diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4858888..6efa14b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,26 @@ Also check the changes in springql-core: <https://github.com/SpringQL/SpringQL/b
 <!-- markdownlint-disable MD024 -->
 ## [Unreleased]
 
+## [v0.16.0+4] - 2022-07-12
+
+### Fixed
+
+- Undefined behaviors on the following structures: ([#62](https://github.com/SpringQL/SpringQL-client-c/pull/62))
+  - SpringConfig
+  - SpringPipeline
+  - SpringSinkRow
+  - SpringSourceRow
+  - SpringSourceRowBuilder
+
+### Changed
+
+- `spring_push()` takes `SpringSourceRow *` instead of `const SpringSourceRow *`. It de-allocates `SpringSourceRow *`. ([#62](https://github.com/SpringQL/SpringQL-client-c/pull/62))
+- `spring_source_row_add_column_blob()` returns new builder instead of modifying the existing one. ([#62](https://github.com/SpringQL/SpringQL-client-c/pull/62))
+
+### Removed
+
+- `spring_source_row_close()` ([#62](https://github.com/SpringQL/SpringQL-client-c/pull/62))
+
 ## [v0.16.0+3] - 2022-07-11
 
 ### Fixed
@@ -124,8 +144,9 @@ Depends on springql-core v0.7.1.
 [Semantic Versioning]: https://semver.org/
 
 <!-- Versions -->
-[Unreleased]: https://github.com/SpringQL/SpringQL-client-c/compare/v0.16.0+3...HEAD
+[Unreleased]: https://github.com/SpringQL/SpringQL-client-c/compare/v0.16.0+4...HEAD
 [Released]: https://github.com/SpringQL/SpringQL-client-c/releases
+[v0.16.0+4]: https://github.com/SpringQL/SpringQL-client-c/compare/v0.16.0+4...v0.16.0+4
 [v0.16.0+3]: https://github.com/SpringQL/SpringQL-client-c/compare/v0.16.0+2...v0.16.0+3
 [v0.16.0+2]: https://github.com/SpringQL/SpringQL-client-c/compare/v0.16.0...v0.16.0+2
 [v0.16.0]: https://github.com/SpringQL/SpringQL-client-c/compare/v0.15.0+2...v0.16.0
diff --git a/springql.h b/springql.h
index f35e43d..8db9e44 100644
--- a/springql.h
+++ b/springql.h
@@ -42,27 +42,27 @@ typedef enum SpringErrno {
 /**
  * Configuration.
  */
-typedef void *SpringConfig;
+typedef struct SpringConfig SpringConfig;
 
 /**
  * Pipeline (dataflow definition) in SpringQL.
  */
-typedef void *SpringPipeline;
+typedef struct SpringPipeline SpringPipeline;
 
 /**
  * Row object to pop from an in memory queue.
  */
-typedef void *SpringSinkRow;
+typedef struct SpringSinkRow SpringSinkRow;
 
 /**
  * Row object to push into an in memory queue.
  */
-typedef void *SpringSourceRow;
+typedef struct SpringSourceRow SpringSourceRow;
 
 /**
  * Builder of SpringSourceRow
  */
-typedef void *SpringSourceRowBuilder;
+typedef struct SpringSourceRowBuilder SpringSourceRowBuilder;
 
 /**
  * Returns default configuration.
@@ -70,7 +70,7 @@ typedef void *SpringSourceRowBuilder;
  * Returned value is not modifiable (it is just a void pointer).
  * If you would like to change the default configuration, use `spring_config_toml()` instead.
  */
-SpringConfig *spring_config_default(void);
+struct SpringConfig *spring_config_default(void);
 
 /**
  * Configuration by TOML format string.
@@ -89,7 +89,7 @@ SpringConfig *spring_config_default(void);
  * - `overwrite_config_toml` includes invalid key and/or value.
  * - `overwrite_config_toml` is not valid as TOML.
  */
-SpringConfig *spring_config_toml(const char *overwrite_config_toml);
+struct SpringConfig *spring_config_toml(const char *overwrite_config_toml);
 
 /**
  * Frees heap occupied by a `SpringConfig`.
@@ -99,7 +99,7 @@ SpringConfig *spring_config_toml(const char *overwrite_config_toml);
  * - `Ok`: on success.
  * - `CNull`: `config` is a NULL pointer.
  */
-enum SpringErrno spring_config_close(SpringConfig *config);
+enum SpringErrno spring_config_close(struct SpringConfig *config);
 
 /**
  * Creates and open an in-process stream pipeline.
@@ -113,7 +113,7 @@ enum SpringErrno spring_config_close(SpringConfig *config);
  *
  * No errors are expected currently.
  */
-SpringPipeline *spring_open(const SpringConfig *config);
+struct SpringPipeline *spring_open(const struct SpringConfig *config);
 
 /**
  * Frees heap occupied by a `SpringPipeline`.
@@ -123,7 +123,7 @@ SpringPipeline *spring_open(const SpringConfig *config);
  * - `Ok`: on success.
  * - `CNull`: `pipeline` is a NULL pointer.
  */
-enum SpringErrno spring_close(SpringPipeline *pipeline);
+enum SpringErrno spring_close(struct SpringPipeline *pipeline);
 
 /**
  * Execute commands (DDL) to modify the pipeline.
@@ -138,7 +138,7 @@ enum SpringErrno spring_close(SpringPipeline *pipeline);
  * - `InvalidOption`:
  *   - `OPTIONS` in `CREATE` statement includes invalid key or value.
  */
-enum SpringErrno spring_command(const SpringPipeline *pipeline, const char *sql);
+enum SpringErrno spring_command(const struct SpringPipeline *pipeline, const char *sql);
 
