samba-mirror/source3/rpc_parse/parse_prs.c

/* 
   Unix SMB/CIFS implementation.
   Samba memory buffer functions
   Copyright (C) Andrew Tridgell              1992-1997
   Copyright (C) Luke Kenneth Casson Leighton 1996-1997
   Copyright (C) Jeremy Allison               1999
   Copyright (C) Andrew Bartlett              2003.
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "../librpc/gen_ndr/ndr_schannel.h"

#undef DBGC_CLASS
#define DBGC_CLASS DBGC_RPC_PARSE

/**
 * Dump a prs to a file: from the current location through to the end.
 **/
void prs_dump(const char *name, int v, prs_struct *ps)
{
	prs_dump_region(name, v, ps, ps->data_offset, ps->buffer_size);
}

/**
 * Dump from the start of the prs to the current location.
 **/
void prs_dump_before(const char *name, int v, prs_struct *ps)
{
	prs_dump_region(name, v, ps, 0, ps->data_offset);
}

/**
 * Dump everything from the start of the prs up to the current location.
 **/
void prs_dump_region(const char *name, int v, prs_struct *ps,
		     int from_off, int to_off)
{
	int fd, i;
	char *fname = NULL;
	ssize_t sz;
	if (DEBUGLEVEL < 50) return;
	for (i=1;i<100;i++) {
		if (v != -1) {
			if (asprintf(&fname,"/tmp/%s_%d.%d.prs", name, v, i) < 0) {
				return;
			}
		} else {
			if (asprintf(&fname,"/tmp/%s.%d.prs", name, i) < 0) {
				return;
			}
		}
		fd = open(fname, O_WRONLY|O_CREAT|O_EXCL, 0644);
		if (fd != -1 || errno != EEXIST) break;
	}
	if (fd != -1) {
		sz = write(fd, ps->data_p + from_off, to_off - from_off);
		i = close(fd);
		if ( (sz != to_off-from_off) || (i != 0) ) {
			DEBUG(0,("Error writing/closing %s: %ld!=%ld %d\n", fname, (unsigned long)sz, (unsigned long)to_off-from_off, i ));
		} else {
			DEBUG(0,("created %s\n", fname));
		}
	}
	SAFE_FREE(fname);
}

/*******************************************************************
 Debug output for parsing info

 XXXX side-effect of this function is to increase the debug depth XXXX.

********************************************************************/

void prs_debug(prs_struct *ps, int depth, const char *desc, const char *fn_name)
{
	DEBUG(5+depth, ("%s%06x %s %s\n", tab_depth(5+depth,depth), ps->data_offset, fn_name, desc));
}

/**
 * Initialise an expandable parse structure.
 *
 * @param size Initial buffer size.  If >0, a new buffer will be
 * created with malloc().
 *
 * @return False if allocation fails, otherwise True.
 **/

bool prs_init(prs_struct *ps, uint32 size, TALLOC_CTX *ctx, bool io)
{
	ZERO_STRUCTP(ps);
	ps->io = io;
	ps->bigendian_data = RPC_LITTLE_ENDIAN;
	ps->align = RPC_PARSE_ALIGN;
	ps->is_dynamic = False;
	ps->data_offset = 0;
	ps->buffer_size = 0;
	ps->data_p = NULL;
	ps->mem_ctx = ctx;

	if (size != 0) {
		ps->buffer_size = size;
		if((ps->data_p = (char *)SMB_MALLOC((size_t)size)) == NULL) {
			DEBUG(0,("prs_init: malloc fail for %u bytes.\n", (unsigned int)size));
			return False;
		}
		memset(ps->data_p, '\0', (size_t)size);
		ps->is_dynamic = True; /* We own this memory. */
	} else if (MARSHALLING(ps)) {
		/* If size is zero and we're marshalling we should allocate memory on demand. */
		ps->is_dynamic = True;
	}

	return True;
}

/*******************************************************************
 Delete the memory in a parse structure - if we own it.

