grpc-native: Optimize String encoding by avoiding converting Kotlin string to std::string

Signed-off-by: Johannes Zottele <[email protected]>

Author: Jozott00

grpc/grpc-core/src/nativeInterop/cinterop/libprotowire.def

@@ -1,4 +1,6 @@
 headers = protowire.h
 headerFilter = protowire.h
 
+noStringConversion = pw_encoder_write_string
+
 staticLibraries = libprotowire_static.a

grpc/grpc-core/src/nativeMain/kotlin/kotlinx/rpc/grpc/internal/WireEncoder.native.kt

@@ -11,6 +11,8 @@ import kotlin.experimental.ExperimentalNativeApi
 import kotlin.native.ref.createCleaner
 
 
+// TODO: Evaluate if we should implement a ZeroCopyOutputSink (similar to the ZeroCopyInputSource)
+//      to reduce the number of copies during encoding.
 @OptIn(ExperimentalForeignApi::class, ExperimentalNativeApi::class)
 internal class WireEncoderNative(private val sink: Sink): WireEncoder {
     /**
@@ -94,10 +96,12 @@ internal class WireEncoderNative(private val sink: Sink): WireEncoder {
     }
 
     override fun writeString(fieldNr: Int, value: String): Boolean {
-        val str = pw_string_new(value) ?: error("Failed to create string")
-        val result = pw_encoder_write_string(raw, fieldNr, str)
-        pw_string_delete(str)
-        return result;
+        if (value.isEmpty()) {
+            return pw_encoder_write_string(raw, fieldNr, null, 0)
+        }
+        return value.usePinned {
+            pw_encoder_write_string(raw, fieldNr, it.addressOf(0).reinterpret(), value.length)
+        }
     }
 
     override fun flush() {

grpc/grpc-core/src/nativeTest/kotlin/kotlinx/rpc/grpc/internal/WireCodecTest.kt

@@ -553,4 +553,24 @@ class WireCodecTest {
         }
         assertTrue(buffer.exhausted())
     }
+
+    @Test
+    fun testEmptyString() {
+        val buffer = Buffer()
+
+        val encoder = WireEncoder(buffer)
+        assertTrue(encoder.writeString(1, ""))
+        encoder.flush()
+
+        val decoder = WireDecoder(buffer)
+
+        val tag = decoder.readTag()
+        assertNotNull(tag)
+        assertEquals(1, tag.fieldNr)
+        assertEquals(WireType.LENGTH_DELIMITED, tag.wireType)
+
+        val str = decoder.readString()
+        assertNotNull(str)
+        assertEquals("", str)
+    }
 }

grpc/grpcpp-c/include/protowire.h

@@ -48,7 +48,7 @@ extern "C" {
     bool pw_encoder_write_float(pw_encoder_t *self, int field_no, float value);
     bool pw_encoder_write_double(pw_encoder_t *self, int field_no, double value);
     bool pw_encoder_write_enum(pw_encoder_t *self, int field_no, int value);
-    bool pw_encoder_write_string(pw_encoder_t *self, int field_no, pw_string_t *value);
+    bool pw_encoder_write_string(pw_encoder_t *self, int field_no, const char *data, int size);
     bool pw_encoder_write_bytes(pw_encoder_t *self, int field_no, pw_string_t *value);
 
 
@@ -70,6 +70,7 @@ extern "C" {
         int64_t (*byteCount)(void *ctx);
     } pw_zero_copy_input_t;
 
+
     /**
      * Create a new pw_decoder_t that wraps a CodedInputStream to decode values from a wire format stream.
      *

grpc/grpcpp-c/src/protowire.cpp

@@ -101,7 +101,9 @@ struct pw_encoder {
     explicit pw_encoder(protowire::SinkStream sink)
     : sinkStream(std::move(sink)),
       cosa(&sinkStream),
-      cos(&cosa) {}
+      cos(&cosa) {
+        cos.EnableAliasing(true);
+    }
 };
 
 struct pw_decoder {
@@ -166,8 +168,10 @@ extern "C" {
     WRITE_FIELD_FUNC( sfixed64, SFixed64, int64_t)
     WRITE_FIELD_FUNC( enum, Enum, int)
 
-    bool pw_encoder_write_string(pw_encoder_t *self, int field_no, pw_string_t *value) {
-        WireFormatLite::WriteString(field_no, value->str, &self->cos);
+    bool pw_encoder_write_string(pw_encoder_t *self, int field_no, const char *data, int size) {
+        WireFormatLite::WriteTag(field_no, WireFormatLite::WIRETYPE_LENGTH_DELIMITED, &self->cos);
+        self->cos.WriteVarint32(size);
+        self->cos.WriteRawMaybeAliased(data, size);
         return check(self);
     }
     bool pw_encoder_write_bytes(pw_encoder_t *self, int field_no, pw_string_t *value) {