feat: Hook up amendment_enabled host function

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

@@ -121,6 +121,13 @@ host_functions! {
     #[wasm_name = "base_fee"]
     fn get_base_fee(&self, out: &mut [u8]) -> HostResult<usize>;
 
+    /// Whether an amendment is enabled. The input is either its 32-byte id or its
+    /// name; the answer is `1` if enabled and `0` if not. Unlike the getters, this
+    /// reads an input region and returns the flag directly rather than writing bytes.
+    #[gas = 100]
+    #[wasm_name = "amendment_enabled"]
+    fn is_amendment_enabled(&self, amendment: &[u8]) -> HostResult<i32>;
+
     /// 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

@@ -43,6 +43,11 @@ impl HostFunctions for FakeHost {
         put(out, &10u32.to_le_bytes())
     }
 
+    /// Returns a flag rather than bytes, and reads its input: enabled unless empty.
+    fn is_amendment_enabled(&self, amendment: &[u8]) -> HostResult<i32> {
+        Ok(i32::from(!amendment.is_empty()))
+    }
+
     /// 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 {
@@ -83,6 +88,8 @@ fn the_trait_is_implementable() {
     assert_eq!(out[0], 0xab);
     assert_eq!(host.get_base_fee(&mut out), Ok(4));
     assert_eq!(out[..4], [10, 0, 0, 0]);
+    assert_eq!(host.is_amendment_enabled(&[1; 32]), Ok(1));
+    assert_eq!(host.is_amendment_enabled(&[]), Ok(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));
@@ -156,6 +163,7 @@ fn the_spec_table_matches_the_declarations() {
             ("parent_ldgr_time", 60),
             ("parent_ldgr_hash", 60),
             ("base_fee", 60),
+            ("amendment_enabled", 100),
             ("home_le_field", 70),
             ("sha512_half", 2000),
             ("trace", 500),

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

@@ -171,6 +171,12 @@ mod ffi {
         #[cxx_name = "getBaseFee"]
         fn get_base_fee(self: &HostContext, out: &mut [u8]) -> i32;
 
+        /// Reads the amendment (id or name) and answers `1`/`0`, or a negative
+        /// `HostError` code.
+        #[namespace = "xrpl"]
+        #[cxx_name = "isAmendmentEnabled"]
+        fn is_amendment_enabled(self: &HostContext, amendment: &[u8]) -> i32;
+
         #[namespace = "xrpl"]
         #[cxx_name = "getCurrentLedgerObjField"]
         fn get_current_ledger_obj_field(self: &HostContext, field: i32, out: &mut [u8]) -> i32;
@@ -219,6 +225,15 @@ fn reported(n: i32) -> HostResult<()> {
     Ok(())
 }
 
+/// A call whose answer is the scalar the guest reads directly (a flag): a
+/// non-negative value is that answer, a negative one its error code.
+fn flag(n: i32) -> HostResult<i32> {
+    if n < 0 {
+        return Err(HostError::from_code(n));
+    }
+    Ok(n)
+}
+
 impl HostFunctions for CxxHost<'_> {
     fn get_ledger_sqn(&self, out: &mut [u8]) -> HostResult<usize> {
         bytes_written(self.ctx.get_ledger_sqn(out))
@@ -236,6 +251,10 @@ impl HostFunctions for CxxHost<'_> {
         bytes_written(self.ctx.get_base_fee(out))
     }
 
+    fn is_amendment_enabled(&self, amendment: &[u8]) -> HostResult<i32> {
+        flag(self.ctx.is_amendment_enabled(amendment))
+    }
+
     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))
     }
@@ -534,6 +553,9 @@ mod tests {
         assert_eq!(bytes_written(-3), Err(HostError::BufferTooSmall));
         assert_eq!(reported(0), Ok(()));
         assert_eq!(reported(-14), Err(HostError::NoMemExported));
+        assert_eq!(flag(1), Ok(1));
+        assert_eq!(flag(0), Ok(0));
+        assert_eq!(flag(-2), Err(HostError::FieldNotFound));
     }
 
