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SQLite Loadable Extensions

04 Mar 2018

SQLite has the ability to load extensions at run-time. I've now implemented this functionality in UDBC-SQLite.

An SQLite extension is built as a .so/dylib/dll shared library file. Let's use SQLite's rot13 extension as our example. The source file rot13.c is located in the SQLite source code's ext/misc directory. To build the rot13 extension, also download the amalgamation. Unzip the amalgamation and copy rot13.c into its directory. Build the extension:

% gcc -fPIC -shared -o rot13.so -I. rot13.c

Verify that the extension works:

% sqlite3
SQLite version 3.22.0 2018-01-22 18:45:57
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database.
sqlite> select rot13('qwerty');
Error: no such function: rot13
sqlite> .load "./rot13.so"
sqlite> select rot13('qwerty');
sqlite> select rot13('djregl');

For use with Pharo, copy rot13.so into the Pharo VM directory where all the other .so files are.

Next steps are done in Pharo. For the purpose of this blog post, I downloaded a fresh Pharo 60536 64-bit image. Start the image and install GlorpSQLite from the Catalog browser, which installs the latest UDBC-SQLite. (This also installs Glorp, of course. If you run Glorp's unit tests from Test Runner you should get all 890 tests passed.)

In a playground, run this snippet and Transcript should show, first, the text "no such function: rot13" and then the rot13 outputs.

| db rs r1 r2 |
Transcript clear.
db := UDBCSQLite3Connection openOn: ':memory:'.
[   [ db execute: 'select rot13(''qwerty'')' ]
      on: UDBCSQLite3Error
      do: [ ex: | Transcript show: ex messageText; cr ].
    db enableExtensions;          "<== New stuff."
      loadExtension: 'rot13.so'.  "<== New stuff."
    rs := db execute: 'select rot13(''qwerty'') as r1'.
    r1 := rs next at: 'r1'.
    Transcript show: r1; cr. 
    rs := db execute: 'select rot13(?) as r2' with: (Array with: r1).
    r2 := rs next at: 'r2'.
    Transcript show: r2; cr.
] ensure: [ db close ]

Note the messages #enableExtensions and #loadExtension:. For security reasons, extension loading is disabled by default.

Tested on Linux latest Pharo 64-bit 60536.

Tags: SQLite