src/lib/istream-chain.c

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

#include "lib.h"
#include "llist.h"
#include "istream-private.h"
#include "istream-chain.h"

struct chain_istream;

struct istream_chain_link {
    struct istream_chain_link *prev, *next;

    struct istream *stream;
    bool eof;
};

struct istream_chain {
    struct istream_chain_link *head, *tail;

    struct chain_istream *stream;
};

struct chain_istream {
    struct istream_private istream;

    /* how much of the previous link's stream still exists at the
       beginning of our buffer. skipping through this should point to
       the beginning of the current link's stream. */
    size_t prev_stream_left;
    size_t prev_skip;
    bool have_explicit_max_buffer_size;

    struct istream_chain chain;
};

static void ATTR_NULL(2)
i_stream_chain_append_internal(struct istream_chain *chain,
                   struct istream *stream)
{
    struct istream_chain_link *link;

    if (stream == NULL && chain->tail != NULL && chain->tail->stream == NULL)
        return;

    link = i_new(struct istream_chain_link, 1);
    link->stream = stream;
    link->eof = stream == NULL;

    if (stream != NULL)
        i_stream_ref(stream);

    if (chain->head == NULL && stream != NULL) {
        struct chain_istream *cstream = (struct chain_istream *)chain->stream;

        if (cstream->have_explicit_max_buffer_size) {
            i_stream_set_max_buffer_size(stream,
                chain->stream->istream.max_buffer_size);
        } else {
            size_t max_size = i_stream_get_max_buffer_size(stream);

            if (cstream->istream.max_buffer_size < max_size)
                cstream->istream.max_buffer_size = max_size;
        }
    }
    DLLIST2_APPEND(&chain->head, &chain->tail, link);
    /* if io_add_istream() has been added to this chain stream, notify
       the callback that we have more data available. */
    if (stream != NULL)
        i_stream_set_input_pending(stream, TRUE);
}

void i_stream_chain_append(struct istream_chain *chain, struct istream *stream)
{
    i_stream_chain_append_internal(chain, stream);
}

void i_stream_chain_append_eof(struct istream_chain *chain)
{
    i_stream_chain_append_internal(chain, NULL);
}

static void
i_stream_chain_set_max_buffer_size(struct iostream_private *stream,
                    size_t max_size)
{
    struct chain_istream *cstream = (struct chain_istream *)stream;
    struct istream_chain_link *link = cstream->chain.head;

    cstream->have_explicit_max_buffer_size = TRUE;
    cstream->istream.max_buffer_size = max_size;
    while (link != NULL) {
        if (link->stream != NULL)
            i_stream_set_max_buffer_size(link->stream, max_size);
        link = link->next;
    }
}

static void i_stream_chain_destroy(struct iostream_private *stream)
{
    struct chain_istream *cstream = (struct chain_istream *)stream;
    struct istream_chain_link *link = cstream->chain.head;

    while (link != NULL) {
        struct istream_chain_link *next = link->next;

        i_stream_unref(&link->stream);
        i_free(link);
        link = next;
    }
    i_stream_free_buffer(&cstream->istream);
}

static void i_stream_chain_read_next(struct chain_istream *cstream)
{
    struct istream_chain_link *link = cstream->chain.head;
    struct istream *prev_input;
    const unsigned char *data;
    size_t data_size, cur_data_pos;

    i_assert(link != NULL && link->stream != NULL);
    i_assert(link->stream->eof);

    prev_input = link->stream;
    data = i_stream_get_data(prev_input, &data_size);

    DLLIST2_REMOVE(&cstream->chain.head, &cstream->chain.tail, link);
    i_free(link);

    /* a) we have more streams, b) we have EOF, c) we need to wait
       for more streams */
    link = cstream->chain.head;
    if (link != NULL && link->stream != NULL)
        i_stream_seek(link->stream, 0);

    if (cstream->prev_stream_left > 0) {
        /* we've already buffered some of the prev_input. continue
           appending the rest to it. if it's already at EOF, there's
           nothing more to append. */
        cur_data_pos = cstream->istream.pos -
            (cstream->istream.skip + cstream->prev_stream_left);
        i_assert(cur_data_pos <= data_size);
        data += cur_data_pos;
        data_size -= cur_data_pos;
        /* the stream has now become "previous", so its contents in
           buffer are now part of prev_stream_left. */
        cstream->prev_stream_left += cur_data_pos;
    } else {
        cstream->istream.pos = 0;
        cstream->istream.skip = 0;
        cstream->prev_stream_left = 0;
    }

    if (data_size > 0) {
        memcpy(i_stream_alloc(&cstream->istream, data_size),
               data, data_size);
        cstream->istream.pos += data_size;
        cstream->prev_stream_left += data_size;
    }

    i_stream_skip(prev_input, i_stream_get_data_size(prev_input));
    i_stream_unref(&prev_input);
}

static bool i_stream_chain_skip(struct chain_istream *cstream)
{
    struct istream_private *stream = &cstream->istream;
    struct istream_chain_link *link = cstream->chain.head;
    size_t bytes_skipped;

