src/lib/istream-sized.c

/* Copyright (c) 2003-2018 Dovecot authors, see the included COPYING file */

#include "lib.h"
#include "istream-private.h"
#include "istream-sized.h"

struct sized_istream {
    struct istream_private istream;

    istream_sized_callback_t *error_callback;
    void *error_context;

    uoff_t size;
    bool min_size_only;
};

static void i_stream_sized_destroy(struct iostream_private *stream)
{
    struct sized_istream *sstream = (struct sized_istream *)stream;
    uoff_t v_offset;

    v_offset = sstream->istream.parent_start_offset +
        sstream->istream.istream.v_offset;
    if (sstream->istream.parent->seekable ||
        v_offset > sstream->istream.parent->v_offset) {
        /* get to same position in parent stream */
        i_stream_seek(sstream->istream.parent, v_offset);
    }
}

static const char *
i_stream_create_sized_default_error_callback(
    const struct istream_sized_error_data *data, void *context ATTR_UNUSED)
{
    if (data->v_offset + data->new_bytes < data->wanted_size) {
        return t_strdup_printf("Stream is smaller than expected "
            "(%"PRIuUOFF_T" < %"PRIuUOFF_T")",
            data->v_offset + data->new_bytes, data->wanted_size);
    } else {
        return t_strdup_printf("Stream is larger than expected "
            "(%"PRIuUOFF_T" > %"PRIuUOFF_T", eof=%d)",
            data->v_offset + data->new_bytes, data->wanted_size,
            data->eof ? 1 : 0);
    }
}

static ssize_t
i_stream_sized_parent_read(struct istream_private *stream, size_t *pos_r)
{
    ssize_t ret;

    do {
        if ((ret = i_stream_read_memarea(stream->parent)) == -2)
            break;

        stream->istream.stream_errno = stream->parent->stream_errno;
        stream->istream.eof = stream->parent->eof;
        stream->buffer = i_stream_get_data(stream->parent, pos_r);
    } while (*pos_r <= stream->pos && ret > 0);
    return ret;
}

static ssize_t i_stream_sized_read(struct istream_private *stream)
{
    struct sized_istream *sstream =
        (struct sized_istream *)stream;
    struct istream_sized_error_data data;
    const char *error;
    uoff_t left;
    ssize_t ret;
    size_t pos;

    i_stream_seek(stream->parent, sstream->istream.parent_start_offset +
              stream->istream.v_offset);

    stream->pos -= stream->skip;
    stream->skip = 0;

    stream->buffer = i_stream_get_data(stream->parent, &pos);
    if (pos > stream->pos)
        ret = 0;
    else {
        if ((ret = i_stream_sized_parent_read(stream, &pos)) == -2)
            return -2;
    }

    left = sstream->size - stream->istream.v_offset;
    if (pos == left && ret != -1) {
        /* we have exactly the wanted amount of data left, but we
           don't know yet if there is more data in parent. */
        ret = i_stream_sized_parent_read(stream, &pos);
    }

    i_zero(&data);
    data.v_offset = stream->istream.v_offset;
    data.new_bytes = pos;
    data.wanted_size = sstream->size;
    data.eof = stream->istream.eof;

    if (pos == left) {
        /* we may or may not be finished, depending on whether
           parent is at EOF. */
    } else if (pos > left) {
        /* parent has more data available than expected */
        if (!sstream->min_size_only) {
            error = sstream->error_callback(&data, sstream->error_context);
            io_stream_set_error(&stream->iostream, "%s", error);
            stream->istream.stream_errno = EINVAL;
            return -1;
        }
        pos = left;
        if (pos <= stream->pos) {
            stream->istream.eof = TRUE;
            ret = -1;
        }
    } else if (!stream->istream.eof) {
        /* still more to read */
    } else if (stream->istream.stream_errno == ENOENT) {
        /* lost the file */
    } else {
        /* EOF before we reached the wanted size */
        error = sstream->error_callback(&data, sstream->error_context);
        io_stream_set_error(&stream->iostream, "%s", error);
        stream->istream.stream_errno = EPIPE;
    }

    ret = pos > stream->pos ? (ssize_t)(pos - stream->pos) :
        (ret == 0 ? 0 : -1);
    stream->pos = pos;
    i_assert(ret != -1 || stream->istream.eof ||
         stream->istream.stream_errno != 0);
    return ret;
}

static int
i_stream_sized_stat(struct istream_private *stream, bool exact ATTR_UNUSED)
{
    struct sized_istream *sstream = (struct sized_istream *)stream;
    const struct stat *st;

    /* parent stream may be base64-decoder. don't waste time decoding the
       entire stream, since we already know what the size is supposed
       to be. */
    if (i_stream_stat(stream->parent, FALSE, &st) < 0) {
        stream->istream.stream_errno = stream->parent->stream_errno;
        return -1;
    }

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

static struct sized_istream *
i_stream_create_sized_common(struct istream *input, uoff_t size)
{
    struct sized_istream *sstream;

    sstream = i_new(struct sized_istream, 1);
    sstream->size = size;
    sstream->istream.max_buffer_size = input->real_stream->max_buffer_size;

    sstream->istream.iostream.destroy = i_stream_sized_destroy;
    sstream->istream.read = i_stream_sized_read;
    sstream->istream.stat = i_stream_sized_stat;

    sstream->istream.istream.readable_fd = input->readable_fd;
    sstream->istream.istream.blocking = input->blocking;
    sstream->istream.istream.seekable = input->seekable;
    (void)i_stream_create(&sstream->istream, input,
                  i_stream_get_fd(input), 0);
    return sstream;
}

struct istream *i_stream_create_sized(struct istream *input, uoff_t size)
{
    struct sized_istream *sstream;

    sstream = i_stream_create_sized_common(input, size);
    sstream->error_callback = i_stream_create_sized_default_error_callback;
    sstream->error_context = sstream;
    return &sstream->istream.istream;
}

struct istream *i_stream_create_sized_range(struct istream *input,
                        uoff_t offset, uoff_t size)
{
    uoff_t orig_offset = input->v_offset;
    struct istream *ret;

    input->v_offset = offset;
    ret = i_stream_create_sized(input, size);
    input->v_offset = orig_offset;
    return ret;
}

struct istream *i_stream_create_min_sized(struct istream *input, uoff_t min_size)
{
    struct istream *ret;

    ret= i_stream_create_sized(input, min_size);
    ((struct sized_istream *)ret->real_stream)->min_size_only = TRUE;
    return ret;
}

struct istream *i_stream_create_min_sized_range(struct istream *input,
                        uoff_t offset, uoff_t min_size)
{
    struct istream *ret;

    ret = i_stream_create_sized_range(input, offset, min_size);
    ((struct sized_istream *)ret->real_stream)->min_size_only = TRUE;
    return ret;
}

#undef i_stream_create_sized_with_callback
struct istream *
i_stream_create_sized_with_callback(struct istream *input, uoff_t size,
                    istream_sized_callback_t *error_callback,
                    void *context)
{
    struct sized_istream *sstream;

    sstream = i_stream_create_sized_common(input, size);
    sstream->error_callback = error_callback;
    sstream->error_context = context;
    return &sstream->istream.istream;
}