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/dhcp.h | 116 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 lib/dhcp/dhcp.h

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

diff --git a/lib/dhcp/dhcp.h b/lib/dhcp/dhcp.h
new file mode 100644
index 0000000..ce904f0
--- /dev/null
+++ b/lib/dhcp/dhcp.h
@@ -0,0 +1,116 @@
+// Copyright (c) 2022 Johannes Stoelp
+//
+// dhcp protocol: https://datatracker.ietf.org/doc/html/rfc2131
+// dhcp options : https://datatracker.ietf.org/doc/html/rfc2132
+
+#ifndef DHCP_H
+#define DHCP_H
+
+#include "types.h"
+
+#include <optional>
+
+// -- Global constants.
+
+constexpr u16 DHCP_SERVER_PORT = 67;
+constexpr u16 DHCP_CLIENT_PORT = 68;
+
+constexpr usize DHCP_MESSAGE_LEN = 576;
+constexpr usize DHCP_MESSAGE_MIN_LEN = 243;
+
+constexpr u32 DHCP_OPTION_COOKIE = 0x63538263;
+
+enum class dhcp_operation : u8 {
+    BOOTREQUEST = 1,
+    BOOTREPLY,
+};
+
+enum class dhcp_option : u8 {
+    PAD = 0,
+    END = 255,
+
+    // Vendor Extensions.
+    SUBNET_MASK = 1,
+    ROUTER = 3,
+    DNS = 6,
+
+    // IP Layer Parameters per Interface.
+    BROADCAST_ADDR = 28,
+
+    // DHCP Extensions.
+    REQUESTED_IP = 50,
+    IP_ADDRESS_LEASE_TIME,
+    OPTION_OVERLOAD,
+    DHCP_MESSAGE_TYPE,
+    SERVER_IDENTIFIER,
+    PARAMETER_REQUEST_LIST,
+    MESSAGE,
+    MAX_DHCP_MESSAGE_SIZE,
+    RENEWAL_TIME_T1,
+    REBINDING_TIME_T2,
+    CLASS_ID,
+    CLIENT_ID,
+};
+
+// -- DHCP message.
+
+enum class dhcp_message_type : u8 {
+    DHCP_DISCOVER = 1,
+    DHCP_OFFER,
+    DHCP_REQUEST,
+    DHCP_DECLINE,
+    DHCP_ACK,
+    DHCP_NAK,
+    DHCP_RELEAE,
+};
+
+struct dhcp_message {
+    dhcp_operation op;
+    u8 htype;
+    u8 hlen;
+    u8 hops;
+    u32 xid;
+    u16 secs;
+    u16 flags;
+    u32 ciaddr;
+    u32 yiaddr;
+    u32 siaddr;
+    u32 giaddr;
+    u8 chaddr[16];
+    u8 sname[64];
+    u8 file[128];
+    u32 cookie;
+    u8 options[312 - 4 /* cookie len */];
+} __attribute__((packed));
+
+static_assert(DHCP_MESSAGE_MIN_LEN == offsetof(dhcp_message, options) + 3 /* DHCP_MESSAGE_TYPE size */,
+              "Declare min size as dhcp_message with the DHCP_MESSAGE_TYPE option.");
+
+// -- DHCP Utilities.
+
+struct option_view {
+    const u8* data;
+    usize len;
+};
+
+// Search for the option with tag 'search_tag' in the options 'opt' of length 'len'.
+std::optional<struct option_view> get_option(const u8* opt, usize len, dhcp_option search_tag);
+
+template<typename T>
+constexpr T get_opt_val(const u8* opt_data) {
+    T ret = 0;
+    for (size_t i = 0; i < sizeof(T); ++i) {
+        ret = (ret << 8) | *opt_data++;
+    }
+    return ret;
+}
+
+template<typename T>
+u8* put_opt_val(u8* opt_data, T val) {
+    for (size_t i = sizeof(T); i; --i) {
+        *opt_data++ = (val >> ((i - 1) * 8)) & 0xff;
+    }
+    return opt_data;
+}
+
+#endif
-- 
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