xref: /freebsd-11-stable/contrib/subversion/subversion/libsvn_delta/text_delta.c (revision 3c9339f7792540596bf97077a8f403e944af7f39)

/*
 * text-delta.c -- Internal text delta representation
 *
 * ====================================================================
 *    Licensed to the Apache Software Foundation (ASF) under one
 *    or more contributor license agreements.  See the NOTICE file
 *    distributed with this work for additional information
 *    regarding copyright ownership.  The ASF licenses this file
 *    to you under the Apache License, Version 2.0 (the
 *    "License"); you may not use this file except in compliance
 *    with the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing,
 *    software distributed under the License is distributed on an
 *    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *    KIND, either express or implied.  See the License for the
 *    specific language governing permissions and limitations
 *    under the License.
 * ====================================================================
 */


#include <assert.h>
#include <string.h>

#include <apr_general.h>        /* for APR_INLINE */
#include <apr_md5.h>            /* for, um...MD5 stuff */

#include "svn_delta.h"
#include "svn_io.h"
#include "svn_pools.h"
#include "svn_checksum.h"

#include "delta.h"


/* Text delta stream descriptor. */

struct svn_txdelta_stream_t {
  /* Copied from parameters to svn_txdelta_stream_create. */
  void *baton;
  svn_txdelta_next_window_fn_t next_window;
  svn_txdelta_md5_digest_fn_t md5_digest;
};

/* Delta stream baton. */
struct txdelta_baton {
  /* These are copied from parameters passed to svn_txdelta. */
  svn_stream_t *source;
  svn_stream_t *target;

  /* Private data */
  svn_boolean_t more_source;    /* FALSE if source stream hit EOF. */
  svn_boolean_t more;           /* TRUE if there are more data in the pool. */
  svn_filesize_t pos;           /* Offset of next read in source file. */
  char *buf;                    /* Buffer for input data. */

  svn_checksum_ctx_t *context;  /* If not NULL, the context for computing
                                   the checksum. */
  svn_checksum_t *checksum;     /* If non-NULL, the checksum of TARGET. */

  apr_pool_t *result_pool;      /* For results (e.g. checksum) */
};


/* Target-push stream descriptor. */

struct tpush_baton {
  /* These are copied from parameters passed to svn_txdelta_target_push. */
  svn_stream_t *source;
  svn_txdelta_window_handler_t wh;
  void *whb;
  apr_pool_t *pool;

  /* Private data */
  char *buf;
  svn_filesize_t source_offset;
  apr_size_t source_len;
  svn_boolean_t source_done;
  apr_size_t target_len;
};


/* Text delta applicator.  */

struct apply_baton {
  /* These are copied from parameters passed to svn_txdelta_apply.  */
  svn_stream_t *source;
  svn_stream_t *target;

  /* Private data.  Between calls, SBUF contains the data from the
   * last window's source view, as specified by SBUF_OFFSET and
   * SBUF_LEN.  The contents of TBUF are not interesting between
   * calls.  */
  apr_pool_t *pool;             /* Pool to allocate data from */
  char *sbuf;                   /* Source buffer */
  apr_size_t sbuf_size;         /* Allocated source buffer space */
  svn_filesize_t sbuf_offset;   /* Offset of SBUF data in source stream */
  apr_size_t sbuf_len;          /* Length of SBUF data */
  char *tbuf;                   /* Target buffer */
  apr_size_t tbuf_size;         /* Allocated target buffer space */

  svn_checksum_ctx_t *md5_context; /* Leads to result_digest below. */
  unsigned char *result_digest; /* MD5 digest of resultant fulltext;
                                   must point to at least APR_MD5_DIGESTSIZE
                                   bytes of storage. */

  const char *error_info;       /* Optional extra info for error returns. */
};



svn_txdelta_window_t *
svn_txdelta__make_window(const svn_txdelta__ops_baton_t *build_baton,
                         apr_pool_t *pool)
{
  svn_txdelta_window_t *window;
  svn_string_t *new_data = apr_palloc(pool, sizeof(*new_data));

  window = apr_palloc(pool, sizeof(*window));
  window->sview_offset = 0;
  window->sview_len = 0;
  window->tview_len = 0;

  window->num_ops = build_baton->num_ops;
  window->src_ops = build_baton->src_ops;
  window->ops = build_baton->ops;

