Simple PostgreSQL connector for Arduino, ESP32 and ESP8266.

Only simple queries are implemented. COPY is not implemented due to code size limit, but probably will be for ESP32 only. Large objects are not implemented as obsolete and never be.

Available authorization method are trust, password and md5. Due to code size limit, md5 method may be disabled in compilation time, decreasing code size for Arduino by some kilobytes.

All methods are asynchronous, but sometimes may block for a while in case of poor network connection.

As column names and notifications are rarely needed in microcontrollers applications, may be disabled. In this case only number of fields will be fetched from row description packet, and notification rows will be simply skipped.

All methods uses single internal buffer, allocated at setDbLogin and freed on close. It's possible to provide external (statically allocated) buffer, which may be reused in rest of application.

Parameter progmem has no meaning for ESP32.

• PGconnection
• setDbLogin
• status
• close
• execute
• getData
• getColumn
• getValue
• getMessage
• dataStatus
• nfields
• ntuples
• escapeString
• escapeName;
• executeFormat;

PGconnection(Client *c, int flags = 0, int memory = 0, char *foreignBuffer = NULL);

Class constructor.

• Client - Client instance (WiFi or Ethernet)
• flags - some flags:
  • PG_FLAG_IGNORE_NOTICES - ignore notices and notifications
  • PG_FLAG_IGNORE_COLUMNS - ignore column names
• memory - internal buffer size. Defaults to PG_BUFFER_SIZE
• foreignBuffer - static buffer address

int setDbLogin(IPAddress server,
            const char *user,
            const char *passwd = NULL,
            const char *db = NULL,
            const char *charset = NULL,
            int port = 5432);

Initialize connection.

• server - IP address of backend server
• user - database user name
• passwd - database user password
• db - database name (defaults to user name)
• charset - client encoding
• port - server port

connection status (see below)

int status(void);

Check current connection status and perform authorization action if needed. Must be called after setDbLogin until CONNECTION_OK, CONNECTION_BAD or CONNECTION_NEEDED.

Current connection status. May be one of:

• CONNECTION_NEEDED - no connection yet, call setDbLogin.
• CONNECTION_OK - ready for queries.
• CONNECTION_BAD - connection can't be realized or was abandoned. Call close().
• CONNECTION_AWAITING_RESPONSE - Waiting for a response from the postmaster. Call status() again.
• CONNECTION_AUTH_OK - Received authentication; waiting for backend startup. Call status() again.

void close(void);

Send termination command if needed and close connection. Free internal buffers.

execute(const char *query, int progmem = 0);

Send query to backend. Invalidates data in internal buffer.

• query - PostgreSQL query
• progmem - if not zero, query is in Flash memory

Negative value on error or zero on success. In case of error you must check connection status - some errors invalidates connection.

int getData(void);

Retrieve any response from backend. Must be called after execute() until PG_RSTAT_READY. May be called even in READY state and fetch possible notifications. Each call invalidates data in internal buffer, so values returned by getColumn(), getValue() and getMessage() will be valid only until next getData() or execute() call.

• Negative value on error
• Zero if no interesting data arrived
• Positive value if some data was fetched (see below)

int dataStatus(void);

Get current data status.

Combination of bits:

• PG_RSTAT_READY - ready for next query
• PG_RSTAT_COMMAND_SENT - command was sent to backend
• PG_RSTAT_HAVE_COLUMNS - column names in buffer
• PG_RSTAT_HAVE_ROW - row data in buffer
• PG_RSTAT_HAVE_SUMMARY - execution finished, number of affected rows available
• PG_RSTAT_HAVE_ERROR - error message in buffer
• PG_RSTAT_HAVE_NOTICE - notice/notification in buffer

char *getColumn(int n);

Get n-th column name if available

• Pointer to n-th column name in internal buffer
• NULL if not in PG_RSTAT_HAVE_COLUMNS state or n out of range.

char *getValue(int n);

Get n-th row value if available

• Pointer to n-th column value in internal buffer
• NULL if value is NULL, n is out of range or not in PG_RSTAT_HAVE_ROW state

char *getMessage(void);

Get current error or notification message

Pointer to message text in internal buffer or NULL if no message.

int nfields(void);

Get column count in result. Valid only after PG_RSTAT_HAVE_COLUMNS or first PG_RSTAT_HAVE_ROW.

Column count or zero if not known.

int ntuples(void);

Get number of tuples in result. Valid only after PG_RSTAT_HAVE_SUMMARY.

• Number of returned tuples in case of SELECT or INSERT/UPDATE...RETURNING
• Number of affected rows in case of INSERT, UPDATE or DELETE
• Zero if not available.

int escapeString(const char *inbuf, char *outbuf);

Creates escaped version of literal. Single quotes and 'E' marker (if needed) will be added.

• inbuf - string to escape
• outbuf - output buffer or NULL if we only count length of result

Length of escaped string

int escapeName(const char *inbuf, char *outbuf);

Creates escaped version of name. Double quotes will be added.

• inbuf - string to escape
• outbuf - output buffer or NULL if we only count length of result

Length of escaped string

int executeFormat(int progmem, const char *format, ...);

Send formatted query to backend. Format string may be placed in Flash memory. Formatting sequences are:

• %s - string literal (will be escaped with escapeString)
• %n - name (will be escaped with escapeName)
• %d - int (single quotes will be added)
• %l - long int (single quotes will be added)
• %% - % character

Any % character not followed by 's', 'n', 'd', 'l' or '%' causes error. Query may be long, but results of any formatted value must fit in internal buffer.

• progmem - indicates format in Flash memory
• format - formatting string

Zero on success or negative value on error.