99 lines
5.4 KiB
C
99 lines
5.4 KiB
C
/*
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* simple_buffer.c
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* Copyright : Kyle Harper
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* License : Follows same licensing as the lz4.c/lz4.h program at any given time. Currently, BSD 2.
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* Description: Example program to demonstrate the basic usage of the compress/decompress functions within lz4.c/lz4.h.
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* The functions you'll likely want are LZ4_compress_default and LZ4_decompress_safe.
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* Both of these are documented in the lz4.h header file; I recommend reading them.
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*/
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/* Dependencies */
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#include <stdio.h> // For printf()
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#include <string.h> // For memcmp()
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#include <stdlib.h> // For exit()
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#include "lz4.h" // This is all that is required to expose the prototypes for basic compression and decompression.
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/*
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* Simple show-error-and-bail function.
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*/
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void run_screaming(const char* message, const int code) {
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printf("%s \n", message);
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exit(code);
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}
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/*
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* main
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*/
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int main(void) {
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/* Introduction */
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// Below we will have a Compression and Decompression section to demonstrate.
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// There are a few important notes before we start:
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// 1) The return codes of LZ4_ functions are important.
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// Read lz4.h if you're unsure what a given code means.
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// 2) LZ4 uses char* pointers in all LZ4_ functions.
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// This is baked into the API and not going to change, for consistency.
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// If your program uses different pointer types,
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// you may need to do some casting or set the right -Wno compiler flags to ignore those warnings (e.g.: -Wno-pointer-sign).
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/* Compression */
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// We'll store some text into a variable pointed to by *src to be compressed later.
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const char* const src = "Lorem ipsum dolor sit amet, consectetur adipiscing elit.";
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// The compression function needs to know how many bytes exist. Since we're using a string, we can use strlen() + 1 (for \0).
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const int src_size = (int)(strlen(src) + 1);
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// LZ4 provides a function that will tell you the maximum size of compressed output based on input data via LZ4_compressBound().
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const int max_dst_size = LZ4_compressBound(src_size);
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// We will use that size for our destination boundary when allocating space.
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char* compressed_data = malloc((size_t)max_dst_size);
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if (compressed_data == NULL)
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run_screaming("Failed to allocate memory for *compressed_data.", 1);
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// That's all the information and preparation LZ4 needs to compress *src into *compressed_data.
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// Invoke LZ4_compress_default now with our size values and pointers to our memory locations.
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// Save the return value for error checking.
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const int compressed_data_size = LZ4_compress_default(src, compressed_data, src_size, max_dst_size);
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// Check return_value to determine what happened.
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if (compressed_data_size <= 0)
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run_screaming("A 0 or negative result from LZ4_compress_default() indicates a failure trying to compress the data. ", 1);
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if (compressed_data_size > 0)
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printf("We successfully compressed some data!\n");
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// Not only does a positive return_value mean success, the value returned == the number of bytes required.
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// You can use this to realloc() *compress_data to free up memory, if desired. We'll do so just to demonstrate the concept.
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compressed_data = (char *)realloc(compressed_data, (size_t)compressed_data_size);
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if (compressed_data == NULL)
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run_screaming("Failed to re-alloc memory for compressed_data. Sad :(", 1);
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/* Decompression */
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// Now that we've successfully compressed the information from *src to *compressed_data, let's do the opposite!
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// The decompression will need to know the compressed size, and an upper bound of the decompressed size.
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// In this example, we just re-use this information from previous section,
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// but in a real-world scenario, metadata must be transmitted to the decompression side.
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// Each implementation is in charge of this part. Oftentimes, it adds some header of its own.
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// Sometimes, the metadata can be extracted from the local context.
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// First, let's create a *new_src location of size src_size since we know that value.
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char* const regen_buffer = malloc(src_size);
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if (regen_buffer == NULL)
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run_screaming("Failed to allocate memory for *regen_buffer.", 1);
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// The LZ4_decompress_safe function needs to know where the compressed data is, how many bytes long it is,
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// where the regen_buffer memory location is, and how large regen_buffer (uncompressed) output will be.
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// Again, save the return_value.
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const int decompressed_size = LZ4_decompress_safe(compressed_data, regen_buffer, compressed_data_size, src_size);
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free(compressed_data); /* no longer useful */
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if (decompressed_size < 0)
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run_screaming("A negative result from LZ4_decompress_safe indicates a failure trying to decompress the data. See exit code (echo $?) for value returned.", decompressed_size);
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if (decompressed_size >= 0)
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printf("We successfully decompressed some data!\n");
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// Not only does a positive return value mean success,
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// value returned == number of bytes regenerated from compressed_data stream.
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if (decompressed_size != src_size)
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run_screaming("Decompressed data is different from original! \n", 1);
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/* Validation */
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// We should be able to compare our original *src with our *new_src and be byte-for-byte identical.
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if (memcmp(src, regen_buffer, src_size) != 0)
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run_screaming("Validation failed. *src and *new_src are not identical.", 1);
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printf("Validation done. The string we ended up with is:\n%s\n", regen_buffer);
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return 0;
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}
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