fix(cpp): Handle npos in PathToDirectory for S3 URIs without query strings

[shivendra-dev54]

Reason for this PR

Fixes #881

PathToDirectory was crashing with a std::out_of_range exception when parsing valid S3 URIs that do not contain a query string (?). This happens because find_last_of('?') returns std::string::npos, which was being passed directly into path.substr().

What changes are included in this PR?

Added an explicit check for std::string::npos in PathToDirectory. When an S3 URI without a query string is processed, it now correctly identifies the entire path as the prefix and sets the suffix to an empty string, safely avoiding the out-of-bounds crash.

Are these changes tested?

Yes, the C++ test suite was compiled and run locally, and all tests pass successfully.

Are there any user-facing changes?

No.

Critical Fix: Fixes a bug that causes a crash (std::out_of_range exception) when parsing valid S3 URIs without query strings.

[shivendra-dev54]

@Sober7135
check the code and also the title of the PR

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.86%. Comparing base (d535a43) to head (60923ec).

Files with missing lines	Patch %	Lines
cpp/src/graphar/graph_info.cc	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #888      +/-   ##
============================================
+ Coverage     79.81%   79.86%   +0.04%     
  Complexity      615      615              
============================================
  Files            93       93              
  Lines         10296    10296              
  Branches       1055     1055              
============================================
+ Hits           8218     8223       +5     
+ Misses         1838     1833       -5     
  Partials        240      240              

Flag	Coverage Δ
cpp	70.89% <0.00%> (+0.09%)	⬆️

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[Sober7135]

Yes, the C++ test suite was compiled and run locally, and all tests pass successfully.

This is not quite accurate, since no test case was added for this bug.

Testing this bug is also somewhat complicated, because PathToDirectory is a static helper inside an anonymous namespace rather than a public API. In practice, we cannot test it directly in the current test suite.

More importantly, this bug is only exercised through GraphInfo::Load(const std::string& path): Load() first reads the graph metadata file, and then calls PathToDirectory(path). So to reproduce this bug in a test, we need to drive the full GraphInfo::Load code path rather than test the helper in isolation.

incubator-graphar/cpp/src/graphar/graph_info.cc

Lines 1405 to 1416 in d535a43

	Result<std::shared_ptr<GraphInfo>> GraphInfo::Load(const std::string& path) {
	std::string no_url_path;
	GAR_ASSIGN_OR_RAISE(auto fs, FileSystemFromUriOrPath(path, &no_url_path));
	GAR_ASSIGN_OR_RAISE(auto yaml_content,
	fs->ReadFileToValue<std::string>(no_url_path));
	GAR_ASSIGN_OR_RAISE(auto graph_meta, Yaml::Load(yaml_content));
	std::string default_name = "graph";
	std::string default_prefix = PathToDirectory(path);
	no_url_path = PathToDirectory(no_url_path);
	return ConstructGraphInfo(graph_meta, default_name, default_prefix, fs,
	no_url_path);
	}

I can think of two possible solutions:

• Set up a mock S3 server so that we can exercise the full workflow and reliably trigger this bug.
• Expose this function — for example, move it into a namespace like graphar::details / graphar::internal, and avoid installing that header into the user system.

Actually, I am not familiar with this kind of problem.

Any advice? CC @yangxk1