How to extract embedded files from pdf using MuPDF

Question

My app on iOS extracts embedded files from PDF. Now, i try to make Android app with same functionality using MuPDF.

On iOS, I can use Quartz2d to extract embedded files:

1. Access to root PDF dictionary (CGPDFDocumentGetCatalog)
2. Get files array (Names > EmbeddedFiles > Names) and itarate through it
3. Copy file stream contents from file dictionary (EF > F) to NSData and save it.

Is there any way to do this with MuPDF?

Answer 1

Solution, based on pdfextact.c seems like bruteforce, but it works:

1. itarate through all pdf objects (pdf_load_object)
2. determine if object is embedded file (isembed)
3. if it is - access it's stream and save file (saveembed)

Embedded files stored at the end of file in most test cases, so, reverce iteration makes sence.

static int isembed(pdf_obj *obj) {
    pdf_obj *type = pdf_dict_gets(obj, "Type");
    return pdf_is_name(type) && !strcmp(pdf_to_name(type), "Filespec");
}


static void saveembed(pdf_obj *dict) {
    char *filename;

    pdf_obj *obj = pdf_dict_gets(dict, "F");
    if (obj) filename = pdf_to_str_buf(obj);

    obj = pdf_dict_gets(dict, "EF");
    if (!obj) return;

    pdf_obj *stream = pdf_dict_gets(obj, "F");
    if (!stream) return;

    FILE *f;
    fz_buffer *buf;
    int n, len;
    unsigned char *data;

    buf = pdf_load_stream(doc, pdf_to_num(stream), pdf_to_gen(stream));

    printf("extracting embedded file %s\n", filename);

    f = fopen(filename, "wb");

    len = fz_buffer_storage(ctx, buf, &data);
    n = fwrite(data, 1, len, f);

    fclose(f);
    fz_drop_buffer(ctx, buf);
}