1 files changed, 53 insertions, 0 deletions
diff --git a/third_party/rust/uniffi_bindgen/src/bindings/kotlin/templates/StringHelper.kt b/third_party/rust/uniffi_bindgen/src/bindings/kotlin/templates/StringHelper.kt
new file mode 100644
index 0000000000..68324be4f9
--- /dev/null
+++ b/third_party/rust/uniffi_bindgen/src/bindings/kotlin/templates/StringHelper.kt
@@ -0,0 +1,53 @@
+public object FfiConverterString: FfiConverter<String, RustBuffer.ByValue> {
+    // Note: we don't inherit from FfiConverterRustBuffer, because we use a
+    // special encoding when lowering/lifting.  We can use `RustBuffer.len` to
+    // store our length and avoid writing it out to the buffer.
+    override fun lift(value: RustBuffer.ByValue): String {
+        try {
+            val byteArr = ByteArray(value.len)
+            value.asByteBuffer()!!.get(byteArr)
+            return byteArr.toString(Charsets.UTF_8)
+        } finally {
+            RustBuffer.free(value)
+        }
+    }
+
+    override fun read(buf: ByteBuffer): String {
+        val len = buf.getInt()
+        val byteArr = ByteArray(len)
+        buf.get(byteArr)
+        return byteArr.toString(Charsets.UTF_8)
+    }
+
+    fun toUtf8(value: String): ByteBuffer {
+        // Make sure we don't have invalid UTF-16, check for lone surrogates.
+        return Charsets.UTF_8.newEncoder().run {
+            onMalformedInput(CodingErrorAction.REPORT)
+            encode(CharBuffer.wrap(value))
+        }
+    }
+
+    override fun lower(value: String): RustBuffer.ByValue {
+        val byteBuf = toUtf8(value)
+        // Ideally we'd pass these bytes to `ffi_bytebuffer_from_bytes`, but doing so would require us
+        // to copy them into a JNA `Memory`. So we might as well directly copy them into a `RustBuffer`.
+        val rbuf = RustBuffer.alloc(byteBuf.limit())
+        rbuf.asByteBuffer()!!.put(byteBuf)
+        return rbuf
+    }
+
+    // We aren't sure exactly how many bytes our string will be once it's UTF-8
+    // encoded.  Allocate 3 bytes per UTF-16 code unit which will always be
+    // enough.
+    override fun allocationSize(value: String): Int {
+        val sizeForLength = 4
+        val sizeForString = value.length * 3
+        return sizeForLength + sizeForString
+    }
+
+    override fun write(value: String, buf: ByteBuffer) {
+        val byteBuf = toUtf8(value)
+        buf.putInt(byteBuf.limit())
+        buf.put(byteBuf)
+    }
+}