  /* just copy the fields over, rather than alloc/copying into a whole new
     svn_string_t structure. */
  /* ### would be much nicer if window->new_data were not a ptr... */
  new_data->data = build_baton->new_data->data;
  new_data->len = build_baton->new_data->len;
  window->new_data = new_data;

  return window;
}


/* Compute and return a delta window using the xdelta algorithm on
   DATA, which contains SOURCE_LEN bytes of source data and TARGET_LEN
   bytes of target data.  SOURCE_OFFSET gives the offset of the source
   data, and is simply copied into the window's sview_offset field. */
static svn_txdelta_window_t *
compute_window(const char *data, apr_size_t source_len, apr_size_t target_len,
               svn_filesize_t source_offset, apr_pool_t *pool)
{
  svn_txdelta__ops_baton_t build_baton = { 0 };
  svn_txdelta_window_t *window;

  /* Compute the delta operations. */
  build_baton.new_data = svn_stringbuf_create_empty(pool);

  if (source_len == 0)
    svn_txdelta__insert_op(&build_baton, svn_txdelta_new, 0, target_len, data,
                           pool);
  else
    svn_txdelta__xdelta(&build_baton, data, source_len, target_len, pool);

  /* Create and return the delta window. */
  window = svn_txdelta__make_window(&build_baton, pool);
  window->sview_offset = source_offset;
  window->sview_len = source_len;
  window->tview_len = target_len;
  return window;
}



svn_txdelta_window_t *
svn_txdelta_window_dup(const svn_txdelta_window_t *window,
                       apr_pool_t *pool)
{
  svn_txdelta__ops_baton_t build_baton = { 0 };
  svn_txdelta_window_t *new_window;
  const apr_size_t ops_size = (window->num_ops * sizeof(*build_baton.ops));

  build_baton.num_ops = window->num_ops;
  build_baton.src_ops = window->src_ops;
  build_baton.ops_size = window->num_ops;
  build_baton.ops = apr_pmemdup(pool, window->ops, ops_size);
  build_baton.new_data =
    svn_stringbuf_create_from_string(window->new_data, pool);

  new_window = svn_txdelta__make_window(&build_baton, pool);
  new_window->sview_offset = window->sview_offset;
  new_window->sview_len = window->sview_len;
  new_window->tview_len = window->tview_len;
  return new_window;
}

/* This is a private interlibrary compatibility wrapper. */
svn_txdelta_window_t *
svn_txdelta__copy_window(const svn_txdelta_window_t *window,
                         apr_pool_t *pool);
svn_txdelta_window_t *
svn_txdelta__copy_window(const svn_txdelta_window_t *window,
                         apr_pool_t *pool)
{
  return svn_txdelta_window_dup(window, pool);
}


/* Insert a delta op into a delta window. */

void
svn_txdelta__insert_op(svn_txdelta__ops_baton_t *build_baton,
                       enum svn_delta_action opcode,
                       apr_size_t offset,
                       apr_size_t length,
                       const char *new_data,
                       apr_pool_t *pool)
{
  svn_txdelta_op_t *op;

  /* Check if this op can be merged with the previous op. The delta
     combiner sometimes generates such ops, and this is the obvious
     place to make the check. */
  if (build_baton->num_ops > 0)
    {
      op = &build_baton->ops[build_baton->num_ops - 1];
      if (op->action_code == opcode
          && (opcode == svn_txdelta_new
              || op->offset + op->length == offset))
        {
          op->length += length;
          if (opcode == svn_txdelta_new)
            svn_stringbuf_appendbytes(build_baton->new_data,
                                      new_data, length);
          return;
        }
    }