    i_assert(stream->skip >= cstream->prev_skip);
    bytes_skipped = stream->skip - cstream->prev_skip;

    if (cstream->prev_stream_left == 0) {
        /* no need to worry about buffers, skip everything */
    } else if (bytes_skipped < cstream->prev_stream_left) {
        /* we're still skipping inside buffer */
        cstream->prev_stream_left -= bytes_skipped;
        bytes_skipped = 0;
    } else {
        /* done with the buffer */
        bytes_skipped -= cstream->prev_stream_left;
        cstream->prev_stream_left = 0;
    }
    stream->pos -= bytes_skipped;
    stream->skip -= bytes_skipped;
    stream->buffer += bytes_skipped;
    cstream->prev_skip = stream->skip;
    if (link == NULL || link->eof) {
        i_assert(bytes_skipped == 0);
        return FALSE;
    }
    i_stream_skip(link->stream, bytes_skipped);
    return TRUE;
}

static ssize_t i_stream_chain_read(struct istream_private *stream)
{
    struct chain_istream *cstream = (struct chain_istream *)stream;
    struct istream_chain_link *link = cstream->chain.head;
    const unsigned char *data;
    size_t data_size, cur_data_pos, new_pos;
    size_t new_bytes_count;
    ssize_t ret;

    if (link != NULL && link->eof) {
        stream->istream.eof = TRUE;
        return -1;
    }

    if (!i_stream_chain_skip(cstream))
        return 0;
    i_assert(link != NULL);

    i_assert(stream->pos >= stream->skip + cstream->prev_stream_left);
    cur_data_pos = stream->pos - (stream->skip + cstream->prev_stream_left);

    data = i_stream_get_data(link->stream, &data_size);
    if (data_size > cur_data_pos)
        ret = 0;
    else {
        /* need to read more - NOTE: Can't use i_stream_read_memarea()
           here, because our stream->buffer may point to the parent
           istream. This could be avoided if we implemented
           snapshotting ourself. */
        i_assert(cur_data_pos == data_size);
        ret = i_stream_read(link->stream);
        if (ret == -2 || ret == 0)
            return ret;

        if (ret == -1) {
            if (link->stream->stream_errno != 0) {
                io_stream_set_error(&stream->iostream,
                    "read(%s) failed: %s",
                    i_stream_get_name(link->stream),
                    i_stream_get_error(link->stream));
                stream->istream.stream_errno =
                    link->stream->stream_errno;
                return -1;
            }
            /* EOF of this stream, go to next stream */
            i_stream_chain_read_next(cstream);
            cstream->prev_skip = stream->skip;
            return i_stream_chain_read(stream);
        }
        /* we read something */
        data = i_stream_get_data(link->stream, &data_size);
    }

    if (data_size == cur_data_pos) {
        /* nothing new read - preserve the buffer as it was */
        i_assert(ret == 0 || ret == -1);
        return ret;
    }
    if (cstream->prev_stream_left == 0) {
        /* we can point directly to the current stream's buffers */
        stream->buffer = data;
        stream->pos -= stream->skip;
        stream->skip = 0;
        new_pos = data_size;
    } else {
        /* we still have some of the previous stream left. merge the
           new data with it. */
        i_assert(data_size > cur_data_pos);
        new_bytes_count = data_size - cur_data_pos;
        memcpy(i_stream_alloc(stream, new_bytes_count),
               data + cur_data_pos, new_bytes_count);
        stream->buffer = stream->w_buffer;
        new_pos = stream->pos + new_bytes_count;
    }

    i_assert(new_pos > stream->pos);
    ret = (ssize_t)(new_pos - stream->pos);
    stream->pos = new_pos;
    cstream->prev_skip = stream->skip;
    return ret;
}

static void i_stream_chain_close(struct iostream_private *stream,
                 bool close_parent)
{
    struct chain_istream *cstream = (struct chain_istream *)stream;

    /* seek to the correct position in parent stream in case it didn't
       end with EOF */
    (void)i_stream_chain_skip(cstream);

    if (close_parent) {
        struct istream_chain_link *link = cstream->chain.head;
        while (link != NULL) {
            i_stream_close(link->stream);
            link = link->next;
        }
    }
}

struct istream *i_stream_create_chain(struct istream_chain **chain_r)
{
    struct chain_istream *cstream;

    cstream = i_new(struct chain_istream, 1);
    cstream->chain.stream = cstream;

    cstream->istream.iostream.close = i_stream_chain_close;
    cstream->istream.iostream.destroy = i_stream_chain_destroy;
    cstream->istream.iostream.set_max_buffer_size =
        i_stream_chain_set_max_buffer_size;

    cstream->istream.read = i_stream_chain_read;

    cstream->istream.istream.readable_fd = FALSE;
    cstream->istream.istream.blocking = FALSE;
    cstream->istream.istream.seekable = FALSE;

    *chain_r = &cstream->chain;
    return i_stream_create(&cstream->istream, NULL, -1,
                   ISTREAM_CREATE_FLAG_NOOP_SNAPSHOT);
}