feat: Hook up le_field host function

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

@@ -146,6 +146,12 @@ host_functions! {
     #[wasm_name = "home_le_field"]
     fn get_current_ledger_obj_field(&self, field: i32, out: &mut [u8]) -> HostResult<usize>;
 
+    /// The serialized bytes of one field of a previously cached ledger object,
+    /// selected by its cache slot and the field's `SField` code.
+    #[gas = 70]
+    #[wasm_name = "le_field"]
+    fn get_ledger_obj_field(&self, cache_idx: i32, field: i32, out: &mut [u8]) -> HostResult<usize>;
+
     /// The XRPL `sha512Half` of `data`: the first [`HASH_LEN`] bytes of its SHA-512.
     #[gas = 2000]
     #[wasm_name = "sha512_half"]

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

@@ -69,6 +69,19 @@ impl HostFunctions for FakeHost {
         put(out, &[field as u8])
     }
 
+    /// A field getter over a cached object, keyed by slot and selector.
+    fn get_ledger_obj_field(
+        &self,
+        cache_idx: i32,
+        field: i32,
+        out: &mut [u8],
+    ) -> HostResult<usize> {
+        if cache_idx <= 0 || field < 0 {
+            return Err(HostError::FieldNotFound);
+        }
+        put(out, &[cache_idx as u8, field as u8])
+    }
+
     fn sha512_half(&self, data: &[u8], out: &mut [u8]) -> HostResult<usize> {
         let mut digest = [0; HASH_LEN];
         digest[0] = data.len() as u8;
@@ -109,6 +122,8 @@ fn the_trait_is_implementable() {
     assert_eq!(out[0], 5);
     assert_eq!(host.get_current_ledger_obj_field(3, &mut out), Ok(1));
     assert_eq!(out[0], 3);
+    assert_eq!(host.get_ledger_obj_field(2, 4, &mut out), Ok(2));
+    assert_eq!(out[..2], [2, 4]);
     assert_eq!(host.sha512_half(b"abc", &mut out), Ok(HASH_LEN));
     assert_eq!(out[0], 3);
     assert_eq!(host.trace("hello", b"xy", true), Ok(()));
@@ -184,6 +199,7 @@ fn the_spec_table_matches_the_declarations() {
             ("cache_le", 5000),
             ("tx_field", 70),
             ("home_le_field", 70),
+            ("le_field", 70),
             ("sha512_half", 2000),
             ("trace", 500),
             ("trace_num", 500),

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

@@ -191,6 +191,15 @@ mod ffi {
         #[cxx_name = "getCurrentLedgerObjField"]
         fn get_current_ledger_obj_field(self: &HostContext, field: i32, out: &mut [u8]) -> i32;
 
+        #[namespace = "xrpl"]
+        #[cxx_name = "getLedgerObjField"]
+        fn get_ledger_obj_field(
+            self: &HostContext,
+            cache_idx: i32,
+            field: i32,
+            out: &mut [u8],
+        ) -> i32;
+
         #[namespace = "xrpl"]
         #[cxx_name = "sha512Half"]
         fn sha512_half(self: &HostContext, data: &[u8], out: &mut [u8]) -> i32;
@@ -277,6 +286,15 @@ impl HostFunctions for CxxHost<'_> {
         bytes_written(self.ctx.get_current_ledger_obj_field(field, out))
     }
 
+    fn get_ledger_obj_field(
+        &self,
+        cache_idx: i32,
+        field: i32,
+        out: &mut [u8],
+    ) -> HostResult<usize> {
+        bytes_written(self.ctx.get_ledger_obj_field(cache_idx, field, out))
+    }
+
     fn sha512_half(&self, data: &[u8], out: &mut [u8]) -> HostResult<usize> {
         bytes_written(self.ctx.sha512_half(data, out))
     }

