fix(read): handle dynamic-buffer max_size without throwing (#318)#340
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mvandeberg merged 1 commit intoJun 26, 2026
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…ce#318) The read dynamic-buffer overloads passed the (grown) amount straight to dynbuf.prepare(), so when it exceeded the remaining capacity (e.g. the default initial_amount of 2048 into a bounded buffer) prepare() threw std::invalid_argument / std::length_error. This was inconsistent with read_until, which already clamps. Clamp the prepared amount to max_size() - size() and treat reaching max_size() as a successful completion. The existing eof-as-success semantics are unchanged, and read_until keeps returning error::not_found at max_size(). The clamp targets the contract that prepare(n) accepts any n with size() + n <= max_size(): string/vector grow and circular wraps to honor it. A fixed-capacity buffer may, but need not, compact; a non-compacting flat_dynamic_buffer reused after a partial consume has capacity() < max_size() - size(), so prepare throws. This is documented as a limitation — such buffers must be passed without a consumed prefix. Clamping to capacity() instead is not viable: it spins growable buffers. Also floor the prepared amount to 1 so initial_amount == 0 cannot spin, and factor the clamp into detail::read_prepare_amount so the two overloads cannot drift. Tests cover bounded string/circular/flat buffers, the flat consumed-prefix throw, and buffer contents.
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The read dynamic-buffer overloads passed the (grown) amount straight to dynbuf.prepare(), so when it exceeded the remaining capacity (e.g. the default initial_amount of 2048 into a bounded buffer) prepare() threw std::invalid_argument / std::length_error. This was inconsistent with read_until, which already clamps.
Clamp the prepared amount to max_size() - size() and treat reaching max_size() as a successful completion. The existing eof-as-success semantics are unchanged, and read_until keeps returning error::not_found at max_size().
The clamp targets the contract that prepare(n) accepts any n with size() + n <= max_size(): string/vector grow and circular wraps to honor it. A fixed-capacity buffer may, but need not, compact; a non-compacting flat_dynamic_buffer reused after a partial consume has capacity() < max_size() - size(), so prepare throws. This is documented as a limitation — such buffers must be passed without a consumed prefix. Clamping to capacity() instead is not viable: it spins growable buffers.
Also floor the prepared amount to 1 so initial_amount == 0 cannot spin, and factor the clamp into detail::read_prepare_amount so the two overloads cannot drift.
Tests cover bounded string/circular/flat buffers, the flat consumed-prefix throw, and buffer contents.
Closes #318