fuzz: add a target for common/bech32

Signed-off-by: Antoine Poinsot <darosior@protonmail.com>

tests/fuzz/fuzz-bech32.c

@@ -0,0 +1,50 @@
+#include <stdint.h>
+#include <string.h>
+#include <tests/fuzz/libfuzz.h>
+
+#include <common/bech32.h>
+
+void init(int *argc, char ***argv)
+{
+}
+
+void run(const uint8_t *data, size_t size)
+{
+	const char hrp_inv[5] = "lnbc\0", hrp_addr[3] = "bc\0";
+	char *bech32_str, *hrp_out, *addr;
+	uint8_t *data_out;
+	size_t data_out_len;
+	int wit_version;
+
+	/* Buffer size is defined in each function's doc comment. */
+	bech32_str = malloc(size + strlen(hrp_inv) + 8);
+	/* FIXME: needs a dictionary / a startup seed corpus to pass this more
+	 * frequently. */
+	if (bech32_encode(bech32_str, hrp_inv, data, size, size) == 1) {
+		hrp_out = malloc(strlen(bech32_str) - 6);
+		data_out = malloc(strlen(bech32_str) - 8);
+		bech32_decode(hrp_out, data_out, &data_out_len, bech32_str, size);
+		free(hrp_out);
+		free(data_out);
+	}
+	free(bech32_str);
+
+	data_out = malloc(size);
+
+	/* This is also used as part of sign and check message. */
+	data_out_len = 0;
+	bech32_convert_bits(data_out, &data_out_len, 8, data, size, 5, 1);
+	data_out_len = 0;
+	bech32_convert_bits(data_out, &data_out_len, 8, data, size, 5, 0);
+
+	addr = malloc(73 + strlen(hrp_addr));
+	wit_version = 0;
+	if (segwit_addr_encode(addr, hrp_addr, wit_version, data, size) == 1)
+		segwit_addr_decode(&wit_version, data_out, &data_out_len, hrp_addr, addr);
+	wit_version = 1;
+	if (segwit_addr_encode(addr, hrp_addr, wit_version, data, size) == 1)
+		segwit_addr_decode(&wit_version, data_out, &data_out_len, hrp_addr, addr);
+	free(addr);
+
+	free(data_out);
+}