feat: Hook up parent_ldgr_time host function

crates/xrpl-host-functions/src/lib.rs

@@ -106,6 +106,11 @@ host_functions! {
     #[wasm_name = "ldgr_index"]
     fn get_ledger_sqn(&self, out: &mut [u8]) -> HostResult<usize>;
 
+    /// The close time of the parent (last-closed) ledger, as 4 little-endian bytes.
+    #[gas = 60]
+    #[wasm_name = "parent_ldgr_time"]
+    fn get_parent_ledger_time(&self, out: &mut [u8]) -> HostResult<usize>;
+
     /// The serialized bytes of one field of the current (escrow) ledger object.
     #[gas = 70]
     #[wasm_name = "home_le_field"]

crates/xrpl-host-functions/tests/generated_abi.rs

@@ -31,6 +31,10 @@ impl HostFunctions for FakeHost {
         put(out, &7u32.to_le_bytes())
     }
 
+    fn get_parent_ledger_time(&self, out: &mut [u8]) -> HostResult<usize> {
+        put(out, &9u32.to_le_bytes())
+    }
+
     /// Fails on a field it doesn't know, so the error channel is exercised too.
     fn get_current_ledger_obj_field(&self, field: i32, out: &mut [u8]) -> HostResult<usize> {
         if field < 0 {
@@ -65,6 +69,8 @@ fn the_trait_is_implementable() {
 
     assert_eq!(host.get_ledger_sqn(&mut out), Ok(4));
     assert_eq!(out[..4], [7, 0, 0, 0]);
+    assert_eq!(host.get_parent_ledger_time(&mut out), Ok(4));
+    assert_eq!(out[..4], [9, 0, 0, 0]);
     assert_eq!(host.get_current_ledger_obj_field(3, &mut out), Ok(1));
     assert_eq!(out[0], 3);
     assert_eq!(host.sha512_half(b"abc", &mut out), Ok(HASH_LEN));
@@ -135,6 +141,7 @@ fn the_spec_table_matches_the_declarations() {
         table,
         [
             ("ldgr_index", 60),
+            ("parent_ldgr_time", 60),
             ("home_le_field", 70),
             ("sha512_half", 2000),
             ("trace", 500),

crates/xrpl-wasm-vm-ffi/src/lib.rs

@@ -159,6 +159,10 @@ mod ffi {
         #[cxx_name = "getLedgerSqn"]
         fn get_ledger_sqn(self: &HostContext, out: &mut [u8]) -> i32;
 
+        #[namespace = "xrpl"]
+        #[cxx_name = "getParentLedgerTime"]
+        fn get_parent_ledger_time(self: &HostContext, out: &mut [u8]) -> i32;
+
         #[namespace = "xrpl"]
         #[cxx_name = "getCurrentLedgerObjField"]
         fn get_current_ledger_obj_field(self: &HostContext, field: i32, out: &mut [u8]) -> i32;
@@ -212,6 +216,10 @@ impl HostFunctions for CxxHost<'_> {
         bytes_written(self.ctx.get_ledger_sqn(out))
     }
 
+    fn get_parent_ledger_time(&self, out: &mut [u8]) -> HostResult<usize> {
+        bytes_written(self.ctx.get_parent_ledger_time(out))
+    }
+
     fn get_current_ledger_obj_field(&self, field: i32, out: &mut [u8]) -> HostResult<usize> {
         bytes_written(self.ctx.get_current_ledger_obj_field(field, out))
     }

crates/xrpl-wasm-vm/src/abi.rs

@@ -188,6 +188,9 @@ mod tests {
         fn get_ledger_sqn(&self, _out: &mut [u8]) -> HostResult<usize> {
             unreachable!("no unit test in this module calls the host")
         }
+        fn get_parent_ledger_time(&self, _out: &mut [u8]) -> HostResult<usize> {
+            unreachable!("no unit test in this module calls the host")
+        }
         fn get_current_ledger_obj_field(&self, _field: i32, _out: &mut [u8]) -> HostResult<usize> {
             unreachable!("no unit test in this module calls the host")
         }

