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nim-ffi/ffi/codegen/cpp.nim
Gabriel Cruz 9ed1fedf96
chore: reduce walls of comments (#132)
2026-07-15 11:46:05 -03:00

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Nim
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## C++ binding generator: header-only binding + CMakeLists, CBOR over the wire.
import std/[os, strutils]
import ./meta, ./string_helpers, ./c_cpp_common, ./types_ir
## Fixed 64-bit wire type for any Nim `ptr T` / `pointer`.
const CppPtrType* = "uint64_t"
const
HeaderPreludeTpl = staticRead("templates/cpp/header_prelude.hpp.tpl")
ResultTpl = staticRead("templates/cpp/result.hpp.tpl")
CborHelpersTpl = staticRead("templates/cpp/cbor_helpers.hpp.tpl")
SyncCallHelperTpl = staticRead("templates/cpp/sync_call_helper.hpp.tpl")
ContextRuleOf5Tpl = staticRead("templates/cpp/context_rule_of_5.hpp.tpl")
CMakeListsTpl = staticRead("templates/cpp/CMakeLists.txt.tpl")
func cppScalar(s: ScalarKind): string =
case s
of skBool: "bool"
of skI8: "int8_t"
of skI16: "int16_t"
of skI32: "int32_t"
of skI64: "int64_t"
of skU8: "uint8_t"
of skU16: "uint16_t"
of skU32: "uint32_t"
of skU64: "uint64_t"
of skF32: "float"
of skF64: "double"
func cppSeq(elem: string): string =
"std::vector<" & elem & ">"
func cppOpt(elem: string): string =
"std::optional<" & elem & ">"
const cppMap = NativeTypeMap(
scalar: cppScalar,
str: "std::string",
bytes: "std::vector<uint8_t>",
ptrType: CppPtrType,
seqOf: cppSeq,
optOf: cppOpt,
) ## structName omitted: C++ uses the user type name verbatim
proc nimTypeToCpp*(typeName: string): string =
renderNative(cppMap, parseFFIType(typeName))
proc emitStructCborCodec(
lines: var seq[string], structName: string, fields: seq[(string, string)]
) =
## Appends per-struct TinyCBOR encode_cbor + decode_cbor functions emitting a
## text-keyed CBOR map. The C++ type in `fields` is unused (overloads dispatch).
let n = fields.len
if n == 0:
lines.add(
"inline CborError encode_cbor(CborEncoder& e, const $1&) {" % [structName]
)
else:
lines.add(
"inline CborError encode_cbor(CborEncoder& e, const $1& v) {" % [structName]
)
lines.add(" CborEncoder m;")
lines.add(" CborError err = cbor_encoder_create_map(&e, &m, $1);" % [$n])
lines.add(" if (err) return err;")
for (name, _) in fields:
lines.add(
" err = cbor_encode_text_stringz(&m, \"$1\"); if (err) return err;" % [name]
)
lines.add(
" err = encode_cbor(m, v.$1); if (err) return err;" % [name]
)
lines.add(" return cbor_encoder_close_container(&e, &m);")
lines.add("}")
if n == 0:
lines.add("inline CborError decode_cbor(CborValue& it, $1&) {" % [structName])
lines.add(" if (!cbor_value_is_map(&it)) return CborErrorImproperValue;")
lines.add(" return cbor_value_advance(&it);")
lines.add("}")
return
lines.add("inline CborError decode_cbor(CborValue& it, $1& v) {" % [structName])
lines.add(" if (!cbor_value_is_map(&it)) return CborErrorImproperValue;")
lines.add(" CborValue field;")
lines.add(" CborError err;")
for (name, _) in fields:
lines.add(
" err = cbor_value_map_find_value(&it, \"$1\", &field); if (err) return err;" %
[name]
)
lines.add(" if (!cbor_value_is_valid(&field)) return CborErrorImproperValue;")
lines.add(" err = decode_cbor(field, v.$1); if (err) return err;" % [name])
lines.add(" return cbor_value_advance(&it);")
lines.add("}")
proc cppBracedInit(structName: string, fieldNames: seq[string]): string =
## C++ braced-init for a Req struct, e.g. `TimerEchoReq{message, count}`.
return structName & "{" & fieldNames.join(", ") & "}"
proc emitEventDispatcher(
lines: var seq[string], ctxTypeName, libName: string, events: seq[FFIEventMeta]