 /**
  * Pop a row from an in memory queue. This is a blocking function.
@@ -156,7 +156,7 @@ enum SpringErrno spring_command(const SpringPipeline *pipeline, const char *sql)
  *
  * - `Unavailable`: queue named `queue` does not exist.
  */
-SpringSinkRow *spring_pop(const SpringPipeline *pipeline, const char *queue);
+struct SpringSinkRow *spring_pop(const struct SpringPipeline *pipeline, const char *queue);
 
 /**
  * Pop a row from an in memory queue. This is a non-blocking function.
@@ -170,21 +170,23 @@ SpringSinkRow *spring_pop(const SpringPipeline *pipeline, const char *queue);
  *
  * - `Unavailable`: queue named `queue` does not exist.
  */
-SpringSinkRow *spring_pop_non_blocking(const SpringPipeline *pipeline,
-                                       const char *queue,
-                                       bool *is_err);
+struct SpringSinkRow *spring_pop_non_blocking(const struct SpringPipeline *pipeline,
+                                              const char *queue,
+                                              bool *is_err);
 
 /**
  * Push a row into an in memory queue. This is a non-blocking function.
  *
+ * `row` is freed internally.
+ *
  * # Returns
  *
  * - `Ok`: on success.
  * - `Unavailable`: queue named `queue` does not exist.
  */
-enum SpringErrno spring_push(const SpringPipeline *pipeline,
+enum SpringErrno spring_push(const struct SpringPipeline *pipeline,
                              const char *queue,
-                             const SpringSourceRow *row);
+                             struct SpringSourceRow *row);
 
 /**
  * Create a source row from JSON string
@@ -198,7 +200,7 @@ enum SpringErrno spring_push(const SpringPipeline *pipeline,
  *
  * - `InvalidFormat`: JSON string is invalid.
  */
-SpringSourceRow *spring_source_row_from_json(const char *json);
+struct SpringSourceRow *spring_source_row_from_json(const char *json);
 
 /**
  * Start creating a source row using a builder.
@@ -207,10 +209,12 @@ SpringSourceRow *spring_source_row_from_json(const char *json);
  *
  * Pointer to the builder
  */
-SpringSourceRowBuilder *spring_source_row_builder(void);
+struct SpringSourceRowBuilder *spring_source_row_builder(void);
 
 /**
- * Add a BLOB column to the builder.
+ * Add a BLOB column to the builder and return the new one.
+ *
+ * `builder` is freed internally.
  *
  * # Parameters
  *
@@ -221,13 +225,17 @@ SpringSourceRowBuilder *spring_source_row_builder(void);
  *
  * # Returns
  *
- * - `Ok`: on success.
+ * - non-NULL: Successfully created a row.
+ * - NULL: Error occurred.
+ *
+ * # Errors
+ *
  * - `Sql`: `column_name` is already added to the builder.
  */
-enum SpringErrno spring_source_row_add_column_blob(SpringSourceRowBuilder *builder,
-                                                   const char *column_name,
-                                                   const void *v,
-                                                   int v_len);
+struct SpringSourceRowBuilder *spring_source_row_add_column_blob(struct SpringSourceRowBuilder *builder,
+                                                                 const char *column_name,
+                                                                 const void *v,
+                                                                 int v_len);
 
 /**
  * Finish creating a source row using a builder.
@@ -238,17 +246,7 @@ enum SpringErrno spring_source_row_add_column_blob(SpringSourceRowBuilder *build
  *
  * SpringSourceRow
  */
-SpringSourceRow *spring_source_row_build(SpringSourceRowBuilder *builder);
-
-/**
- * Frees heap occupied by a `SpringSourceRow`.
- *
- * # Returns
- *
- * - `Ok`: on success.
- * - `CNull`: `pipeline` is a NULL pointer.
- */
-enum SpringErrno spring_source_row_close(SpringSourceRow *row);
+struct SpringSourceRow *spring_source_row_build(struct SpringSourceRowBuilder *builder);
 
 /**
  * Frees heap occupied by a `SpringSinkRow`.
@@ -258,7 +256,7 @@ enum SpringErrno spring_source_row_close(SpringSourceRow *row);
  * - `Ok`: on success.
  * - `CNull`: `pipeline` is a NULL pointer.
  */
-enum SpringErrno spring_sink_row_close(SpringSinkRow *row);
+enum SpringErrno spring_sink_row_close(struct SpringSinkRow *row);
 
 /**
  * Get a 2-byte integer column.
@@ -277,7 +275,7 @@ enum SpringErrno spring_sink_row_close(SpringSinkRow *row);
  *   - `i_col` is out of range.
  * - `CNull`: Column value is NULL.
  */
-enum SpringErrno spring_column_short(const SpringSinkRow *row, uint16_t i_col, short *out);
+enum SpringErrno spring_column_short(const struct SpringSinkRow *row, uint16_t i_col, short *out);
 
 /**
  * Get a 4-byte integer column.
@@ -296,7 +294,7 @@ enum SpringErrno spring_column_short(const SpringSinkRow *row, uint16_t i_col, s
  *   - `i_col` is out of range.
  * - `CNull`: Column value is NULL.
  */
-enum SpringErrno spring_column_int(const SpringSinkRow *row, uint16_t i_col, int *out);
+enum SpringErrno spring_column_int(const struct SpringSinkRow *row, uint16_t i_col, int *out);
 
 /**
  * Get an 8-byte integer column.
@@ -315,7 +313,7 @@ enum SpringErrno spring_column_int(const SpringSinkRow *row, uint16_t i_col, int
  *   - `i_col` is out of range.
  * - `CNull`: Column value is NULL.
  */
-enum SpringErrno spring_column_long(const SpringSinkRow *row, uint16_t i_col, long *out);
+enum SpringErrno spring_column_long(const struct SpringSinkRow *row, uint16_t i_col, long *out);
 