  /* Create space for the new op. */
  if (build_baton->num_ops == build_baton->ops_size)
    {
      svn_txdelta_op_t *const old_ops = build_baton->ops;
      int const new_ops_size = (build_baton->ops_size == 0
                                ? 16 : 2 * build_baton->ops_size);
      build_baton->ops =
        apr_palloc(pool, new_ops_size * sizeof(*build_baton->ops));

      /* Copy any existing ops into the new array */
      if (old_ops)
        memcpy(build_baton->ops, old_ops,
               build_baton->ops_size * sizeof(*build_baton->ops));
      build_baton->ops_size = new_ops_size;
    }

  /* Insert the op. svn_delta_source and svn_delta_target are
     just inserted. For svn_delta_new, the new data must be
     copied into the window. */
  op = &build_baton->ops[build_baton->num_ops];
  switch (opcode)
    {
    case svn_txdelta_source:
      ++build_baton->src_ops;
      /*** FALLTHRU ***/
    case svn_txdelta_target:
      op->action_code = opcode;
      op->offset = offset;
      op->length = length;
      break;
    case svn_txdelta_new:
      op->action_code = opcode;
      op->offset = build_baton->new_data->len;
      op->length = length;
      svn_stringbuf_appendbytes(build_baton->new_data, new_data, length);
      break;
    default:
      assert(!"unknown delta op.");
    }

  ++build_baton->num_ops;
}

apr_size_t
svn_txdelta__remove_copy(svn_txdelta__ops_baton_t *build_baton,
                         apr_size_t max_len)
{
  svn_txdelta_op_t *op;
  apr_size_t len = 0;

  /* remove ops back to front */
  while (build_baton->num_ops > 0)
    {
      op = &build_baton->ops[build_baton->num_ops-1];

      /*  we can't modify svn_txdelta_target ops -> stop there */
      if (op->action_code == svn_txdelta_target)
        break;

      /*  handle the case that we cannot remove the op entirely */
      if (op->length + len > max_len)
        {
          /* truncate only insertions. Copies don't benefit
             from being truncated. */
          if (op->action_code == svn_txdelta_new)
            {
               build_baton->new_data->len -= max_len - len;
               op->length -= max_len - len;
               len = max_len;
            }

          break;
        }

      /* drop the op entirely */
      if (op->action_code == svn_txdelta_new)
        build_baton->new_data->len -= op->length;

      len += op->length;
      --build_baton->num_ops;
    }

  return len;
}



/* Generic delta stream functions. */

svn_txdelta_stream_t *
svn_txdelta_stream_create(void *baton,
                          svn_txdelta_next_window_fn_t next_window,
                          svn_txdelta_md5_digest_fn_t md5_digest,
                          apr_pool_t *pool)
{
  svn_txdelta_stream_t *stream = apr_palloc(pool, sizeof(*stream));

  stream->baton = baton;
  stream->next_window = next_window;
  stream->md5_digest = md5_digest;

  return stream;
}

svn_error_t *
svn_txdelta_next_window(svn_txdelta_window_t **window,
                        svn_txdelta_stream_t *stream,
                        apr_pool_t *pool)
{
  return stream->next_window(window, stream->baton, pool);
}

const unsigned char *
svn_txdelta_md5_digest(svn_txdelta_stream_t *stream)
{
  return stream->md5_digest(stream->baton);
}



static svn_error_t *
txdelta_next_window(svn_txdelta_window_t **window,
                    void *baton,
                    apr_pool_t *pool)
{
  struct txdelta_baton *b = baton;
  apr_size_t source_len = SVN_DELTA_WINDOW_SIZE;
  apr_size_t target_len = SVN_DELTA_WINDOW_SIZE;

  /* Read the source stream. */
  if (b->more_source)
    {
      SVN_ERR(svn_stream_read_full(b->source, b->buf, &source_len));
      b->more_source = (source_len == SVN_DELTA_WINDOW_SIZE);
    }
  else
    source_len = 0;

