Add handling for empty profiles.json. (#5685)

This PR adds handling for empty `profiles.json` files.

Closes CORE-417

---
TYPE: IMPROVEMENT
DESC: Add handling for empty `profiles.json`.

Author: kounelisagis

tiledb/sm/rest/rest_profile.cc

@@ -196,30 +196,36 @@ void RestProfile::save_to_file(const bool overwrite) {
   // If the file already exists, load it into a json object.
   json data;
   if (std::filesystem::exists(filepath_)) {
-    // Read the file into the json object.
-    data = read_file(filepath_);
-
-    // If the file is outdated, throw an error. This behavior will evolve.
-    if (data["version"] < version_) {
+    try {
+      // If the file is empty, treat it as a new json object.
+      if (std::filesystem::file_size(filepath_) == 0) {
+        data = json::object();
+      } else {
+        data = read_file(filepath_);
+      }
+    } catch (const std::filesystem::filesystem_error& e) {
       throw RestProfileException(
-          "The version of your local profile.json file is out of date.");
+          "Failed to access profile file: " + std::string(e.what()));
     }
 
-    // Check that this profile hasn't already been saved.
-    if (data.contains(name_)) {
-      if (overwrite) {
-        // If a profile of the given name exists, remove it.
-        auto it = data.find(name_);
-        if (it != data.end()) {
-          data.erase(it);
-        }
-      } else {
-        // If the user doesn't want to overwrite, throw an error.
+    if (data.empty()) {
+      data["version"] = version_;
+    } else {
+      if (data["version"] < version_) {
+        throw RestProfileException(
+            "The version of your local profile.json file is out of date.");
+      }
+
+      if (data.contains(name_) && !overwrite) {
         throw RestProfileException(
             "Failed to save '" + name_ +
             "'; This profile has already been saved "
             "and must be explicitly removed in order to be replaced.");
       }
+
+      if (overwrite) {
+        data.erase(name_);
+      }
     }
   } else {
     // Write the version number iff this is the first time opening the file.

tiledb/sm/rest/test/unit_rest_profile.cc

@@ -230,3 +230,44 @@ TEST_CASE_METHOD(
   p2_check.load_from_file();
   CHECK(*p2_check.get_param("rest.token") == "token2");
 }
+
+TEST_CASE_METHOD(
+    RestProfileFx, "REST Profile: Empty file", "[rest_profile][empty_file]") {
+  SECTION("Save to empty file succeeds") {
+    // Create an empty profiles.json file.
+    {
+      std::ofstream file(filepath_);
+      file.close();
+    }
+    CHECK(std::filesystem::exists(filepath_));
+
+    // Create a profile and save it to the empty file.
+    RestProfile p(create_profile("test_profile"));
+    p.set_param("rest.token", "test_token");
+    p.set_param("rest.server_address", "https://test.server");
+
+    // This should succeed and treat the empty file as a new file.
+    REQUIRE_NOTHROW(p.save_to_file());
+
+    // Verify we can load the profile back.
+    RestProfile loaded(create_profile("test_profile"));
+    REQUIRE_NOTHROW(loaded.load_from_file());
+    CHECK(*loaded.get_param("rest.token") == "test_token");
+    CHECK(*loaded.get_param("rest.server_address") == "https://test.server");
+  }
+
+  SECTION("Load from empty file fails") {
+    // Create an empty profiles.json file.
+    {
+      std::ofstream file(filepath_);
+      file.close();
+    }
+    CHECK(std::filesystem::exists(filepath_));
+
+    // Try to load from an empty file - should fail with parsing error.
+    RestProfile p(create_profile("test_profile"));
+    REQUIRE_THROWS_WITH(
+        p.load_from_file(),
+        Catch::Matchers::ContainsSubstring("Error parsing file"));
+  }
+}