     /// An exception caught on the C++ side arrives as `-1`, which has to reach the
@@ -543,6 +565,7 @@ mod tests {
     fn a_caught_cxx_exception_arrives_as_internal() {
         assert_eq!(bytes_written(-1), Err(HostError::Internal));
         assert_eq!(reported(-1), Err(HostError::Internal));
+        assert_eq!(flag(-1), Err(HostError::Internal));
     }
 
     // -----------------------------------------------------------------------

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

@@ -197,6 +197,9 @@ mod tests {
         fn get_base_fee(&self, _out: &mut [u8]) -> HostResult<usize> {
             unreachable!("no unit test in this module calls the host")
         }
+        fn is_amendment_enabled(&self, _amendment: &[u8]) -> HostResult<i32> {
+            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

@@ -74,6 +74,20 @@ pub(crate) fn register_host_functions(
                     })
                 },
             ),
+            HostFunctionSpec::IsAmendmentEnabled => linker.func_wrap(
+                HOST_MODULE,
+                op.wasm_name(),
+                |mut caller: Caller<'_, VmState<'_>>,
+                 ptr: i32,
+                 len: i32|
+                 -> Result<i32, wasmi::Error> {
+                    charged(&mut caller, HostFunctionSpec::IsAmendmentEnabled, |c| {
+                        let host = c.data().host;
+                        let amendment = read_borrowed(c, Region::new(ptr, len))?;
+                        host.is_amendment_enabled(amendment)
+                    })
+                },
+            ),
             HostFunctionSpec::GetCurrentLedgerObjField => linker.func_wrap(
                 HOST_MODULE,
                 op.wasm_name(),

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

@@ -71,6 +71,11 @@ fn call_for(op: HostFunctionSpec) -> Call {
             "(call $base_fee (i32.const 0) (i32.const 4))",
             2,
         ),
+        HostFunctionSpec::IsAmendmentEnabled => (
+            import::AMENDMENT_ENABLED,
+            "(call $amendment_enabled (i32.const 0) (i32.const 32))",
+            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

@@ -93,6 +93,33 @@ fn base_fee_writes_the_fee_where_the_guest_asked() {
     assert_eq!(status(&wat, &host), 4, "the byte count");
 }
 
+/// A call that reads an input region and returns a scalar flag, rather than writing
+/// bytes to an output region: the amendment reaches the host, and its verdict comes
+/// back as the call's status.
+#[test]
+fn amendment_enabled_reads_the_input_and_returns_the_flag() {
+    let host = FakeHost::new(); // enabled by default
+
+    let wat = module(
+        &[import::AMENDMENT_ENABLED, ONE_PAGE],
+        "(call $amendment_enabled (i32.const 64) (i32.const 32))",
+    );
+    assert_eq!(status(&wat, &host), 1, "the enabled flag");
+    assert_eq!(
+        *host.amendments_asked.borrow(),
+        [vec![0u8; 32]],
+        "the 32-byte region reached the host"
+    );
+
+    // A host that reports the amendment disabled answers 0 — a value, not an error.
+    let host = FakeHost::new().answering_amendment_enabled(Ok(0));
+    let wat = module(
+        &[import::AMENDMENT_ENABLED, ONE_PAGE],
+        "(call $amendment_enabled (i32.const 0) (i32.const 32))",
+    );
+    assert_eq!(status(&wat, &host), 0, "the disabled flag");
+}
+
 /// 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

@@ -98,11 +98,12 @@ 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; 8] = [
+const ALL_IMPORTS: [&str; 9] = [
     import::LDGR_INDEX,
     import::PARENT_LDGR_TIME,
     import::PARENT_LDGR_HASH,
     import::BASE_FEE,
+    import::AMENDMENT_ENABLED,
     import::HOME_LE_FIELD,
     import::SHA512_HALF,
     import::TRACE,

