LZ4F_decompress requires a valid dctx state

This is now explicitly documented and asserted.
fix #927

3 files changed, 10 insertions, 7 deletions

diff --git a/lib/README.md b/lib/README.md
index ee5d3ba..318106d 100644
--- a/lib/README.md
+++ b/lib/README.md
@@ -49,7 +49,7 @@ and `LZ4F_PUBLISH_STATIC_FUNCTIONS`.
 The following build macro can be selected to adjust source code behavior at compilation time :
 
 - `LZ4_FAST_DEC_LOOP` : this triggers a speed optimized decompression loop, more powerful on modern cpus.
-  This loop works great on x86, x64 and aarch64 cpus, and is automatically enabled for them.
+  This loop works great on `x86`, `x64` and `aarch64` cpus, and is automatically enabled for them.
   It's also possible to enable or disable it manually, by passing `LZ4_FAST_DEC_LOOP=1` or `0` to the preprocessor.
   For example, with `gcc` : `-DLZ4_FAST_DEC_LOOP=1`,
   and with `make` : `CPPFLAGS+=-DLZ4_FAST_DEC_LOOP=1 make lz4`.
@@ -66,8 +66,8 @@ The following build macro can be selected to adjust source code behavior at comp
   Should this be a problem, it's generally possible to make the compiler ignore these warnings,
   for example with `-Wno-deprecated-declarations` on `gcc`,
   or `_CRT_SECURE_NO_WARNINGS` for Visual Studio.
-  Another project-specific method is to define `LZ4_DISABLE_DEPRECATE_WARNINGS`
-  before including the LZ4 header files.
+  This build macro offers another project-specific method
+  by defining `LZ4_DISABLE_DEPRECATE_WARNINGS` before including the LZ4 header files.
 
 - `LZ4_FORCE_SW_BITCOUNT` : by default, the compression algorithm tries to determine lengths
   by using bitcount instructions, generally implemented as fast single instructions in many cpus.
@@ -78,8 +78,8 @@ The following build macro can be selected to adjust source code behavior at comp
   but it can be legitimately considered for less common platforms.
 
 - `LZ4_ALIGN_TEST` : alignment test ensures that the memory area
-  passed as argument to become a compression state is suitable aligned.
-  This test can be disabled, if it proves flaky, by setting this value to 0.
+  passed as argument to become a compression state is suitably aligned.
+  This test can be disabled if it proves flaky, by setting this value to 0.
 
 
 #### Amalgamation
diff --git a/lib/lz4frame.c b/lib/lz4frame.c
index 2976bb1..e02b76c 100644
--- a/lib/lz4frame.c
+++ b/lib/lz4frame.c
@@ -1405,6 +1405,7 @@ size_t LZ4F_decompress(LZ4F_dctx* dctx,
     if (decompressOptionsPtr==NULL) decompressOptionsPtr = &optionsNull;
     *srcSizePtr = 0;
     *dstSizePtr = 0;
+    assert(dctx != NULL);
 
     /* behaves as a state machine */
 
diff --git a/lib/lz4frame.h b/lib/lz4frame.h
index c669aec..6e91e2d 100644
--- a/lib/lz4frame.h
+++ b/lib/lz4frame.h
@@ -431,8 +431,10 @@ LZ4FLIB_API size_t LZ4F_getFrameInfo(LZ4F_dctx* dctx,
                                      const void* srcBuffer, size_t* srcSizePtr);
 
 /*! LZ4F_decompress() :
- *  Call this function repetitively to regenerate compressed data from `srcBuffer`.
- *  The function will read up to *srcSizePtr bytes from srcBuffer,
+ *  Call this function repetitively to regenerate data compressed in `srcBuffer`.
+ *
+ *  The function requires a valid dctx state.
+ *  It will read up to *srcSizePtr bytes from srcBuffer,
  *  and decompress data into dstBuffer, of capacity *dstSizePtr.
  *
  *  The nb of bytes consumed from srcBuffer will be written into *srcSizePtr (necessarily <= original value).