  /* Read the target stream. */
  SVN_ERR(svn_stream_read_full(b->target, b->buf + source_len, &target_len));
  b->pos += source_len;

  if (target_len == 0)
    {
      /* No target data?  We're done; return the final window. */
      if (b->context != NULL)
        SVN_ERR(svn_checksum_final(&b->checksum, b->context, b->result_pool));

      *window = NULL;
      b->more = FALSE;
      return SVN_NO_ERROR;
    }
  else if (b->context != NULL)
    SVN_ERR(svn_checksum_update(b->context, b->buf + source_len, target_len));

  *window = compute_window(b->buf, source_len, target_len,
                           b->pos - source_len, pool);

  /* That's it. */
  return SVN_NO_ERROR;
}


static const unsigned char *
txdelta_md5_digest(void *baton)
{
  struct txdelta_baton *b = baton;
  /* If there are more windows for this stream, the digest has not yet
     been calculated.  */
  if (b->more)
    return NULL;

  /* If checksumming has not been activated, there will be no digest. */
  if (b->context == NULL)
    return NULL;

  /* The checksum should be there. */
  return b->checksum->digest;
}


svn_error_t *
svn_txdelta_run(svn_stream_t *source,
                svn_stream_t *target,
                svn_txdelta_window_handler_t handler,
                void *handler_baton,
                svn_checksum_kind_t checksum_kind,
                svn_checksum_t **checksum,
                svn_cancel_func_t cancel_func,
                void *cancel_baton,
                apr_pool_t *result_pool,
                apr_pool_t *scratch_pool)
{
  apr_pool_t *iterpool = svn_pool_create(scratch_pool);
  struct txdelta_baton tb = { 0 };
  svn_txdelta_window_t *window;

  tb.source = source;
  tb.target = target;
  tb.more_source = TRUE;
  tb.more = TRUE;
  tb.pos = 0;
  tb.buf = apr_palloc(scratch_pool, 2 * SVN_DELTA_WINDOW_SIZE);
  tb.result_pool = result_pool;

  if (checksum != NULL)
    tb.context = svn_checksum_ctx_create(checksum_kind, scratch_pool);

  do
    {
      /* free the window (if any) */
      svn_pool_clear(iterpool);

      /* read in a single delta window */
      SVN_ERR(txdelta_next_window(&window, &tb, iterpool));

      /* shove it at the handler */
      SVN_ERR((*handler)(window, handler_baton));

      if (cancel_func)
        SVN_ERR(cancel_func(cancel_baton));
    }
  while (window != NULL);

  svn_pool_destroy(iterpool);

  if (checksum != NULL)
    *checksum = tb.checksum;  /* should be there! */

  return SVN_NO_ERROR;
}


void
svn_txdelta2(svn_txdelta_stream_t **stream,
             svn_stream_t *source,
             svn_stream_t *target,
             svn_boolean_t calculate_checksum,
             apr_pool_t *pool)
{
  struct txdelta_baton *b = apr_pcalloc(pool, sizeof(*b));

  b->source = source;
  b->target = target;
  b->more_source = TRUE;
  b->more = TRUE;
  b->buf = apr_palloc(pool, 2 * SVN_DELTA_WINDOW_SIZE);
  b->context = calculate_checksum
             ? svn_checksum_ctx_create(svn_checksum_md5, pool)
             : NULL;
  b->result_pool = pool;

  *stream = svn_txdelta_stream_create(b, txdelta_next_window,
                                      txdelta_md5_digest, pool);
}

void
svn_txdelta(svn_txdelta_stream_t **stream,
            svn_stream_t *source,
            svn_stream_t *target,
            apr_pool_t *pool)
{
  svn_txdelta2(stream, source, target, TRUE, pool);
}