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

@@ -209,6 +209,14 @@ mod tests {
         fn get_current_ledger_obj_field(&self, _field: i32, _out: &mut [u8]) -> HostResult<usize> {
             unreachable!("no unit test in this module calls the host")
         }
+        fn get_ledger_obj_field(
+            &self,
+            _cache_idx: i32,
+            _field: i32,
+            _out: &mut [u8],
+        ) -> HostResult<usize> {
+            unreachable!("no unit test in this module calls the host")
+        }
         fn sha512_half(&self, _data: &[u8], _out: &mut [u8]) -> HostResult<usize> {
             unreachable!("no unit test in this module calls the host")
         }

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

@@ -137,6 +137,23 @@ pub(crate) fn register_host_functions(
                     )
                 },
             ),
+            HostFunctionSpec::GetLedgerObjField => linker.func_wrap(
+                HOST_MODULE,
+                op.wasm_name(),
+                |mut caller: Caller<'_, VmState<'_>>,
+                 cache_idx: i32,
+                 field: i32,
+                 out_ptr: i32,
+                 out_len: i32|
+                 -> Result<i32, wasmi::Error> {
+                    charged(&mut caller, HostFunctionSpec::GetLedgerObjField, |c| {
+                        let out = Region::new(out_ptr, out_len);
+                        write_into(c, out, |host, out| {
+                            host.get_ledger_obj_field(cache_idx, field, out)
+                        })
+                    })
+                },
+            ),
             HostFunctionSpec::Sha512Half => linker.func_wrap(
                 HOST_MODULE,
                 op.wasm_name(),

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

@@ -91,6 +91,11 @@ fn call_for(op: HostFunctionSpec) -> Call {
             "(call $home_le_field (i32.const 1) (i32.const 0) (i32.const 4))",
             3,
         ),
+        HostFunctionSpec::GetLedgerObjField => (
+            import::LE_FIELD,
+            "(call $le_field (i32.const 1) (i32.const 1) (i32.const 0) (i32.const 4))",
+            4,
+        ),
         HostFunctionSpec::Sha512Half => (
             import::SHA512_HALF,
             "(call $sha512_half (i32.const 0) (i32.const 4) (i32.const 0) (i32.const 32))",

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

@@ -171,6 +171,21 @@ fn tx_field_passes_the_selector_and_writes_the_field() {
     assert_eq!(*host.tx_fields_asked.borrow(), vec![17]);
 }
 
+/// A field getter over a cached object: both the slot and the selector reach the
+/// host, keyed together, and the answered bytes land where the guest asked.
+#[test]
+fn le_field_passes_the_slot_and_selector_through() {
+    let host =
+        FakeHost::new().answering_le_field(2, 17, support::Answer::bytes([0xab, 0xcd, 0xef]));
+
+    let wat = module(
+        &[import::LE_FIELD, ONE_PAGE],
+        "(call $le_field (i32.const 2) (i32.const 17) (i32.const 0) (i32.const 64))",
+    );
+    assert_eq!(status(&wat, &host), 3);
+    assert_eq!(*host.le_fields_asked.borrow(), vec![(2, 17)]);
+}
+
 /// A leading scalar parameter reaches the host as declared.
 #[test]
 fn home_le_field_passes_the_field_selector_through() {

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

@@ -98,7 +98,7 @@ 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; 11] = [
+const ALL_IMPORTS: [&str; 12] = [
     import::LDGR_INDEX,
     import::PARENT_LDGR_TIME,
     import::PARENT_LDGR_HASH,
@@ -107,6 +107,7 @@ const ALL_IMPORTS: [&str; 11] = [
     import::CACHE_LE,
     import::TX_FIELD,
     import::HOME_LE_FIELD,
+    import::LE_FIELD,
     import::SHA512_HALF,
     import::TRACE,
     import::TRACE_NUM,