 NOTE: Contrary to the somewhat confusing naming, this function is not
       intended for freeing memory allocated by prs_alloc_mem().  That memory
       is attached to the talloc context given by ps->mem_ctx.
 ********************************************************************/

void prs_mem_free(prs_struct *ps)
{
	if(ps->is_dynamic)
		SAFE_FREE(ps->data_p);
	ps->is_dynamic = False;
	ps->buffer_size = 0;
	ps->data_offset = 0;
}

/*******************************************************************
 Clear the memory in a parse structure.
 ********************************************************************/

void prs_mem_clear(prs_struct *ps)
{
	if (ps->buffer_size)
		memset(ps->data_p, '\0', (size_t)ps->buffer_size);
}

/*******************************************************************
 Allocate memory when unmarshalling... Always zero clears.
 ********************************************************************/

#if defined(PARANOID_MALLOC_CHECKER)
char *prs_alloc_mem_(prs_struct *ps, size_t size, unsigned int count)
#else
char *prs_alloc_mem(prs_struct *ps, size_t size, unsigned int count)
#endif
{
	char *ret = NULL;

	if (size && count) {
		/* We can't call the type-safe version here. */
		ret = (char *)_talloc_zero_array(ps->mem_ctx, size, count,
						 "parse_prs");
	}
	return ret;
}

/*******************************************************************
 Return the current talloc context we're using.
 ********************************************************************/

TALLOC_CTX *prs_get_mem_context(prs_struct *ps)
{
	return ps->mem_ctx;
}

/*******************************************************************
 Hand some already allocated memory to a prs_struct.
 ********************************************************************/

void prs_give_memory(prs_struct *ps, char *buf, uint32 size, bool is_dynamic)
{
	ps->is_dynamic = is_dynamic;
	ps->data_p = buf;
	ps->buffer_size = size;
}

/*******************************************************************
 Take some memory back from a prs_struct.
 ********************************************************************/

char *prs_take_memory(prs_struct *ps, uint32 *psize)
{
	char *ret = ps->data_p;
	if(psize)
		*psize = ps->buffer_size;
	ps->is_dynamic = False;
	prs_mem_free(ps);
	return ret;
}

/*******************************************************************
 Set a prs_struct to exactly a given size. Will grow or tuncate if neccessary.
 ********************************************************************/

bool prs_set_buffer_size(prs_struct *ps, uint32 newsize)
{
	if (newsize > ps->buffer_size)
		return prs_force_grow(ps, newsize - ps->buffer_size);

	if (newsize < ps->buffer_size) {
		ps->buffer_size = newsize;

		/* newsize == 0 acts as a free and set pointer to NULL */
		if (newsize == 0) {
			SAFE_FREE(ps->data_p);
		} else {
			ps->data_p = (char *)SMB_REALLOC(ps->data_p, newsize);

			if (ps->data_p == NULL) {
				DEBUG(0,("prs_set_buffer_size: Realloc failure for size %u.\n",
					(unsigned int)newsize));
				DEBUG(0,("prs_set_buffer_size: Reason %s\n",strerror(errno)));
				return False;
			}
		}
	}

	return True;
}

/*******************************************************************
 Attempt, if needed, to grow a data buffer.
 Also depends on the data stream mode (io).
 ********************************************************************/

bool prs_grow(prs_struct *ps, uint32 extra_space)
{
	uint32 new_size;

	ps->grow_size = MAX(ps->grow_size, ps->data_offset + extra_space);

	if(ps->data_offset + extra_space <= ps->buffer_size)
		return True;

	/*
	 * We cannot grow the buffer if we're not reading
	 * into the prs_struct, or if we don't own the memory.
	 */

	if(UNMARSHALLING(ps) || !ps->is_dynamic) {
		DEBUG(0,("prs_grow: Buffer overflow - unable to expand buffer by %u bytes.\n",
				(unsigned int)extra_space));
		return False;
	}
	
