommitService) Get(ctx context.Context, params Params) (*types.Commit,
 	return &out, nil
 }
 
+// GetDiffOrPatch returns a commit diff or patch as raw bytes.
+func (s *CommitService) GetDiffOrPatch(ctx context.Context, owner, repo, sha, diffType string) ([]byte, error) {
+	path := ResolvePath("/api/v1/repos/{owner}/{repo}/git/commits/{sha}.{diffType}", pathParams("owner", owner, "repo", repo, "sha", sha, "diffType", diffType))
+	return s.client.GetRaw(ctx, path)
+}
+
 // GetPullRequest returns the pull request associated with a commit SHA.
 //
 // Usage:

commits_test.go

@@ -3,6 +3,7 @@ package forge
 import (
 	"context"
 	json "github.com/goccy/go-json"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -95,6 +96,29 @@ func TestCommitService_Get_Good(t *testing.T) {
 	}
 }
 
+func TestCommitService_GetDiffOrPatch_Good(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			t.Errorf("expected GET, got %s", r.Method)
+		}
+		if r.URL.Path != "/api/v1/repos/core/go-forge/git/commits/abc123.diff" {
+			t.Errorf("wrong path: %s", r.URL.Path)
+		}
+		w.Header().Set("Content-Type", "text/plain")
+		io.WriteString(w, "diff --git a/README.md b/README.md")
+	}))
+	defer srv.Close()
+
+	f := NewForge(srv.URL, "tok")
+	data, err := f.Commits.GetDiffOrPatch(context.Background(), "core", "go-forge", "abc123", "diff")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(data) != "diff --git a/README.md b/README.md" {
+		t.Fatalf("got body=%q", string(data))
+	}
+}
+
 func TestCommitService_GetPullRequest_Good(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != http.MethodGet {