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 /* =========================================================================
    ub-example.c -- Example code for UsefulBuf

    Copyright (c) 2022, Laurence Lundblade. All rights reserved.

    SPDX-License-Identifier: BSD-3-Clause

    See BSD-3-Clause license in README.md

    Created on 4/8/22
   ========================================================================== */

 #include "ub-example.h"

 #include "UsefulBuf.h"


 /*
  * A considerable number of the security issues with C code come from
  * mistakes made with pointers and lengths.  UsefulBuf adopts a
  * convention that a pointer and length *always* go together to help
  * mitigate this.  With UsefulBuf there are never pointers without
  * lengths, so you always know how big a buffer or some binary data
  * is.
  *
  * C99 allows passing structures so a structure is used. Compilers are
  * smart these days so the object code produced is little different
  * than passing two separate parameters. Passing structures also makes
  * the interfaces prettier. Assignments of structures also can make
  * code prettier.
  *
  * ALong with the UsefulBuf structure, there are a bunch of (tested!)
  * functions to manipulate them so code using it may have no pointer
  * manipulation at all.
  *
  * Constness is also a useful and desirous thing. See
  * https://stackoverflow.com/questions/117293/use-of-const-for-function-parameters
  * Keeping const distinct from non-const is helpful when reading the
  * code and helps avoid some coding mistakes.  In this example the
  * buffers filled in with data are const and the ones that are
  * to-be-filled in are not const.
  *
  * This contrived example copies data from input to output expanding
  * bytes with the value 'x' to 'xx'.
  *
  * Input -- This is the pointer and length of the input, the bytes to
  * copy. Note that UsefulBufC.ptr is a const void * indicating that
  * input data won't be changed by this function.  There is a "C" in
  * "UsefulBufC "to indicate the value is const.  The length here is
  * the length of the valid input data. Note also that the parameter
  * Input is const, so this is fully const and clearly an [in]
  * parameter.
  *
  * OutputBuffer -- This is a pointer and length of the memory to be
  * used to store the output. The correct length here is critical for
  * code security. Note that UsefulBuf.ptr is void *, it is not const
  * indicating data can be written to it. Note that the parameter
  * itself *is* const indicating that the code below will not point
  * this to some other buffer or change the length and clearly marking
  * it as an [in] parameter.
  *
  * Output -- This is the interesting and unusual one. To stay
  * consistent with always pairing a length and a pointer, this is
  * returned as a UsefulBuC. Also, to stay consistent with valid data
  * being const, it is a UsefulBufC, not a UsefulBuf. It is however, an
  * [out] parameter so the parameter is a pointer to a UsefulBufC.
  *
  * In this case and most cases, the pointer in Output->ptr will be the
  * same as OutputBuffer.ptr. This may seem redundant, but there are a
  * few reasons for it. First, is the goal of always pairing a pointer
  * and a length.  Second is being more strict and correct with
  * constness. Third is the code hygiene and clarity of having
  * variables for to-be-filled buffers be distinct from those
  * containing valid data. Fourth, there are no [in,out] parameters,
  * only [in] parameters and [out] parameters (the to-be-filled-in
  * buffer is considered an [in] parameter).
  *
  * Note that the compiler will be smart and should generate pretty
  * much the same code as for a traditional interface. On x86 with
  * gcc-11 and no stack guards, the UB code is 81 bytes and the
  * traditional code is 77 bytes.
  *
  * Finally, this supports computing of the length of the would-be
  * output without actually doing any outputting. Pass {NULL, SIZE_MAX}
  * for the OutputBuffer and the length will be returned in Output.
  */
 int
 ExpandxUB(const UsefulBufC   Input,
           const UsefulBuf    OutputBuffer,
           UsefulBufC        *Output)
 {
     size_t nInputPosition;
     size_t nOutputPosition;

     nOutputPosition = 0;

     /* Loop over all the bytes in Input */
     for(nInputPosition = 0; nInputPosition < Input.len; nInputPosition++) {
         const uint8_t nInputByte = ((uint8_t*)Input.ptr)[nInputPosition];

         /* Copy every byte */
         if(OutputBuffer.ptr != NULL) {
             ((uint8_t *)OutputBuffer.ptr)[nOutputPosition] = nInputByte;
         }
         nOutputPosition++;
         if(nOutputPosition >= OutputBuffer.len) {
             return -1;
         }