	/*
	 * Decide how much extra space we really need.
	 */

	extra_space -= (ps->buffer_size - ps->data_offset);
	if(ps->buffer_size == 0) {

		/*
		 * Start with 128 bytes (arbitrary value), enough for small rpc
		 * requests
		 */
		new_size = MAX(128, extra_space);

		if((ps->data_p = (char *)SMB_MALLOC(new_size)) == NULL) {
			DEBUG(0,("prs_grow: Malloc failure for size %u.\n", (unsigned int)new_size));
			return False;
		}
		memset(ps->data_p, '\0', (size_t)new_size );
	} else {
		/*
		 * If the current buffer size is bigger than the space needed,
		 * just double it, else add extra_space. Always keep 64 bytes
		 * more, so that after we added a large blob we don't have to
		 * realloc immediately again.
		 */
		new_size = MAX(ps->buffer_size*2,
			       ps->buffer_size + extra_space + 64);

		if ((ps->data_p = (char *)SMB_REALLOC(ps->data_p, new_size)) == NULL) {
			DEBUG(0,("prs_grow: Realloc failure for size %u.\n",
				(unsigned int)new_size));
			return False;
		}

		memset(&ps->data_p[ps->buffer_size], '\0', (size_t)(new_size - ps->buffer_size));
	}
	ps->buffer_size = new_size;

	return True;
}

/*******************************************************************
 Attempt to force a data buffer to grow by len bytes.
 This is only used when appending more data onto a prs_struct
 when reading an rpc reply, before unmarshalling it.
 ********************************************************************/

bool prs_force_grow(prs_struct *ps, uint32 extra_space)
{
	uint32 new_size = ps->buffer_size + extra_space;

	if(!UNMARSHALLING(ps) || !ps->is_dynamic) {
		DEBUG(0,("prs_force_grow: Buffer overflow - unable to expand buffer by %u bytes.\n",
				(unsigned int)extra_space));
		return False;
	}

	if((ps->data_p = (char *)SMB_REALLOC(ps->data_p, new_size)) == NULL) {
		DEBUG(0,("prs_force_grow: Realloc failure for size %u.\n",
			(unsigned int)new_size));
		return False;
	}

	memset(&ps->data_p[ps->buffer_size], '\0', (size_t)(new_size - ps->buffer_size));

	ps->buffer_size = new_size;

	return True;
}

/*******************************************************************
 Get the data pointer (external interface).
********************************************************************/

char *prs_data_p(prs_struct *ps)
{
	return ps->data_p;
}

/*******************************************************************
 Get the current data size (external interface).
 ********************************************************************/

uint32 prs_data_size(prs_struct *ps)
{
	return ps->buffer_size;
}

/*******************************************************************
 Fetch the current offset (external interface).
 ********************************************************************/

uint32 prs_offset(prs_struct *ps)
{
	return ps->data_offset;
}

/*******************************************************************
 Set the current offset (external interface).
 ********************************************************************/

bool prs_set_offset(prs_struct *ps, uint32 offset)
{
	if ((offset > ps->data_offset)
	    && !prs_grow(ps, offset - ps->data_offset)) {
		return False;
	}

	ps->data_offset = offset;
	return True;
}

/*******************************************************************
 Append the data from one parse_struct into another.
 ********************************************************************/

bool prs_append_prs_data(prs_struct *dst, prs_struct *src)
{
	if (prs_offset(src) == 0)
		return True;

	if(!prs_grow(dst, prs_offset(src)))
		return False;

	memcpy(&dst->data_p[dst->data_offset], src->data_p, (size_t)prs_offset(src));
	dst->data_offset += prs_offset(src);

	return True;
}

/*******************************************************************
 Append some data from one parse_struct into another.
 ********************************************************************/

bool prs_append_some_data(prs_struct *dst, void *src_base, uint32_t start,
			  uint32_t len)
{
	if (len == 0) {
		return true;
	}

	if(!prs_grow(dst, len)) {
		return false;
	}

	memcpy(&dst->data_p[dst->data_offset], ((char *)src_base) + start, (size_t)len);
	dst->data_offset += len;
	return true;
}

bool prs_append_some_prs_data(prs_struct *dst, prs_struct *src, int32 start,
			      uint32 len)
{
	return prs_append_some_data(dst, src->data_p, start, len);
}