 /**
  * Get a 4-byte unsigned integer column.
@@ -334,7 +332,7 @@ enum SpringErrno spring_column_long(const SpringSinkRow *row, uint16_t i_col, lo
  *   - `i_col` is out of range.
  * - `CNull`: Column value is NULL.
  */
-enum SpringErrno spring_column_unsigned_int(const SpringSinkRow *row,
+enum SpringErrno spring_column_unsigned_int(const struct SpringSinkRow *row,
                                             uint16_t i_col,
                                             unsigned int *out);
 
@@ -356,7 +354,7 @@ enum SpringErrno spring_column_unsigned_int(const SpringSinkRow *row,
  *   - `i_col` is out of range.
  * - `CNull`: Column value is NULL.
  */
-int spring_column_text(const SpringSinkRow *row, uint16_t i_col, char *out, int out_len);
+int spring_column_text(const struct SpringSinkRow *row, uint16_t i_col, char *out, int out_len);
 
 /**
  * Get a BLOB column.
@@ -376,7 +374,7 @@ int spring_column_text(const SpringSinkRow *row, uint16_t i_col, char *out, int
  *   - `i_col` is out of range.
  * - `CNull`: Column value is NULL.
  */
-int spring_column_blob(const SpringSinkRow *row, uint16_t i_col, void *out, int out_len);
+int spring_column_blob(const struct SpringSinkRow *row, uint16_t i_col, void *out, int out_len);
 
 /**
  * Get a bool column.
@@ -395,7 +393,7 @@ int spring_column_blob(const SpringSinkRow *row, uint16_t i_col, void *out, int
  *   - `i_col` is out of range.
  * - `CNull`: Column value is NULL.
  */
-enum SpringErrno spring_column_bool(const SpringSinkRow *row, uint16_t i_col, bool *out);
+enum SpringErrno spring_column_bool(const struct SpringSinkRow *row, uint16_t i_col, bool *out);
 
 /**
  * Get a 4-byte floating point column.
@@ -414,7 +412,7 @@ enum SpringErrno spring_column_bool(const SpringSinkRow *row, uint16_t i_col, bo
  *   - `i_col` is out of range.
  * - `CNull`: Column value is NULL.
  */
-enum SpringErrno spring_column_float(const SpringSinkRow *row, uint16_t i_col, float *out);
+enum SpringErrno spring_column_float(const struct SpringSinkRow *row, uint16_t i_col, float *out);
 
 /**
  * Write the most recent error number into `errno_` and message into a caller-provided buffer as a UTF-8
diff --git a/src/lib.rs b/src/lib.rs
index d708867..ee301c4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,7 +5,8 @@
 #![allow(clippy::missing_safety_doc)] // C header file does not need `Safety` section
 
 pub(crate) mod c_mem;
-mod spring_config;
+
+pub mod spring_config;
 pub mod spring_errno;
 pub mod spring_last_err;
 mod spring_pipeline;
@@ -13,6 +14,9 @@ mod spring_sink_row;
 mod spring_source_row;
 mod spring_source_row_builder;
 
+#[cfg(test)]
+mod tests;
+
 use std::{
     ffi::{c_void, CStr},
     os::raw::{c_char, c_float, c_int, c_long, c_short, c_uint},
@@ -30,7 +34,10 @@ use crate::{
     spring_source_row::SpringSourceRow,
     spring_source_row_builder::SpringSourceRowBuilder,
 };
-use ::springql::{error::SpringError, SpringPipeline as Pipeline};
+use ::springql::{
+    error::SpringError, SpringPipeline as Pipeline, SpringSourceRow as RuSpringSourceRow,
+    SpringSourceRowBuilder as RuSpringSourceRowBuilder,
+};
 
 /// Returns default configuration.
 ///
@@ -38,8 +45,8 @@ use ::springql::{error::SpringError, SpringPipeline as Pipeline};
 /// If you would like to change the default configuration, use `spring_config_toml()` instead.
 #[no_mangle]
 pub extern "C" fn spring_config_default() -> *mut SpringConfig {
-    let config = ::springql::SpringConfig::default();
-    SpringConfig::new(config).into_ptr()
+    let config = SpringConfig::default();
+    config.into_ptr()
 }
 
 /// Configuration by TOML format string.
@@ -64,8 +71,8 @@ pub unsafe extern "C" fn spring_config_toml(
     let s = CStr::from_ptr(overwrite_config_toml);
     let s = s.to_str().expect("failed to parse TOML string into UTF-8");
 
-    let config = springql::SpringConfig::new(s).expect("failed to parse TOML config");
-    SpringConfig::new(config).into_ptr()
+    let config = SpringConfig::from_toml(s).expect("failed to parse TOML config");
+    config.into_ptr()
 }
 
 /// Frees heap occupied by a `SpringConfig`.
@@ -79,7 +86,7 @@ pub unsafe extern "C" fn spring_config_close(config: *mut SpringConfig) -> Sprin
     if config.is_null() {
         SpringErrno::CNull
     } else {
-        SpringConfig::drop(config);
+        let _ = Box::from_raw(config);
         SpringErrno::Ok
     }
 }
@@ -96,13 +103,10 @@ pub unsafe extern "C" fn spring_config_close(config: *mut SpringConfig) -> Sprin
 /// No errors are expected currently.
 #[no_mangle]
 pub unsafe extern "C" fn spring_open(config: *const SpringConfig) -> *mut SpringPipeline {
-    let config = (*config).as_config();
-    let pipeline = Pipeline::new(config);
-    match pipeline {
-        Ok(pipe) => {
-            let ptr = SpringPipeline::new(pipe);
-            ptr.into_ptr()
-        }
+    let config = &*config;
+    let res_ru_pipeline = with_catch(|| Pipeline::new(config.as_ref()));
+    match res_ru_pipeline {
+        Ok(ru_pipeline) => SpringPipeline::from(ru_pipeline).into_ptr(),
         Err(_err) => ptr::null_mut(),
     }
 }
@@ -118,7 +122,7 @@ pub unsafe extern "C" fn spring_close(pipeline: *mut SpringPipeline) -> SpringEr
     if pipeline.is_null() {
         SpringErrno::CNull
     } else {
-        SpringPipeline::drop(pipeline);
+        let _ = Box::from_raw(pipeline);
         SpringErrno::Ok
     }
 }
@@ -139,9 +143,9 @@ pub unsafe extern "C" fn spring_command(
     pipeline: *const SpringPipeline,
     sql: *const c_char,
 ) -> SpringErrno {
-    let pipe = (*pipeline).as_pipeline();
+    let ru_pipeline = (*pipeline).as_ref();
     let sql = CStr::from_ptr(sql).to_string_lossy().into_owned();
-    let result = with_catch(|| pipe.command(sql));
+    let result = with_catch(|| ru_pipeline.command(sql));
 
