Several changes to address a few concerns from Yann. See Google Group LZ4c topic 'Reusing compression/decompression resources' for details.

1 files changed, 90 insertions, 0 deletions

diff --git a/examples/simple_buffer.c b/examples/simple_buffer.c
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+/*
+ * simple_buffer.c
+ * Copyright  : Kyle Harper
+ * License    : Follows same licensing as the lz4.c/lz4.h program at any given time.  Currently, BSD 2.
+ * Description: Example program to demonstrate the basic usage of the compress/decompress functions within lz4.c/lz4.h.
+ *              The functions you'll likely want are LZ4_compress_default and LZ4_decompress_safe.  Both of these are documented in
+ *              the lz4.h header file; I recommend reading them.
+ */
+
+/* Includes, for Power! */
+#include "lz4.h"    // This is all that is required to expose the prototypes for basic compression and decompression.
+#include <stdio.h>  // For printf()
+#include <string.h> // For memcmp()
+#include <stdlib.h> // For exit()
+
+/*
+ * Easy show-error-and-bail function.
+ */
+void run_screaming(const char *message, const int code) {
+  printf("%s\n", message);
+  exit(code);
+  return;
+}
+
+
+/*
+ * main
+ */
+int main(void) {
+  /* Introduction */
+  // Below we will have a Compression and Decompression section to demonstrate.  There are a few important notes before we start:
+  //   1) The return codes of LZ4_ functions are important.  Read lz4.h if you're unsure what a given code means.
+  //   2) LZ4 uses char* pointers in all LZ4_ functions.  This is baked into the API and probably not going to change.  If your
+  //      program uses pointers that are unsigned char*, void*, or otherwise different you may need to do some casting or set the
+  //      right -W compiler flags to ignore those warnings (e.g.: -Wno-pointer-sign).
+
+  /* Compression */
+  // We'll store some text into a variable pointed to by *src to be compressed later.
+  const char *src = "Lorem ipsum dolor sit amet, consectetur adipiscing elit.";
+  // The compression function needs to know how many bytes of exist.  Since we're using a string, we can use strlen() + 1 (for \0).
+  const size_t src_size = strlen(src) + 1;
+  // LZ4 provides a function that will tell you the maximum size of compressed output based on input data via LZ4_compressBound().
+  const size_t max_dst_size = LZ4_compressBound(src_size);
+  // We will use that size for our destination boundary when allocating space.
+  char *compressed_data = malloc(max_dst_size);
+  if (compressed_data == NULL)
+    run_screaming("Failed to allocate memory for *compressed_data.", 1);
+  // That's all the information and preparation LZ4 needs to compress *src into *compressed_data.  Invoke LZ4_compress_default now
+  // with our size values and pointers to our memory locations.  Save the return value for error checking.
+  int return_value = 0;
+  return_value = LZ4_compress_default(src, compressed_data, src_size, max_dst_size);
+  // Check return_value to determine what happened.
+  if (return_value < 0)
+    run_screaming("A negative result from LZ4_compress_default indicates a failure trying to compress the data.  See exit code (echo $?) for value returned.", return_value);
+  if (return_value == 0)
+    run_screaming("A result of 0 means compression worked, but was stopped because the destination buffer couldn't hold all the information.", 1);
+  if (return_value > 0)
+    printf("We successfully compressed some data!\n");
+  // Not only does a positive return_value mean success, the value returned == the number of bytes required.  You can use this to
+  // realloc() *compress_data to free up memory, if desired.  We'll do so just to demonstrate the concept.
+  const size_t compressed_data_size = return_value;
+  compressed_data = (char *)realloc(compressed_data, compressed_data_size);
+  if (compressed_data == NULL)
+    run_screaming("Failed to re-alloc memory for compressed_data.  Sad :(", 1);
+
+  /* Decompression */
+  // Now that we've successfully compressed the information from *src to *compressed_data, let's do the opposite!  We'll create a
+  // *new_src location of size src_size since we know that value.
+  char *new_src = malloc(src_size);
+  if (new_src == NULL)
+    run_screaming("Failed to allocate memory for *new_src.", 1);
+  // The LZ4_decompress_safe function needs to know where the compressed data is, how many bytes long it is, where the new_src
+  // memory location is, and how large the new_src (uncompressed) output will be.  Again, save the return_value.
+  return_value = LZ4_decompress_safe(compressed_data, new_src, compressed_data_size, src_size);
+  if (return_value < 0)
+    run_screaming("A negative result from LZ4_decompress_fast indicates a failure trying to decompress the data.  See exit code (echo $?) for value returned.", return_value);
+  if (return_value == 0)
+    run_screaming("I'm not sure this function can ever return 0.  Documentation in lz4.h doesn't indicate so.", 1);
+  if (return_value > 0)
+    printf("We successfully decompressed some data!\n");
+  // Not only does a positive return value mean success, the value returned == the number of bytes read from the compressed_data
+  // stream.  I'm not sure there's ever a time you'll need to know this in most cases...
+
+  /* Validation */
+  // We should be able to compare our original *src with our *new_src and be byte-for-byte identical.
+  if (memcmp(src, new_src, src_size) != 0)
+    run_screaming("Validation failed.  *src and *new_src are not identical.", 1);
+  printf("Validation done.  The string we ended up with is:\n%s\n", new_src);
+  return 0;
+}