/*******************************************************************
 Append the data from a buffer into a parse_struct.
 ********************************************************************/

bool prs_copy_data_in(prs_struct *dst, const char *src, uint32 len)
{
	if (len == 0)
		return True;

	if(!prs_grow(dst, len))
		return False;

	memcpy(&dst->data_p[dst->data_offset], src, (size_t)len);
	dst->data_offset += len;

	return True;
}

/*******************************************************************
 Copy some data from a parse_struct into a buffer.
 ********************************************************************/

bool prs_copy_data_out(char *dst, prs_struct *src, uint32 len)
{
	if (len == 0)
		return True;

	if(!prs_mem_get(src, len))
		return False;

	memcpy(dst, &src->data_p[src->data_offset], (size_t)len);
	src->data_offset += len;

	return True;
}

/*******************************************************************
 Copy all the data from a parse_struct into a buffer.
 ********************************************************************/

bool prs_copy_all_data_out(char *dst, prs_struct *src)
{
	uint32 len = prs_offset(src);

	if (!len)
		return True;

	prs_set_offset(src, 0);
	return prs_copy_data_out(dst, src, len);
}

/*******************************************************************
 Set the data as X-endian (external interface).
 ********************************************************************/

void prs_set_endian_data(prs_struct *ps, bool endian)
{
	ps->bigendian_data = endian;
}

/*******************************************************************
 Align a the data_len to a multiple of align bytes - filling with
 zeros.
 ********************************************************************/

bool prs_align(prs_struct *ps)
{
	uint32 mod = ps->data_offset & (ps->align-1);

	if (ps->align != 0 && mod != 0) {
		uint32 extra_space = (ps->align - mod);
		if(!prs_grow(ps, extra_space))
			return False;
		memset(&ps->data_p[ps->data_offset], '\0', (size_t)extra_space);
		ps->data_offset += extra_space;
	}

	return True;
}

/******************************************************************
 Align on a 2 byte boundary
 *****************************************************************/
 
bool prs_align_uint16(prs_struct *ps)
{
	bool ret;
	uint8 old_align = ps->align;

	ps->align = 2;
	ret = prs_align(ps);
	ps->align = old_align;
	
	return ret;
}

/******************************************************************
 Align on a 8 byte boundary
 *****************************************************************/
 
bool prs_align_uint64(prs_struct *ps)
{
	bool ret;
	uint8 old_align = ps->align;

	ps->align = 8;
	ret = prs_align(ps);
	ps->align = old_align;
	
	return ret;
}

/******************************************************************
 Align on a specific byte boundary
 *****************************************************************/
 
bool prs_align_custom(prs_struct *ps, uint8 boundary)
{
	bool ret;
	uint8 old_align = ps->align;

	ps->align = boundary;
	ret = prs_align(ps);
	ps->align = old_align;
	
	return ret;
}



/*******************************************************************
 Align only if required (for the unistr2 string mainly)
 ********************************************************************/

bool prs_align_needed(prs_struct *ps, uint32 needed)
{
	if (needed==0)
		return True;
	else
		return prs_align(ps);
}

/*******************************************************************
 Ensure we can read/write to a given offset.
 ********************************************************************/

char *prs_mem_get(prs_struct *ps, uint32 extra_size)
{
	if(UNMARSHALLING(ps)) {
		/*
		 * If reading, ensure that we can read the requested size item.
		 */
		if (ps->data_offset + extra_size > ps->buffer_size) {
			DEBUG(0,("prs_mem_get: reading data of size %u would overrun "
				"buffer by %u bytes.\n",
				(unsigned int)extra_size,
				(unsigned int)(ps->data_offset + extra_size - ps->buffer_size) ));
			return NULL;
		}
	} else {
		/*
		 * Writing - grow the buffer if needed.
		 */
		if(!prs_grow(ps, extra_size))
			return NULL;
	}
	return &ps->data_p[ps->data_offset];
}

/*******************************************************************
 Change the struct type.
 ********************************************************************/

void prs_switch_type(prs_struct *ps, bool io)
{
	if ((ps->io ^ io) == True)
		ps->io=io;
}

/*******************************************************************
 Force a prs_struct to be dynamic even when it's size is 0.
 ********************************************************************/

void prs_force_dynamic(prs_struct *ps)
{
	ps->is_dynamic=True;
}

/*******************************************************************
 Associate a session key with a parse struct.
 ********************************************************************/

void prs_set_session_key(prs_struct *ps, const char sess_key[16])
{
	ps->sess_key = sess_key;
}

/*******************************************************************
 Stream a uint8.
 ********************************************************************/

bool prs_uint8(const char *name, prs_struct *ps, int depth, uint8 *data8)
{
	char *q = prs_mem_get(ps, 1);
	if (q == NULL)
		return False;

	if (UNMARSHALLING(ps))
		*data8 = CVAL(q,0);
	else
		SCVAL(q,0,*data8);