     match result {
         Ok(_) => SpringErrno::Ok,
@@ -168,12 +172,12 @@ pub unsafe extern "C" fn spring_pop(
     pipeline: *const SpringPipeline,
     queue: *const c_char,
 ) -> *mut SpringSinkRow {
-    let pipeline = (*pipeline).as_pipeline();
+    let ru_pipeline = (*pipeline).as_ref();
     let queue = CStr::from_ptr(queue).to_string_lossy().into_owned();
-    let result = with_catch(|| pipeline.pop(&queue));
+    let result = with_catch(|| ru_pipeline.pop(&queue));
     match result {
-        Ok(row) => {
-            let row = SpringSinkRow::new(row);
+        Ok(ru_row) => {
+            let row = SpringSinkRow::from(ru_row);
             row.into_ptr()
         }
         Err(_) => ptr::null_mut(),
@@ -196,14 +200,13 @@ pub unsafe extern "C" fn spring_pop_non_blocking(
     queue: *const c_char,
     is_err: *mut bool,
 ) -> *mut SpringSinkRow {
-    let pipeline = (*pipeline).as_pipeline();
+    let ru_pipeline = (*pipeline).as_ref();
     let queue = CStr::from_ptr(queue).to_string_lossy().into_owned();
-    let result = with_catch(|| pipeline.pop_non_blocking(&queue));
+    let result = with_catch(|| ru_pipeline.pop_non_blocking(&queue));
     match result {
         Ok(Some(row)) => {
-            let ptr = SpringSinkRow::new(row);
             *is_err = false;
-            ptr.into_ptr()
+            SpringSinkRow::from(row).into_ptr()
         }
         Ok(None) => {
             *is_err = false;
@@ -218,6 +221,8 @@ pub unsafe extern "C" fn spring_pop_non_blocking(
 
 /// Push a row into an in memory queue. This is a non-blocking function.
 ///
+/// `row` is freed internally.
+///
 /// # Returns
 ///
 /// - `Ok`: on success.
@@ -226,12 +231,14 @@ pub unsafe extern "C" fn spring_pop_non_blocking(
 pub unsafe extern "C" fn spring_push(
     pipeline: *const SpringPipeline,
     queue: *const c_char,
-    row: *const SpringSourceRow,
+    row: *mut SpringSourceRow,
 ) -> SpringErrno {
-    let pipeline = (*pipeline).as_pipeline();
+    let ru_pipeline = (*pipeline).as_ref();
     let queue = CStr::from_ptr(queue).to_string_lossy().into_owned();
-    let source_row = (*row).to_row();
-    let result = with_catch(|| pipeline.push(&queue, source_row));
+
+    let source_row = Box::from_raw(row);
+    let source_row = RuSpringSourceRow::from(*source_row);
+    let result = with_catch(|| ru_pipeline.push(&queue, source_row));
     match result {
         Ok(()) => SpringErrno::Ok,
         Err(e) => e,
@@ -251,9 +258,9 @@ pub unsafe extern "C" fn spring_push(
 #[no_mangle]
 pub unsafe extern "C" fn spring_source_row_from_json(json: *const c_char) -> *mut SpringSourceRow {
     let json = CStr::from_ptr(json).to_string_lossy().into_owned();
-    let res_source_row = with_catch(|| ::springql::SpringSourceRow::from_json(&json));
-    match res_source_row {
-        Ok(source_row) => SpringSourceRow::new(source_row).into_ptr(),
+    let res_ru_source_row = with_catch(|| ::springql::SpringSourceRow::from_json(&json));
+    match res_ru_source_row {
+        Ok(ru_source_row) => SpringSourceRow::from(ru_source_row).into_ptr(),
         Err(_) => ptr::null_mut(),
     }
 }
@@ -267,7 +274,9 @@ pub unsafe extern "C" fn spring_source_row_from_json(json: *const c_char) -> *mu
 pub unsafe extern "C" fn spring_source_row_builder() -> *mut SpringSourceRowBuilder {
     SpringSourceRowBuilder::default().into_ptr()
 }
-/// Add a BLOB column to the builder.
+/// Add a BLOB column to the builder and return the new one.
+///
+/// `builder` is freed internally.
 ///
 /// # Parameters
 ///
@@ -278,7 +287,11 @@ pub unsafe extern "C" fn spring_source_row_builder() -> *mut SpringSourceRowBuil
 ///
 /// # Returns
 ///
-/// - `Ok`: on success.
+/// - non-NULL: Successfully created a row.
+/// - NULL: Error occurred.
+///
+/// # Errors
+///
 /// - `Sql`: `column_name` is already added to the builder.
 #[no_mangle]
 pub unsafe extern "C" fn spring_source_row_add_column_blob(
@@ -286,21 +299,19 @@ pub unsafe extern "C" fn spring_source_row_add_column_blob(
     column_name: *const c_char,
     v: *const c_void,
     v_len: c_int,
-) -> SpringErrno {
+) -> *mut SpringSourceRowBuilder {
     let column_name = CStr::from_ptr(column_name).to_string_lossy().into_owned();
 
     let v = v as *const u8;
     let v = slice::from_raw_parts(v, v_len as usize);
     let v = v.to_vec();
 