/* Functions for implementing a "target push" delta. */

/* This is the write handler for a target-push delta stream.  It reads
 * source data, buffers target data, and fires off delta windows when
 * the target data buffer is full. */
static svn_error_t *
tpush_write_handler(void *baton, const char *data, apr_size_t *len)
{
  struct tpush_baton *tb = baton;
  apr_size_t chunk_len, data_len = *len;
  apr_pool_t *pool = svn_pool_create(tb->pool);
  svn_txdelta_window_t *window;

  while (data_len > 0)
    {
      svn_pool_clear(pool);

      /* Make sure we're all full up on source data, if possible. */
      if (tb->source_len == 0 && !tb->source_done)
        {
          tb->source_len = SVN_DELTA_WINDOW_SIZE;
          SVN_ERR(svn_stream_read_full(tb->source, tb->buf, &tb->source_len));
          if (tb->source_len < SVN_DELTA_WINDOW_SIZE)
            tb->source_done = TRUE;
        }

      /* Copy in the target data, up to SVN_DELTA_WINDOW_SIZE. */
      chunk_len = SVN_DELTA_WINDOW_SIZE - tb->target_len;
      if (chunk_len > data_len)
        chunk_len = data_len;
      memcpy(tb->buf + tb->source_len + tb->target_len, data, chunk_len);
      data += chunk_len;
      data_len -= chunk_len;
      tb->target_len += chunk_len;

      /* If we're full of target data, compute and fire off a window. */
      if (tb->target_len == SVN_DELTA_WINDOW_SIZE)
        {
          window = compute_window(tb->buf, tb->source_len, tb->target_len,
                                  tb->source_offset, pool);
          SVN_ERR(tb->wh(window, tb->whb));
          tb->source_offset += tb->source_len;
          tb->source_len = 0;
          tb->target_len = 0;
        }
    }

  svn_pool_destroy(pool);
  return SVN_NO_ERROR;
}


/* This is the close handler for a target-push delta stream.  It sends
 * a final window if there is any buffered target data, and then sends
 * a NULL window signifying the end of the window stream. */
static svn_error_t *
tpush_close_handler(void *baton)
{
  struct tpush_baton *tb = baton;
  svn_txdelta_window_t *window;

  /* Send a final window if we have any residual target data. */
  if (tb->target_len > 0)
    {
      window = compute_window(tb->buf, tb->source_len, tb->target_len,
                              tb->source_offset, tb->pool);
      SVN_ERR(tb->wh(window, tb->whb));
    }

  /* Send a final NULL window signifying the end. */
  return tb->wh(NULL, tb->whb);
}


svn_stream_t *
svn_txdelta_target_push(svn_txdelta_window_handler_t handler,
                        void *handler_baton, svn_stream_t *source,
                        apr_pool_t *pool)
{
  struct tpush_baton *tb;
  svn_stream_t *stream;

  /* Initialize baton. */
  tb = apr_palloc(pool, sizeof(*tb));
  tb->source = source;
  tb->wh = handler;
  tb->whb = handler_baton;
  tb->pool = pool;
  tb->buf = apr_palloc(pool, 2 * SVN_DELTA_WINDOW_SIZE);
  tb->source_offset = 0;
  tb->source_len = 0;
  tb->source_done = FALSE;
  tb->target_len = 0;

  /* Create and return writable stream. */
  stream = svn_stream_create(tb, pool);
  svn_stream_set_write(stream, tpush_write_handler);
  svn_stream_set_close(stream, tpush_close_handler);
  return stream;
}



