From f9928a1a08c57fe853888119a996c3acc98ee09d Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Fri, 14 Jan 2022 23:51:05 +0100
Subject: Initial version of nodemcuv2 dhcp server

Able to offer IP address + DNS/Gateway ...
Worked with devices at my hand.
---
 lib/dhcp/lease_db.h | 111 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 lib/dhcp/lease_db.h

(limited to 'lib/dhcp/lease_db.h')

diff --git a/lib/dhcp/lease_db.h b/lib/dhcp/lease_db.h
new file mode 100644
index 0000000..86b959f
--- /dev/null
+++ b/lib/dhcp/lease_db.h
@@ -0,0 +1,111 @@
+// Copyright (c) 2022 Johannes Stoelp
+
+#ifndef LEASE_DB_H
+#define LEASE_DB_H
+
+#include "types.h"
+
+#include <array>
+#include <optional>
+
+struct lease {
+    u32 client_hash;
+    usize lease_end;
+};
+
+// Lease database, for managing client leases, which includes
+//   - allocation of new leases
+//   - lookup of existing leases
+//   - update of existing leases
+//   - flushing of expired leases
+//
+// The database supports 'LEASE' number of clients.
+//
+// The lease APIs return an idx which represents the allocated client lease and
+// should be interpreted as offset to the start address of the dhcp address
+// range.
+//
+// For example, the dhcp server starts to assing addresses starting with
+// 10.0.0.100, and the lease database returns idx=4, this would represent the
+// allocated client address 10.0.0.104.
+template<usize LEASES>
+class lease_db {
+  public:
+    constexpr lease_db() = default;
+
+    lease_db(const lease_db&) = delete;
+    lease_db& operator=(const lease_db&) = delete;
+
+    // Try to allocate a new client lease for the client represented by
+    // 'client_hash'.
+    //
+    // If a lease could be allocated return the corresponding idx.
+    //
+    // If a lease for the client already exist or all leases are allocated,
+    // return nullopt.
+    //
+    // 'lease_end' sets the expiration time of the lease (should be absolute time).
+    std::optional<usize> new_lease(u32 client_hash, usize lease_end) {
+        if (get_lease(client_hash)) {
+            return std::nullopt;
+        }
+
+        for (usize l = 0; client_hash != 0 && l < LEASES; ++l) {
+            if (leases[l].client_hash == 0) {
+                leases[l].client_hash = client_hash;
+                leases[l].lease_end = lease_end;
+                return l;
+            }
+        }
+        return std::nullopt;
+    }
+
+    // Try to get the lease for the client if it exists.
+    std::optional<usize> get_lease(u32 client_hash) const {
+        for (usize l = 0; client_hash != 0 && l < LEASES; ++l) {
+            if (leases[l].client_hash == client_hash) {
+                return l;
+            }
+        }
+        return std::nullopt;
+    }
+
+    // Update expiration time for client if the client has an allocated lease.
+    // Similar to 'new_lease' the 'lease_end' should be an absolute time value.
+    bool update_lease(u32 client_hash, usize lease_end) {
+        for (usize l = 0; client_hash != 0 && l < LEASES; ++l) {
+            if (leases[l].client_hash == client_hash) {
+                leases[l].lease_end = lease_end;
+                return true;
+            }
+        }
+        return false;
+    }
+
+    // Check for expired leases and free them accordingly.
+    // 'curr_time' should be the current time as absolute time value.
+    void flush_expired(usize curr_time) {
+        for (lease& l : leases) {
+            if (l.lease_end <= curr_time) {
+                l.client_hash = 0;
+                l.lease_end = 0;
+            }
+        }
+    }
+
+    // Get the number of active leases.
+    usize active_leases() const {
+        usize cnt = 0;
+        for (const lease& l : leases) {
+            if (l.client_hash != 0) {
+                ++cnt;
+            }
+        }
+        return cnt;
+    }
+
+  private:
+    std::array<lease, LEASES> leases = {0, 0};
+};
+
+#endif
-- 
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