fix: missing file engine with default options (#2519)

Signed-off-by: Zhenchi <zhongzc_arch@outlook.com>

src/cmd/src/error.rs

@@ -179,6 +179,13 @@ pub enum Error {
         error: etcd_client::Error,
         location: Location,
     },
+
+    #[snafu(display("Failed to serde json"))]
+    SerdeJson {
+        #[snafu(source)]
+        error: serde_json::error::Error,
+        location: Location,
+    },
 }
 
 pub type Result<T> = std::result::Result<T, Error>;
@@ -214,6 +221,8 @@ impl ErrorExt for Error {
             }
             Error::SubstraitEncodeLogicalPlan { source, .. } => source.status_code(),
             Error::StartCatalogManager { source, .. } => source.status_code(),
+
+            Error::SerdeJson { .. } => StatusCode::Unexpected,
         }
     }
 

src/cmd/src/options.rs

@@ -21,7 +21,7 @@ use meta_srv::metasrv::MetaSrvOptions;
 use serde::{Deserialize, Serialize};
 use snafu::ResultExt;
 
-use crate::error::{LoadLayeredConfigSnafu, Result};
+use crate::error::{LoadLayeredConfigSnafu, Result, SerdeJsonSnafu};
 
 pub const ENV_VAR_SEP: &str = "__";
 pub const ENV_LIST_SEP: &str = ",";
@@ -94,9 +94,16 @@ impl Options {
                 .ignore_empty(true)
         };
 
+        // Workaround: Replacement for `Config::try_from(&default_opts)` due to
+        // `ConfigSerializer` cannot handle the case of an empty struct contained
+        // within an iterative structure.
+        // See: https://github.com/mehcode/config-rs/issues/461
+        let json_str = serde_json::to_string(&default_opts).context(SerdeJsonSnafu)?;
+        let default_config = File::from_str(&json_str, FileFormat::Json);
+
         // Add default values and environment variables as the sources of the configuration.
         let mut layered_config = Config::builder()
-            .add_source(Config::try_from(&default_opts).context(LoadLayeredConfigSnafu)?)
+            .add_source(default_config)
             .add_source(env_source);
 
         // Add config file as the source of the configuration if it is specified.

src/cmd/src/standalone.rs

@@ -593,4 +593,25 @@ mod tests {
             },
         );
     }
+
+    #[test]
+    fn test_load_default_standalone_options() {
+        let options: StandaloneOptions =
+            Options::load_layered_options(None, "GREPTIMEDB_FRONTEND", None).unwrap();
+        let default_options = StandaloneOptions::default();
+        assert_eq!(options.mode, default_options.mode);
+        assert_eq!(options.enable_telemetry, default_options.enable_telemetry);
+        assert_eq!(options.http, default_options.http);
+        assert_eq!(options.grpc, default_options.grpc);
+        assert_eq!(options.mysql, default_options.mysql);
+        assert_eq!(options.postgres, default_options.postgres);
+        assert_eq!(options.opentsdb, default_options.opentsdb);
+        assert_eq!(options.influxdb, default_options.influxdb);
+        assert_eq!(options.prom_store, default_options.prom_store);
+        assert_eq!(options.wal, default_options.wal);
+        assert_eq!(options.kv_store, default_options.kv_store);
+        assert_eq!(options.procedure, default_options.procedure);
+        assert_eq!(options.logging, default_options.logging);
+        assert_eq!(options.region_engine, default_options.region_engine);
+    }
 }