/* Functions for applying deltas.  */

/* Ensure that BUF has enough space for VIEW_LEN bytes.  */
static APR_INLINE svn_error_t *
size_buffer(char **buf, apr_size_t *buf_size,
            apr_size_t view_len, apr_pool_t *pool)
{
  if (view_len > *buf_size)
    {
      *buf_size *= 2;
      if (*buf_size < view_len)
        *buf_size = view_len;
      SVN_ERR_ASSERT(APR_ALIGN_DEFAULT(*buf_size) >= *buf_size);
      *buf = apr_palloc(pool, *buf_size);
    }

  return SVN_NO_ERROR;
}

/* Copy LEN bytes from SOURCE to TARGET.  Unlike memmove() or memcpy(),
 * create repeating patterns if the source and target ranges overlap.
 * Return a pointer to the first byte after the copied target range.  */
static APR_INLINE char *
patterning_copy(char *target, const char *source, apr_size_t len)
{
  /* If the source and target overlap, repeat the overlapping pattern
     in the target buffer. Always copy from the source buffer because
     presumably it will be in the L1 cache after the first iteration
     and doing this should avoid pipeline stalls due to write/read
     dependencies. */
  const apr_size_t overlap = target - source;
  while (len > overlap)
    {
      memcpy(target, source, overlap);
      target += overlap;
      len -= overlap;
    }

  /* Copy any remaining source pattern. */
  if (len)
    {
      memcpy(target, source, len);
      target += len;
    }

  return target;
}

void
svn_txdelta_apply_instructions(svn_txdelta_window_t *window,
                               const char *sbuf, char *tbuf,
                               apr_size_t *tlen)
{
  const svn_txdelta_op_t *op;
  apr_size_t tpos = 0;

  /* Nothing to do for empty buffers.
   * This check allows for NULL TBUF in that case. */
  if (*tlen == 0)
    return;

  for (op = window->ops; op < window->ops + window->num_ops; op++)
    {
      const apr_size_t buf_len = (op->length < *tlen - tpos
                                  ? op->length : *tlen - tpos);

      /* Check some invariants common to all instructions.  */
      assert(tpos + op->length <= window->tview_len);

      switch (op->action_code)
        {
        case svn_txdelta_source:
          /* Copy from source area.  */
          assert(sbuf);
          assert(op->offset + op->length <= window->sview_len);
          memcpy(tbuf + tpos, sbuf + op->offset, buf_len);
          break;

        case svn_txdelta_target:
          /* Copy from target area.  We can't use memcpy() or the like
           * since we need a specific semantics for overlapping copies:
           * they must result in repeating patterns.
           * Note that most copies won't have overlapping source and
           * target ranges (they are just a result of self-compressed
           * data) but a small percentage will.  */
          assert(op->offset < tpos);
          patterning_copy(tbuf + tpos, tbuf + op->offset, buf_len);
          break;

        case svn_txdelta_new:
          /* Copy from window new area.  */
          assert(op->offset + op->length <= window->new_data->len);
          memcpy(tbuf + tpos,
                 window->new_data->data + op->offset,
                 buf_len);
          break;

        default:
          assert(!"Invalid delta instruction code");
        }

      tpos += op->length;
      if (tpos >= *tlen)
        return;                 /* The buffer is full. */
    }

  /* Check that we produced the right amount of data.  */
  assert(tpos == window->tview_len);
  *tlen = tpos;
}

/* Apply WINDOW to the streams given by APPL.  */
static svn_error_t *
apply_window(svn_txdelta_window_t *window, void *baton)
{
  struct apply_baton *ab = (struct apply_baton *) baton;
  apr_size_t len;

  if (window == NULL)
    {
      svn_error_t *err = SVN_NO_ERROR;

      /* We're done; just clean up.  */
      if (ab->result_digest)
        {
          svn_checksum_t *md5_checksum;

          err = svn_checksum_final(&md5_checksum, ab->md5_context, ab->pool);
          if (!err)
            memcpy(ab->result_digest, md5_checksum->digest,
                   svn_checksum_size(md5_checksum));
        }

      err = svn_error_compose_create(err, svn_stream_close(ab->target));
      svn_pool_destroy(ab->pool);

      return err;
    }

  /* Make sure the source view didn't slide backwards.  */
  SVN_ERR_ASSERT(window->sview_len == 0
                 || (window->sview_offset >= ab->sbuf_offset
                     && (window->sview_offset + window->sview_len
                         >= ab->sbuf_offset + ab->sbuf_len)));

