TransactionView: Message Header Meta

transaction-view/src/lib.rs

@@ -6,4 +6,6 @@ pub mod bytes;
 #[allow(dead_code)]
 mod bytes;
 
+#[allow(dead_code)]
+mod message_header_meta;
 pub mod result;

transaction-view/src/message_header_meta.rs

@@ -0,0 +1,123 @@
+use {
+    crate::{
+        bytes::read_byte,
+        result::{Result, TransactionParsingError},
+    },
+    solana_sdk::message::MESSAGE_VERSION_PREFIX,
+};
+
+/// A byte that represents the version of the transaction.
+#[derive(Copy, Clone, Default)]
+#[repr(u8)]
+pub enum TransactionVersion {
+    #[default]
+    Legacy = u8::MAX,
+    V0 = 0,
+}
+
+/// Meta data for accessing message header fields in a transaction view.
+pub(crate) struct MessageHeaderMeta {
+    /// The offset to the first byte of the message in the transaction packet.
+    pub(crate) offset: u16,
+    /// The version of the transaction.
+    pub(crate) version: TransactionVersion,
+    /// The number of signatures required for this message to be considered
+    /// valid.
+    pub(crate) num_required_signatures: u8,
+    /// The last `num_readonly_signed_accounts` of the signed keys are
+    /// read-only.
+    pub(crate) num_readonly_signed_accounts: u8,
+    /// The last `num_readonly_unsigned_accounts` of the unsigned keys are
+    /// read-only accounts.
+    pub(crate) num_readonly_unsigned_accounts: u8,
+}
+
+impl MessageHeaderMeta {
+    pub fn try_new(bytes: &[u8], offset: &mut usize) -> Result<Self> {
+        // Get the message offset.
+        // We know the offset does not exceed packet length, and our packet
+        // length is less than u16::MAX, so we can safely cast to u16.
+        let message_offset = *offset as u16;
+
+        // Read the message prefix byte if present. This byte is present in V0
+        // transactions but not in legacy transactions.
+        // The message header begins immediately after the message prefix byte
+        // if present.
+        let message_prefix = read_byte(bytes, offset)?;
+        let (version, message_header_offset) = if message_prefix & MESSAGE_VERSION_PREFIX != 0 {
+            let version = message_prefix & !MESSAGE_VERSION_PREFIX;
+            match version {
+                // add one byte for prefix byte. Do not need to check for
+                // overflow here, because we have already checked.
+                0 => (TransactionVersion::V0, message_offset + 1),
+                _ => return Err(TransactionParsingError),
+            }
+        } else {
+            (TransactionVersion::Legacy, message_offset)
+        };
+
+        // Offset should get reset to header offset - the byte we read may have
+        // actually been part of the header instead of the prefix (Legacy).
+        *offset = usize::from(message_header_offset);
+
+        let num_required_signatures = read_byte(bytes, offset)?;
+        let num_readonly_signed_accounts = read_byte(bytes, offset)?;
+        let num_readonly_unsigned_accounts = read_byte(bytes, offset)?;
+
+        Ok(Self {
+            offset: message_offset,
+            version,
+            num_required_signatures,
+            num_readonly_signed_accounts,
+            num_readonly_unsigned_accounts,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_invalid_version() {
+        let bytes = [0b1000_0001];
+        let mut offset = 0;
+        assert!(MessageHeaderMeta::try_new(&bytes, &mut offset).is_err());
+    }
+
+    #[test]
+    fn test_legacy_transaction_missing_header_byte() {
+        let bytes = [5, 0];
+        let mut offset = 0;
+        assert!(MessageHeaderMeta::try_new(&bytes, &mut offset).is_err());
+    }
+
+    #[test]
+    fn test_legacy_transaction_valid() {
+        let bytes = [5, 1, 2];
+        let mut offset = 0;
+        let header = MessageHeaderMeta::try_new(&bytes, &mut offset).unwrap();
+        assert!(matches!(header.version, TransactionVersion::Legacy));
+        assert_eq!(header.num_required_signatures, 5);
+        assert_eq!(header.num_readonly_signed_accounts, 1);
+        assert_eq!(header.num_readonly_unsigned_accounts, 2);
+    }
+
+    #[test]
+    fn test_v0_transaction_missing_header_byte() {
+        let bytes = [MESSAGE_VERSION_PREFIX, 5, 1];
+        let mut offset = 0;
+        assert!(MessageHeaderMeta::try_new(&bytes, &mut offset).is_err());
+    }
+
+    #[test]
+    fn test_v0_transaction_valid() {
+        let bytes = [MESSAGE_VERSION_PREFIX, 5, 1, 2];
+        let mut offset = 0;
+        let header = MessageHeaderMeta::try_new(&bytes, &mut offset).unwrap();
+        assert!(matches!(header.version, TransactionVersion::V0));
+        assert_eq!(header.num_required_signatures, 5);
+        assert_eq!(header.num_readonly_signed_accounts, 1);
+        assert_eq!(header.num_readonly_unsigned_accounts, 2);
+    }
+}