Database abstraction library written in C.

Simple and easy to use database access library. Works with SQLite 3, MariaDB and PostgreSQL databases. Uses a JSON-based language with jansson to execute simple queries based on one table.

See the online documentation for a doxygen format of the API documentation.

Install Jansson library for JSON manipulation, minimum version 2.4. On a Debian-based platform, run the following command:

$ sudo apt-get install libjansson-dev

Install Hoel database dependencies based on your requirements:

• SQLite3: Install the package libsqlite3-dev
• MariaDB: Install the package libmariadb-dev
• PostgreSQL: Install the package libpq-dev

Hoel is available in multiple distributions as official package. Check out your distribution documentation to install the package automatically.

$ # Example for Debian testing
$ sudo apt install libhoel-dev

You can install Hoel with a pre-compiled package available in the release pages. jansson, sqlite3, libmariadb-client and libpq development files packages are required to install Hoel. The packages files hoel-dev-full_* contain the libraries orcania, yder and hoel. It's also compiled with all the database backends.

For example, to install Hoel with the hoel-dev-full_2.3.0_Debian_stretch_x86_64.tar.gz package downloaded on the releases page, you must execute the following commands:

$ sudo apt install -y libjansson-dev libmariadb-dev libsqlite3-dev libpq-dev libsystemd-dev
$ wget https://github.com/babelouest/hoel/releases/download/v1.4.0/hoel-dev-full_1.4.0_Debian_stretch_x86_64.tar.gz
$ tar xf hoel-dev-full_1.4.0_Debian_stretch_x86_64.tar.gz
$ sudo dpkg -i liborcania-dev_1.2.0_Debian_stretch_x86_64.deb
$ sudo dpkg -i libyder-dev_1.2.0_Debian_stretch_x86_64.deb
$ sudo dpkg -i libhoel-dev_1.4.0_Debian_stretch_x86_64.deb

If there's no package available for your distribution, you can recompile it manually using CMake or Makefile.

CMake minimum 3.5 is required.

Run the CMake script in a sub-directory, example:

$ git clone https://github.com/babelouest/hoel.git
$ cd hoel/
$ mkdir build
$ cd build
$ cmake ..
$ make && sudo make install

The available options for CMake are:

• -DWITH_SQLITE3=[on|off] (default on): Enable/disable SQLite3 database backend
• -DWITH_MARIADB=[on|off] (default on): Enable/disable MariaDB database backend
• -DWITH_PGSQL=[on|off] (default on): Enable/disable PostgreSQL database backend
• -DWITH_JOURNALD=[on|off] (default on): Build with journald (SystemD) support for logging
• -DBUILD_STATIC=[on|off] (default off): Build the static archive in addition to the shared library
• -DBUILD_HOEL_TESTING=[on|off] (default off): Build unit tests
• -DBUILD_HOEL_DOCUMENTATION=[on|off] (default off): Build the documentation, doxygen is required
• -DINSTALL_HEADER=[on|off] (default on): Install header file hoel.h
• -DBUILD_RPM=[on|off] (default off): Build RPM package when running make package
• -DCMAKE_BUILD_TYPE=[Debug|Release] (default Release): Compile with debugging symbols or not

Clone, compile and install Orcania and Yder libraries.

$ git clone https://github.com/babelouest/orcania.git
$ cd orcania/src
$ make && sudo make install

$ git clone https://github.com/babelouest/yder.git
$ cd yder/src
$ make
$ sudo make install

Download Hoel from GitHub repository.

$ git clone https://github.com/babelouest/hoel.git
$ cd hoel/src
$ make
$ sudo make install

By default, Hoel is compiled with the 3 databases support. If you don't need one or more database, follow these instructions

Add DISABLE_SQLITE=1 to the make command:

$ cd hoel/src
$ make DISABLE_SQLITE=1
$ sudo make install

Add DISABLE_MARIADB=1 to the make command:

$ cd hoel/src
$ make DISABLE_MARIADB=1
$ sudo make install

Add DISABLE_POSTGRESQL=1 to the make command:

$ cd hoel/src
$ make DISABLE_POSTGRESQL=1
$ sudo make install

You can disable 2 databases backends to keep just one, simply add both parameters to the make command:

$ cd hoel/src
$ make DISABLE_MARIADB=1 DISABLE_POSTGRESQL=1
$ sudo make install

By default, the shared library and the header file will be installed in the /usr/local location. To change this setting, you can modify the DESTDIR value in the src/Makefile.