	DEBUGADD(5,("%s%04x %s: %02x\n", tab_depth(5,depth), ps->data_offset, name, *data8));

	ps->data_offset += 1;

	return True;
}

/*******************************************************************
 Stream a uint16.
 ********************************************************************/

bool prs_uint16(const char *name, prs_struct *ps, int depth, uint16 *data16)
{
	char *q = prs_mem_get(ps, sizeof(uint16));
	if (q == NULL)
		return False;

	if (UNMARSHALLING(ps)) {
		if (ps->bigendian_data)
			*data16 = RSVAL(q,0);
		else
			*data16 = SVAL(q,0);
	} else {
		if (ps->bigendian_data)
			RSSVAL(q,0,*data16);
		else
			SSVAL(q,0,*data16);
	}

	DEBUGADD(5,("%s%04x %s: %04x\n", tab_depth(5,depth), ps->data_offset, name, *data16));

	ps->data_offset += sizeof(uint16);

	return True;
}

/*******************************************************************
 Stream a uint32.
 ********************************************************************/

bool prs_uint32(const char *name, prs_struct *ps, int depth, uint32 *data32)
{
	char *q = prs_mem_get(ps, sizeof(uint32));
	if (q == NULL)
		return False;

	if (UNMARSHALLING(ps)) {
		if (ps->bigendian_data)
			*data32 = RIVAL(q,0);
		else
			*data32 = IVAL(q,0);
	} else {
		if (ps->bigendian_data)
			RSIVAL(q,0,*data32);
		else
			SIVAL(q,0,*data32);
	}

	DEBUGADD(5,("%s%04x %s: %08x\n", tab_depth(5,depth), ps->data_offset, name, *data32));

	ps->data_offset += sizeof(uint32);

	return True;
}

/*******************************************************************
 Stream an int32.
 ********************************************************************/

bool prs_int32(const char *name, prs_struct *ps, int depth, int32 *data32)
{
	char *q = prs_mem_get(ps, sizeof(int32));
	if (q == NULL)
		return False;

	if (UNMARSHALLING(ps)) {
		if (ps->bigendian_data)
			*data32 = RIVALS(q,0);
		else
			*data32 = IVALS(q,0);
	} else {
		if (ps->bigendian_data)
			RSIVALS(q,0,*data32);
		else
			SIVALS(q,0,*data32);
	}

	DEBUGADD(5,("%s%04x %s: %08x\n", tab_depth(5,depth), ps->data_offset, name, *data32));

	ps->data_offset += sizeof(int32);

	return True;
}

/*******************************************************************
 Stream a uint64_struct
 ********************************************************************/
bool prs_uint64(const char *name, prs_struct *ps, int depth, uint64 *data64)
{
	if (UNMARSHALLING(ps)) {
		uint32 high, low;

		if (!prs_uint32(name, ps, depth+1, &low))
			return False;

		if (!prs_uint32(name, ps, depth+1, &high))
			return False;

		*data64 = ((uint64_t)high << 32) + low;

		return True;
	} else {
		uint32 high = (*data64) >> 32, low = (*data64) & 0xFFFFFFFF;
		return prs_uint32(name, ps, depth+1, &low) &&
			   prs_uint32(name, ps, depth+1, &high);
	}
}

/*******************************************************************
 Stream a DCE error code
 ********************************************************************/

bool prs_dcerpc_status(const char *name, prs_struct *ps, int depth, NTSTATUS *status)
{
	char *q = prs_mem_get(ps, sizeof(uint32));
	if (q == NULL)
		return False;

	if (UNMARSHALLING(ps)) {
		if (ps->bigendian_data)
			*status = NT_STATUS(RIVAL(q,0));
		else
			*status = NT_STATUS(IVAL(q,0));
	} else {
		if (ps->bigendian_data)
			RSIVAL(q,0,NT_STATUS_V(*status));
		else
			SIVAL(q,0,NT_STATUS_V(*status));
	}

