1# sqlite3-api.js And Friends 2 3This is the README for the files `sqlite3-*.js` and 4`sqlite3-wasm.c`. This collection of files is used to build a 5single-file distribution of the sqlite3 WASM API. It is broken into 6multiple JS files because: 7 81. To facilitate including or excluding certain components for 9 specific use cases. e.g. by removing `sqlite3-api-oo1.js` if the 10 OO#1 API is not needed. 11 122. To facilitate modularizing the pieces for use in different WASM 13 build environments. e.g. the files `post-js-*.js` are for use with 14 Emscripten's `--post-js` feature, and nowhere else. 15 163. Certain components must be in their own standalone files in order 17 to be loaded as JS Workers. 18 19Note that the structure described here is the current state of things, 20not necessarily the "final" state. 21 22The overall idea is that the following files get concatenated 23together, in the listed order, the resulting file is loaded by a 24browser client: 25 26- `post-js-header.js`\ 27 Emscripten-specific header for the `--post-js` input. 28- `sqlite3-api-prologue.js`\ 29 Contains the initial bootstrap setup of the sqlite3 API 30 objects. This is exposed as a function, rather than objects, so that 31 the next step can pass in a config object which abstracts away parts 32 of the WASM environment, to facilitate plugging it in to arbitrary 33 WASM toolchains. 34- `../common/whwasmutil.js`\ 35 A semi-third-party collection of JS/WASM utility code intended to 36 replace much of the Emscripten glue. The sqlite3 APIs internally use 37 these APIs instead of their Emscripten counterparts, in order to be 38 more portable to arbitrary WASM toolchains. This API is 39 configurable, in principle, for use with arbitrary WASM 40 toolchains. It is "semi-third-party" in that it was created in order 41 to support this tree but is standalone and maintained together 42 with... 43- `../jaccwabyt/jaccwabyt.js`\ 44 Another semi-third-party API which creates bindings between JS 45 and C structs, such that changes to the struct state from either JS 46 or C are visible to the other end of the connection. This is also an 47 independent spinoff project, conceived for the sqlite3 project but 48 maintained separately. 49- `sqlite3-api-glue.js`\ 50 Invokes functionality exposed by the previous two files to 51 flesh out low-level parts of `sqlite3-api-prologue.js`. Most of 52 these pieces related to the `sqlite3.capi.wasm` object. 53- `sqlite3-api-oo1.js`\ 54 Provides a high-level object-oriented wrapper to the lower-level C 55 API, colloquially known as OO API #1. Its API is similar to other 56 high-level sqlite3 JS wrappers and should feel relatively familiar 57 to anyone familiar with such APIs. That said, it is not a "required 58 component" and can be elided from builds which do not want it. 59- `sqlite3-api-worker1.js`\ 60 A Worker-thread-based API which uses OO API #1 to provide an 61 interface to a database which can be driven from the main Window 62 thread via the Worker message-passing interface. Like OO API #1, 63 this is an optional component, offering one of any number of 64 potential implementations for such an API. 65 - `../sqlite3-worker1.js`\ 66 Is not part of the amalgamated sources and is intended to be 67 loaded by a client Worker thread. It loads the sqlite3 module 68 and runs the Worker #1 API which is implemented in 69 `sqlite3-api-worker1.js`. 70 - `../sqlite3-worker1-promiser.js`\ 71 Is likewise not part of the amalgamated sources and provides 72 a Promise-based interface into the Worker #1 API. This is 73 a far user-friendlier way to interface with databases running 74 in a Worker thread. 75- `sqlite3-api-opfs.js`\ 76 is an sqlite3 VFS implementation which supports Google Chrome's 77 Origin-Private FileSystem (OPFS) as a storage layer to provide 78 persistent storage for database files in a browser. It requires... 79 - `../sqlite3-opfs-async-proxy.js`\ 80 is the asynchronous backend part of the OPFS proxy. It speaks 81 directly to the (async) OPFS API and channels those results back 82 to its synchronous counterpart. This file, because it must be 83 started in its own Worker, is not part of the amalgamation. 84- `sqlite3-api-cleanup.js`\ 85 the previous files temporarily create global objects in order to 86 communicate their state to the files which follow them, and _this_ 87 file connects any final components together and cleans up those 88 globals. As of this writing, this code ensures that the previous 89 files leave no more than a single global symbol installed. When 90 adapting the API for non-Emscripten toolchains, this "should" 91 be the only file where changes are needed. 92- `post-js-footer.js`\ 93 Emscripten-specific footer for the `--post-js` input. This closes 94 off the lexical scope opened by `post-js-header.js`. 95 96The build process glues those files together, resulting in 97`sqlite3-api.js`, which is everything except for the `post-js-*.js` 98files, and `sqlite3.js`, which is the Emscripten-generated amalgamated 99output and includes the `post-js-*.js` parts, as well as the 100Emscripten-provided module loading pieces. 101 102The non-JS outlier file is `sqlite3-wasm.c`: it is a proxy for 103`sqlite3.c` which `#include`'s that file and adds a couple more 104WASM-specific helper functions, at least one of which requires access 105to private/static `sqlite3.c` internals. `sqlite3.wasm` is compiled 106from this file rather than `sqlite3.c`. 107 108The following files are part of the build process but are injected 109into the build-generated `sqlite3.js` along with `sqlite3-api.js`. 110 111- `extern-pre-js.js`\ 112 Emscripten-specific header for Emscripten's `--extern-pre-js` 113 flag. As of this writing, that file is only used for experimentation 114 purposes and holds no code relevant to the production deliverables. 115- `pre-js.js`\ 116 Emscripten-specific header for Emscripten's `--pre-js` flag. This 117 file is intended as a place to override certain Emscripten behavior 118 before it starts up, but corner-case Emscripten bugs keep that from 119 being a reality. 120- `extern-post-js.js`\ 121 Emscripten-specific header for Emscripten's `--extern-post-js` 122 flag. This file overwrites the Emscripten-installed 123 `sqlite3InitModule()` function with one which, after the module is 124 loaded, also initializes the asynchronous parts of the sqlite3 125 module. For example, the OPFS VFS support. 126