crates/xrpl-wasm-vm/src/register.rs

@@ -35,6 +35,19 @@ pub(crate) fn register_host_functions(
                     })
                 },
             ),
+            HostFunctionSpec::GetParentLedgerTime => linker.func_wrap(
+                HOST_MODULE,
+                op.wasm_name(),
+                |mut caller: Caller<'_, VmState<'_>>,
+                 out_ptr: i32,
+                 out_len: i32|
+                 -> Result<i32, wasmi::Error> {
+                    charged(&mut caller, HostFunctionSpec::GetParentLedgerTime, |c| {
+                        let out = Region::new(out_ptr, out_len);
+                        write_into(c, out, |host, out| host.get_parent_ledger_time(out))
+                    })
+                },
+            ),
             HostFunctionSpec::GetCurrentLedgerObjField => linker.func_wrap(
                 HOST_MODULE,
                 op.wasm_name(),

crates/xrpl-wasm-vm/tests/budgets.rs

@@ -56,6 +56,11 @@ fn call_for(op: HostFunctionSpec) -> Call {
             "(call $ldgr_index (i32.const 0) (i32.const 4))",
             2,
         ),
+        HostFunctionSpec::GetParentLedgerTime => (
+            import::PARENT_LDGR_TIME,
+            "(call $parent_ldgr_time (i32.const 0) (i32.const 4))",
+            2,
+        ),
         HostFunctionSpec::GetCurrentLedgerObjField => (
             import::HOME_LE_FIELD,
             "(call $home_le_field (i32.const 1) (i32.const 0) (i32.const 4))",

crates/xrpl-wasm-vm/tests/host_calls.rs

@@ -27,6 +27,28 @@ fn ldgr_index_writes_the_sequence_number_where_the_guest_asked() {
     assert_eq!(status(&wat, &host), 4, "the byte count");
 }
 
+/// A second scalar getter travels the same path: the value the host supplies lands
+/// where the guest asked, and the status is the byte count. The default parent
+/// ledger time is distinct from the sequence number, so this cannot pass by reading
+/// the wrong one.
+#[test]
+fn parent_ldgr_time_writes_the_close_time_where_the_guest_asked() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[import::PARENT_LDGR_TIME, ONE_PAGE],
+        "(drop (call $parent_ldgr_time (i32.const 64) (i32.const 4)))
+         (i32.load (i32.const 64))",
+    );
+    assert_eq!(status(&wat, &host), 9, "the 4 LE bytes the host wrote");
+
+    let wat = module(
+        &[import::PARENT_LDGR_TIME, ONE_PAGE],
+        "(call $parent_ldgr_time (i32.const 64) (i32.const 4))",
+    );
+    assert_eq!(status(&wat, &host), 4, "the byte count");
+}
+
 /// The output region is wherever the guest points, not a fixed address.
 #[test]
 fn the_output_region_is_the_pointer_the_guest_gave() {

crates/xrpl-wasm-vm/tests/preflight.rs

@@ -98,8 +98,9 @@ fn a_disabled_feature_does_not_pass() {
 
 /// Every host function the ABI declares, spelled as a guest imports it. The count
 /// is asserted against the ABI so a function added to it cannot be left out here.
-const ALL_IMPORTS: [&str; 5] = [
+const ALL_IMPORTS: [&str; 6] = [
     import::LDGR_INDEX,
+    import::PARENT_LDGR_TIME,
     import::HOME_LE_FIELD,
     import::SHA512_HALF,
     import::TRACE,