	DEBUGADD(5,("%s%04x %s: %s\n", tab_depth(5,depth), ps->data_offset, name,
		 dcerpc_errstr(talloc_tos(), NT_STATUS_V(*status))));

	ps->data_offset += sizeof(uint32);

	return True;
}

/******************************************************************
 Stream an array of uint8s. Length is number of uint8s.
 ********************************************************************/

bool prs_uint8s(bool charmode, const char *name, prs_struct *ps, int depth, uint8 *data8s, int len)
{
	int i;
	char *q = prs_mem_get(ps, len);
	if (q == NULL)
		return False;

	if (UNMARSHALLING(ps)) {
		for (i = 0; i < len; i++)
			data8s[i] = CVAL(q,i);
	} else {
		for (i = 0; i < len; i++)
			SCVAL(q, i, data8s[i]);
	}

	DEBUGADD(5,("%s%04x %s: ", tab_depth(5,depth), ps->data_offset ,name));
	if (charmode)
		print_asc(5, (unsigned char*)data8s, len);
	else {
		for (i = 0; i < len; i++)
			DEBUGADD(5,("%02x ", data8s[i]));
	}
	DEBUGADD(5,("\n"));

	ps->data_offset += len;

	return True;
}

/******************************************************************
 Stream an array of uint16s. Length is number of uint16s.
 ********************************************************************/

bool prs_uint16s(bool charmode, const char *name, prs_struct *ps, int depth, uint16 *data16s, int len)
{
	int i;
	char *q = prs_mem_get(ps, len * sizeof(uint16));
	if (q == NULL)
		return False;

	if (UNMARSHALLING(ps)) {
		if (ps->bigendian_data) {
			for (i = 0; i < len; i++)
				data16s[i] = RSVAL(q, 2*i);
		} else {
			for (i = 0; i < len; i++)
				data16s[i] = SVAL(q, 2*i);
		}
	} else {
		if (ps->bigendian_data) {
			for (i = 0; i < len; i++)
				RSSVAL(q, 2*i, data16s[i]);
		} else {
			for (i = 0; i < len; i++)
				SSVAL(q, 2*i, data16s[i]);
		}
	}

	DEBUGADD(5,("%s%04x %s: ", tab_depth(5,depth), ps->data_offset, name));
	if (charmode)
		print_asc(5, (unsigned char*)data16s, 2*len);
	else {
		for (i = 0; i < len; i++)
			DEBUGADD(5,("%04x ", data16s[i]));
	}
	DEBUGADD(5,("\n"));

	ps->data_offset += (len * sizeof(uint16));

	return True;
}

/******************************************************************
 Stream an array of uint32s. Length is number of uint32s.
 ********************************************************************/

bool prs_uint32s(bool charmode, const char *name, prs_struct *ps, int depth, uint32 *data32s, int len)
{
	int i;
	char *q = prs_mem_get(ps, len * sizeof(uint32));
	if (q == NULL)
		return False;

	if (UNMARSHALLING(ps)) {
		if (ps->bigendian_data) {
			for (i = 0; i < len; i++)
				data32s[i] = RIVAL(q, 4*i);
		} else {
			for (i = 0; i < len; i++)
				data32s[i] = IVAL(q, 4*i);
		}
	} else {
		if (ps->bigendian_data) {
			for (i = 0; i < len; i++)
				RSIVAL(q, 4*i, data32s[i]);
		} else {
			for (i = 0; i < len; i++)
				SIVAL(q, 4*i, data32s[i]);
		}
	}

	DEBUGADD(5,("%s%04x %s: ", tab_depth(5,depth), ps->data_offset, name));
	if (charmode)
		print_asc(5, (unsigned char*)data32s, 4*len);
	else {
		for (i = 0; i < len; i++)
			DEBUGADD(5,("%08x ", data32s[i]));
	}
	DEBUGADD(5,("\n"));

	ps->data_offset += (len * sizeof(uint32));

	return True;
}

/*******************************************************************
 Stream a unicode  null-terminated string. As the string is already
 in little-endian format then do it as a stream of bytes.
 ********************************************************************/

bool prs_unistr(const char *name, prs_struct *ps, int depth, UNISTR *str)
{
	unsigned int len = 0;
	unsigned char *p = (unsigned char *)str->buffer;
	uint8 *start;
	char *q;
	uint32 max_len;
	uint16* ptr;

	if (MARSHALLING(ps)) {

		for(len = 0; str->buffer[len] != 0; len++)
			;

		q = prs_mem_get(ps, (len+1)*2);
		if (q == NULL)
			return False;

		start = (uint8*)q;

		for(len = 0; str->buffer[len] != 0; len++) {
			if(ps->bigendian_data) {
				/* swap bytes - p is little endian, q is big endian. */
				q[0] = (char)p[1];
				q[1] = (char)p[0];
				p += 2;
				q += 2;
			} 
			else 
			{
				q[0] = (char)p[0];
				q[1] = (char)p[1];
				p += 2;
				q += 2;
			}
		}