-    let rust_builder = (*builder).to_row_builder();
-    let res_rust_builder = with_catch(|| rust_builder.add_column(column_name, v));
-    match res_rust_builder {
-        Ok(rust_builder) => {
-            *builder = SpringSourceRowBuilder::new(rust_builder);
-            SpringErrno::Ok
-        }
-        Err(e) => e,
+    let builder = Box::from_raw(builder);
+    let ru_builder = RuSpringSourceRowBuilder::from(*builder);
+    let res_ru_builder = with_catch(|| ru_builder.add_column(column_name, v));
+    match res_ru_builder {
+        Ok(ru_builder) => SpringSourceRowBuilder::from(ru_builder).into_ptr(),
+        Err(_) => ptr::null_mut(),
     }
 }
 /// Finish creating a source row using a builder.
@@ -314,26 +325,9 @@ pub unsafe extern "C" fn spring_source_row_add_column_blob(
 pub unsafe extern "C" fn spring_source_row_build(
     builder: *mut SpringSourceRowBuilder,
 ) -> *mut SpringSourceRow {
-    let rust_builder = (*builder).to_row_builder();
-    let ret = SpringSourceRow::new(rust_builder.build()).into_ptr();
-    SpringSourceRowBuilder::drop(builder);
-    ret
-}
-
-/// Frees heap occupied by a `SpringSourceRow`.
-///
-/// # Returns
-///
-/// - `Ok`: on success.
-/// - `CNull`: `pipeline` is a NULL pointer.
-#[no_mangle]
-pub extern "C" fn spring_source_row_close(row: *mut SpringSourceRow) -> SpringErrno {
-    if row.is_null() {
-        SpringErrno::CNull
-    } else {
-        SpringSourceRow::drop(row);
-        SpringErrno::Ok
-    }
+    let builder = Box::from_raw(builder);
+    let ru_builder = RuSpringSourceRowBuilder::from(*builder);
+    SpringSourceRow::from(ru_builder.build()).into_ptr()
 }
 
 /// Frees heap occupied by a `SpringSinkRow`.
@@ -343,11 +337,11 @@ pub extern "C" fn spring_source_row_close(row: *mut SpringSourceRow) -> SpringEr
 /// - `Ok`: on success.
 /// - `CNull`: `pipeline` is a NULL pointer.
 #[no_mangle]
-pub extern "C" fn spring_sink_row_close(row: *mut SpringSinkRow) -> SpringErrno {
+pub unsafe extern "C" fn spring_sink_row_close(row: *mut SpringSinkRow) -> SpringErrno {
     if row.is_null() {
         SpringErrno::CNull
     } else {
-        SpringSinkRow::drop(row);
+        let _ = Box::from_raw(row);
         SpringErrno::Ok
     }
 }
@@ -373,7 +367,7 @@ pub unsafe extern "C" fn spring_column_short(
     i_col: u16,
     out: *mut c_short,
 ) -> SpringErrno {
-    let row = (*row).as_row();
+    let row = &*row;
     let i_col = i_col as usize;
     let result = with_catch(|| row.get_not_null_by_index(i_col as usize));
     match result {
@@ -406,7 +400,7 @@ pub unsafe extern "C" fn spring_column_int(
     i_col: u16,
     out: *mut c_int,
 ) -> SpringErrno {
-    let row = (*row).as_row();
+    let row = &*row;
     let i_col = i_col as usize;
     let result = with_catch(|| row.get_not_null_by_index(i_col as usize));
     match result {
@@ -439,7 +433,7 @@ pub unsafe extern "C" fn spring_column_long(
     i_col: u16,
     out: *mut c_long,
 ) -> SpringErrno {
-    let row = (*row).as_row();
+    let row = &*row;
     let i_col = i_col as usize;
     let result = with_catch(|| row.get_not_null_by_index(i_col as usize));
     match result {
@@ -472,7 +466,7 @@ pub unsafe extern "C" fn spring_column_unsigned_int(
     i_col: u16,
     out: *mut c_uint,
 ) -> SpringErrno {
-    let row = (*row).as_row();
+    let row = &*row;
     let i_col = i_col as usize;
     let result = with_catch(|| row.get_not_null_by_index(i_col as usize));
     match result {
@@ -507,7 +501,7 @@ pub unsafe extern "C" fn spring_column_text(
     out: *mut c_char,
     out_len: c_int,
 ) -> c_int {
-    let row = (*row).as_row();
+    let row = &*row;
     let i_col = i_col as usize;
     let result: Result<String, SpringErrno> =
         with_catch(|| row.get_not_null_by_index(i_col as usize));
@@ -543,7 +537,7 @@ pub unsafe extern "C" fn spring_column_blob(
     out: *mut c_void,
     out_len: c_int,
 ) -> c_int {
-    let row = (*row).as_row();
+    let row = &*row;
     let i_col = i_col as usize;
     let result: Result<Vec<u8>, SpringErrno> =
         with_catch(|| row.get_not_null_by_index(i_col as usize));
@@ -577,7 +571,7 @@ pub unsafe extern "C" fn spring_column_bool(
     i_col: u16,
     out: *mut bool,
 ) -> SpringErrno {
-    let row = (*row).as_row();
+    let row = &*row;
     let i_col = i_col as usize;
     let result = with_catch(|| row.get_not_null_by_index(i_col as usize));
     match result {
@@ -610,7 +604,7 @@ pub unsafe extern "C" fn spring_column_float(
     i_col: u16,
     out: *mut c_float,
 ) -> SpringErrno {
-    let row = (*row).as_row();
+    let row = &*row;
     let i_col = i_col as usize;
     let result = with_catch(|| row.get_not_null_by_index(i_col as usize));
     match result {
diff --git a/src/spring_config.rs b/src/spring_config.rs
index abd5337..1193712 100644
--- a/src/spring_config.rs
+++ b/src/spring_config.rs
@@ -1,28 +1,24 @@
 // This file is part of https://github.com/SpringQL/SpringQL-client-c which is licensed under MIT OR Apache-2.0. See file LICENSE-MIT or LICENSE-APACHE for full license details.
-use ::springql::SpringConfig as RawSpringConfig;
-use std::{ffi::c_void, mem};
+use ::springql::{Result, SpringConfig as RuSpringConfig};
+
 /// Configuration.
 #[non_exhaustive]
-#[repr(transparent)]
-pub struct SpringConfig(*mut c_void);
-
-impl SpringConfig {
-    pub fn new(config: RawSpringConfig) -> Self {
-        SpringConfig(unsafe { mem::transmute(Box::new(config)) })
-    }
+#[derive(Clone, Eq, PartialEq, Debug, Default)]
+pub struct SpringConfig(RuSpringConfig);
 
