Adding code to see if it improves crash on computeHash.

Also add a test case to verify behaviour on empty files is correct.

Sentry-Id: FLIGHTGEAR-AY2

simgear/io/sg_file.cxx

@@ -82,7 +82,9 @@ std::string SGFile::computeHash()
         [](char* p) { free(p); }};
 
     if (!buf) {
-        SG_LOG(SG_IO, SG_ALERT, "Failed to malloc buffer for SHA1 check");
+        // @TODO report out of memory error
+        SG_LOG(SG_IO, SG_ALERT, "Failed to malloc buffer for SHA1 check:" << file_name);
+        return {};
     }
 
     size_t readLen;

simgear/io/test_repository.cxx

@@ -901,6 +901,27 @@ void testPersistentSocketFailure(HTTP::Client *cl) {
   verifyRequestCount("dirD/subdirDB/fileDBA", 1);
 }
 
+void testHashOnEmptyFile()
+{
+    std::unique_ptr<HTTPRepository> repo;
+    SGPath p(simgear::Dir::current().path());
+    p.append("sgfile_compute_hash");
+    simgear::Dir pd(p);
+    if (pd.exists()) {
+        pd.removeChildren();
+    } else {
+        pd.create(0700);
+    }
+
+    SGPath fPath = p / "test_empty_file";
+    
+    SGFile file(fPath);
+    file.open(SG_IO_OUT);
+    file.close();
+
+    const auto hash = file.computeHash();
+}
+
 int main(int argc, char* argv[])
 {
   sglog().setLogLevels( SG_ALL, SG_INFO );
@@ -951,6 +972,8 @@ int main(int argc, char* argv[])
     testRetryAfterSocketFailure(&cl);
     testPersistentSocketFailure(&cl);
 
+    testHashOnEmptyFile();
+
     std::cout << "all tests passed ok" << std::endl;
     return 0;
 }