crates/xrpl-wasm-vm/tests/support/mod.rs

@@ -103,6 +103,8 @@ pub enum Trace {
 pub struct FakeHost {
     /// What `get_ledger_sqn` answers.
     pub ledger_sqn: Answer,
+    /// What `get_parent_ledger_time` answers.
+    pub parent_ledger_time: Answer,
     /// What `get_current_ledger_obj_field` answers, by field selector. An
     /// unlisted selector answers `FieldNotFound`.
     pub fields: HashMap<i32, Answer>,
@@ -121,6 +123,9 @@ impl Default for FakeHost {
         FakeHost {
             // 4 little-endian bytes, as the declaration's doc comment specifies.
             ledger_sqn: Answer::bytes(7u32.to_le_bytes()),
+            // A distinct value from the sequence number, so a test cannot pass by
+            // reading one where it meant the other.
+            parent_ledger_time: Answer::bytes(9u32.to_le_bytes()),
             fields: HashMap::new(),
             digest: Answer::filler(32),
             fields_asked: RefCell::new(Vec::new()),
@@ -140,6 +145,11 @@ impl FakeHost {
         self
     }
 
+    pub fn answering_parent_ledger_time(mut self, answer: Answer) -> FakeHost {
+        self.parent_ledger_time = answer;
+        self
+    }
+
     pub fn answering_field(mut self, field: i32, answer: Answer) -> FakeHost {
         self.fields.insert(field, answer);
         self
@@ -160,6 +170,10 @@ impl HostFunctions for FakeHost {
         self.ledger_sqn.fill(out)
     }
 
+    fn get_parent_ledger_time(&self, out: &mut [u8]) -> HostResult<usize> {
+        self.parent_ledger_time.fill(out)
+    }
+
     fn get_current_ledger_obj_field(&self, field: i32, out: &mut [u8]) -> HostResult<usize> {
         self.fields_asked.borrow_mut().push(field);
         match self.fields.get(&field) {
@@ -201,6 +215,7 @@ impl HostFunctions for FakeHost {
 pub mod import {
     pub const LDGR_INDEX: &str =
         r#"(import "host_lib" "ldgr_index" (func $ldgr_index (param i32 i32) (result i32)))"#;
+    pub const PARENT_LDGR_TIME: &str = r#"(import "host_lib" "parent_ldgr_time" (func $parent_ldgr_time (param i32 i32) (result i32)))"#;
     pub const HOME_LE_FIELD: &str = r#"(import "host_lib" "home_le_field" (func $home_le_field (param i32 i32 i32) (result i32)))"#;
     pub const SHA512_HALF: &str = r#"(import "host_lib" "sha512_half" (func $sha512_half (param i32 i32 i32 i32) (result i32)))"#;
     pub const TRACE: &str =

include/xrpl/tx/wasm/HostContext.h

@@ -44,6 +44,9 @@ public:
     [[nodiscard]] std::int32_t
     getLedgerSqn(rust::Slice<std::uint8_t> out) const noexcept;
 
+    [[nodiscard]] std::int32_t
+    getParentLedgerTime(rust::Slice<std::uint8_t> out) const noexcept;
+
     [[nodiscard]] std::int32_t
     getCurrentLedgerObjField(std::int32_t field, rust::Slice<std::uint8_t> out) const noexcept;
 

src/libxrpl/tx/wasm/HostContext.cpp

@@ -71,6 +71,18 @@ HostContext::getLedgerSqn(rust::Slice<std::uint8_t> out) const noexcept
     });
 }
 
+std::int32_t
+HostContext::getParentLedgerTime(rust::Slice<std::uint8_t> out) const noexcept
+{
+    return guarded(hostFunctions_.getJournal(), kHostInternal, [&] {
+        auto const time = hostFunctions_.getParentLedgerTime();
+        if (!time)
+            return hfErrorToInt(time.error());
+
+        return answerScalar(out, *time);
+    });
+}
+
 std::int32_t
 HostContext::getCurrentLedgerObjField(std::int32_t field, rust::Slice<std::uint8_t> out)
     const noexcept