Add TOX_NOSPAM_SIZE to the public API.

Fixes #456.

toxcore/tox.api.h

@@ -240,6 +240,11 @@ const PUBLIC_KEY_SIZE              = 32;
  */
 const SECRET_KEY_SIZE              = 32;
 
+/**
+ * The size of the nospam in bytes when written in a Tox address.
+ */
+const NOSPAM_SIZE                  = sizeof(uint32_t);
+
 /**
  * The size of a Tox address in bytes. Tox addresses are in the format
  * [Public Key ($PUBLIC_KEY_SIZE bytes)][nospam (4 bytes)][checksum (2 bytes)].
@@ -248,7 +253,7 @@ const SECRET_KEY_SIZE              = 32;
  * byte is an XOR of all the even bytes (0, 2, 4, ...), the second byte is an
  * XOR of all the odd bytes (1, 3, 5, ...) of the Public Key and nospam.
  */
-const ADDRESS_SIZE                = PUBLIC_KEY_SIZE + sizeof(uint32_t) + sizeof(uint16_t);
+const ADDRESS_SIZE                = PUBLIC_KEY_SIZE + NOSPAM_SIZE + sizeof(uint16_t);
 
 /**
  * Maximum length of a nickname in bytes.

toxcore/tox.h

@@ -245,6 +245,13 @@ uint32_t tox_public_key_size(void);
 
 uint32_t tox_secret_key_size(void);
 
+/**
+ * The size of the nospam in bytes when written in a Tox address.
+ */
+#define TOX_NOSPAM_SIZE                (sizeof(uint32_t))
+
+uint32_t tox_nospam_size(void);
+
 /**
  * The size of a Tox address in bytes. Tox addresses are in the format
  * [Public Key (TOX_PUBLIC_KEY_SIZE bytes)][nospam (4 bytes)][checksum (2 bytes)].
@@ -253,7 +260,7 @@ uint32_t tox_secret_key_size(void);
  * byte is an XOR of all the even bytes (0, 2, 4, ...), the second byte is an
  * XOR of all the odd bytes (1, 3, 5, ...) of the Public Key and nospam.
  */
-#define TOX_ADDRESS_SIZE               (TOX_PUBLIC_KEY_SIZE + sizeof(uint32_t) + sizeof(uint16_t))
+#define TOX_ADDRESS_SIZE               (TOX_PUBLIC_KEY_SIZE + TOX_NOSPAM_SIZE + sizeof(uint16_t))
 
 uint32_t tox_address_size(void);
 
@@ -2938,3 +2945,4 @@ uint16_t tox_self_get_tcp_port(const Tox *tox, TOX_ERR_GET_PORT *error);
 #endif
 
 #endif
+