Simplify some stuff

Author: NicolasHug

src/torchcodec/_core/AVIOContextHolder.cpp

@@ -23,10 +23,10 @@ void AVIOContextHolder::createAVIOContext(
       buffer != nullptr,
       "Failed to allocate buffer of size " + std::to_string(bufferSize));
 
-  //   TORCH_CHECK(
-  //       (seek != nullptr) && ((write != nullptr) ^ (read != nullptr)),
-  //       "seek method must be defined, and either write or read must be
-  //       defined. " "But not both!")
+  TORCH_CHECK(
+      (seek != nullptr) && ((write != nullptr) || (read != nullptr)),
+      "seek method must be defined, and at least one of write or read must be "
+      "defined too");
   avioContext_.reset(avioAllocContext(
       buffer,
       bufferSize,

src/torchcodec/_core/AVIOFileLikeContext.cpp

@@ -9,16 +9,20 @@
 
 namespace facebook::torchcodec {
 
-AVIOFileLikeContext::AVIOFileLikeContext(py::object fileLike)
+AVIOFileLikeContext::AVIOFileLikeContext(
+    py::object fileLike,
+    std::string_view neededMethod)
     : fileLike_{UniquePyObject(new py::object(fileLike))} {
   {
     // TODO: Is it necessary to acquire the GIL here? Is it maybe even
     // harmful? At the moment, this is only called from within a pybind
     // function, and pybind guarantees we have the GIL.
     py::gil_scoped_acquire gil;
-    // TORCH_CHECK(
-    //     py::hasattr(fileLike, "read"),
-    //     "File like object must implement a read method.");
+    TORCH_CHECK(
+        py::hasattr(fileLike, neededMethod.data()),
+        "File like object must implement a ",
+        neededMethod,
+        " method.");
     TORCH_CHECK(
         py::hasattr(fileLike, "seek"),
         "File like object must implement a seek method.");

src/torchcodec/_core/AVIOFileLikeContext.h

@@ -17,10 +17,13 @@ namespace facebook::torchcodec {
 
 // Enables uers to pass in a Python file-like object. We then forward all read
 // and seek calls back up to the methods on the Python object.
+// TODO: explain this. We probably don't want it.
 class __attribute__((visibility("default"))) AVIOFileLikeContext
     : public AVIOContextHolder {
  public:
-  explicit AVIOFileLikeContext(py::object fileLike);
+  explicit AVIOFileLikeContext(
+      py::object fileLike,
+      std::string_view neededMethod);
 
  private:
   static int read(void* opaque, uint8_t* buf, int buf_size);

src/torchcodec/_core/pybind_ops.cpp

@@ -33,7 +33,8 @@ int64_t create_from_file_like(
     realSeek = seekModeFromString(seek_mode.value());
   }
 
-  auto avioContextHolder = std::make_unique<AVIOFileLikeContext>(file_like);
+  auto avioContextHolder =
+      std::make_unique<AVIOFileLikeContext>(file_like, /*neededMethod=*/"read");
 
   SingleStreamDecoder* decoder =
       new SingleStreamDecoder(std::move(avioContextHolder), realSeek);
@@ -60,7 +61,8 @@ void encode_audio_to_file_like(
   audioStreamOptions.bitRate = bit_rate;
   audioStreamOptions.numChannels = num_channels;
 
-  auto avioContextHolder = std::make_unique<AVIOFileLikeContext>(file_like);
+  auto avioContextHolder = std::make_unique<AVIOFileLikeContext>(
+      file_like, /*neededMethod=*/"write");
 
   AudioEncoder encoder(
       samples,