		/*
		 * even if the string is 'empty' (only an \0 char)
		 * at this point the leading \0 hasn't been parsed.
		 * so parse it now
		 */

		q[0] = 0;
		q[1] = 0;
		q += 2;

		len++;

		DEBUGADD(5,("%s%04x %s: ", tab_depth(5,depth), ps->data_offset, name));
		print_asc(5, (unsigned char*)start, 2*len);	
		DEBUGADD(5, ("\n"));
	}
	else { /* unmarshalling */
	
		uint32 alloc_len = 0;
		q = ps->data_p + prs_offset(ps);

		/*
		 * Work out how much space we need and talloc it.
		 */
		max_len = (ps->buffer_size - ps->data_offset)/sizeof(uint16);

		/* the test of the value of *ptr helps to catch the circumstance
		   where we have an emtpty (non-existent) string in the buffer */
		for ( ptr = (uint16 *)q; *ptr++ && (alloc_len <= max_len); alloc_len++)
			/* do nothing */ 
			;

		if (alloc_len < max_len)
			alloc_len += 1;

		/* should we allocate anything at all? */
		str->buffer = PRS_ALLOC_MEM(ps,uint16,alloc_len);
		if ((str->buffer == NULL) && (alloc_len > 0))
			return False;

		p = (unsigned char *)str->buffer;

		len = 0;
		/* the (len < alloc_len) test is to prevent us from overwriting
		   memory that is not ours...if we get that far, we have a non-null
		   terminated string in the buffer and have messed up somewhere */
		while ((len < alloc_len) && (*(uint16 *)q != 0)) {
			if(ps->bigendian_data) 
			{
				/* swap bytes - q is big endian, p is little endian. */
				p[0] = (unsigned char)q[1];
				p[1] = (unsigned char)q[0];
				p += 2;
				q += 2;
			} else {

				p[0] = (unsigned char)q[0];
				p[1] = (unsigned char)q[1];
				p += 2;
				q += 2;
			}

			len++;
		} 
		if (len < alloc_len) {
			/* NULL terminate the UNISTR */
			str->buffer[len++] = '\0';
		}

		DEBUGADD(5,("%s%04x %s: ", tab_depth(5,depth), ps->data_offset, name));
		print_asc(5, (unsigned char*)str->buffer, 2*len);	
		DEBUGADD(5, ("\n"));
	}

	/* set the offset in the prs_struct; 'len' points to the
	   terminiating NULL in the UNISTR so we need to go one more
	   uint16 */
	ps->data_offset += (len)*2;
	
	return True;
}

/*******************************************************************
creates a new prs_struct containing a DATA_BLOB
********************************************************************/
bool prs_init_data_blob(prs_struct *prs, DATA_BLOB *blob, TALLOC_CTX *mem_ctx)
{
	if (!prs_init( prs, RPC_MAX_PDU_FRAG_LEN, mem_ctx, MARSHALL ))
		return False;


	if (!prs_copy_data_in(prs, (char *)blob->data, blob->length))
		return False;

	return True;
}

/*******************************************************************
return the contents of a prs_struct in a DATA_BLOB
********************************************************************/
bool prs_data_blob(prs_struct *prs, DATA_BLOB *blob, TALLOC_CTX *mem_ctx)
{
	blob->length = prs_data_size(prs);
	blob->data = (uint8 *)TALLOC_ZERO_SIZE(mem_ctx, blob->length);
	
	/* set the pointer at the end of the buffer */
	prs_set_offset( prs, prs_data_size(prs) );

	if (!prs_copy_all_data_out((char *)blob->data, prs))
		return False;
	
	return True;
}