  /* Make sure there's enough room in the target buffer.  */
  SVN_ERR(size_buffer(&ab->tbuf, &ab->tbuf_size, window->tview_len, ab->pool));

  /* Prepare the source buffer for reading from the input stream.  */
  if (window->sview_offset != ab->sbuf_offset
      || window->sview_len > ab->sbuf_size)
    {
      char *old_sbuf = ab->sbuf;

      /* Make sure there's enough room.  */
      SVN_ERR(size_buffer(&ab->sbuf, &ab->sbuf_size, window->sview_len,
              ab->pool));

      /* If the existing view overlaps with the new view, copy the
       * overlap to the beginning of the new buffer.  */
      if (  (apr_size_t)ab->sbuf_offset + ab->sbuf_len
          > (apr_size_t)window->sview_offset)
        {
          apr_size_t start =
            (apr_size_t)(window->sview_offset - ab->sbuf_offset);
          memmove(ab->sbuf, old_sbuf + start, ab->sbuf_len - start);
          ab->sbuf_len -= start;
        }
      else
        ab->sbuf_len = 0;
      ab->sbuf_offset = window->sview_offset;
    }

  /* Read the remainder of the source view into the buffer.  */
  if (ab->sbuf_len < window->sview_len)
    {
      len = window->sview_len - ab->sbuf_len;
      SVN_ERR(svn_stream_read_full(ab->source, ab->sbuf + ab->sbuf_len, &len));
      if (len != window->sview_len - ab->sbuf_len)
        return svn_error_create(SVN_ERR_INCOMPLETE_DATA, NULL,
                                "Delta source ended unexpectedly");
      ab->sbuf_len = window->sview_len;
    }

  /* Apply the window instructions to the source view to generate
     the target view.  */
  len = window->tview_len;
  svn_txdelta_apply_instructions(window, ab->sbuf, ab->tbuf, &len);
  SVN_ERR_ASSERT(len == window->tview_len);

  /* Write out the output. */

  /* Just update the context here. */
  if (ab->result_digest)
    SVN_ERR(svn_checksum_update(ab->md5_context, ab->tbuf, len));

  return svn_stream_write(ab->target, ab->tbuf, &len);
}


void
svn_txdelta_apply(svn_stream_t *source,
                  svn_stream_t *target,
                  unsigned char *result_digest,
                  const char *error_info,
                  apr_pool_t *pool,
                  svn_txdelta_window_handler_t *handler,
                  void **handler_baton)
{
  apr_pool_t *subpool = svn_pool_create(pool);
  struct apply_baton *ab;

  ab = apr_palloc(subpool, sizeof(*ab));
  ab->source = source;
  ab->target = target;
  ab->pool = subpool;
  ab->sbuf = NULL;
  ab->sbuf_size = 0;
  ab->sbuf_offset = 0;
  ab->sbuf_len = 0;
  ab->tbuf = NULL;
  ab->tbuf_size = 0;
  ab->result_digest = result_digest;

  if (result_digest)
    ab->md5_context = svn_checksum_ctx_create(svn_checksum_md5, subpool);

  if (error_info)
    ab->error_info = apr_pstrdup(subpool, error_info);
  else
    ab->error_info = NULL;

  *handler = apply_window;
  *handler_baton = ab;
}



/* Convenience routines */

svn_error_t *
svn_txdelta_send_string(const svn_string_t *string,
                        svn_txdelta_window_handler_t handler,
                        void *handler_baton,
                        apr_pool_t *pool)
{
  svn_txdelta_window_t window = { 0 };
  svn_txdelta_op_t op;

  /* Build a single `new' op */
  op.action_code = svn_txdelta_new;
  op.offset = 0;
  op.length = string->len;

  /* Build a single window containing a ptr to the string. */
  window.tview_len = string->len;
  window.num_ops = 1;
  window.ops = &op;
  window.new_data = string;

