1 files changed, 71 insertions, 0 deletions
diff --git a/third_party/rust/uniffi_bindgen/src/bindings/kotlin/templates/FfiConverterTemplate.kt b/third_party/rust/uniffi_bindgen/src/bindings/kotlin/templates/FfiConverterTemplate.kt
new file mode 100644
index 0000000000..3b2c9d225a
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+++ b/third_party/rust/uniffi_bindgen/src/bindings/kotlin/templates/FfiConverterTemplate.kt
@@ -0,0 +1,71 @@
+// The FfiConverter interface handles converter types to and from the FFI
+//
+// All implementing objects should be public to support external types.  When a
+// type is external we need to import it's FfiConverter.
+public interface FfiConverter<KotlinType, FfiType> {
+    // Convert an FFI type to a Kotlin type
+    fun lift(value: FfiType): KotlinType
+
+    // Convert an Kotlin type to an FFI type
+    fun lower(value: KotlinType): FfiType
+
+    // Read a Kotlin type from a `ByteBuffer`
+    fun read(buf: ByteBuffer): KotlinType
+
+    // Calculate bytes to allocate when creating a `RustBuffer`
+    //
+    // This must return at least as many bytes as the write() function will
+    // write. It can return more bytes than needed, for example when writing
+    // Strings we can't know the exact bytes needed until we the UTF-8
+    // encoding, so we pessimistically allocate the largest size possible (3
+    // bytes per codepoint).  Allocating extra bytes is not really a big deal
+    // because the `RustBuffer` is short-lived.
+    fun allocationSize(value: KotlinType): Int
+
+    // Write a Kotlin type to a `ByteBuffer`
+    fun write(value: KotlinType, buf: ByteBuffer)
+
+    // Lower a value into a `RustBuffer`
+    //
+    // This method lowers a value into a `RustBuffer` rather than the normal
+    // FfiType.  It's used by the callback interface code.  Callback interface
+    // returns are always serialized into a `RustBuffer` regardless of their
+    // normal FFI type.
+    fun lowerIntoRustBuffer(value: KotlinType): RustBuffer.ByValue {
+        val rbuf = RustBuffer.alloc(allocationSize(value))
+        try {
+            val bbuf = rbuf.data!!.getByteBuffer(0, rbuf.capacity.toLong()).also {
+                it.order(ByteOrder.BIG_ENDIAN)
+            }
+            write(value, bbuf)
+            rbuf.writeField("len", bbuf.position())
+            return rbuf
+        } catch (e: Throwable) {
+            RustBuffer.free(rbuf)
+            throw e
+        }
+    }
+
+    // Lift a value from a `RustBuffer`.
+    //
+    // This here mostly because of the symmetry with `lowerIntoRustBuffer()`.
+    // It's currently only used by the `FfiConverterRustBuffer` class below.
+    fun liftFromRustBuffer(rbuf: RustBuffer.ByValue): KotlinType {
+        val byteBuf = rbuf.asByteBuffer()!!
+        try {
+           val item = read(byteBuf)
+           if (byteBuf.hasRemaining()) {
+               throw RuntimeException("junk remaining in buffer after lifting, something is very wrong!!")
+           }
+           return item
+        } finally {
+            RustBuffer.free(rbuf)
+        }
+    }
+}
+
+// FfiConverter that uses `RustBuffer` as the FfiType
+public interface FfiConverterRustBuffer<KotlinType>: FfiConverter<KotlinType, RustBuffer.ByValue> {
+    override fun lift(value: RustBuffer.ByValue) = liftFromRustBuffer(value)
+    override fun lower(value: KotlinType) = lowerIntoRustBuffer(value)
+}