To use Hoel in your code, include the file hoel.h.

#include <hoel.h>

Use the flag -lhoel to include Hoel library in the linking process.

When specified, some functions return H_OK on success, and other values otherwise. H_OK is 0, other values are non-0 values. The defined errors list is the following:

#define H_OK                0  // No error
#define H_ERROR             1  // Generic error
#define H_ERROR_PARAMS      2  // Error in input parameters
#define H_ERROR_CONNECTION  3  // Error in database connection
#define H_ERROR_DISABLED    4  // Database connection is disabled
#define H_ERROR_QUERY       5  // Error executing query
#define H_ERROR_MEMORY      99 // Error allocating memory

Some function return allocated values. When the value is not a structure, you must use the function h_free to clean it. Otherwise, use the dedicated functions.

/**
 * free data allocated by hoel functions
 */
void h_free(void * data);

To create a connection to a database, use its dedicated function

/**
 * h_connect_sqlite
 * Opens a database connection to a sqlite3 db file
 * return pointer to a struct _h_connection * on sucess, NULL on error
 */
struct _h_connection * h_connect_sqlite(const char * db_path);

/**
 * h_connect_mariadb
 * Opens a database connection to a mariadb server
 * return pointer to a struct _h_connection * on success, NULL on error
 */
struct _h_connection * h_connect_mariadb(const char * host, const char * user, const char * passwd, const char * db, const unsigned int port, const char * unix_socket);

/**
 * h_connect_pgsql
 * Opens a database connection to a PostgreSQL server
 * return pointer to a struct _h_connection * on sucess, NULL on error
 */
struct _h_connection * h_connect_pgsql(char * conninfo);

All these functions return a struct _h_connection * on success. This pointer will be needed on every call to Hoel functions.

When you no longer need your connection, close it using the function h_close_db. This will close the connection to the database and free the memory allocated by the connection.

/**
 * Close a database connection
 * return H_OK on success
 */
int h_close_db(struct _h_connection * conn);

The connection must be cleaned when it's no longer needed.

/**
 * h_clean_connection
 * free memory allocated by the struct _h_connection
 * return H_OK on success
 */
int h_clean_connection(struct _h_connection * conn);

If you need to escape parameters, you can use the functions h_escape_string, the returned value must be h_free'd after use.

The meaning of existence of the function h_escape_string_with_quotes is because of PostgreSQL ways to escape an unsafe string.

TL;DR:

• Use h_escape_string_with_quotes only if you use a PostgreSQL database.
• You can use both h_escape_string_with_quotes and h_escape_string if you use only SQLite3 and/or MariaDB databases.

If the unsafe string contains backslashes "\", the escaped string will have the pattern E'<safe>', otherwise it will have the pattern '<safe>'. Since the function h_escape_string must return the safe string only, without surroundings quotes ', the format E'<safe>' is incompatible with Hoel API.

Therefore, using h_escape_string with PostgreSQL could lead to undefined behaviour and more importantly exploitable bugs.

To avoid this, on a PostgreSQL database, an escaped string using h_escape_string that should return the format E'<safe>' will return NULL, and an escaped string using h_escape_string_with_quotes will return the format E'<safe>'.

/**
 * h_escape_string
 * Escapes a string
 * returned value must be h_free'd after use
 */
char * h_escape_string(const struct _h_connection * conn, const char * unsafe);

/**
 * h_escape_string_with_quotes
 * Escapes a string and returns it ready to be inserted in the query
 * returned value must be h_h_free'd after use
 */
char * h_escape_string_with_quotes(const struct _h_connection * conn, const char * unsafe);

To execute a SQL query, you can use the function h_execute_query which will run the query in the database specified by the parameter conn. If a result parameter is specified, the result of the query (if any) will be stored in the result structure.