) =
## Emits the public per-event `addOn<X>Listener` / `removeEventListener` API.
## Callables are owned by `listeners_` (unique_ptr keyed by id); the raw
## pointer is the dylib's `user_data`, stable until removal.
if events.len == 0:
return
lines.add(
" // ── Event listener API ──────────────────────────────────"
)
lines.add(" struct ListenerHandle { std::uint64_t id = 0; };")
lines.add("")
for ev in events:
let methodName =
"addOn" & capitalizeFirstLetter(ev.nimProcName).substr(2) & "Listener"
lines.add(
" ListenerHandle $1(std::function<void(const $2&)> handler) {" %
[methodName, ev.payloadTypeName]
)
lines.add(
" auto owned = std::make_unique<TypedListener<$1>>(std::move(handler));" %
[ev.payloadTypeName]
)
lines.add(" auto* raw = owned.get();")
lines.add(" const auto id = $1_add_event_listener(" % [libName])
lines.add(
" ptr_, \"$1\", &$2::typedTrampoline<$3>, raw);" %
[ev.wireName, ctxTypeName, ev.payloadTypeName]
)
lines.add(" if (id == 0) return ListenerHandle{0};")
lines.add(" listeners_.emplace(id, std::move(owned));")
lines.add(" return ListenerHandle{id};")
lines.add(" }")
lines.add("")
lines.add(" bool removeEventListener(ListenerHandle handle) {")
lines.add(" if (handle.id == 0) return false;")
lines.add(
" const auto rc = $1_remove_event_listener(ptr_, handle.id);" % [libName]
)
lines.add(" listeners_.erase(handle.id);")
lines.add(" return rc == 0;")
lines.add(" }")
lines.add("")
proc emitEventTrampoline(lines: var seq[string], events: seq[FFIEventMeta]) =
## Private listener machinery for `emitEventDispatcher`: polymorphic
## `ListenerBase`, `TypedListener<T>` and the `typedTrampoline<T>` decoder.
if events.len == 0:
return
lines.add(" struct ListenerBase {")
lines.add(" virtual ~ListenerBase() = default;")
lines.add(" };")
lines.add("")
lines.add(" template <class T>")
lines.add(" struct TypedListener : ListenerBase {")
lines.add(" std::function<void(const T&)> fn;")
lines.add(
" explicit TypedListener(std::function<void(const T&)> f) : fn(std::move(f)) {}"
)
lines.add(" };")
lines.add("")
lines.add(" template <class T>")
lines.add(
" static void typedTrampoline(int ret, const char* msg, std::size_t len, void* ud) {"
)
lines.add(" if (!ud || ret != 0 || !msg || len == 0) return;")
lines.add(" auto* listener = static_cast<TypedListener<T>*>(ud);")
lines.add(" if (!listener->fn) return;")
lines.add(" CborParser parser; CborValue it;")
lines.add(
" if (cbor_parser_init(reinterpret_cast<const std::uint8_t*>(msg), len, 0, &parser, &it) != CborNoError) return;"
)
lines.add(" if (!cbor_value_is_map(&it)) return;")
lines.add(" CborValue payloadField;")
lines.add(
" if (cbor_value_map_find_value(&it, \"payload\", &payloadField) != CborNoError) return;"
)
lines.add(" T payload{};")
lines.add(" if (decode_cbor(payloadField, payload) != CborNoError) return;")
lines.add(" listener->fn(payload);")
lines.add(" }")
lines.add("")
proc generateCppHeader*(
procs: seq[FFIProcMeta],
types: seq[FFITypeMeta],
libName: string,
events: seq[FFIEventMeta] = @[],
): string =
var lines: seq[string] = @[]
lines.add(HeaderPreludeTpl)
if events.len > 0:
lines.add("#include <unordered_map>")
lines.add(ResultTpl)
# Generic CBOR overloads must precede the non-template struct codecs that call them (parse-time name lookup).
lines.add(CborHelpersTpl)
if types.len > 0:
lines.add("// ============================================================")
lines.add("// User-declared FFI types")
lines.add("// ============================================================")
lines.add("")
for t in types:
lines.add("struct $1 {" % [t.name])
for f in t.fields:
lines.add(" $1 $2;" % [nimTypeToCpp(f.typeName), f.name])
lines.add("};")
var fields: seq[(string, string)] = @[]
for f in t.fields:
fields.add((f.name, nimTypeToCpp(f.typeName)))
emitStructCborCodec(lines, t.name, fields)
lines.add("")
lines.add("// ============================================================")
lines.add("// Per-proc request envelopes (CBOR encoded on the wire)")
lines.add("// ============================================================")
lines.add("")
for p in procs:
if p.kind == FFIKind.DTOR:
continue
let reqName = reqStructName(p)
lines.add("struct $1 {" % [reqName])
for ep in p.extraParams:
let cppType =
if ep.ridesAsPtr():
CppPtrType
else:
nimTypeToCpp(ep.typeName)
lines.add(" $1 $2;" % [cppType, ep.name])
lines.add("};")
var fields: seq[(string, string)] = @[]
for ep in p.extraParams:
let cppType =
if ep.ridesAsPtr():
CppPtrType
else:
nimTypeToCpp(ep.typeName)
fields.add((ep.name, cppType))
emitStructCborCodec(lines, reqName, fields)
lines.add("")
lines.add("// ============================================================")
lines.add("// C FFI declarations")
lines.add("// ============================================================")
lines.add("")
lines.add("extern \"C\" {")
lines.add(
"typedef void (*FFICallback)(int ret, const char* msg, size_t len, void* user_data);"
)
lines.add("")
for p in procs:
case p.kind
of FFIKind.FFI:
lines.add(
"int $1(void* ctx, FFICallback callback, void* user_data, const uint8_t* req_cbor, size_t req_cbor_len);" %
[p.procName]
)
of FFIKind.CTOR:
lines.add(
"void* $1(const uint8_t* req_cbor, size_t req_cbor_len, FFICallback callback, void* user_data);" %
[p.procName]
)
of FFIKind.DTOR:
lines.add("int $1(void* ctx);" % [p.procName])
