From 94e5fd0c63bf8e7253956983db1a08bec31da007 Mon Sep 17 00:00:00 2001
From: Andrew Fitzgerald <apfitzge@gmail.com>
Date: Wed, 7 Aug 2024 13:07:52 -0500
Subject: [PATCH] TransactionView: Static Account Keys Meta (#2410)

---
 transaction-view/src/lib.rs                   |  2 +
 .../src/static_account_keys_meta.rs           | 95 +++++++++++++++++++
 2 files changed, 97 insertions(+)
 create mode 100644 transaction-view/src/static_account_keys_meta.rs

diff --git a/transaction-view/src/lib.rs b/transaction-view/src/lib.rs
index 41870f9d690d91..aa16270fb7313d 100644
--- a/transaction-view/src/lib.rs
+++ b/transaction-view/src/lib.rs
@@ -11,3 +11,5 @@ mod message_header_meta;
 pub mod result;
 #[allow(dead_code)]
 mod signature_meta;
+#[allow(dead_code)]
+mod static_account_keys_meta;
diff --git a/transaction-view/src/static_account_keys_meta.rs b/transaction-view/src/static_account_keys_meta.rs
new file mode 100644
index 00000000000000..46bf95c15b5e58
--- /dev/null
+++ b/transaction-view/src/static_account_keys_meta.rs
@@ -0,0 +1,95 @@
+use {
+    crate::{
+        bytes::{advance_offset_for_array, read_byte},
+        result::{Result, TransactionParsingError},
+    },
+    solana_sdk::{packet::PACKET_DATA_SIZE, pubkey::Pubkey},
+};
+
+/// Contains meta-data about the static account keys in a transaction packet.
+#[derive(Default)]
+pub struct StaticAccountKeysMeta {
+    /// The number of static accounts in the transaction.
+    pub(crate) num_static_accounts: u16,
+    /// The offset to the first static account in the transaction.
+    pub(crate) offset: u16,
+}
+
+impl StaticAccountKeysMeta {
+    pub fn try_new(bytes: &[u8], offset: &mut usize) -> Result<Self> {
+        // The packet has a maximum length of 1232 bytes.
+        // This means the maximum number of 32 byte keys is 38.
+        // 38 as an min-sized encoded u16 is 1 byte.
+        // We can simply read this byte, if it's >38 we can return None.
+        const MAX_STATIC_ACCOUNTS_PER_PACKET: u16 =
+            (PACKET_DATA_SIZE / core::mem::size_of::<Pubkey>()) as u16;
+        // Max size must not have the MSB set so that it is size 1.
+        const _: () = assert!(MAX_STATIC_ACCOUNTS_PER_PACKET & 0b1000_0000 == 0);
+
+        let num_static_accounts = read_byte(bytes, offset)? as u16;
+        if num_static_accounts == 0 || num_static_accounts > MAX_STATIC_ACCOUNTS_PER_PACKET {
+            return Err(TransactionParsingError);
+        }
+
+        // We also know that the offset must be less than 3 here, since the
+        // compressed u16 can only use up to 3 bytes, so there is no need to
+        // check if the offset is greater than u16::MAX.
+        let static_accounts_offset = *offset as u16;
+        // Update offset for array of static accounts.
+        advance_offset_for_array::<Pubkey>(bytes, offset, num_static_accounts)?;
+
+        Ok(Self {
+            num_static_accounts,
+            offset: static_accounts_offset,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use {super::*, solana_sdk::short_vec::ShortVec};
+
+    #[test]
+    fn test_zero_accounts() {
+        let bytes = bincode::serialize(&ShortVec(Vec::<Pubkey>::new())).unwrap();
+        let mut offset = 0;
+        assert!(StaticAccountKeysMeta::try_new(&bytes, &mut offset).is_err());
+    }
+
+    #[test]
+    fn test_one_account() {
+        let bytes = bincode::serialize(&ShortVec(vec![Pubkey::default()])).unwrap();
+        let mut offset = 0;
+        let meta = StaticAccountKeysMeta::try_new(&bytes, &mut offset).unwrap();
+        assert_eq!(meta.num_static_accounts, 1);
+        assert_eq!(meta.offset, 1);
+        assert_eq!(offset, 1 + core::mem::size_of::<Pubkey>());
+    }
+
+    #[test]
+    fn test_max_accounts() {
+        let signatures = vec![Pubkey::default(); 38];
+        let bytes = bincode::serialize(&ShortVec(signatures)).unwrap();
+        let mut offset = 0;
+        let meta = StaticAccountKeysMeta::try_new(&bytes, &mut offset).unwrap();
+        assert_eq!(meta.num_static_accounts, 38);
+        assert_eq!(meta.offset, 1);
+        assert_eq!(offset, 1 + 38 * core::mem::size_of::<Pubkey>());
+    }
+
+    #[test]
+    fn test_too_many_accounts() {
+        let signatures = vec![Pubkey::default(); 39];
+        let bytes = bincode::serialize(&ShortVec(signatures)).unwrap();
+        let mut offset = 0;
+        assert!(StaticAccountKeysMeta::try_new(&bytes, &mut offset).is_err());
+    }
+
+    #[test]
+    fn test_u16_max_accounts() {
+        let signatures = vec![Pubkey::default(); u16::MAX as usize];
+        let bytes = bincode::serialize(&ShortVec(signatures)).unwrap();
+        let mut offset = 0;
+        assert!(StaticAccountKeysMeta::try_new(&bytes, &mut offset).is_err());
+    }
+}