source: trunk/essentials/dev-lang/perl/ext/ByteLoader/ByteLoader.xs

#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "byterun.h"

/* Something arbitary for a buffer size */
#define BYTELOADER_BUFFER 8096

int
bl_getc(struct byteloader_fdata *data)
{
    dTHX;
    if (SvCUR(data->datasv) <= (STRLEN)data->next_out) {
      int result;
      /* Run out of buffered data, so attempt to read some more */
      *(SvPV_nolen (data->datasv)) = '\0';
      SvCUR_set (data->datasv, 0);
      data->next_out = 0;
      result = FILTER_READ (data->idx + 1, data->datasv, BYTELOADER_BUFFER);

      /* Filter returned error, or we got EOF and no data, then return EOF.
         Not sure if filter is allowed to return EOF and add data simultaneously
         Think not, but will bullet proof against it. */
      if (result < 0 || SvCUR(data->datasv) == 0)
        return EOF;
      /* Else there must be at least one byte present, which is good enough */
    }

    return *((U8 *) SvPV_nolen (data->datasv) + data->next_out++);
}

int
bl_read(struct byteloader_fdata *data, char *buf, size_t size, size_t n)
{
    dTHX;
    char *start;
    STRLEN len;
    size_t wanted = size * n;

    start = SvPV (data->datasv, len);
    if (len < (data->next_out + wanted)) {
      int result;

      /* Shuffle data to start of buffer */
      len -= data->next_out;
      if (len) {
        memmove (start, start + data->next_out, len + 1);
      } else {
        *start = '\0';  /* Avoid call to memmove. */
      }
      SvCUR_set(data->datasv, len);
      data->next_out = 0;

      /* Attempt to read more data. */
      do {
        result = FILTER_READ (data->idx + 1, data->datasv, BYTELOADER_BUFFER);
        
        start = SvPV (data->datasv, len);
      } while (result > 0 && len < wanted);
      /* Loop while not (EOF || error) and short reads */

      /* If not enough data read, truncate copy */
      if (wanted > len)
        wanted = len;
    }

    if (wanted > 0) {
      memcpy (buf, start + data->next_out, wanted);
        data->next_out += wanted;
      wanted /= size;
    }
    return (int) wanted;
}

static I32
byteloader_filter(pTHX_ int idx, SV *buf_sv, int maxlen)
{
    OP *saveroot = PL_main_root;
    OP *savestart = PL_main_start;
    struct byteloader_state bstate;
    struct byteloader_fdata data;
    int len;
    (void)buf_sv;
    (void)maxlen;

    data.next_out = 0;
    data.datasv = FILTER_DATA(idx);
    data.idx = idx;

    bstate.bs_fdata = &data;
    bstate.bs_obj_list = Null(void**);
    bstate.bs_obj_list_fill = -1;
    bstate.bs_sv = Nullsv;
    bstate.bs_iv_overflows = 0;

/* KLUDGE */
    if (byterun(aTHX_ &bstate)
            && (len = SvCUR(data.datasv) - (STRLEN)data.next_out))
    {
        PerlIO_seek(PL_rsfp, -len, SEEK_CUR);
        PL_rsfp = NULL;
    }
    filter_del(byteloader_filter);

    if (PL_in_eval) {
        OP *o;

        PL_eval_start = PL_main_start;

        o = newSVOP(OP_CONST, 0, newSViv(1));
        PL_eval_root = newLISTOP(OP_LINESEQ, 0, PL_main_root, o);
        PL_main_root->op_next = o;
        PL_eval_root = newUNOP(OP_LEAVEEVAL, 0, PL_eval_root);
        o->op_next = PL_eval_root;
    
        PL_main_root = saveroot;
        PL_main_start = savestart;
    }

    return 0;
}

MODULE = ByteLoader             PACKAGE = ByteLoader

PROTOTYPES:     ENABLE

void
import(package="ByteLoader", ...)
  char *package
  PREINIT:
    SV *sv = newSVpvn ("", 0);
  PPCODE:
    if (!sv)
      croak ("Could not allocate ByteLoader buffers");
    filter_add(byteloader_filter, sv);