# Listener-registration ABI is always exported.
lines.add(
"uint64_t $1_add_event_listener(void* ctx, const char* event_name, FFICallback callback, void* user_data);" %
[libName]
)
lines.add(
"int $1_remove_event_listener(void* ctx, uint64_t listener_id);" % [libName]
)
lines.add("} // extern \"C\"")
lines.add("")
lines.add(SyncCallHelperTpl)
let classified = classifyProcs(procs)
let ctors = classified.ctors
let methods = classified.methods
let ctxTypeName = libTypeName(ctors, libName) & "Ctx"
lines.add("// ============================================================")
lines.add("// High-level C++ context class")
lines.add("// ============================================================")
lines.add("")
lines.add("class $1 {" % [ctxTypeName])
lines.add("public:")
for ctor in ctors:
let reqName = reqStructName(ctor)
var ctorParams: seq[string] = @[]
var epNames: seq[string] = @[]
for ep in ctor.extraParams:
let cppType =
if ep.ridesAsPtr():
CppPtrType
else:
nimTypeToCpp(ep.typeName)
ctorParams.add("const $1& $2" % [cppType, ep.name])
epNames.add(ep.name)
let timeoutParam = "std::chrono::milliseconds timeout = std::chrono::seconds{30}"
let ctorParamsWithTimeout =
if ctorParams.len > 0:
ctorParams.join(", ") & ", " & timeoutParam
else:
timeoutParam
let reqInit = cppBracedInit(reqName, epNames)
# `create` yields the ctx via the callback's CBOR address (sync void* return discarded), owned as a unique_ptr since the class forbids copy/move.
let createRet = "Result<std::unique_ptr<$1>>" % [ctxTypeName]
lines.add(" static $1 create($2) {" % [createRet, ctorParamsWithTimeout])
lines.add(" const auto ffi_req_ = $1;" % [reqInit])
lines.add(" auto ffi_enc_ = encodeCborFFI(ffi_req_);")
lines.add(
" if (ffi_enc_.isErr()) return $1::err(ffi_enc_.error());" % [createRet]
)
lines.add(" const auto& ffi_req_bytes_ = ffi_enc_.value();")
lines.add(" auto ffi_raw_ = ffi_call_([&](FFICallback cb, void* ud) {")
lines.add(
" (void)$1(ffi_req_bytes_.data(), ffi_req_bytes_.size(), cb, ud);" %
[ctor.procName]
)
lines.add(" return 0;")
lines.add(" }, timeout);")
lines.add(
" if (ffi_raw_.isErr()) return $1::err(ffi_raw_.error());" % [createRet]
)
lines.add(" auto ffi_addr_ = decodeCborFFI<std::string>(ffi_raw_.value());")
lines.add(
" if (ffi_addr_.isErr()) return $1::err(ffi_addr_.error());" % [createRet]
)
lines.add(" const auto& addr_str = ffi_addr_.value();")
# from_chars (not stoull) so a bad payload is an err() Result, not a throw.
lines.add(" std::uint64_t addr = 0;")
lines.add(" const char* addr_begin = addr_str.data();")
lines.add(" const char* addr_end = addr_begin + addr_str.size();")
lines.add(" const auto fc_ = std::from_chars(addr_begin, addr_end, addr);")
lines.add(" if (fc_.ec != std::errc() || fc_.ptr != addr_end) {")
lines.add(
" return $1::err(\"FFI create returned non-numeric address: \" + addr_str);" %
[createRet]
)
lines.add(" }")
