Combining fuzz_data_producer restrict calls into a single function

tests/fuzz/block_round_trip.c

@@ -55,8 +55,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
     /* Give a random portion of src data to the producer, to use for
     parameter generation. The rest will be used for (de)compression */
     FUZZ_dataProducer_t *producer = FUZZ_dataProducer_create(src, size);
-    size_t producerSliceSize = FUZZ_dataProducer_uint32Range(producer, 0, size);
-    size = FUZZ_dataProducer_contract(producer, producerSliceSize);
+    size = FUZZ_dataProducer_reserveDataPrefix(producer);
 
     int cLevel = FUZZ_dataProducer_uint32(producer) % kMaxClevel;
 

tests/fuzz/dictionary_decompress.c

@@ -27,8 +27,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
     /* Give a random portion of src data to the producer, to use for
     parameter generation. The rest will be used for (de)compression */
     FUZZ_dataProducer_t *producer = FUZZ_dataProducer_create(src, size);
-    size_t producerSliceSize = FUZZ_dataProducer_uint32Range(producer, 0, size);
-    size = FUZZ_dataProducer_contract(producer, producerSliceSize);
+    size = FUZZ_dataProducer_reserveDataPrefix(producer);
 
     FUZZ_dict_t dict;
     ZSTD_DDict* ddict = NULL;

tests/fuzz/dictionary_round_trip.c

@@ -71,8 +71,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
     /* Give a random portion of src data to the producer, to use for
     parameter generation. The rest will be used for (de)compression */
     FUZZ_dataProducer_t *producer = FUZZ_dataProducer_create(src, size);
-    size_t producerSliceSize = FUZZ_dataProducer_uint32Range(producer, 0, size);
-    size = FUZZ_dataProducer_contract(producer, producerSliceSize);
+    size = FUZZ_dataProducer_reserveDataPrefix(producer);
 
     size_t const rBufSize = size;
     void* rBuf = malloc(rBufSize);

tests/fuzz/fuzz_data_producer.c

@@ -65,3 +65,10 @@ size_t FUZZ_dataProducer_contract(FUZZ_dataProducer_t *producer, size_t newSize)
     producer->size = newSize;
     return remaining;
 }
+
+size_t FUZZ_dataProducer_reserveDataPrefix(FUZZ_dataProducer_t *producer)
+{
+    size_t producerSliceSize = FUZZ_dataProducer_uint32Range(
+                                  producer, 0, producer->size);
+    return FUZZ_dataProducer_contract(producer, producerSliceSize);
+}

tests/fuzz/fuzz_data_producer.h

@@ -44,10 +44,13 @@ uint32_t FUZZ_dataProducer_uint32(FUZZ_dataProducer_t *producer);
 /* Returns the size of the remaining bytes of data in the producer */
 size_t FUZZ_dataProducer_remainingBytes(FUZZ_dataProducer_t *producer);
 
-/* Tells the producer to contract to newSize bytes of data it currently uses,
-counted from the end, and forget about the rest. If newSize > current data size,
-nothing happens. Returns the number of bytes the producer won't use anymore,
-after contracting. */
+/* Restricts the producer to only the last newSize bytes of data.
+If newSize > current data size, nothing happens. Returns the number of bytes
+the producer won't use anymore, after contracting. */
 size_t FUZZ_dataProducer_contract(FUZZ_dataProducer_t *producer, size_t newSize);
 
+/* Restricts the producer to use only the last X bytes of data, where X is
+ a random number in the interval [0, data_size]. Returns the size of the
+ remaining data the producer won't use anymore (the prefix). */
+size_t FUZZ_dataProducer_reserveDataPrefix(FUZZ_dataProducer_t *producer);
 #endif // FUZZ_DATA_PRODUCER_H

tests/fuzz/simple_compress.c

@@ -27,8 +27,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
     /* Give a random portion of src data to the producer, to use for
     parameter generation. The rest will be used for (de)compression */
     FUZZ_dataProducer_t *producer = FUZZ_dataProducer_create(src, size);
-    size_t producerSliceSize = FUZZ_dataProducer_uint32Range(producer, 0, size);
-    size = FUZZ_dataProducer_contract(producer, producerSliceSize);
+    size = FUZZ_dataProducer_reserveDataPrefix(producer);
 
     size_t const maxSize = ZSTD_compressBound(size);
     size_t const bufSize = FUZZ_dataProducer_uint32Range(producer, 0, maxSize);

tests/fuzz/simple_decompress.c

@@ -26,8 +26,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
     /* Give a random portion of src data to the producer, to use for
     parameter generation. The rest will be used for (de)compression */
     FUZZ_dataProducer_t *producer = FUZZ_dataProducer_create(src, size);
-    size_t producerSliceSize = FUZZ_dataProducer_uint32Range(producer, 0, size);
-    size = FUZZ_dataProducer_contract(producer, producerSliceSize);
+    size = FUZZ_dataProducer_reserveDataPrefix(producer);
 
     if (!dctx) {
         dctx = ZSTD_createDCtx();

tests/fuzz/simple_round_trip.c

@@ -55,8 +55,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
     /* Give a random portion of src data to the producer, to use for
     parameter generation. The rest will be used for (de)compression */
     FUZZ_dataProducer_t *producer = FUZZ_dataProducer_create(src, size);
-    size_t producerSliceSize = FUZZ_dataProducer_uint32Range(producer, 0, size);
-    size = FUZZ_dataProducer_contract(producer, producerSliceSize);
+    size = FUZZ_dataProducer_reserveDataPrefix(producer);
 
     /* Half of the time fuzz with a 1 byte smaller output size.
      * This will still succeed because we don't use a dictionary, so the dictID

tests/fuzz/stream_decompress.c

@@ -56,8 +56,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
     /* Give a random portion of src data to the producer, to use for
     parameter generation. The rest will be used for (de)compression */
     FUZZ_dataProducer_t *producer = FUZZ_dataProducer_create(src, size);
-    size_t producerSliceSize = FUZZ_dataProducer_uint32Range(producer, 0, size);
-    size = FUZZ_dataProducer_contract(producer, producerSliceSize);
+    size = FUZZ_dataProducer_reserveDataPrefix(producer);
 
     /* Allocate all buffers and contexts if not already allocated */
     if (!buf) {

tests/fuzz/stream_round_trip.c

@@ -128,8 +128,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
     /* Give a random portion of src data to the producer, to use for
     parameter generation. The rest will be used for (de)compression */
     FUZZ_dataProducer_t *producer = FUZZ_dataProducer_create(src, size);
-    size_t producerSliceSize = FUZZ_dataProducer_uint32Range(producer, 0, size);
-    size = FUZZ_dataProducer_contract(producer, producerSliceSize);
+    size = FUZZ_dataProducer_reserveDataPrefix(producer);
 
     size_t neededBufSize;
     neededBufSize = ZSTD_compressBound(size) * 5;