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

@@ -109,6 +109,10 @@ pub struct FakeHost {
     pub parent_ledger_hash: Answer,
     /// What `get_base_fee` answers.
     pub base_fee: Answer,
+    /// What `is_amendment_enabled` answers, whatever amendment it is given.
+    pub amendment_enabled: HostResult<i32>,
+    /// Every amendment `is_amendment_enabled` was asked about.
+    pub amendments_asked: RefCell<Vec<Vec<u8>>>,
     /// What `get_current_ledger_obj_field` answers, by field selector. An
     /// unlisted selector answers `FieldNotFound`.
     pub fields: HashMap<i32, Answer>,
@@ -134,6 +138,9 @@ impl Default for FakeHost {
             parent_ledger_hash: Answer::filler(32),
             // A distinct value again, so no getter can pass by reading another's answer.
             base_fee: Answer::bytes(10u32.to_le_bytes()),
+            // Enabled by default; the id-or-name dispatch is the host's job, not the ABI's.
+            amendment_enabled: Ok(1),
+            amendments_asked: RefCell::new(Vec::new()),
             fields: HashMap::new(),
             digest: Answer::filler(32),
             fields_asked: RefCell::new(Vec::new()),
@@ -168,6 +175,11 @@ impl FakeHost {
         self
     }
 
+    pub fn answering_amendment_enabled(mut self, answer: HostResult<i32>) -> FakeHost {
+        self.amendment_enabled = answer;
+        self
+    }
+
     pub fn answering_field(mut self, field: i32, answer: Answer) -> FakeHost {
         self.fields.insert(field, answer);
         self
@@ -200,6 +212,11 @@ impl HostFunctions for FakeHost {
         self.base_fee.fill(out)
     }
 
+    fn is_amendment_enabled(&self, amendment: &[u8]) -> HostResult<i32> {
+        self.amendments_asked.borrow_mut().push(amendment.to_vec());
+        self.amendment_enabled
+    }
+
     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) {
@@ -245,6 +262,7 @@ pub mod import {
     pub const PARENT_LDGR_HASH: &str = r#"(import "host_lib" "parent_ldgr_hash" (func $parent_ldgr_hash (param i32 i32) (result i32)))"#;
     pub const BASE_FEE: &str =
         r#"(import "host_lib" "base_fee" (func $base_fee (param i32 i32) (result i32)))"#;
+    pub const AMENDMENT_ENABLED: &str = r#"(import "host_lib" "amendment_enabled" (func $amendment_enabled (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

@@ -53,6 +53,12 @@ public:
     [[nodiscard]] std::int32_t
     getBaseFee(rust::Slice<std::uint8_t> out) const noexcept;
 
+    // The amendment is either a 32-byte id or a name; a 32-byte input is tried as an
+    // id first and falls back to a name lookup. Answers 1 or 0, or a negative
+    // `HostFunctionError` code.
+    [[nodiscard]] std::int32_t
+    isAmendmentEnabled(rust::Slice<std::uint8_t const> amendment) 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

@@ -107,6 +107,34 @@ HostContext::getBaseFee(rust::Slice<std::uint8_t> out) const noexcept
     });
 }
 
+std::int32_t
+HostContext::isAmendmentEnabled(rust::Slice<std::uint8_t const> amendment) const noexcept
+{
+    return guarded(hostFunctions_.getJournal(), kHostInternal, [&] {
+        // A 32-byte input may be an amendment id; try that first and fall through to
+        // a name lookup if it is not an enabled amendment - the 32 bytes could spell
+        // a name instead.
+        if (amendment.size() == uint256::size())
+        {
+            auto const enabled =
+                hostFunctions_.isAmendmentEnabled(uint256::fromVoid(amendment.data()));
+            if (enabled && *enabled == 1)
+                return *enabled;
+        }
+
+        if (amendment.size() > 64)
+            return hfErrorToInt(HostFunctionError::DataFieldTooLarge);
+
+        auto const name =
+            std::string_view(reinterpret_cast<char const*>(amendment.data()), amendment.size());
+        auto const enabled = hostFunctions_.isAmendmentEnabled(name);
+        if (!enabled)
+            return hfErrorToInt(enabled.error());
+
+        return *enabled;
+    });
+}
+
 std::int32_t
 HostContext::getCurrentLedgerObjField(std::int32_t field, rust::Slice<std::uint8_t> out)
     const noexcept