4 files changed, 54 insertions, 1 deletions
diff --git a/lib/include/defs.h b/lib/include/defs.h
index a15a2fd..d4a57a9 100644
--- a/lib/include/defs.h
+++ b/lib/include/defs.h
@@ -58,4 +58,7 @@
 /* Fixed paths */
 #define OSMORA_TRUST "/etc/ostp/trusted_users.osmt"
 
+/* Maximum length of an IP */
+#define IP_LEN_MAX 46
+
 #endif
diff --git a/lib/include/net/stpsession.h b/lib/include/net/stpsession.h
index 731b8ce..9735678 100644
--- a/lib/include/net/stpsession.h
+++ b/lib/include/net/stpsession.h
@@ -46,6 +46,17 @@
 
 /* Session Request option bits */
 #define SESSION_REQ_USER BIT(0)
+#define SESSION_REQ_P2P  BIT(1)
+
+/*
+ * For ACKing/TRUNCing packets e.g.,
+ * peer blocks
+ */
+#define ACK_WORD 0xAC7E
+#define TRUNC_WORD 0x782C
+
+#define PB_N_PEERS 16
+#define PB_N_BLOCKS 16
 
 /*
  * The Session Request is sent from the client to the
@@ -63,11 +74,12 @@
  *                        /
  *           0 1 2 3 4 5 6
  *           ~ ~ ~ ~ ~ ~ ~
- *           U R R R R R R
+ *           U P R R R R R
  *                        \
  *                         Purpose
  *
  * U: User auth.
+ * P: Peer-to-peer.
  * R: Reserved, keep zero.
  */
 struct session_request {
@@ -77,6 +89,42 @@ struct session_request {
 } PACKED;
 
 /*
+ * The `peer' structure describes a peer on
+ * an OSTP server running in peer-to-peer mode.
+ *
+ * @pad: Must be all 1s, treat invalid otherwise
+ * @port: Port peer accepts connections on
+ * @host: Host peer is at
+ */
+struct peer {
+    uint8_t pad[1];
+    uint16_t port;
+    char host[IP_LEN_MAX];
+};
+
+/*
+ * If P2P is enabled and supported, the OCS
+ * sends one or more peer blocks in a consecutive
+ * manner. Each peer block can list up to 16 peers
+ * max. If the `seq' field is greater than zero and
+ * the list of peers within the current block is full,
+ * the client may either request the next peer block by
+ * sending an ACK packet or terminating the connection
+ * by sending a TRUNC packet.
+ *
+ * @peers: List of available peers within this block
+ * @seq: Descending one-based block sequence number (0=invalid)
+ */
+struct peer_block {
+    struct peer peers[PB_N_PEERS];
+    uint8_t seq;
+} PACKED;
+
+/* Peer/block counts must be powers of two */
+CTASSERT((PB_N_PEERS & 1) == 0, "PB_N_PEERS not power-of-two!");
+CTASSERT((PB_N_BLOCKS & 1) == 0, "PB_N_BLOCKS not power-of-two!");
+
+/*
  * Structure containing user information
  * for password protected channels.
  */
diff --git a/lib/include/otconfig.h b/lib/include/otconfig.h
index 96cac38..e8400b1 100644
--- a/lib/include/otconfig.h
+++ b/lib/include/otconfig.h
@@ -34,6 +34,7 @@
 #define DIAGNOSTIC 0            /* 1 for verbosity */
 #define CONNECTION_TIMEOUT 60   /* In seconds */
 #define ENABLE_MOTD 1           /* Enable message of the day */
+#define ENABLE_P2P  1           /* Enable peer-to-peer sessions */
 #define ARBITRATION_MAX 5       /* Maximum number of arbitration attempts */
 #define REQUIRE_USER_AUTH 1     /* 1: true, 0: false */
 #define OSTP_PORT 5352
diff --git a/lib/include/server.h b/lib/include/server.h
index c8eff9c..33d2b7e 100644
--- a/lib/include/server.h
+++ b/lib/include/server.h
@@ -40,6 +40,7 @@
 
 struct ostp_client {
     struct ostp_session session;
+    char host[IP_LEN_MAX];
     int sockfd;
     pthread_t td;
     volatile uint8_t authed : 1;