net/nanocoap: add block slicer init function

sys/include/net/nanocoap.h

@@ -610,6 +610,18 @@ static inline void coap_block2_finish(coap_block_slicer_t *slicer)
  */
 void coap_block2_init(coap_pkt_t *pkt, coap_block_slicer_t *slicer);
 
+/**
+ * @brief Initialize a block slicer struct from content information
+ *
+ * @param[out]   slicer     slicer struct to initialize
+ * @param[in]    blknum     offset from the beginning of content, in terms of
+                            @p blksize byte blocks
+ * @param[in]    blksize    size of each block; must be a power of 2 between 16
+ *                          and 2 raised to #NANOCOAP_BLOCK_SIZE_EXP_MAX
+ */
+void coap_block_slicer_init(coap_block_slicer_t *slicer, size_t blknum,
+                            size_t blksize);
+
 /**
  * @brief Add a byte array to a block2 reply.
  *

sys/net/application_layer/nanocoap/nanocoap.c

@@ -883,6 +883,14 @@ void coap_block_object_init(coap_block1_t *block, size_t blknum, size_t blksize,
     block->more = more;
 }
 
+void coap_block_slicer_init(coap_block_slicer_t *slicer, size_t blknum,
+                            size_t blksize)
+{
+    slicer->start = blknum * blksize;
+    slicer->end = slicer->start + blksize;
+    slicer->cur = 0;
+}
+
 void coap_block2_init(coap_pkt_t *pkt, coap_block_slicer_t *slicer)
 {
     uint32_t blknum;
@@ -896,9 +904,8 @@ void coap_block2_init(coap_pkt_t *pkt, coap_block_slicer_t *slicer)
             szx = NANOCOAP_BLOCK_SIZE_EXP_MAX - 4;
         }
     }
-    slicer->start = blknum * coap_szx2size(szx);
-    slicer->end = slicer->start + coap_szx2size(szx);
-    slicer->cur = 0;
+
+    coap_block_slicer_init(slicer, blknum, coap_szx2size(szx));
 }
 
 void coap_block_finish(coap_block_slicer_t *slicer, uint16_t option)