From 7aff2e1d279a4e442b32f49ca0a0eca065355787 Mon Sep 17 00:00:00 2001
From: murilo ijanc
Date: Wed, 25 Mar 2026 02:07:37 -0300
Subject: Initial commit: tesseras-paste decentralized pastebin

DHT-backed encrypted pastebin with two binaries (tp/tpd),
XChaCha20-Poly1305 encryption, content-addressed storage,
and Unix socket + HTTP interfaces.
---
 src/paste.rs | 128 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)
 create mode 100644 src/paste.rs

(limited to 'src/paste.rs')

diff --git a/src/paste.rs b/src/paste.rs
new file mode 100644
index 0000000..50b32b1
--- /dev/null
+++ b/src/paste.rs
@@ -0,0 +1,128 @@
+//! Paste record format.
+//!
+//! Binary format (no external serialization deps):
+//!   version: u8
+//!   created_at: u64 (big-endian)
+//!   ttl_secs: u64 (big-endian)
+//!   content: [u8] (remaining bytes)
+
+use tesseras_dht::sha2::{Digest, Sha256};
+
+/// Maximum paste size: 64 KiB.
+pub const MAX_PASTE_SIZE: usize = 64 * 1024;
+
+/// Current format version.
+const FORMAT_VERSION: u8 = 1;
+
+/// Header size: version(1) + created_at(8) + ttl(8) = 17.
+const HEADER_SIZE: usize = 17;
+
+/// A paste record stored locally and replicated via the DHT.
+#[derive(Debug, Clone)]
+pub struct Paste {
+    pub version: u8,
+    pub content: Vec<u8>,
+    pub created_at: u64,
+    pub ttl_secs: u64,
+}
+
+impl Paste {
+    /// Create a new paste with the current timestamp.
+    pub fn new(content: Vec<u8>, ttl_secs: u64) -> Self {
+        let created_at = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_secs();
+        Paste {
+            version: FORMAT_VERSION,
+            content,
+            created_at,
+            ttl_secs,
+        }
+    }
+
+    /// Compute the SHA-256 content-addressed key (32 bytes).
+    pub fn content_key(content: &[u8]) -> [u8; 32] {
+        let mut h = Sha256::new();
+        h.update(content);
+        h.finalize().into()
+    }
+
+    /// Serialize to bytes.
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let mut buf = Vec::with_capacity(HEADER_SIZE + self.content.len());
+        buf.push(self.version);
+        buf.extend_from_slice(&self.created_at.to_be_bytes());
+        buf.extend_from_slice(&self.ttl_secs.to_be_bytes());
+        buf.extend_from_slice(&self.content);
+        buf
+    }
+
+    /// Deserialize from bytes.
+    pub fn from_bytes(data: &[u8]) -> Option<Self> {
+        if data.len() < HEADER_SIZE {
+            return None;
+        }
+        let version = data[0];
+        let created_at = u64::from_be_bytes(data[1..9].try_into().ok()?);
+        let ttl_secs = u64::from_be_bytes(data[9..17].try_into().ok()?);
+        let content = data[HEADER_SIZE..].to_vec();
+        Some(Paste {
+            version,
+            content,
+            created_at,
+            ttl_secs,
+        })
+    }
+
+    /// Whether this paste has expired.
+    pub fn is_expired(&self) -> bool {
+        let now = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_secs();
+        now > self.created_at + self.ttl_secs
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn round_trip() {
+        let paste = Paste::new(b"hello world".to_vec(), 3600);
+        let bytes = paste.to_bytes();
+        let decoded = Paste::from_bytes(&bytes).unwrap();
+        assert_eq!(decoded.content, b"hello world");
+        assert_eq!(decoded.ttl_secs, 3600);
+        assert_eq!(decoded.version, FORMAT_VERSION);
+    }
+
+    #[test]
+    fn content_key_deterministic() {
+        let k1 = Paste::content_key(b"test");
+        let k2 = Paste::content_key(b"test");
+        assert_eq!(k1, k2);
+    }
+
+    #[test]
+    fn content_key_differs() {
+        let k1 = Paste::content_key(b"aaa");
+        let k2 = Paste::content_key(b"bbb");
+        assert_ne!(k1, k2);
+    }
+
+    #[test]
+    fn too_short_fails() {
+        assert!(Paste::from_bytes(&[0u8; 5]).is_none());
+    }
+
+    #[test]
+    fn empty_content() {
+        let paste = Paste::new(Vec::new(), 60);
+        let bytes = paste.to_bytes();
+        let decoded = Paste::from_bytes(&bytes).unwrap();
+        assert!(decoded.content.is_empty());
+    }
+}
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