         /* Double output 'x' because that is what this contrived example does */
         if(nInputByte== 'x') {
             if(OutputBuffer.ptr != NULL) {
                 ((uint8_t *)OutputBuffer.ptr)[nOutputPosition] = 'x';
             }
             nOutputPosition++;
             if(nOutputPosition >= OutputBuffer.len) {
                 return -1;
             }
         }
     }

     *Output = (UsefulBufC){OutputBuffer.ptr, nOutputPosition};

     return 0; /* success */
 }


 /* This is the more tradional way to implement this. */
 int
 ExpandxTraditional(const uint8_t  *pInputPointer,
                    const size_t    uInputLength,
                    uint8_t        *pOutputBuffer,
                    const size_t    uOutputBufferLength,
                    size_t         *puOutputLength)
 {
     size_t nInputPosition;
     size_t nOutputPosition;

     nOutputPosition = 0;

     /* Loop over all the bytes in Input */
     for(nInputPosition = 0; nInputPosition < uInputLength; nInputPosition++) {
         const uint8_t nInputByte = ((uint8_t*)pInputPointer)[nInputPosition];

         /* Copy every byte */
         if(pOutputBuffer != NULL) {
             ((uint8_t *)pOutputBuffer)[nOutputPosition] = nInputByte;
         }
         nOutputPosition++;
         if(nOutputPosition >= uOutputBufferLength) {
             return -1;
         }

         /* Double output 'x' because that is what this contrived example does */
         if(nInputByte== 'x') {
             if(pOutputBuffer != NULL) {
                 ((uint8_t *)pOutputBuffer)[nOutputPosition] = 'x';
             }
             nOutputPosition++;
             if(nOutputPosition >= uOutputBufferLength) {
                 return -1;
             }
         }
     }

    *puOutputLength = nOutputPosition;

     return 0; /* success */
 }


 /*
  * Here's an example of going from a traditional interface
  * interface to a UsefulBuf interface.
  */
 int
 ExpandxTraditionalAdaptor(const uint8_t  *pInputPointer,
                           size_t          uInputLength,
                           uint8_t        *pOutputBuffer,
                           size_t          uOutputBufferLength,
                           size_t         *puOutputLength)
 {
     UsefulBufC  Input;
     UsefulBuf   OutputBuffer;
     UsefulBufC  Output;
     int         nReturn;

     Input = (UsefulBufC){pInputPointer, uInputLength};
     OutputBuffer = (UsefulBuf){pOutputBuffer, uOutputBufferLength};

     nReturn = ExpandxUB(Input, OutputBuffer, &Output);

     *puOutputLength = Output.len;

     return nReturn;
 }


 /* Here's an example for going from a UsefulBuf interface
  to a traditional interface. */
 int
 ExpandxUBAdaptor(const UsefulBufC   Input,
                  const UsefulBuf    OutputBuffer,
                  UsefulBufC        *Output)
 {
    Output->ptr = OutputBuffer.ptr;

    return ExpandxTraditional(Input.ptr, Input.len,
                              OutputBuffer.ptr, OutputBuffer.len,
                            &(Output->len));
 }


 #define INPUT "xyz123xyz"

 int32_t RunUsefulBufExample()
 {
    /* ------------ UsefulBuf examples ------------- */
    UsefulBufC Input = UsefulBuf_FROM_SZ_LITERAL(INPUT);

    /* This macros makes a 20 byte buffer on the stack. It also makes
     * a UsefulBuf on the stack. It sets up the UsefulBuf to point to
     * the 20 byte buffer and sets it's length to 20 bytes. This
     * is the empty, to-be-filled in memory for the output. It is not
     * const. */
    MakeUsefulBufOnStack(OutBuf, sizeof(INPUT) * 2);

    /* This is were the pointer and the length of the completed output
     * will be placed. Output.ptr is a pointer to const bytes. */
    UsefulBufC           Output;

    ExpandxUB(Input, OutBuf, &Output);

    ExpandxUBAdaptor(Input, OutBuf, &Output);


    /* ------ Get Size example  -------- */
    ExpandxUB(Input, (UsefulBuf){NULL, SIZE_MAX}, &Output);

    /* Size is in Output.len */


    /* ---------- Traditional examples (for comparison) --------- */
    uint8_t puBuffer[sizeof(INPUT) * 2];
    size_t  uOutputSize;

    ExpandxTraditional((const uint8_t *)INPUT, sizeof(INPUT),
                      puBuffer, sizeof(puBuffer),
                      &uOutputSize);


    ExpandxTraditionalAdaptor((const uint8_t *)INPUT, sizeof(INPUT),
                             puBuffer, sizeof(puBuffer),
                            &uOutputSize);

    return 0;
 }
	/* =========================================================================
	ub-example.c -- Example code for UsefulBuf

	Copyright (c) 2022, Laurence Lundblade. All rights reserved.

