lidavidm commented on code in PR #49897:
URL: https://github.com/apache/arrow/pull/49897#discussion_r3164920167
##########
cpp/src/arrow/io/interfaces.h:
##########
@@ -279,24 +280,56 @@ class ARROW_EXPORT RandomAccessFile : public InputStream,
public Seekable {
///
/// \param[in] position Where to read bytes from
/// \param[in] nbytes The number of bytes to read
+ /// \param[in] allow_short_read Whether to allow reading less than `nbytes`
+ /// \param[out] out The buffer to read bytes into
+ /// \return The number of bytes read, or an error
+ virtual Result<int64_t> ReadAt(int64_t position, int64_t nbytes, bool
allow_short_read,
+ void* out);
+
+ /// \brief Read data from given file position.
+ ///
+ /// Like `ReadAt(position, nbytes, allow_short_read, out)` with
`allow_short_read`
+ /// set to true.
Review Comment:
I wonder if we should deprecate these overloads over time (it feels like it
would be safer to have `allow_short_read` be the opt-in rather than opt-out
behavior at least)
##########
cpp/src/arrow/io/interfaces.cc:
##########
@@ -149,38 +149,73 @@ RandomAccessFile::~RandomAccessFile() = default;
RandomAccessFile::RandomAccessFile() : interface_impl_(new Impl()) {}
+Result<int64_t> RandomAccessFile::ReadAt(int64_t position, int64_t nbytes,
+ bool allow_short_read, void* out) {
+ ARROW_ASSIGN_OR_RAISE(auto real_nbytes, ReadAt(position, nbytes, out));
+ if (!allow_short_read && real_nbytes != nbytes) {
+ return Status::IOError("File too short: expected to be able to read ",
nbytes,
+ " bytes, got ", real_nbytes);
+ }
+ return real_nbytes;
+}
+
Result<int64_t> RandomAccessFile::ReadAt(int64_t position, int64_t nbytes,
void* out) {
std::lock_guard<std::mutex> lock(interface_impl_->lock_);
RETURN_NOT_OK(Seek(position));
return Read(nbytes, out);
}
+Result<std::shared_ptr<Buffer>> RandomAccessFile::ReadAt(int64_t position,
int64_t nbytes,
+ bool
allow_short_read) {
+ ARROW_ASSIGN_OR_RAISE(auto buffer, ReadAt(position, nbytes));
+ // XXX the internal `IoRecordedRandomAccessFile` can return a null buffer
+ if (!allow_short_read && buffer && buffer->size() != nbytes) {
+ return Status::IOError("File too short: expected to be able to read ",
nbytes,
+ " bytes, got ", buffer->size());
+ }
Review Comment:
If the buffer is null and nbytes is > 0 then we should also fail right? Or
is it only possible for nbytes == 0 in the first place?
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