-    pub fn as_config(&self) -> &RawSpringConfig {
-        unsafe { &*(self.0 as *const RawSpringConfig) }
+impl AsRef<RuSpringConfig> for SpringConfig {
+    fn as_ref(&self) -> &RuSpringConfig {
+        &self.0
     }
+}
 
-    pub fn drop(ptr: *mut SpringConfig) {
-        let outer = unsafe { Box::from_raw(ptr) };
-        let inner = unsafe { Box::from_raw(outer.0) };
-        drop(inner);
-        drop(outer);
+impl SpringConfig {
+    pub(crate) fn from_toml(toml: &str) -> Result<Self> {
+        let config = RuSpringConfig::from_toml(toml)?;
+        Ok(Self(config))
     }
 
-    pub fn into_ptr(self) -> *mut SpringConfig {
+    pub(crate) fn into_ptr(self) -> *mut SpringConfig {
         Box::into_raw(Box::new(self))
     }
 }
diff --git a/src/spring_errno.rs b/src/spring_errno.rs
index 6bc0a6f..ac33ae0 100644
--- a/src/spring_errno.rs
+++ b/src/spring_errno.rs
@@ -7,6 +7,7 @@ use crate::spring_last_err::LastError;
 /// Errno (error number) to be returned erroneous functions.
 #[non_exhaustive]
 #[repr(C)]
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
 pub enum SpringErrno {
     Ok = 0,
 
diff --git a/src/spring_pipeline.rs b/src/spring_pipeline.rs
index b5a34f5..0b71302 100644
--- a/src/spring_pipeline.rs
+++ b/src/spring_pipeline.rs
@@ -1,29 +1,26 @@
 // This file is part of https://github.com/SpringQL/SpringQL-client-c which is licensed under MIT OR Apache-2.0. See file LICENSE-MIT or LICENSE-APACHE for full license details.
-use ::springql::SpringPipeline as Pipeline;
 
-use std::{ffi::c_void, mem};
+use ::springql::SpringPipeline as RuSpringPipeline;
+
 /// Pipeline (dataflow definition) in SpringQL.
 #[non_exhaustive]
-#[repr(transparent)]
-pub struct SpringPipeline(*mut c_void);
-
-impl SpringPipeline {
-    pub fn new(pipe: Pipeline) -> Self {
-        SpringPipeline(unsafe { mem::transmute(Box::new(pipe)) })
-    }
+#[derive(Debug)]
+pub struct SpringPipeline(RuSpringPipeline);
 
-    pub fn as_pipeline(&self) -> &Pipeline {
-        unsafe { &*(self.0 as *const Pipeline) }
+impl From<RuSpringPipeline> for SpringPipeline {
+    fn from(pipeline: RuSpringPipeline) -> Self {
+        SpringPipeline(pipeline)
     }
+}
 
-    pub fn drop(ptr: *mut SpringPipeline) {
-        let outer = unsafe { Box::from_raw(ptr) };
-        let inner = unsafe { Box::from_raw(outer.0) };
-        drop(inner);
-        drop(outer);
+impl AsRef<RuSpringPipeline> for SpringPipeline {
+    fn as_ref(&self) -> &RuSpringPipeline {
+        &self.0
     }
+}
 
-    pub fn into_ptr(self) -> *mut SpringPipeline {
+impl SpringPipeline {
+    pub(crate) fn into_ptr(self) -> *mut SpringPipeline {
         Box::into_raw(Box::new(self))
     }
 }
diff --git a/src/spring_sink_row.rs b/src/spring_sink_row.rs
index 1415254..b482f45 100644
--- a/src/spring_sink_row.rs
+++ b/src/spring_sink_row.rs
@@ -1,31 +1,27 @@
 // This file is part of https://github.com/SpringQL/SpringQL-client-c which is licensed under MIT OR Apache-2.0. See file LICENSE-MIT or LICENSE-APACHE for full license details.
 
