1 files changed, 101 insertions, 0 deletions
diff --git a/src/packet/header.rs b/src/packet/header.rs
new file mode 100644
index 0000000..a75f6ba
--- /dev/null
+++ b/src/packet/header.rs
@@ -0,0 +1,101 @@
+use super::{buffer::PacketBuffer, result::ResultCode, Result};
+
+#[derive(Clone, Debug)]
+pub struct DnsHeader {
+    pub id: u16, // 16 bits
+
+    pub recursion_desired: bool,    // 1 bit
+    pub truncated_message: bool,    // 1 bit
+    pub authoritative_answer: bool, // 1 bit
+    pub opcode: u8,                 // 4 bits
+    pub response: bool,             // 1 bit
+
+    pub rescode: ResultCode,       // 4 bits
+    pub checking_disabled: bool,   // 1 bit
+    pub authed_data: bool,         // 1 bit
+    pub z: bool,                   // 1 bit
+    pub recursion_available: bool, // 1 bit
+
+    pub questions: u16,             // 16 bits
+    pub answers: u16,               // 16 bits
+    pub authoritative_entries: u16, // 16 bits
+    pub resource_entries: u16,      // 16 bits
+}
+
+impl DnsHeader {
+    pub fn new() -> Self {
+        Self {
+            id: 0,
+
+            recursion_desired: false,
+            truncated_message: false,
+            authoritative_answer: false,
+            opcode: 0,
+            response: false,
+
+            rescode: ResultCode::NOERROR,
+            checking_disabled: false,
+            authed_data: false,
+            z: false,
+            recursion_available: false,
+
+            questions: 0,
+            answers: 0,
+            authoritative_entries: 0,
+            resource_entries: 0,
+        }
+    }
+
+    pub fn read(&mut self, buffer: &mut PacketBuffer) -> Result<()> {
+        self.id = buffer.read_u16()?;
+        let flags = buffer.read_u16()?;
+        let a = (flags >> 8) as u8;
+        let b = (flags & 0xFF) as u8;
+        self.recursion_desired = (a & (1 << 0)) > 0;
+        self.truncated_message = (a & (1 << 1)) > 0;
+        self.authoritative_answer = (a & (1 << 2)) > 0;
+        self.opcode = (a >> 3) & 0x0F;
+        self.response = (a & (1 << 7)) > 0;
+
+        self.rescode = ResultCode::from_num(b & 0x0F);
+        self.checking_disabled = (b & (1 << 4)) > 0;
+        self.authed_data = (b & (1 << 5)) > 0;
+        self.z = (b & (1 << 6)) > 0;
+        self.recursion_available = (b & (1 << 7)) > 0;
+
+        self.questions = buffer.read_u16()?;
+        self.answers = buffer.read_u16()?;
+        self.authoritative_entries = buffer.read_u16()?;
+        self.resource_entries = buffer.read_u16()?;
+
+        // Return the constant header size
+        Ok(())
+    }
+
+    pub fn write(&self, buffer: &mut PacketBuffer) -> Result<()> {
+        buffer.write_u16(self.id)?;
+
+        buffer.write_u8(
+            (self.recursion_desired as u8)
+                | ((self.truncated_message as u8) << 1)
+                | ((self.authoritative_answer as u8) << 2)
+                | (self.opcode << 3)
+                | ((self.response as u8) << 7),
+        )?;
+
+        buffer.write_u8(
+            (self.rescode as u8)
+                | ((self.checking_disabled as u8) << 4)
+                | ((self.authed_data as u8) << 5)
+                | ((self.z as u8) << 6)
+                | ((self.recursion_available as u8) << 7),
+        )?;
+
+        buffer.write_u16(self.questions)?;
+        buffer.write_u16(self.answers)?;
+        buffer.write_u16(self.authoritative_entries)?;
+        buffer.write_u16(self.resource_entries)?;
+
+        Ok(())
+    }
+}