src/lib/istream-base64-encoder.c

/* Copyright (c) 2003-2018 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_encoder_istream {
    struct istream_private istream;

    /* current encoded line length. */
    size_t cur_line_len;

    unsigned int chars_per_line;
    bool crlf;
};

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 >= 3)
        return 1;

    /* we have less than one base64 block.
       see if there is more data available. */
    ret = i_stream_read_memarea(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_encode_line(struct base64_encoder_istream *bstream)
{
    struct istream_private *stream = &bstream->istream;
    const unsigned char *data;
    size_t size, avail, buffer_avail;
    buffer_t buf;

    data = i_stream_get_data(stream->parent, &size);
    if (size == 0 || (size < 3 && !stream->parent->eof))
        return 0;

    if (bstream->cur_line_len == bstream->chars_per_line) {
        /* @UNSAFE: end of line, add newline */
        if (!i_stream_try_alloc(stream, bstream->crlf ? 2 : 1, &avail))
            return -2;

        if (bstream->crlf)
            stream->w_buffer[stream->pos++] = '\r';
        stream->w_buffer[stream->pos++] = '\n';
        bstream->cur_line_len = 0;
    }

    i_stream_try_alloc(stream, (size+2)/3*4, &avail);
    buffer_avail = stream->buffer_size - stream->pos;

    if ((size + 2) / 3 * 4 > buffer_avail) {
        /* can't fit everything to destination buffer.
           write as much as we can. */
        size = (buffer_avail / 4) * 3;
        if (size == 0)
            return -2;
    } else if (!stream->parent->eof && size % 3 != 0) {
        /* encode 3 chars at a time, so base64_encode() doesn't
           add '=' characters in the middle of the stream */
        size -= (size % 3);
    }
    i_assert(size != 0);

    if (bstream->cur_line_len + (size+2)/3*4 > bstream->chars_per_line) {
        size = (bstream->chars_per_line - bstream->cur_line_len)/4 * 3;
        i_assert(size != 0);
    }

    buffer_create_from_data(&buf, stream->w_buffer + stream->pos,
                buffer_avail);
    base64_encode(data, size, &buf);
    i_assert(buf.used > 0);

    bstream->cur_line_len += buf.used;
    i_assert(bstream->cur_line_len <= bstream->chars_per_line);
    stream->pos += buf.used;
    i_stream_skip(stream->parent, size);
    return 1;
}

static ssize_t i_stream_base64_encoder_read(struct istream_private *stream)
{
    struct base64_encoder_istream *bstream =
        (struct base64_encoder_istream *)stream;
    size_t pre_count, post_count;
    int ret;

    do {
        ret = i_stream_read_parent(stream);
        if (ret == 0)
            return 0;
        if (ret < 0) {
            if (i_stream_get_data_size(stream->parent) == 0)
                return -1;
            /* add the final partial block */
        }

        /* encode as many lines as fits into destination buffer */
        pre_count = stream->pos - stream->skip;
        while ((ret = i_stream_base64_try_encode_line(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_encoder_seek(struct istream_private *stream,
                 uoff_t v_offset, bool mark)
{
    struct base64_encoder_istream *bstream =
        (struct base64_encoder_istream *)stream;

    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;
        bstream->cur_line_len = 0;
        i_stream_seek(stream->parent, 0);
    }
    i_stream_default_seek_nonseekable(stream, v_offset, mark);
}

static int
i_stream_base64_encoder_stat(struct istream_private *stream,
    bool exact ATTR_UNUSED)
{
    struct base64_encoder_istream *bstream =
        (struct base64_encoder_istream *)stream;
    const struct stat *st;
    off_t newlines, size;

    if (i_stream_stat(stream->parent, exact, &st) < 0) {
        stream->istream.stream_errno = stream->parent->stream_errno;
        return -1;
    }

    stream->statbuf = *st;
    if (st->st_size == 0)
        return 0;

    /* calculate size of encoded data */
    size = (st->st_size / 3) * 4 +
        ((st->st_size % 3) == 0 ? 0 : 4);

    /* update size with added newlines */
    newlines = (size / bstream->chars_per_line - 1) +
        ((size % bstream->chars_per_line) == 0 ? 0 : 1);
    size += newlines * (bstream->crlf ? 2 : 1);

    stream->statbuf.st_size = size;
    return 0;
}

struct istream *
i_stream_create_base64_encoder(struct istream *input,
                   unsigned int chars_per_line, bool crlf)
{
    struct base64_encoder_istream *bstream;

    i_assert(chars_per_line % 4 == 0);

    bstream = i_new(struct base64_encoder_istream, 1);
    bstream->chars_per_line = chars_per_line;
    bstream->crlf = crlf;
    bstream->istream.max_buffer_size = input->real_stream->max_buffer_size;

    bstream->istream.read = i_stream_base64_encoder_read;
    bstream->istream.seek = i_stream_base64_encoder_seek;
    bstream->istream.stat = i_stream_base64_encoder_stat;

    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), 0);
}