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

@@ -125,6 +125,11 @@ pub struct FakeHost {
     /// What `get_current_ledger_obj_field` answers, by field selector. An
     /// unlisted selector answers `FieldNotFound`.
     pub fields: HashMap<i32, Answer>,
+    /// What `get_ledger_obj_field` answers, by (cache slot, field selector). An
+    /// unlisted key answers `FieldNotFound`.
+    pub le_fields: HashMap<(i32, i32), Answer>,
+    /// Every (cache slot, field selector) `get_ledger_obj_field` was asked for.
+    pub le_fields_asked: RefCell<Vec<(i32, i32)>>,
     /// What `sha512_half` answers, whatever it is given.
     pub digest: Answer,
     /// Every field selector `get_current_ledger_obj_field` was asked for.
@@ -156,6 +161,8 @@ impl Default for FakeHost {
             tx_fields: HashMap::new(),
             tx_fields_asked: RefCell::new(Vec::new()),
             fields: HashMap::new(),
+            le_fields: HashMap::new(),
+            le_fields_asked: RefCell::new(Vec::new()),
             digest: Answer::filler(32),
             fields_asked: RefCell::new(Vec::new()),
             digested: RefCell::new(Vec::new()),
@@ -209,6 +216,11 @@ impl FakeHost {
         self
     }
 
+    pub fn answering_le_field(mut self, cache_idx: i32, field: i32, answer: Answer) -> FakeHost {
+        self.le_fields.insert((cache_idx, field), answer);
+        self
+    }
+
     pub fn answering_digest(mut self, answer: Answer) -> FakeHost {
         self.digest = answer;
         self
@@ -262,6 +274,19 @@ impl HostFunctions for FakeHost {
         }
     }
 
+    fn get_ledger_obj_field(
+        &self,
+        cache_idx: i32,
+        field: i32,
+        out: &mut [u8],
+    ) -> HostResult<usize> {
+        self.le_fields_asked.borrow_mut().push((cache_idx, field));
+        match self.le_fields.get(&(cache_idx, field)) {
+            Some(answer) => answer.fill(out),
+            None => Err(HostError::FieldNotFound),
+        }
+    }
+
     fn sha512_half(&self, data: &[u8], out: &mut [u8]) -> HostResult<usize> {
         self.digested.borrow_mut().push(data.to_vec());
         self.digest.fill(out)
@@ -305,6 +330,8 @@ pub mod import {
     pub const TX_FIELD: &str =
         r#"(import "host_lib" "tx_field" (func $tx_field (param i32 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 LE_FIELD: &str =
+        r#"(import "host_lib" "le_field" (func $le_field (param i32 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 =
         r#"(import "host_lib" "trace" (func $trace (param i32 i32 i32 i32 i32) (result i32)))"#;

include/xrpl/tx/wasm/HostContext.h

@@ -71,6 +71,10 @@ public:
     [[nodiscard]] std::int32_t
     getCurrentLedgerObjField(std::int32_t field, rust::Slice<std::uint8_t> out) const noexcept;
 
+    [[nodiscard]] std::int32_t
+    getLedgerObjField(std::int32_t cacheIdx, std::int32_t field, rust::Slice<std::uint8_t> out)
+        const noexcept;
+
     [[nodiscard]] std::int32_t
     sha512Half(rust::Slice<std::uint8_t const> data, rust::Slice<std::uint8_t> out) const noexcept;
 

src/libxrpl/tx/wasm/HostContext.cpp

@@ -186,6 +186,26 @@ HostContext::getCurrentLedgerObjField(std::int32_t field, rust::Slice<std::uint8
     });
 }
 
+std::int32_t
+HostContext::getLedgerObjField(
+    std::int32_t cacheIdx,
+    std::int32_t field,
+    rust::Slice<std::uint8_t> out) const noexcept
+{
+    return guarded(hostFunctions_.getJournal(), kHostInternal, [&] {
+        auto const& knownSFields = SField::getKnownCodeToField();
+        auto const it = knownSFields.find(field);
+        if (it == knownSFields.end())
+            return hfErrorToInt(HostFunctionError::InvalidField);
+
+        auto const value = hostFunctions_.getLedgerObjField(cacheIdx, *it->second);
+        if (!value)
+            return hfErrorToInt(value.error());
+
+        return answer(out, value->data(), value->size());
+    });
+}
+
 std::int32_t
 HostContext::sha512Half(rust::Slice<std::uint8_t const> data, rust::Slice<std::uint8_t> out)
     const noexcept