/**
 * h_execute_query
 * Execute a query, set the result structure with the returned values if available
 * if result is NULL, the query is executed but no value will be returned
 * options available
 * H_OPTION_NONE (0): no option
 * H_OPTION_SELECT: Execute a prepare statement (sqlite only)
 * H_OPTION_EXEC: Execute an exec statement (sqlite only)
 * return H_OK on success
 */
int h_execute_query(const struct _h_connection * conn, const char * query, struct _h_result * result, int options);

The struct _h_result is a structure containing the values returned by a query. The definition of the structure is:

/**
 * sql result structure
 */
struct _h_result {
  unsigned int nb_rows;
  unsigned int nb_columns;
  struct _h_data ** data;
};

The data value is a 2 dimensional array with struct _h_data variables. A struct _h_data is defined as:

/**
 * sql data container
 */
struct _h_data {
  int type;
  void * t_data;
};

where type can be the following values:

#define HOEL_COL_TYPE_INT    0
#define HOEL_COL_TYPE_DOUBLE 1
#define HOEL_COL_TYPE_TEXT   2
#define HOEL_COL_TYPE_DATE   3
#define HOEL_COL_TYPE_BLOB   4
#define HOEL_COL_TYPE_NULL   5

t_data will point to a struct _h_type_* corresponding to the type. The struct _h_type_* available are:

/**
 * sql value integer type
 */
struct _h_type_int {
  int value;
};

/**
 * sql value double type
 */
struct _h_type_double {
  double value;
};

/**
 * sql value date/time type
 */
struct _h_type_datetime {
  struct tm value;
};

/**
 * sql value string type
 */
struct _h_type_text {
  char * value;
};

/**
 * sql value blob type
 */
struct _h_type_blob {
  size_t length;
  void * value;
};

To clean a result or a data structure, you can use its dedicated functions:

/**
 * h_clean_result
 * Free all the memory allocated by the struct _h_result
 * return H_OK on success
 */
int h_clean_result(struct _h_result * result);

/**
 * h_clean_data
 * Free memory allocated by the struct _h_data
 * return H_OK on success
 */
int h_clean_data(struct _h_data * data);

If you need the last id generated after an insert query, you can use the following function:

/**
 * h_query_last_insert_id
 * return the id of the last inserted value
 * return a pointer to `struct _h_data *` on success, NULL otherwise.
 */
struct _h_data * h_query_last_insert_id(const struct _h_connection * conn);

You can use additional functions for specific needs. All these function will use h_execute_query but check input parameters before.

/**
 * h_query_insert
 * Execute an insert query
 * return H_OK on success
 */
int h_query_insert(const struct _h_connection * conn, const char * query);

/**
 * h_query_update
 * Execute an update query
 * return H_OK on success
 */
int h_query_update(const struct _h_connection * conn, const char * query);

/**
 * h_query_delete
 * Execute an delete query
 * return H_OK on success
 */
int h_query_delete(const struct _h_connection * conn, const char * query);

/**
 * h_execute_query
 * Execute a select query, set the result structure with the returned values
 * return H_OK on success
 */
int h_query_select(const struct _h_connection * conn, const char * query, struct _h_result * result);

Hoel allows to use JSON objects for simple queries with jansson library. In the simple JSON queries, a JSON object called json_t * j_query is used to generate the query.

All json_t * returned and updated values must be free after use.

A j_query has the following form:

