inflate: Add helper for getting decompressed data size

Helper for another semi-typical operation: find out how big of a
buffer should be allocated before decompressing. This can be useful
when the stream container doesn't specify the decompressed size.

Change-Id: I5f1536f809bb6f9bc6023120c024c3de7cea4269

firmware/common/inflate.c

@@ -782,3 +782,12 @@ uint32_t inflate_buffer_writer(const void* block, uint32_t block_size, void* ctx
     struct inflate_bufferctx* c = ctx;
     return inflate_buffer_rw(c, c->buf, block, block_size);
 }
+
+uint32_t inflate_getsize_writer(const void* block, uint32_t block_size, void* ctx)
+{
+    (void)block;
+
+    size_t* size = ctx;
+    *size += block_size;
+    return block_size;
+}

firmware/include/inflate.h

@@ -58,4 +58,13 @@ struct inflate_bufferctx {
 uint32_t inflate_buffer_reader(void* block, uint32_t block_size, void* ctx);
 uint32_t inflate_buffer_writer(const void* block, uint32_t block_size, void* ctx);
 
+// dummy writer used if you just want to figure out how big the decompressed
+// data will be. It does not actually write any data. Example usage:
+//
+//   size_t size = 0;
+//   inflate(it, st, read, rctx, inflate_getsize_writer, &size);
+//
+// Now 'size' will be the size of the decompressed data (assuming no errors).
+uint32_t inflate_getsize_writer(const void* block, uint32_t block_size, void* ctx);
+
 #endif