	SPDX-License-Identifier: BSD-3-Clause

	See BSD-3-Clause license in README.md

	Created on 4/8/22
	========================================================================== */

	#include "ub-example.h"

	#include "UsefulBuf.h"


	/*
	* A considerable number of the security issues with C code come from
	* mistakes made with pointers and lengths. UsefulBuf adopts a
	* convention that a pointer and length always go together to help
	* mitigate this. With UsefulBuf there are never pointers without
	* lengths, so you always know how big a buffer or some binary data
	* is.
	*
	* C99 allows passing structures so a structure is used. Compilers are
	* smart these days so the object code produced is little different
	* than passing two separate parameters. Passing structures also makes
	* the interfaces prettier. Assignments of structures also can make
	* code prettier.
	*
	* ALong with the UsefulBuf structure, there are a bunch of (tested!)
	* functions to manipulate them so code using it may have no pointer
	* manipulation at all.
	*
	* Constness is also a useful and desirous thing. See
	* https://stackoverflow.com/questions/117293/use-of-const-for-function-parameters
	* Keeping const distinct from non-const is helpful when reading the
	* code and helps avoid some coding mistakes. In this example the
	* buffers filled in with data are const and the ones that are
	* to-be-filled in are not const.
	*
	* This contrived example copies data from input to output expanding
	* bytes with the value 'x' to 'xx'.
	*
	* Input -- This is the pointer and length of the input, the bytes to
	* copy. Note that UsefulBufC.ptr is a const void * indicating that
	* input data won't be changed by this function. There is a "C" in
	* "UsefulBufC "to indicate the value is const. The length here is
	* the length of the valid input data. Note also that the parameter
	* Input is const, so this is fully const and clearly an [in]
	* parameter.
	*
	* OutputBuffer -- This is a pointer and length of the memory to be
	* used to store the output. The correct length here is critical for
	* code security. Note that UsefulBuf.ptr is void *, it is not const
	* indicating data can be written to it. Note that the parameter
	* itself is const indicating that the code below will not point
	* this to some other buffer or change the length and clearly marking
	* it as an [in] parameter.
	*
	* Output -- This is the interesting and unusual one. To stay
	* consistent with always pairing a length and a pointer, this is
	* returned as a UsefulBuC. Also, to stay consistent with valid data
	* being const, it is a UsefulBufC, not a UsefulBuf. It is however, an
	* [out] parameter so the parameter is a pointer to a UsefulBufC.
	*
	* In this case and most cases, the pointer in Output->ptr will be the
	* same as OutputBuffer.ptr. This may seem redundant, but there are a
	* few reasons for it. First, is the goal of always pairing a pointer
	* and a length. Second is being more strict and correct with
	* constness. Third is the code hygiene and clarity of having
	* variables for to-be-filled buffers be distinct from those
	* containing valid data. Fourth, there are no [in,out] parameters,
	* only [in] parameters and [out] parameters (the to-be-filled-in
	* buffer is considered an [in] parameter).
	*
	* Note that the compiler will be smart and should generate pretty
	* much the same code as for a traditional interface. On x86 with
	* gcc-11 and no stack guards, the UB code is 81 bytes and the
	* traditional code is 77 bytes.
	*
	* Finally, this supports computing of the length of the would-be
	* output without actually doing any outputting. Pass {NULL, SIZE_MAX}
	* for the OutputBuffer and the length will be returned in Output.
	*/
	int
	ExpandxUB(const UsefulBufC Input,
	const UsefulBuf OutputBuffer,
	UsefulBufC *Output)
	{
	size_t nInputPosition;
	size_t nOutputPosition;

	nOutputPosition = 0;

	/* Loop over all the bytes in Input */
	for(nInputPosition = 0; nInputPosition < Input.len; nInputPosition++) {
	const uint8_t nInputByte = ((uint8_t*)Input.ptr)[nInputPosition];

	/* Copy every byte */
	if(OutputBuffer.ptr != NULL) {
	((uint8_t *)OutputBuffer.ptr)[nOutputPosition] = nInputByte;
	}
	nOutputPosition++;
	if(nOutputPosition >= OutputBuffer.len) {
	return -1;
	}