{
  "table": "table_name"             // String, mandatory, the table name where the query is executed
  "columns": ["col1", "col2"]       // Array of strings, available for h_select, optional. If not specified,will be used
  "order_by": "col_name [asc|desc]" // String, available for h_select, specify the order by clause, optional
  "limit": integer_value            // Integer, available for h_select, specify the limit value, optional
  "offset"                          // Integer, available for h_select, specify the limit value, optional but available only if limit is set
  "values": [{                      // JSON object or JSON array of JSON objects, available for h_insert, mandatory, specify the values to update
    "col1": "value1",               // Generates col1='value1' for an update query
    "col2": value_integer,          // Generates col2=value_integer for an update query
    "col3", "value3",               // Generates col3='value3' for an update query
    "col4", null                    // Generates col4=NULL for an update query
  }]
  "set": {                          // JSON object, available for h_update, mandatory, specify the values to update
    "col1": "value1",               // Generates col1='value1' for an update query
    "col2": value_integer,          // Generates col2=value_integer for an update query
    "col3", "value3",               // Generates col3='value3' for an update query
    "col4", null                    // Generates col4=NULL for an update query
  }
  "where": {                        // JSON object, available for h_select, h_update and h_delete, mandatory, specify the where clause. All clauses are separated with an AND operator
    "col1": "value1",               // Generates col1='value1'
    "col2": value_integer,          // Generates col2=value_integer
    "col3": null,                   // Generates col3=NULL
    "col4": {                       // Generates col4<12
      "operator": "<",
      "value": 12
    },
    "col5": {                       // Generates col5 IS NOT NULL
      "operator": "NOT NULL"
    },
    "col6": {                       // Generates col6 LIKE '%value6%'
      "operator": "raw",
      "value": "LIKE '%value6%'"
    },
    "col7": {
      "operator": "IN",             // Generates col7 IN ('value1',42,4.2)
      "value": [                    // Values can be string, real or integer
        "value1",
        42,
        4.2
      ]
    }
  }
}

A where clause is a JSON object containing a series of clauses. A clause can have 2 different forms:

• col_name: value
• col_name: {operator: "operator_value", value: value}

In the first case, col_name: value, the clause becomes col_name = value. Value is always escaped.

In the second case, col_name: {operator: "operator_value", value: value}, depending on the operator value, the clause can have different forms:

• operator: "NOT NULL", the clause becomes col_name IS NOT NULL
• operator: "raw", the value value becomes the clause itself, not escaped, for example in { "operator": "raw", "value": "LIKE '%value6%'" }, the clause becomes col6 LIKE '%value6%'
• otherwise, the clause becomes col_name operator value, value is escaped

All clauses are separated by an AND operator.

As en example, here is a JSON object and its generated where clause:

JSON object:

{
  "col1": "value1",
  "col2": 42,
  "col3": {
    "operator": ">=",
    "value": 55.5
  },
  "col4": {
    "operator": "raw",
    "value": "LIKE '%alu%'"
  }
}

SQL Where clause:

WHERE col1 = 'value1'
  AND col2 = 42
  AND col3 >= 55.5
  AND col4 LIKE '%alu%'

If you need less simple clauses, you can build it on your own and use the h_execute_query or the h_execute_query_json functions.

The simple JSON queries functions are:

/**
 * h_select
 * Execute a select query
 * Uses a json_t * parameter for the query parameters
 * Store the result of the query in j_result if specified. j_result must be decref'd after use
 * Duplicate the generated query in generated_query if specified, must be h_free'd after use
 * return H_OK on success
 */
int h_select(const struct _h_connection * conn, const json_t * j_query, json_t ** j_result, char ** generated_query);

/**
 * h_insert
 * Execute an insert query
 * Uses a json_t * parameter for the query parameters
 * Duplicate the generated query in generated_query if specified, must be h_free'd after use
 * return H_OK on success
 */
int h_insert(const struct _h_connection * conn, const json_t * j_query, char ** generated_query);

/**
 * h_last_insert_id
 * return the id of the last inserted value
 * return a pointer to `json_t *` on success, NULL otherwise.
 * The returned value is of type JSON_INTEGER
 */
json_t * h_last_insert_id(const struct _h_connection * conn);

/**
 * h_update
 * Execute an update query
 * Uses a json_t * parameter for the query parameters
 * Duplicate the generated query in generated_query if specified, must be h_free'd after use
 * return H_OK on success
 */
int h_update(const struct _h_connection * conn, const json_t * j_query, char ** generated_query);

/**
 * h_delete
 * Execute a delete query
 * Uses a json_t * parameter for the query parameters
 * Duplicate the generated query in generated_query if specified, must be h_free'd after use
 * return H_OK on success
 */
int h_delete(const struct _h_connection * conn, const json_t * j_query, char ** generated_query);

The function h_last_insert_id returns the last inserted id in a json_t * format.

/**
 * h_last_insert_id
 * return the id of the last inserted value
 * return a pointer to `json_t *` on success, NULL otherwise.
 * The returned value is of type JSON_INTEGER
 */
json_t * h_last_insert_id(const struct _h_connection * conn);

See examples folder for detailed sample source codes.