paleolimbot commented on code in PR #12323:
URL: https://github.com/apache/arrow/pull/12323#discussion_r848520733
##########
r/src/io.cpp:
##########
@@ -207,7 +209,209 @@ void io___BufferOutputStream__Write(
StopIfNotOk(stream->Write(RAW(bytes), bytes.size()));
}
-// TransformInputStream::TransformFunc wrapper
+// ------ RConnectionInputStream / RConnectionOutputStream
+
+class RConnectionFileInterface : public virtual arrow::io::FileInterface {
+ public:
+ explicit RConnectionFileInterface(cpp11::sexp connection_sexp)
+ : connection_sexp_(connection_sexp), closed_(false) {
+ check_closed();
+ }
+
+ arrow::Status Close() {
+ if (closed_) {
+ return arrow::Status::OK();
+ }
+
+ auto result = SafeCallIntoR<bool>([&]() {
+ cpp11::package("base")["close"](connection_sexp_);
+ return true;
+ });
+
+ RETURN_NOT_OK(result);
+ closed_ = true;
+ return arrow::Status::OK();
+ }
+
+ arrow::Result<int64_t> Tell() const {
+ if (closed()) {
+ return arrow::Status::IOError("R connection is closed");
+ }
+
+ cpp11::sexp result = cpp11::package("base")["seek"](connection_sexp_);
+ return cpp11::as_cpp<int64_t>(result);
+ }
+
+ bool closed() const { return closed_; }
+
+ protected:
+ cpp11::sexp connection_sexp_;
+
+ // Define the logic here because multiple inheritance makes it difficult
+ // for this base class, the InputStream and the RandomAccessFile
+ // interfaces to co-exist.
+ arrow::Result<int64_t> ReadBase(int64_t nbytes, void* out) {
+ if (closed()) {
+ return arrow::Status::IOError("R connection is closed");
+ }
+
+ return SafeCallIntoR<int64_t>([&] {
Review Comment:
I spent a bit of time trying this but I don't feel that I know how to do it
safely...for `CloseAsync()` it feels like we run the risk of the event loop
ending before the file is actually closed; for `ReadAsync()` feels like it's
better suited to something like "open a new connection, read from it, and close
it" and I end up with nested futures that feel wrong to me. I'm happy to take
another try at this if you think it's important for this usage.
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