-use ::springql::SpringSinkRow as SinkRow;
-
-use std::{ffi::c_void, mem};
+use springql::{Result, SpringSinkRow as RuSpringSinkRow, SpringValue};
 
 /// Row object to pop from an in memory queue.
 #[non_exhaustive]
-#[repr(transparent)]
-pub struct SpringSinkRow(*mut c_void);
-
-impl SpringSinkRow {
-    pub fn new(sink_row: SinkRow) -> Self {
-        SpringSinkRow(unsafe { mem::transmute(Box::new(sink_row)) })
-    }
+#[derive(Debug)]
+pub struct SpringSinkRow(RuSpringSinkRow);
 
-    pub fn as_row(&self) -> &SinkRow {
-        unsafe { &*(self.0 as *const SinkRow) }
+impl From<RuSpringSinkRow> for SpringSinkRow {
+    fn from(sink_row: RuSpringSinkRow) -> Self {
+        SpringSinkRow(sink_row)
     }
+}
 
-    pub fn drop(ptr: *mut SpringSinkRow) {
-        let outer = unsafe { Box::from_raw(ptr) };
-        let inner = unsafe { Box::from_raw(outer.0) };
-        drop(inner);
-        drop(outer);
+impl SpringSinkRow {
+    pub(crate) fn get_not_null_by_index<T>(&self, i_col: usize) -> Result<T>
+    where
+        T: SpringValue,
+    {
+        self.0.get_not_null_by_index(i_col)
     }
 
-    pub fn into_ptr(self) -> *mut SpringSinkRow {
+    pub(crate) fn into_ptr(self) -> *mut Self {
         Box::into_raw(Box::new(self))
     }
 }
diff --git a/src/spring_source_row.rs b/src/spring_source_row.rs
index f792a7c..4177593 100644
--- a/src/spring_source_row.rs
+++ b/src/spring_source_row.rs
@@ -1,30 +1,24 @@
 // This file is part of https://github.com/SpringQL/SpringQL-client-c which is licensed under MIT OR Apache-2.0. See file LICENSE-MIT or LICENSE-APACHE for full license details.
 
-use ::springql::SpringSourceRow as SourceRow;
-
-use std::{ffi::c_void, mem};
+use ::springql::SpringSourceRow as RuSpringSourceRow;
 
 /// Row object to push into an in memory queue.
 #[non_exhaustive]
-#[repr(transparent)]
-pub struct SpringSourceRow(*mut c_void);
-
-impl SpringSourceRow {
-    pub fn new(source_row: SourceRow) -> Self {
-        SpringSourceRow(unsafe { mem::transmute(Box::new(source_row)) })
-    }
+#[derive(Clone, Debug)]
+pub struct SpringSourceRow(RuSpringSourceRow);
 
-    pub fn to_row(&self) -> SourceRow {
-        unsafe { &*(self.0 as *const SourceRow) }.clone()
+impl From<RuSpringSourceRow> for SpringSourceRow {
+    fn from(source_row: RuSpringSourceRow) -> Self {
+        SpringSourceRow(source_row)
     }
-
-    pub fn drop(ptr: *mut SpringSourceRow) {
-        let outer = unsafe { Box::from_raw(ptr) };
-        let inner = unsafe { Box::from_raw(outer.0) };
-        drop(inner);
-        drop(outer);
+}
+impl From<SpringSourceRow> for RuSpringSourceRow {
+    fn from(source_row: SpringSourceRow) -> Self {
+        source_row.0
     }
+}
 
+impl SpringSourceRow {
     pub fn into_ptr(self) -> *mut SpringSourceRow {
         Box::into_raw(Box::new(self))
     }
diff --git a/src/spring_source_row_builder.rs b/src/spring_source_row_builder.rs
index 7391f7c..e553ce0 100644
--- a/src/spring_source_row_builder.rs
+++ b/src/spring_source_row_builder.rs
@@ -1,37 +1,25 @@
 // This file is part of https://github.com/SpringQL/SpringQL-client-c which is licensed under MIT OR Apache-2.0. See file LICENSE-MIT or LICENSE-APACHE for full license details.
 
-use ::springql::SpringSourceRowBuilder as SourceRowBuilder;
-
-use std::{ffi::c_void, mem};
+use ::springql::SpringSourceRowBuilder as RuSpringSourceRowBuilder;
 
 /// Builder of SpringSourceRow
 #[non_exhaustive]
-#[repr(transparent)]
-pub struct SpringSourceRowBuilder(*mut c_void);
-
-impl SpringSourceRowBuilder {
-    pub fn new(underlying: SourceRowBuilder) -> Self {
-        SpringSourceRowBuilder(unsafe { mem::transmute(Box::new(underlying)) })
-    }
+#[derive(PartialEq, Debug, Default)]
+pub struct SpringSourceRowBuilder(RuSpringSourceRowBuilder);
 
-    pub fn to_row_builder(&self) -> SourceRowBuilder {
-        unsafe { &*(self.0 as *const SourceRowBuilder) }.clone()
+impl From<RuSpringSourceRowBuilder> for SpringSourceRowBuilder {
+    fn from(builder: RuSpringSourceRowBuilder) -> Self {
+        SpringSourceRowBuilder(builder)
     }
-
-    pub fn drop(ptr: *mut SpringSourceRowBuilder) {
-        let outer = unsafe { Box::from_raw(ptr) };
-        let inner = unsafe { Box::from_raw(outer.0) };
-        drop(inner);
-        drop(outer);
+}
+impl From<SpringSourceRowBuilder> for RuSpringSourceRowBuilder {
+    fn from(builder: SpringSourceRowBuilder) -> Self {
+        builder.0
     }
+}
 
