Streaming transport interfaces: input

[Denis Koroskin]

On Fri, 15 Oct 2010 08:37:24 +0400, Brad Roberts <braddr at puremagic.com>  
wrote:

> On 10/14/2010 8:34 AM, Andrei Alexandrescu wrote:
>> Starting a new thread from Denis' question:
>>
>>> Can we outline basic Stream interface now so that we could move on?
>>
>> Here's the input transport layer. Transport has no concern for  
>> formatting - it
>> just moves stuff around.
>>
>
> I suggest having read and write with offset style apis.  See also:  man  
> pread
>
> The value here is that you can safely concurrently access a file  
> descriptor and
> not have to worry about atomicity of seek+read or seek+write at the app  
> layer.
>

In my original API proposal I included reading from offsets:

interface SeekableInputStream : SeekableStream, InputStream
{
	...

	// reads up to buffer.length bytes from a stream
	// returns number of bytes read
	// throws on error
	size_t read(ubyte[] buffer, long offset);

	// reads up to buffer.length bytes from a specified offset
	AsyncReadFromOffsetRequest readAsync(ubyte[] buffer, long offset,  
Mailbox* mailbox = null);
	
	...
}

interface SeekableOutputStream : SeekableStream, OutputStream
{
	...

	// returns number of bytes written
	// throws on error
	size_t write(const(ubyte)[] buffer, long offset);

	// writes from from a specified offset
	AsyncWriteFromOffsetRequest writeAsync(const(ubyte)[] buffer, long  
offset, Mailbox* mailbox = null);

	...
}

Although it complicates an API quite a bit, it has its advantages, too.  
However, not all Stream types support reading/writing from an offset (e.g.  
SocketStream doesn't).