elements: Implement block parsing for elements block headers

Since the difference between non-elements and elements block headers is just
the middle 2 fields, I split the old parsing code so I could add the middle
part.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

bitcoin/block.c

@@ -26,7 +26,28 @@ bitcoin_block_from_hex(const tal_t *ctx, const struct chainparams *chainparams,
 	if (!hex_decode(hex, hexlen, linear_tx, len))
 		return tal_free(b);
 
-	pull(&p, &len, &b->hdr, sizeof(b->hdr));
+	b->hdr.version = pull_le32(&p, &len);
+	pull(&p, &len, &b->hdr.prev_hash, sizeof(b->hdr.prev_hash));
+	pull(&p, &len, &b->hdr.merkle_hash, sizeof(b->hdr.merkle_hash));
+	b->hdr.timestamp = pull_le32(&p, &len);
+
+	if (is_elements) {
+		b->elements_hdr = tal(b, struct elements_block_hdr);
+		b->elements_hdr->block_height = pull_le32(&p, &len);
+
+		size_t challenge_len = pull_varint(&p, &len);
+		b->elements_hdr->proof.challenge = tal_arr(b->elements_hdr, u8, challenge_len);
+		pull(&p, &len, b->elements_hdr->proof.challenge, challenge_len);
+
+		size_t solution_len = pull_varint(&p, &len);
+		b->elements_hdr->proof.solution = tal_arr(b->elements_hdr, u8, solution_len);
+		pull(&p, &len, b->elements_hdr->proof.solution, solution_len);
+
+	} else {
+		b->hdr.target = pull_le32(&p, &len);
+		b->hdr.nonce = pull_le32(&p, &len);
+	}
+
 	num = pull_varint(&p, &len);
 	b->tx = tal_arr(b, struct bitcoin_tx *, num);
 	for (i = 0; i < num; i++) {

bitcoin/block.h

@@ -25,8 +25,19 @@ struct bitcoin_block_hdr {
 	le32 nonce;
 };
 
+struct elements_block_proof {
+	u8 *challenge;
+	u8 *solution;
+};
+
+struct elements_block_hdr {
+	u32 block_height;
+	struct elements_block_proof proof;
+};
+
 struct bitcoin_block {
 	struct bitcoin_block_hdr hdr;
+	struct elements_block_hdr *elements_hdr;
 	/* tal_count shows now many */
 	struct bitcoin_tx **tx;
 };