1 /*
2 * simple_buffer.c
3 * Copyright : Kyle Harper
4 * License : Follows same licensing as the lz4.c/lz4.h program at any given time. Currently, BSD 2.
5 * Description: Example program to demonstrate the basic usage of the compress/decompress functions within lz4.c/lz4.h.
6 * The functions you'll likely want are LZ4_compress_default and LZ4_decompress_safe. Both of these are documented in
7 * the lz4.h header file; I recommend reading them.
8 */
9
10 /* Includes, for Power! */
11 #include "lz4.h" // This is all that is required to expose the prototypes for basic compression and decompression.
12 #include <stdio.h> // For printf()
13 #include <string.h> // For memcmp()
14 #include <stdlib.h> // For exit()
15
16 /*
17 * Easy show-error-and-bail function.
18 */
run_screaming(const char * message,const int code)19 void run_screaming(const char *message, const int code) {
20 printf("%s\n", message);
21 exit(code);
22 return;
23 }
24
25
26 /*
27 * main
28 */
main(void)29 int main(void) {
30 /* Introduction */
31 // Below we will have a Compression and Decompression section to demonstrate.
32 // There are a few important notes before we start:
33 // 1) The return codes of LZ4_ functions are important.
34 // Read lz4.h if you're unsure what a given code means.
35 // 2) LZ4 uses char* pointers in all LZ4_ functions.
36 // This is baked into the API and probably not going to change.
37 // If your program uses pointers that are unsigned char*, void*, or otherwise different,
38 // you may need to do some casting or set the right -W compiler flags to ignore those warnings (e.g.: -Wno-pointer-sign).
39
40 /* Compression */
41 // We'll store some text into a variable pointed to by *src to be compressed later.
42 const char* const src = "Lorem ipsum dolor sit amet, consectetur adipiscing elit.";
43 // The compression function needs to know how many bytes exist. Since we're using a string, we can use strlen() + 1 (for \0).
44 const int src_size = (int)(strlen(src) + 1);
45 // LZ4 provides a function that will tell you the maximum size of compressed output based on input data via LZ4_compressBound().
46 const int max_dst_size = LZ4_compressBound(src_size);
47 // We will use that size for our destination boundary when allocating space.
48 char* compressed_data = malloc(max_dst_size);
49 if (compressed_data == NULL)
50 run_screaming("Failed to allocate memory for *compressed_data.", 1);
51 // That's all the information and preparation LZ4 needs to compress *src into *compressed_data.
52 // Invoke LZ4_compress_default now with our size values and pointers to our memory locations.
53 // Save the return value for error checking.
54 const int compressed_data_size = LZ4_compress_default(src, compressed_data, src_size, max_dst_size);
55 // Check return_value to determine what happened.
56 if (compressed_data_size < 0)
57 run_screaming("A negative result from LZ4_compress_default indicates a failure trying to compress the data. See exit code (echo $?) for value returned.", compressed_data_size);
58 if (compressed_data_size == 0)
59 run_screaming("A result of 0 means compression worked, but was stopped because the destination buffer couldn't hold all the information.", 1);
60 if (compressed_data_size > 0)
61 printf("We successfully compressed some data!\n");
62 // Not only does a positive return_value mean success, the value returned == the number of bytes required.
63 // You can use this to realloc() *compress_data to free up memory, if desired. We'll do so just to demonstrate the concept.
64 compressed_data = (char *)realloc(compressed_data, compressed_data_size);
65 if (compressed_data == NULL)
66 run_screaming("Failed to re-alloc memory for compressed_data. Sad :(", 1);
67
68 /* Decompression */
69 // Now that we've successfully compressed the information from *src to *compressed_data, let's do the opposite! We'll create a
70 // *new_src location of size src_size since we know that value.
71 char* const regen_buffer = malloc(src_size);
72 if (regen_buffer == NULL)
73 run_screaming("Failed to allocate memory for *regen_buffer.", 1);
74 // The LZ4_decompress_safe function needs to know where the compressed data is, how many bytes long it is,
75 // where the regen_buffer memory location is, and how large regen_buffer (uncompressed) output will be.
76 // Again, save the return_value.
77 const int decompressed_size = LZ4_decompress_safe(compressed_data, regen_buffer, compressed_data_size, src_size);
78 free(compressed_data); /* no longer useful */
79 if (decompressed_size < 0)
80 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);
81 if (decompressed_size == 0)
82 run_screaming("I'm not sure this function can ever return 0. Documentation in lz4.h doesn't indicate so.", 1);
83 if (decompressed_size > 0)
84 printf("We successfully decompressed some data!\n");
85 // Not only does a positive return value mean success,
86 // value returned == number of bytes regenerated from compressed_data stream.
87
88 /* Validation */
89 // We should be able to compare our original *src with our *new_src and be byte-for-byte identical.
90 if (memcmp(src, regen_buffer, src_size) != 0)
91 run_screaming("Validation failed. *src and *new_src are not identical.", 1);
92 printf("Validation done. The string we ended up with is:\n%s\n", regen_buffer);
93 return 0;
94 }
95