  /* Push the one window at the handler. */
  SVN_ERR((*handler)(&window, handler_baton));

  /* Push a NULL at the handler, because we're done. */
  return (*handler)(NULL, handler_baton);
}

svn_error_t *svn_txdelta_send_stream(svn_stream_t *stream,
                                     svn_txdelta_window_handler_t handler,
                                     void *handler_baton,
                                     unsigned char *digest,
                                     apr_pool_t *pool)
{
  svn_txdelta_window_t delta_window = { 0 };
  svn_txdelta_op_t delta_op;
  svn_string_t window_data;
  char read_buf[SVN__STREAM_CHUNK_SIZE + 1];
  svn_checksum_ctx_t *md5_checksum_ctx;

  if (digest)
    md5_checksum_ctx = svn_checksum_ctx_create(svn_checksum_md5, pool);

  while (1)
    {
      apr_size_t read_len = SVN__STREAM_CHUNK_SIZE;

      SVN_ERR(svn_stream_read_full(stream, read_buf, &read_len));
      if (read_len == 0)
        break;

      window_data.data = read_buf;
      window_data.len = read_len;

      delta_op.action_code = svn_txdelta_new;
      delta_op.offset = 0;
      delta_op.length = read_len;

      delta_window.tview_len = read_len;
      delta_window.num_ops = 1;
      delta_window.ops = &delta_op;
      delta_window.new_data = &window_data;

      SVN_ERR(handler(&delta_window, handler_baton));

      if (digest)
        SVN_ERR(svn_checksum_update(md5_checksum_ctx, read_buf, read_len));

      if (read_len < SVN__STREAM_CHUNK_SIZE)
        break;
    }
  SVN_ERR(handler(NULL, handler_baton));

  if (digest)
    {
      svn_checksum_t *md5_checksum;

      SVN_ERR(svn_checksum_final(&md5_checksum, md5_checksum_ctx, pool));
      memcpy(digest, md5_checksum->digest, APR_MD5_DIGESTSIZE);
    }

  return SVN_NO_ERROR;
}

svn_error_t *svn_txdelta_send_txstream(svn_txdelta_stream_t *txstream,
                                       svn_txdelta_window_handler_t handler,
                                       void *handler_baton,
                                       apr_pool_t *pool)
{
  svn_txdelta_window_t *window;

  /* create a pool just for the windows */
  apr_pool_t *wpool = svn_pool_create(pool);

  do
    {
      /* free the window (if any) */
      svn_pool_clear(wpool);

      /* read in a single delta window */
      SVN_ERR(svn_txdelta_next_window(&window, txstream, wpool));

      /* shove it at the handler */
      SVN_ERR((*handler)(window, handler_baton));
    }
  while (window != NULL);

  svn_pool_destroy(wpool);

  return SVN_NO_ERROR;
}

svn_error_t *
svn_txdelta_send_contents(const unsigned char *contents,
                          apr_size_t len,
                          svn_txdelta_window_handler_t handler,
                          void *handler_baton,
                          apr_pool_t *pool)
{
  svn_string_t new_data;
  svn_txdelta_op_t op = { svn_txdelta_new, 0, 0 };
  svn_txdelta_window_t window = { 0, 0, 0, 1, 0 };
  window.ops = &op;
  window.new_data = &new_data;

  /* send CONTENT as a series of max-sized windows */
  while (len > 0)
    {
      /* stuff next chunk into the window */
      window.tview_len = len < SVN_DELTA_WINDOW_SIZE
                       ? len
                       : SVN_DELTA_WINDOW_SIZE;
      op.length = window.tview_len;
      new_data.len = window.tview_len;
      new_data.data = (const char*)contents;

      /* update remaining */
      contents += window.tview_len;
      len -= window.tview_len;

      /* shove it at the handler */
      SVN_ERR((*handler)(&window, handler_baton));
    }

  /* indicate end of stream */
  SVN_ERR((*handler)(NULL, handler_baton));

  return SVN_NO_ERROR;
}