Allowing construction of NoAllocSliceSegments with buffer and NoAllocBufferSegmentType about capnproto-rust HOT 7 CLOSED

I removed the first parameter in 9738fed.

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I opened a PR for adding public visibility tot he relevant items: #489.

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What if we add public visibility to ReadSegmentTableResult, read_segment_table(), and NoAllocBufferSegments::from_segment_table()? (These things are currently at private or crate-only visibility.)

Then I think you would be able get the message length from ReadSegmentTableResult before constructing the BufferSegments.

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What if we add public visibility to ReadSegmentTableResult, read_segment_table(), and NoAllocBufferSegments::from_segment_table()? (These things are currently at private or crate-only visibility.)

Then I think you would be able get the message length from ReadSegmentTableResult before constructing the BufferSegments.

In my case, I don't need to use read_segment_table() which requires a complete slice because I need to parse the header while reading from the socket to get complete messages.
So I am reading bytes partially from the socket and parsing the header directly to determine the total message length. In fact, exposing NoAllocBufferSegments::from_segment_table() to public seems sufficient.

BTW, is there a reason why NoAllocBufferSegmentType is defined as:

enum NoAllocBufferSegmentType {
    SingleSegment(usize, usize),
    MultipleSegments,
}

Instead of:

enum NoAllocBufferSegmentType {
    SingleSegment,
    MultipleSegments,
}

In the case of SingleSegment, segment_table_length_bytes must always be 8, and the message length is also inferred from the buffer. In fact, in version 0.17, NoAllocSliceSegments requires buffer only for both of SingleSegment and MultipleSegments

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In the case of SingleSegment, segment_table_length_bytes must always be 8, and the message length is also inferred from the buffer.

Hm... I agree that it looks like the first parameter is not needed. The second parameter however might point to before the end of the buffer if from_buffer() is called on something that's longer than the message:

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@dwrensha Thanks for your prompt help. I really appreciate it!

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Closed by #489.

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