src/lib/istream-base64-decoder.c

	istream-base64-decoder.c revision 13984f1ae4258317236228de92adc1481ae4fc40
/* Copyright (c) 2012 Dovecot authors, see the included COPYING file */

#include "lib.h"
#include "buffer.h"
#include "base64.h"
#include "istream-private.h"
#include "istream-base64.h"

struct base64_decoder_istream {
    struct istream_private istream;
};

static int i_stream_read_parent(struct istream_private *stream)
{
    size_t size;
    ssize_t ret;

    size = i_stream_get_data_size(stream->parent);
    if (size >= 4)
        return 1;

    /* we have less than one base64 block.
       see if there is more data available. */
    ret = i_stream_read(stream->parent);
    if (ret <= 0) {
        stream->istream.stream_errno = stream->parent->stream_errno;
        stream->istream.eof = stream->parent->eof;
        return ret;
    }
    size = i_stream_get_data_size(stream->parent);
    i_assert(size != 0);
    return 1;
}

static int
i_stream_base64_try_decode_block(struct base64_decoder_istream *bstream)
{
    struct istream_private *stream = &bstream->istream;
    const unsigned char *data;
    size_t size, avail, buffer_avail, pos;
    buffer_t buf;

    data = i_stream_get_data(stream->parent, &size);
    if (size == 0)
        return 0;

    i_stream_try_alloc(stream, (size+3)/4*3, &avail);
    buffer_avail = stream->buffer_size - stream->pos;

    if ((size + 3) / 4 * 3 > buffer_avail) {
        /* can't fit everything to destination buffer.
           write as much as we can. */
        size = (buffer_avail / 3) * 4;
        if (size == 0)
            return -2;
    }

    buffer_create_data(&buf, stream->w_buffer + stream->pos, buffer_avail);
    if (base64_decode(data, size, &pos, &buf) < 0) {
        stream->istream.stream_errno = EINVAL;
        return -1;
    }

    stream->pos += buf.used;
    i_stream_skip(stream->parent, pos);
    return pos > 0 ? 1 : 0;
}

static ssize_t i_stream_base64_decoder_read(struct istream_private *stream)
{
    struct base64_decoder_istream *bstream =
        (struct base64_decoder_istream *)stream;
    size_t pre_count, post_count;
    int ret;

    do {
        ret = i_stream_read_parent(stream);
        if (ret <= 0) {
            if (ret < 0 && stream->istream.stream_errno == 0 &&
                i_stream_get_data_size(stream->parent) > 0) {
                /* base64 input with a partial block */
                stream->istream.stream_errno = EINVAL;
            }
            return ret;
        }

        /* encode as many blocks as fits into destination buffer */
        pre_count = stream->pos - stream->skip;
        while ((ret = i_stream_base64_try_decode_block(bstream)) > 0) ;
        post_count = stream->pos - stream->skip;
    } while (ret == 0 && pre_count == post_count);

    if (ret < 0 && pre_count == post_count)
        return ret;

    i_assert(post_count > pre_count);
    return post_count - pre_count;
}

static void
i_stream_base64_decoder_seek(struct istream_private *stream,
                 uoff_t v_offset, bool mark)
{
    if (v_offset < stream->istream.v_offset) {
        /* seeking backwards - go back to beginning and seek
           forward from there. */
        stream->parent_expected_offset = stream->parent_start_offset;
        stream->skip = stream->pos = 0;
        stream->istream.v_offset = 0;
        i_stream_seek(stream->parent, 0);
    }
    i_stream_default_seek_nonseekable(stream, v_offset, mark);
}

struct istream *
i_stream_create_base64_decoder(struct istream *input)
{
    struct base64_decoder_istream *bstream;

    bstream = i_new(struct base64_decoder_istream, 1);
    bstream->istream.max_buffer_size = input->real_stream->max_buffer_size;

    bstream->istream.read = i_stream_base64_decoder_read;
    bstream->istream.seek = i_stream_base64_decoder_seek;

    bstream->istream.istream.readable_fd = FALSE;
    bstream->istream.istream.blocking = input->blocking;
    bstream->istream.istream.seekable = input->seekable;
    return i_stream_create(&bstream->istream, input,
                   i_stream_get_fd(input));
}