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https://github.com/llimllib/wasm_sqlite_with_stats

Documentation and demonstration of how to build WASM versions of SQLite with extensions embedded
https://github.com/llimllib/wasm_sqlite_with_stats

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Documentation and demonstration of how to build WASM versions of SQLite with extensions embedded

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README 

        
# Building a WASM sqlite with an embedded extension



I wanted to build a wasm version of sqlite, but I also wanted to include [an

extension](https://github.com/nalgeon/sqlean/blob/main/docs/stats.md) in it.



As far as I know, you can't dynamically load extensions into the wasm version

of sqlite, so I wanted to build a version that had it statically linked in.



As I don't know C very well, this seemed pretty hopeless - but thankfully I

found [sqlite-lines](https://github.com/asg017/sqlite-lines/) by @asg017 (who

also kindly [helped me on

twitter](https://twitter.com/agarcia_me/status/1565775569664430080)), which

[demonstrated](https://observablehq.com/@asg017/introducing-sqlite-lines) that

it was possible.



- [The pieces](#the-pieces)

- [The idea](#the-idea)

- [The steps](#the-steps)

- [Build it yourself](#build-it-yourself)

- [SQLite fiddle with extension](#sqlite-fiddle-with-extension)



**update** (Nov 11 2024): there are [official instructions](https://sqlite.org/wasm/doc/trunk/building.md#:~:text=see.md%20for%20details.-,adding%20client-custom%20init%20code,-The%20WASM%20build) for adding an extension to the official WASM build (this uses sql.js instead, as the official wasm build did not exist at the time of its writing). I have not yet tried them out



## The pieces



To build it, I followed in Alex's footsteps and used these pieces:



- [Emscripten](https://emscripten.org/)

- The [sqlite amalgamation file](https://www.sqlite.org/amalgamation.html) and

  [extension header

  file](https://github.com/sqlite/sqlite/blob/master/src/sqlite3ext.h)

  - I just copied the versions Alex used

- The [stats

  file](https://github.com/nalgeon/sqlean/blob/main/src/sqlite3-stats.c) from

  sqlean

- The [sqlite wasm API](https://github.com/sql-js/sql.js/) from sql.js

- The [Makefile](https://github.com/asg017/sqlite-lines/blob/main/Makefile) and

  [core-init.c](https://github.com/asg017/sqlite-lines/blob/main/core_init.c)

  file from [sqlite-lines](https://github.com/asg017/sqlite-lines)



## The idea



The basic idea of building a sqlite that has an extension statically linked is

that you can use an undocumented C preprocessor macro called

`SQLITE_EXTRA_INIT` which will, if defined, load extra code into sqlite after

finishing up its own initialization. If you point `SQLITE_EXTRA_INIT` at a

function that calls

[`sqlite3_auto_extension`](https://www.sqlite.org/c3ref/auto_extension.html)

with a pointer to your extension's init function, it will load right after

sqlite loads itself and the functions defined within will be available to

sqlite.



## The steps



To make the idea happen, this code:



- sets `SQLITE_EXTRA_INIT` [here](https://github.com/llimllib/wasm_sqlite_with_stats/blob/83bdf9e1bf6808590a281d8f2d32cafafa750b33/Makefile#L13), pointing to the `core_init` function

- defines the `core_init` function [here](https://github.com/llimllib/wasm_sqlite_with_stats/blob/83bdf9e1bf6808590a281d8f2d32cafafa750b33/core_init.c)

- makes `core_init` available to sqlite by [appending it](https://github.com/llimllib/wasm_sqlite_with_stats/blob/83bdf9e1bf6808590a281d8f2d32cafafa750b33/Makefile#L52) to the end of the amalgamation file as the first step of our build process

- uses emscripten [to build](https://github.com/llimllib/wasm_sqlite_with_stats/blob/83bdf9e1bf6808590a281d8f2d32cafafa750b33/Makefile#L38) sqlite3-stats.c and the amalgamation file (with the appended `SQLITE_EXTRA_INIT` bit) together into a wasm output



Finally, I made an [HTML page](https://github.com/llimllib/wasm_sqlite_with_stats/blob/e057459ef636de80091bbc781751055b9bf5395d/index.html) that makes the most basic possible use of the sqlite binary to make sure that the stats extension has been loaded.



## Build it yourself



`make clean wasm`



To visit the web page that demonstrates how to use the file, serve the `dist`

directory with a web server that serves proper mime types. I like to use

[`devd`](https://github.com/cortesi/devd), so I run `devd -ol dist`



## SQLite fiddle with extension



I used the knowledge I gained in this effort to a [SQLite fiddle with an embedded extension](https://llimllib.github.io/wasm_sqlite_with_stats/). Instructions for building the fiddle can be found in the [build-fiddle](https://github.com/llimllib/wasm_sqlite_with_stats/tree/build-fiddle) branch.