# `new` (not make_unique) so the ctor can stay private.
lines.add(
" return $1::ok(std::unique_ptr<$2>(new $2(reinterpret_cast<void*>(static_cast<uintptr_t>(addr)), timeout)));" %
[createRet, ctxTypeName]
)
lines.add(" }")
lines.add("")
let captureList =
if epNames.len > 0:
epNames.join(", ") & ", timeout"
else:
"timeout"
let callList =
if epNames.len > 0:
epNames.join(", ") & ", timeout"
else:
"timeout"
lines.add(
" static std::future<Result<std::unique_ptr<$1>>> createAsync($2) {" %
[ctxTypeName, ctorParamsWithTimeout]
)
lines.add(
" return std::async(std::launch::async, [$1]() { return create($2); });" %
[captureList, callList]
)
lines.add(" }")
lines.add("")
lines.add(
ContextRuleOf5Tpl.multiReplace(("{{CTX}}", ctxTypeName), ("{{LIB}}", libName))
)
emitEventDispatcher(lines, ctxTypeName, libName, events)
for m in methods:
let methodName = stripLibPrefix(m.procName, libName)
let retCppType =
if m.returnRidesAsPtr():
CppPtrType
else:
nimTypeToCpp(m.returnTypeName)
let reqName = reqStructName(m)
var methParams: seq[string] = @[]
var methParamNames: seq[string] = @[]
for ep in m.extraParams:
let cppType =
if ep.ridesAsPtr():
CppPtrType
else:
nimTypeToCpp(ep.typeName)
methParams.add("const $1& $2" % [cppType, ep.name])
methParamNames.add(ep.name)
let methParamsStr = methParams.join(", ")
let methParamNamesStr = methParamNames.join(", ")
let reqInit = cppBracedInit(reqName, methParamNames)
let methRet = "Result<$1>" % [retCppType]
lines.add(" $1 $2($3) const {" % [methRet, methodName, methParamsStr])
lines.add(" const auto ffi_req_ = $1;" % [reqInit])
lines.add(" auto ffi_enc_ = encodeCborFFI(ffi_req_);")
lines.add(
" if (ffi_enc_.isErr()) return $1::err(ffi_enc_.error());" % [methRet]
)
lines.add(" const auto& ffi_req_bytes_ = ffi_enc_.value();")
lines.add(" auto ffi_raw_ = ffi_call_([&](FFICallback cb, void* ud) {")
lines.add(
" return $1(ptr_, cb, ud, ffi_req_bytes_.data(), ffi_req_bytes_.size());" %
[m.procName]
)
lines.add(" }, timeout_);")
lines.add(
" if (ffi_raw_.isErr()) return $1::err(ffi_raw_.error());" % [methRet]
)
lines.add(" return decodeCborFFI<$1>(ffi_raw_.value());" % [retCppType])
lines.add(" }")
lines.add("")
# `this->methodName(...)` so a same-named param can't shadow the call target.
if methParamsStr.len > 0:
lines.add(
" std::future<$1> $2Async($3) const {" % [methRet, methodName, methParamsStr]
)
lines.add(
" return std::async(std::launch::async, [this, $1]() { return this->$2($3); });" %
[methParamNamesStr, methodName, methParamNamesStr]
)
lines.add(" }")
else:
lines.add(" std::future<$1> $2Async() const {" % [methRet, methodName])
lines.add(
" return std::async(std::launch::async, [this]() { return this->$1(); });" %
[methodName]
)
lines.add(" }")
lines.add("")
lines.add("private:")
# Listener machinery must precede the `listeners_` member (its value type must be complete at declaration).
emitEventTrampoline(lines, events)
lines.add(" void* ptr_;")
lines.add(" std::chrono::milliseconds timeout_;")
if events.len > 0:
lines.add(
" std::unordered_map<std::uint64_t, std::unique_ptr<ListenerBase>> listeners_;"
)
lines.add(
" explicit $1(void* p, std::chrono::milliseconds t) : ptr_(p), timeout_(t) {}" %
[ctxTypeName]
)
lines.add("};")
lines.add("")
return lines.join("\n")
proc generateCppCMakeLists*(libName: string, nimSrcRelPath: string): string =
let src = nimSrcRelPath.replace("\\", "/")
return CMakeListsTpl.multiReplace(("{{LIB}}", libName), ("{{SRC}}", src))
proc generateCppBindings*(
procs: seq[FFIProcMeta],
types: seq[FFITypeMeta],
libName: string,
outputDir: string,
nimSrcRelPath: string,
events: seq[FFIEventMeta] = @[],
) =
createDir(outputDir)
writeFile(
outputDir / (libName & ".hpp"), generateCppHeader(procs, types, libName, events)
)
writeFile(outputDir / "CMakeLists.txt", generateCppCMakeLists(libName, nimSrcRelPath))
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