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i bet a lot of people didn't know what ssh 1.2.16 had a nice license.
well, except for the patent issues.  someone in sweden (forget their
name at the moment) cleaned out most of the patented code, and now
this code removes rsa code.  when this is done, it will link against
libssl, but the work isn't completely done yet.  then we need to bring
this up to modern days, featurewise.

/*

buffer.c

Author: Tatu Ylonen <ylo@cs.hut.fi>

Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
                   All rights reserved

Created: Sat Mar 18 04:15:33 1995 ylo

Functions for manipulating fifo buffers (that can grow if needed).

*/

#include "includes.h"
RCSID("$Id: buffer.c,v 1.1 1999/09/26 20:53:34 deraadt Exp $");

#include "xmalloc.h"
#include "buffer.h"
#include "ssh.h"

/* Initializes the buffer structure. */

void buffer_init(Buffer *buffer)
{
  buffer->alloc = 4096;
  buffer->buf = xmalloc(buffer->alloc);
  buffer->offset = 0;
  buffer->end = 0;
}

/* Frees any memory used for the buffer. */

void buffer_free(Buffer *buffer)
{
  memset(buffer->buf, 0, buffer->alloc);
  xfree(buffer->buf);
}

/* Clears any data from the buffer, making it empty.  This does not actually
   zero the memory. */

void buffer_clear(Buffer *buffer)
{
  buffer->offset = 0;
  buffer->end = 0;
}

/* Appends data to the buffer, expanding it if necessary. */

void buffer_append(Buffer *buffer, const char *data, unsigned int len)
{
  char *cp;
  buffer_append_space(buffer, &cp, len);
  memcpy(cp, data, len);
}

/* Appends space to the buffer, expanding the buffer if necessary.
   This does not actually copy the data into the buffer, but instead
   returns a pointer to the allocated region. */

void buffer_append_space(Buffer *buffer, char **datap, unsigned int len)
{
  /* If the buffer is empty, start using it from the beginning. */
  if (buffer->offset == buffer->end)
    {
      buffer->offset = 0;
      buffer->end = 0;
    }

 restart:
  /* If there is enough space to store all data, store it now. */
  if (buffer->end + len < buffer->alloc)
    {
      *datap = buffer->buf + buffer->end;
      buffer->end += len;
      return;
    }

  /* If the buffer is quite empty, but all data is at the end, move the
     data to the beginning and retry. */
  if (buffer->offset > buffer->alloc / 2)
    {
      memmove(buffer->buf, buffer->buf + buffer->offset,
	      buffer->end - buffer->offset);
      buffer->end -= buffer->offset;
      buffer->offset = 0;
      goto restart;
    }

  /* Increase the size of the buffer and retry. */
  buffer->alloc += len + 32768;
  buffer->buf = xrealloc(buffer->buf, buffer->alloc);
  goto restart;
}

/* Returns the number of bytes of data in the buffer. */

unsigned int buffer_len(Buffer *buffer)
{
  return buffer->end - buffer->offset;
}

/* Gets data from the beginning of the buffer. */

void buffer_get(Buffer *buffer, char *buf, unsigned int len)
{
  if (len > buffer->end - buffer->offset)
    fatal("buffer_get trying to get more bytes than in buffer");
  memcpy(buf, buffer->buf + buffer->offset, len);
  buffer->offset += len;
}

/* Consumes the given number of bytes from the beginning of the buffer. */

void buffer_consume(Buffer *buffer, unsigned int bytes)
{
  if (bytes > buffer->end - buffer->offset)
    fatal("buffer_get trying to get more bytes than in buffer");
  buffer->offset += bytes;
}  

/* Consumes the given number of bytes from the end of the buffer. */

void buffer_consume_end(Buffer *buffer, unsigned int bytes)
{
  if (bytes > buffer->end - buffer->offset)
    fatal("buffer_get trying to get more bytes than in buffer");
  buffer->end -= bytes;
}  

/* Returns a pointer to the first used byte in the buffer. */

char *buffer_ptr(Buffer *buffer)
{
  return buffer->buf + buffer->offset;
}

/* Dumps the contents of the buffer to stderr. */

void buffer_dump(Buffer *buffer)
{
  int i;
  unsigned char *ucp = (unsigned char *)buffer->buf;
  
  for (i = buffer->offset; i < buffer->end; i++)
    fprintf(stderr, " %02x", ucp[i]);
  fprintf(stderr, "\n");
}