vlc/modules/access/emjsfile.c

/*****************************************************************************
 * emjsfile.c: emscripten js file access plugin
 *****************************************************************************
 * Copyright (C) 2022 VLC authors Videolabs, and VideoLAN
 *
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
 *****************************************************************************/

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <vlc_common.h>
#include <vlc_plugin.h>
#include <vlc_access.h>
#include <vlc_threads.h>

#include <emscripten.h>

typedef struct
{
    uint64_t offset;
    uint64_t js_file_size;
} access_sys_t;

static ssize_t Read (stream_t *p_access, void *buffer, size_t size) {
    access_sys_t *p_sys = p_access->p_sys;

    size_t offset = p_sys->offset;
    size_t js_file_size = p_sys->js_file_size; 

    if (offset >= js_file_size)
        return 0;
    if (size > offset + js_file_size) {
        size = js_file_size - offset;
    }
    EM_ASM({
        const offset = $0;
        const buffer = $1;
        const size = $2;
        const blob = Module.vlcAccess[$3].worker_js_file.slice(offset, offset + size);
        HEAPU8.set(new Uint8Array(Module.vlcAccess[$3].reader.readAsArrayBuffer(blob)), buffer);
    }, offset, buffer, size, p_access);
    p_sys->offset += size;
    return size;
}

static int Seek (stream_t *p_access, uint64_t offset) {
    access_sys_t *p_sys = p_access->p_sys;

    p_sys->offset = offset;
    return VLC_SUCCESS;
}

static int get_js_file_size(stream_t *p_access, uint64_t *value) {
    /*
      to avoid RangeError on BigUint64 view creation,
      the start offset must be a multiple of 8.
    */
    if ((uintptr_t)value % 8 != 0) {
        msg_Err(p_access, "error: value is not aligned in get_js_file_size!");
        return VLC_EGENERIC;
    }        
    return (EM_ASM_INT({
        try {
            var v = new BigUint64Array(wasmMemory.buffer, $0, 1);
            v[0] = BigInt(Module.vlcAccess[$1].worker_js_file.size);
            return 0;
        }
        catch (error) {
            console.error("get_js_file_size error: " + error);
            return 1;
        }
    }, value, p_access) == 0) ? VLC_SUCCESS: VLC_EGENERIC;
}

static int Control( stream_t *p_access, int i_query, va_list args )
{
    bool    *pb_bool;
    vlc_tick_t *pi_64;
    access_sys_t *p_sys = p_access->p_sys;

    switch( i_query )
    {
        case STREAM_CAN_SEEK:
        case STREAM_CAN_FASTSEEK:
            pb_bool = va_arg( args, bool * );
            *pb_bool = true;
            break;

        case STREAM_CAN_PAUSE:
        case STREAM_CAN_CONTROL_PACE:
            pb_bool = va_arg( args, bool * );
            *pb_bool = true;
            break;

        case STREAM_GET_SIZE:
        {
            *va_arg( args, uint64_t * ) = p_sys->js_file_size;
            break;
        }

        case STREAM_GET_PTS_DELAY:
            pi_64 = va_arg( args, vlc_tick_t * );
            *pi_64 = VLC_TICK_FROM_MS(
                var_InheritInteger (p_access, "file-caching") );
            break;

        case STREAM_SET_PAUSE_STATE:
            break;

        default:
            return VLC_EGENERIC;

    }
    return VLC_SUCCESS;
}

EM_ASYNC_JS(int, init_js_file, (stream_t *p_access, long id), {
    let p = new Promise((resolve, reject) => {
        function handleFileResult(e) {
            const msg = e['data'];
            if (msg.type === 'FileResult') {
                self.removeEventListener('message', handleFileResult);
                if (msg.file !== undefined) {
                    Module.vlcAccess[p_access].worker_js_file = msg.file;
                    Module.vlcAccess[p_access].reader = new FileReaderSync();
                    resolve();
                }
                else {
                    reject("error: sent an undefined File object from the main thread");
                }
            }
            else if (msg.type === 'ErrorVLCAccessFileUndefined') {
                reject("error: vlc_access_file object is not defined");
            }
            else if (msg.type === 'ErrorRequestFileMessageWithoutId') {
                reject("error: request file message send without an id");
            }
            else if (msg.type === 'ErrorMissingFile') {
                reject("error: missing file, bad id or vlc_access_file[id] is not defined");
            }
        }
        self.addEventListener('message', handleFileResult);
    });
    let timer = undefined;
    let timeout = new Promise(function (resolve, reject) {
            timer = setTimeout(resolve, 1000, 'timeout')
        });
    let promises = [p, timeout];
    /* id must be unique */
    self.postMessage({ cmd: "customCmd", type: "requestFile", id: id});
    let return_value = 0;
    try {
        let value = await Promise.race(promises);
        if (value === 'timeout') {
            console.error("vlc_access timeout: could not get file!");
            return_value = 1;
        }
    }
    catch(error) {
        console.error("vlc_access error in init_js_file(): ", error);
        return_value = 1;
    }
    clearTimeout(timer);
    return return_value;
});

static int EmFileOpen( vlc_object_t *p_this ) {
    stream_t *p_access = (stream_t*)p_this;

