fix: Add SHA to get_file_contents while preserving MCP behavior (#595)

Enhance get_file_contents to include SHA information without changing
the existing MCP server response format.

Changes:
- Add Contents API call to retrieve SHA before fetching raw content
- Include SHA in resourceURI (repo://owner/repo/sha/{SHA}/contents/path)
- Add SHA to success messages
- Update tests to verify SHA inclusion
- Maintain original behavior: text files return raw text, binaries return base64

This preserves backward compatibility while providing SHA information
for better file versioning support.

Closes #595

Author: yonaka15

pkg/github/repositories.go

@@ -507,6 +507,14 @@ func GetFileContents(getClient GetClientFn, getRawClient raw.GetRawClientFn, t t
 			// If the path is (most likely) not to be a directory, we will
 			// first try to get the raw content from the GitHub raw content API.
 			if path != "" && !strings.HasSuffix(path, "/") {
+				// First, get file info from Contents API to retrieve SHA
+				var fileSHA string
+				opts := &github.RepositoryContentGetOptions{Ref: ref}
+				fileContent, _, respContents, errContents := client.Repositories.GetContents(ctx, owner, repo, path, opts)
+				if errContents == nil && respContents.StatusCode == http.StatusOK && fileContent != nil && fileContent.SHA != nil {
+					fileSHA = *fileContent.SHA
+					defer func() { _ = respContents.Body.Close() }()
+				}
 
 				rawClient, err := getRawClient(ctx)
 				if err != nil {
@@ -530,6 +538,11 @@ func GetFileContents(getClient GetClientFn, getRawClient raw.GetRawClientFn, t t
 
 					var resourceURI string
 					switch {
+					case fileSHA != "":
+						resourceURI, err = url.JoinPath("repo://", owner, repo, "sha", fileSHA, "contents", path)
+						if err != nil {
+							return nil, fmt.Errorf("failed to create resource URI: %w", err)
+						}
 					case sha != "":
 						resourceURI, err = url.JoinPath("repo://", owner, repo, "sha", sha, "contents", path)
 						if err != nil {
@@ -548,18 +561,28 @@ func GetFileContents(getClient GetClientFn, getRawClient raw.GetRawClientFn, t t
 					}
 
 					if strings.HasPrefix(contentType, "application") || strings.HasPrefix(contentType, "text") {
-						return mcp.NewToolResultResource("successfully downloaded text file", mcp.TextResourceContents{
+						result := mcp.TextResourceContents{
 							URI:      resourceURI,
 							Text:     string(body),
 							MIMEType: contentType,
-						}), nil
+						}
+						// Include SHA in the result metadata
+						if fileSHA != "" {
+							return mcp.NewToolResultResource(fmt.Sprintf("successfully downloaded text file (SHA: %s)", fileSHA), result), nil
+						}
+						return mcp.NewToolResultResource("successfully downloaded text file", result), nil
 					}
 
-					return mcp.NewToolResultResource("successfully downloaded binary file", mcp.BlobResourceContents{
+					result := mcp.BlobResourceContents{
 						URI:      resourceURI,
 						Blob:     base64.StdEncoding.EncodeToString(body),
 						MIMEType: contentType,
-					}), nil
+					}
+					// Include SHA in the result metadata
+					if fileSHA != "" {
+						return mcp.NewToolResultResource(fmt.Sprintf("successfully downloaded binary file (SHA: %s)", fileSHA), result), nil
+					}
+					return mcp.NewToolResultResource("successfully downloaded binary file", result), nil
 
 				}
 			}

pkg/github/repositories_test.go

@@ -76,6 +76,20 @@ func Test_GetFileContents(t *testing.T) {
 						_, _ = w.Write([]byte(`{"ref": "refs/heads/main", "object": {"sha": ""}}`))
 					}),
 				),
+				mock.WithRequestMatchHandler(
+					mock.GetReposContentsByOwnerByRepoByPath,
+					http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+						w.WriteHeader(http.StatusOK)
+						fileContent := &github.RepositoryContent{
+							Name: github.Ptr("README.md"),
+							Path: github.Ptr("README.md"),
+							SHA:  github.Ptr("abc123"),
+							Type: github.Ptr("file"),
+						}
+						contentBytes, _ := json.Marshal(fileContent)
+						_, _ = w.Write(contentBytes)
+					}),
+				),
 				mock.WithRequestMatchHandler(
 					raw.GetRawReposContentsByOwnerByRepoByBranchByPath,
 					http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
@@ -92,7 +106,7 @@ func Test_GetFileContents(t *testing.T) {
 			},
 			expectError: false,
 			expectedResult: mcp.TextResourceContents{
-				URI:      "repo://owner/repo/refs/heads/main/contents/README.md",
+				URI:      "repo://owner/repo/sha/abc123/contents/README.md",
 				Text:     "# Test Repository\n\nThis is a test repository.",
 				MIMEType: "text/markdown",
 			},
@@ -107,6 +121,20 @@ func Test_GetFileContents(t *testing.T) {
 						_, _ = w.Write([]byte(`{"ref": "refs/heads/main", "object": {"sha": ""}}`))
 					}),
 				),
+				mock.WithRequestMatchHandler(
+					mock.GetReposContentsByOwnerByRepoByPath,
+					http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+						w.WriteHeader(http.StatusOK)
+						fileContent := &github.RepositoryContent{
+							Name: github.Ptr("test.png"),
+							Path: github.Ptr("test.png"),
+							SHA:  github.Ptr("def456"),
+							Type: github.Ptr("file"),
+						}
+						contentBytes, _ := json.Marshal(fileContent)
+						_, _ = w.Write(contentBytes)
+					}),
+				),
 				mock.WithRequestMatchHandler(
 					raw.GetRawReposContentsByOwnerByRepoByBranchByPath,
 					http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
@@ -123,7 +151,7 @@ func Test_GetFileContents(t *testing.T) {
 			},
 			expectError: false,
 			expectedResult: mcp.BlobResourceContents{
-				URI:      "repo://owner/repo/refs/heads/main/contents/test.png",
+				URI:      "repo://owner/repo/sha/def456/contents/test.png",
 				Blob:     base64.StdEncoding.EncodeToString(mockRawContent),
 				MIMEType: "image/png",
 			},