added support for get_pull_request_diff (#119)

This function call is needed to be able to do AI code review to actually get the diff from the PR.

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/119
Reviewed-by: silverwind <silverwind@noreply.gitea.com>
Reviewed-by: hiifong <f@f.style>
Co-authored-by: Gustav <tvarsis@hotmail.com>
Co-committed-by: Gustav <tvarsis@hotmail.com>

operation/pull/pull_test.go

@@ -0,0 +1,140 @@
+package pull
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"sync"
+	"testing"
+
+	"gitea.com/gitea/gitea-mcp/pkg/flag"
+	"github.com/mark3labs/mcp-go/mcp"
+)
+
+func TestGetPullRequestDiffFn(t *testing.T) {
+	const (
+		owner   = "octo"
+		repo    = "demo"
+		index   = 12
+		diffRaw = "diff --git a/file.txt b/file.txt\n+line\n"
+	)
+
+	var (
+		mu            sync.Mutex
+		diffRequested bool
+		binaryValue   string
+	)
+	errCh := make(chan error, 1)
+
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/api/v1/version":
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(`{"version":"1.12.0"}`))
+		case fmt.Sprintf("/api/v1/repos/%s/%s", owner, repo):
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(`{"private":false}`))
+		case fmt.Sprintf("/%s/%s/pulls/%d.diff", owner, repo, index):
+			if r.Method != http.MethodGet {
+				select {
+				case errCh <- fmt.Errorf("unexpected method: %s", r.Method):
+				default:
+				}
+			}
+			mu.Lock()
+			diffRequested = true
+			binaryValue = r.URL.Query().Get("binary")
+			mu.Unlock()
+			w.Header().Set("Content-Type", "text/plain")
+			_, _ = w.Write([]byte(diffRaw))
+		default:
+			select {
+			case errCh <- fmt.Errorf("unexpected request path: %s", r.URL.Path):
+			default:
+			}
+		}
+	})
+
+	server := httptest.NewServer(handler)
+	defer server.Close()
+
+	origHost := flag.Host
+	origToken := flag.Token
+	origVersion := flag.Version
+	flag.Host = server.URL
+	flag.Token = ""
+	flag.Version = "test"
+	defer func() {
+		flag.Host = origHost
+		flag.Token = origToken
+		flag.Version = origVersion
+	}()
+
+	req := mcp.CallToolRequest{
+		Params: mcp.CallToolParams{
+			Arguments: map[string]any{
+				"owner":  owner,
+				"repo":   repo,
+				"index":  float64(index),
+				"binary": true,
+			},
+		},
+	}
+
+	result, err := GetPullRequestDiffFn(context.Background(), req)
+	if err != nil {
+		t.Fatalf("GetPullRequestDiffFn() error = %v", err)
+	}
+
+	select {
+	case reqErr := <-errCh:
+		t.Fatalf("handler error: %v", reqErr)
+	default:
+	}
+
+	mu.Lock()
+	requested := diffRequested
+	gotBinary := binaryValue
+	mu.Unlock()
+
+	if !requested {
+		t.Fatalf("expected diff request to be made")
+	}
+	if gotBinary != "true" {
+		t.Fatalf("expected binary=true query param, got %q", gotBinary)
+	}
+
+	if len(result.Content) == 0 {
+		t.Fatalf("expected content in result")
+	}
+
+	textContent, ok := mcp.AsTextContent(result.Content[0])
+	if !ok {
+		t.Fatalf("expected text content, got %T", result.Content[0])
+	}
+
+	var parsed struct {
+		Result map[string]any `json:"Result"`
+	}
+	if err := json.Unmarshal([]byte(textContent.Text), &parsed); err != nil {
+		t.Fatalf("unmarshal result text: %v", err)
+	}
+
+	if got, ok := parsed.Result["diff"].(string); !ok || got != diffRaw {
+		t.Fatalf("diff = %q, want %q", got, diffRaw)
+	}
+	if got, ok := parsed.Result["binary"].(bool); !ok || got != true {
+		t.Fatalf("binary = %v, want true", got)
+	}
+	if got, ok := parsed.Result["index"].(float64); !ok || int64(got) != int64(index) {
+		t.Fatalf("index = %v, want %d", got, index)
+	}
+	if got, ok := parsed.Result["owner"].(string); !ok || got != owner {
+		t.Fatalf("owner = %q, want %q", got, owner)
+	}
+	if got, ok := parsed.Result["repo"].(string); !ok || got != repo {
+		t.Fatalf("repo = %q, want %q", got, repo)
+	}
+}