Fix ReadIOAdapter max_len handling

[fallintoplace]

Summary

• fix ReadIOAdapter#read_enum so read(max_len) returns exactly max_len bytes instead of max_len + 1
• return nil when an enumerator-backed adapter is exhausted for bounded reads, matching IO#read(max_len)
• add a regression that reads across chunk boundaries and verifies exact-length slices through EOF

Why

ReadIOAdapter#read_enum currently uses an inclusive slice when draining its buffer. That means a bounded read can return one extra byte, which is risky in the request-body path because the adapter feeds Net::HTTP.

While validating the fix, the same path also showed an EOF mismatch for bounded reads: after the final chunk, the adapter returned "" once before returning nil. Tightening that behavior keeps the adapter aligned with IO#read(max_len) semantics.

Validation

• ASDF_RUBY_VERSION=3.4.9 asdf exec bundle exec ruby -Itest test/openai/internal/util_test.rb --name=/read/
• ASDF_RUBY_VERSION=3.4.9 asdf exec bundle exec ruby -Itest test/openai/internal/util_test.rb

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 7add883c98

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Handle EOF when read receives an output buffer

When an enumerator-backed body ends exactly on the IO.copy_stream buffer boundary, IO.copy_stream makes one more call as read(16384, outbuf). This new EOF branch now returns nil while still inside the Enumerator path, so read reaches out_string.replace(read) with read == nil and raises TypeError instead of letting Net::HTTP finish the upload. For example, an enumerator yielding exactly 16 KiB reproduces the failure through IO.copy_stream.

Useful? React with 👍 / 👎.