    /* init per worker module.vlcAccess object */
    EM_ASM({
            if (Module.vlcAccess === undefined) {
                Module.vlcAccess = {};
            }
            (Module.vlcAccess[$0] = {worker_js_file: undefined, reader: undefined});            
    }, p_access);

    /*
      This block will run in the main thread, to access the DOM.
      When the user selects a file, it is assigned to the Module.vlc_access_file
      array.
      
      We listen to 'message' events so that when the file is requested by the
      input thread, we can answer and send the File object from the main thread.
    */
    MAIN_THREAD_EM_ASM({
        const thread_id = $0;
        let w = Module.PThread.pthreads[thread_id].worker;
        function handleFileRequest(e) {
            const msg = e.data;
            if (msg.type === "requestFile") {
                w.removeEventListener('message', handleFileRequest);
                if (Module.vlc_access_file === undefined) {
                    console.error("vlc_access_file property missing!");
                    w.postMessage({ cmd: "customCmd",
                            type: "ErrorVLCAccessFileUndefined"
                        });
                    return ;
                }
                if (msg.id === undefined) {
                    console.error("id property missing in requestFile message!");
                    w.postMessage({ cmd: "customCmd",
                            type: "ErrorRequestFileMessageWithoutId"
                        });
                    return ;
                }
                if (Module.vlc_access_file[msg.id] === undefined) {
                    console.error("error file missing!");
                    w.postMessage({ cmd: "customCmd",
                            type: "ErrorMissingFile"
                        });
                    return ;
                }
                /*
                  keeping the File object in the main thread too,
                  in case we want to reopen the media, without re-selecting
                  the file.
                */
                w.postMessage({ cmd: "customCmd",
                    type: "FileResult",
                    file: Module.vlc_access_file[msg.id]
                });
            }
        }
        w.addEventListener('message', handleFileRequest);
    }, pthread_self());

    char *endPtr;
    long id = strtol(p_access->psz_location, &endPtr, 10);
    if ((endPtr == p_access->psz_location) || (*endPtr != '\0')) {
        msg_Err(p_access, "error: failed init uri has invalid id!");
        return VLC_EGENERIC;
    }

    /*
      Request the file from the main thread.
      If it was not selected, it will return an error.

      To open a file, we need to call libvlc_media_new_location with
      the following uri : emjsfile://<id>
      To avoid confusion with atoi() return error, id starts at 1.
    */
    if (init_js_file(p_access, id)) {
        msg_Err(p_access, "EMJsFile error: failed init!");
        return VLC_EGENERIC;
    }

    access_sys_t *p_sys = vlc_obj_malloc(p_this, sizeof (*p_sys));
    if (unlikely(p_sys == NULL))
        return VLC_ENOMEM;

    p_access->pf_read = Read;
    p_access->pf_block = NULL;
    p_access->pf_control = Control;
    p_access->pf_seek = Seek;
    p_access->p_sys = p_sys;
    p_sys->js_file_size = 0;
    p_sys->offset = 0;
    if (get_js_file_size(p_access, &p_sys->js_file_size)) {
        msg_Err(p_access, "EMJsFile error: could not get file size!");
        return VLC_EGENERIC;
    } 

    return VLC_SUCCESS;
}

static void EmFileClose (vlc_object_t * p_this) {
    stream_t *p_access = (stream_t*)p_this;
    EM_ASM({
            Module.vlcAccess[$0].worker_js_file = undefined;
            Module.vlcAccess[$0].reader = undefined;            
        }, p_access);
}

vlc_module_begin ()
    set_description( N_("Emscripten module to allow reading local files from the DOM's <input>") )
    set_shortname( N_("Emscripten Local File Input") )
    set_subcategory( SUBCAT_INPUT_ACCESS )
    set_capability( "access", 0 )
    add_shortcut( "emjsfile" )
    set_callbacks( EmFileOpen, EmFileClose )
vlc_module_end()