	/* Double output 'x' because that is what this contrived example does */
	if(nInputByte== 'x') {
	if(OutputBuffer.ptr != NULL) {
	((uint8_t *)OutputBuffer.ptr)[nOutputPosition] = 'x';
	}
	nOutputPosition++;
	if(nOutputPosition >= OutputBuffer.len) {
	return -1;
	}
	}
	}

	*Output = (UsefulBufC){OutputBuffer.ptr, nOutputPosition};

	return 0; /* success */
	}


	/* This is the more tradional way to implement this. */
	int
	ExpandxTraditional(const uint8_t *pInputPointer,
	const size_t uInputLength,
	uint8_t *pOutputBuffer,
	const size_t uOutputBufferLength,
	size_t *puOutputLength)
	{
	size_t nInputPosition;
	size_t nOutputPosition;

	nOutputPosition = 0;

	/* Loop over all the bytes in Input */
	for(nInputPosition = 0; nInputPosition < uInputLength; nInputPosition++) {
	const uint8_t nInputByte = ((uint8_t*)pInputPointer)[nInputPosition];

	/* Copy every byte */
	if(pOutputBuffer != NULL) {
	((uint8_t *)pOutputBuffer)[nOutputPosition] = nInputByte;
	}
	nOutputPosition++;
	if(nOutputPosition >= uOutputBufferLength) {
	return -1;
	}

	/* Double output 'x' because that is what this contrived example does */
	if(nInputByte== 'x') {
	if(pOutputBuffer != NULL) {
	((uint8_t *)pOutputBuffer)[nOutputPosition] = 'x';
	}
	nOutputPosition++;
	if(nOutputPosition >= uOutputBufferLength) {
	return -1;
	}
	}
	}

	*puOutputLength = nOutputPosition;

	return 0; /* success */
	}


	/*
	* Here's an example of going from a traditional interface
	* interface to a UsefulBuf interface.
	*/
	int
	ExpandxTraditionalAdaptor(const uint8_t *pInputPointer,
	size_t uInputLength,
	uint8_t *pOutputBuffer,
	size_t uOutputBufferLength,
	size_t *puOutputLength)
	{
	UsefulBufC Input;
	UsefulBuf OutputBuffer;
	UsefulBufC Output;
	int nReturn;

	Input = (UsefulBufC){pInputPointer, uInputLength};
	OutputBuffer = (UsefulBuf){pOutputBuffer, uOutputBufferLength};

	nReturn = ExpandxUB(Input, OutputBuffer, &Output);

	*puOutputLength = Output.len;

	return nReturn;
	}


	/* Here's an example for going from a UsefulBuf interface
	to a traditional interface. */
	int
	ExpandxUBAdaptor(const UsefulBufC Input,
	const UsefulBuf OutputBuffer,
	UsefulBufC *Output)
	{
	Output->ptr = OutputBuffer.ptr;

	return ExpandxTraditional(Input.ptr, Input.len,
	OutputBuffer.ptr, OutputBuffer.len,
	&(Output->len));
	}



	#define INPUT "xyz123xyz"

	int32_t RunUsefulBufExample()
	{
	/* ------------ UsefulBuf examples ------------- */
	UsefulBufC Input = UsefulBuf_FROM_SZ_LITERAL(INPUT);

	/* This macros makes a 20 byte buffer on the stack. It also makes
	* a UsefulBuf on the stack. It sets up the UsefulBuf to point to
	* the 20 byte buffer and sets it's length to 20 bytes. This
	* is the empty, to-be-filled in memory for the output. It is not
	* const. */
	MakeUsefulBufOnStack(OutBuf, sizeof(INPUT) * 2);

	/* This is were the pointer and the length of the completed output
	* will be placed. Output.ptr is a pointer to const bytes. */
	UsefulBufC Output;

	ExpandxUB(Input, OutBuf, &Output);

	ExpandxUBAdaptor(Input, OutBuf, &Output);



	/* ------ Get Size example -------- */
	ExpandxUB(Input, (UsefulBuf){NULL, SIZE_MAX}, &Output);

	/* Size is in Output.len */



	/* ---------- Traditional examples (for comparison) --------- */
	uint8_t puBuffer[sizeof(INPUT) * 2];
	size_t uOutputSize;

	ExpandxTraditional((const uint8_t *)INPUT, sizeof(INPUT),
	puBuffer, sizeof(puBuffer),
	&uOutputSize);


	ExpandxTraditionalAdaptor((const uint8_t *)INPUT, sizeof(INPUT),
	puBuffer, sizeof(puBuffer),
	&uOutputSize);

	return 0;
	}