+impl SpringSourceRowBuilder {
     pub fn into_ptr(self) -> *mut SpringSourceRowBuilder {
         Box::into_raw(Box::new(self))
     }
 }
-
-impl Default for SpringSourceRowBuilder {
-    fn default() -> Self {
-        Self::new(SourceRowBuilder::default())
-    }
-}
diff --git a/src/tests.rs b/src/tests.rs
new file mode 100644
index 0000000..4328343
--- /dev/null
+++ b/src/tests.rs
@@ -0,0 +1,6 @@
+// This file is part of https://github.com/SpringQL/SpringQL-client-c which is licensed under MIT OR Apache-2.0. See file LICENSE-MIT or LICENSE-APACHE for full license details.
+
+mod spring_config;
+mod spring_open;
+mod spring_sink_row;
+mod spring_source_row_builder;
diff --git a/src/tests/spring_config.rs b/src/tests/spring_config.rs
new file mode 100644
index 0000000..1cb5dd0
--- /dev/null
+++ b/src/tests/spring_config.rs
@@ -0,0 +1,24 @@
+// This file is part of https://github.com/SpringQL/SpringQL-client-c which is licensed under MIT OR Apache-2.0. See file LICENSE-MIT or LICENSE-APACHE for full license details.
+
+use std::ffi::CString;
+
+use crate::*;
+
+#[test]
+fn test_spring_config_default() {
+    unsafe {
+        let config = spring_config_default();
+        assert!(!config.is_null());
+        spring_config_close(config);
+    }
+}
+
+#[test]
+fn test_spring_config_toml() {
+    let toml = CString::new("").unwrap();
+    unsafe {
+        let config = spring_config_toml(toml.as_ptr());
+        assert!(!config.is_null());
+        spring_config_close(config);
+    }
+}
diff --git a/src/tests/spring_open.rs b/src/tests/spring_open.rs
new file mode 100644
index 0000000..2a2fbf0
--- /dev/null
+++ b/src/tests/spring_open.rs
@@ -0,0 +1,17 @@
+// This file is part of https://github.com/SpringQL/SpringQL-client-c which is licensed under MIT OR Apache-2.0. See file LICENSE-MIT or LICENSE-APACHE for full license details.
+
+use crate::*;
+
+#[test]
+fn test_spring_open() {
+    unsafe {
+        let config = spring_config_default();
+        assert!(!config.is_null());
+
+        let pipeline = spring_open(config);
+        assert!(!config.is_null());
+
+        spring_close(pipeline);
+        spring_config_close(config);
+    }
+}
diff --git a/src/tests/spring_sink_row.rs b/src/tests/spring_sink_row.rs
new file mode 100644
index 0000000..f8d7760
--- /dev/null
+++ b/src/tests/spring_sink_row.rs
@@ -0,0 +1,75 @@
+// This file is part of https://github.com/SpringQL/SpringQL-client-c which is licensed under MIT OR Apache-2.0. See file LICENSE-MIT or LICENSE-APACHE for full license details.
+
+use std::ffi::CString;
+
+use crate::*;
+
+unsafe fn command(pipeline: *const SpringPipeline, sql: &str) {
+    let sql = CString::new(sql).unwrap();
+    let errno = spring_command(pipeline, sql.as_ptr());
+    assert_eq!(errno, SpringErrno::Ok);
+}
+
+#[test]
+fn test_spring_sink_row() {
+    unsafe {
+        let config = spring_config_default();
+        assert!(!config.is_null());
+
+        let pipeline = spring_open(config);
+        assert!(!config.is_null());
+
+        command(pipeline, "CREATE SOURCE STREAM source_1 (b BLOB NOT NULL);");
+        command(pipeline, "CREATE SINK STREAM sink_1 (b BLOB NOT NULL);");
+        command(
+            pipeline,
+            "
+            CREATE PUMP pump_1 AS
+                INSERT INTO sink_1 (b)
+                SELECT STREAM source_1.b FROM source_1;
+            ",
+        );
+        command(
+            pipeline,
+            "
+            CREATE SINK WRITER queue_sink FOR sink_1
+                TYPE IN_MEMORY_QUEUE OPTIONS (NAME 'q_sink');
+            ",
+        );
+        command(
+            pipeline,
+            "
+            CREATE SOURCE READER queue_src FOR source_1
+                TYPE IN_MEMORY_QUEUE OPTIONS (NAME 'q_src');
+            ",
+        );
+
+        let source_row = {
+            let col = CString::new("b").unwrap();
+            let val = vec![0x01u8, 0x02, 0x03];
+
+            let builder = spring_source_row_builder();
+            let builder = spring_source_row_add_column_blob(
+                builder,
+                col.as_ptr(),
+                val.as_ptr().cast(),
+                val.len().try_into().unwrap(),
+            );
+            assert!(!builder.is_null());
+
+            spring_source_row_build(builder)
+        };
+
+        let q_src = CString::new("q_src").unwrap();
+        let errno = spring_push(pipeline, q_src.as_ptr(), source_row);
+        assert_eq!(errno, SpringErrno::Ok);
+
+        let q_sink = CString::new("q_sink").unwrap();
+        let sink_row = spring_pop(pipeline, q_sink.as_ptr());
+
+        spring_sink_row_close(sink_row);
+
+        spring_close(pipeline);
+        spring_config_close(config);
+    }
+}
diff --git a/src/tests/spring_source_row_builder.rs b/src/tests/spring_source_row_builder.rs
new file mode 100644
index 0000000..e4f922b
--- /dev/null
+++ b/src/tests/spring_source_row_builder.rs
@@ -0,0 +1,24 @@
+// This file is part of https://github.com/SpringQL/SpringQL-client-c which is licensed under MIT OR Apache-2.0. See file LICENSE-MIT or LICENSE-APACHE for full license details.
+
+use std::ffi::CString;
+
+use crate::*;
+
+#[test]
+fn test_spring_source_row_builder() {
+    unsafe {
+        let c1_col = CString::new("c1").unwrap();
+        let c1_value = vec![0x01u8, 0x02, 0x03];
+
+        let builder = spring_source_row_builder();
+        let builder = spring_source_row_add_column_blob(
+            builder,
+            c1_col.as_ptr(),
+            c1_value.as_ptr().cast(),
+            c1_value.len().try_into().unwrap(),
+        );
+        assert!(!builder.is_null());
+
+        let _row = spring_source_row_build(builder);
+    }
+}