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  <title>P3185R0: A proposed direction for C++ Standard Networking based on IETF TAPS</title>
<style data-fill-with="stylesheet">/******************************************************************************
 *                   Style sheet for the W3C specifications                   *
 *
 * Special classes handled by this style sheet include:
 *
 * Indices
 *   - .toc for the Table of Contents (<ol class="toc">)
 *     + <span class="secno"> for the section numbers
 *   - #toc for the Table of Contents (<nav id="toc">)
 *   - ul.index for Indices (<a href="#ref">term</a><span>, in § N.M</span>)
 *   - table.index for Index Tables (e.g. for properties or elements)
 *
 * Structural Markup
 *   - table.data for general data tables
 *     -> use 'scope' attribute, <colgroup>, <thead>, and <tbody> for best results !
 *     -> use <table class='complex data'> for extra-complex tables
 *     -> use <td class='long'> for paragraph-length cell content
 *     -> use <td class='pre'> when manual line breaks/indentation would help readability
 *   - dl.switch for switch statements
 *   - ol.algorithm for algorithms (helps to visualize nesting)
 *   - .figure and .caption (HTML4) and figure and figcaption (HTML5)
 *     -> .sidefigure for right-floated figures
 *   - ins/del
 *     -> ins/del.c### for candidate and proposed changes (amendments)
 *
 * Code
 *   - pre and code
 *
 * Special Sections
 *   - .note       for informative notes             (div, p, span, aside, details)
 *   - .example    for informative examples          (div, p, pre, span)
 *   - .issue      for issues                        (div, p, span)
 *   - .advisement for loud normative statements     (div, p, strong)
 *   - .annoying-warning for spec obsoletion notices (div, aside, details)
 *   - .correction for "candidate corrections"       (div, aside, details, section)
 *   - .addition   for "candidate additions"         (div, aside, details, section)
 *   - .correction.proposed for "proposed corrections" (div, aside, details, section)
 *   - .addition.proposed   for "proposed additions"   (div, aside, details, section)
 *
 * Definition Boxes
 *   - pre.def   for WebIDL definitions
 *   - table.def for tables that define other entities (e.g. CSS properties)
 *   - dl.def    for definition lists that define other entitles (e.g. HTML elements)
 *
 * Numbering
 *   - .secno for section numbers in .toc and headings (<span class='secno'>3.2</span>)
 *   - .marker for source-inserted example/figure/issue numbers (<span class='marker'>Issue 4</span>)
 *   - ::before styled for CSS-generated issue/example/figure numbers:
 *     -> Documents wishing to use this only need to add
 *        figcaption::before,
 *        .caption::before { content: "Figure "  counter(figure) " ";  }
 *        .example::before { content: "Example " counter(example) " "; }
 *        .issue::before   { content: "Issue "   counter(issue) " ";   }
 *
 * Header Stuff (ignore, just don't conflict with these classes)
 *   - .head for the header
 *   - .copyright for the copyright
 *
 * Outdated warning for old specs
 *
 * Miscellaneous
 *   - .overlarge for things that should be as wide as possible, even if
 *     that overflows the body text area. This can be used on an item or
 *     on its container, depending on the effect desired.
 *     Note that this styling basically doesn't help at all when printing,
 *     since A4 paper isn't much wider than the max-width here.
 *     It's better to design things to fit into a narrower measure if possible.
 *
 *   - js-added ToC jump links (see fixup.js)
 *
 ******************************************************************************/

/* color variables included separately for reliability */

/******************************************************************************/
/*                                    Body                                    */
/******************************************************************************/

	html {
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	body {
		counter-reset: example figure issue;

		/* Layout */
		max-width: 50em;			  /* limit line length to 50em for readability   */
		margin: 0 auto;				/* center text within page                    */
		padding: 1.6em 1.5em 2em 50px; /* assume 16px font size for downlevel clients */
		padding: 1.6em 1.5em 2em calc(26px + 1.5em); /* leave space for status flag    */

		/* Typography */
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		color: black;
		color: var(--text);
		background: white top left fixed no-repeat;
		background: var(--bg) top left fixed no-repeat;
		background-size: 25px auto;
	}


/******************************************************************************/
/*                         Front Matter & Navigation                          */
/******************************************************************************/

/** Header ********************************************************************/

	div.head { margin-bottom: 1em; }
	div.head hr { border-style: solid; }

	div.head h1 {
		font-weight: bold;
		margin: 0 0 .1em;
		font-size: 220%;
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	div.head h2 { margin-bottom: 1.5em;}

/** W3C Logo ******************************************************************/

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	.head img[src*="logos/W3C"] {
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	.head a:hover > img[src*="logos/W3C"],
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	.head a:active > img[src*="logos/W3C"] {
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		background: var(--logo-active-bg);
		border-color: #c00;
		border-color: var(--logo-active-bg);
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	/* see also additional rules in Link Styling section */

/** Copyright *****************************************************************/

	p.copyright,
	p.copyright small { font-size: small; }

/** Back to Top / ToC Toggle **************************************************/

	@media print {
		#toc-nav {
			display: none;
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	}
	@media not print {
		#toc-nav {
			position: fixed;
			z-index: 3;
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			box-shadow: 0 0 2px;
			font-size: 1.5em;
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			white-space: nowrap;

			height: 1.33em;
			padding: .1em 0.3em;
			margin: 0;

			box-shadow: 0 0 2px;
			border: none;
			border-top-right-radius: 1.33em;

			color: #707070;
			color: var(--tocnav-normal-text);
			background: white;
			background: var(--tocnav-normal-bg);
		}
		#toc-nav > a:hover,
		#toc-nav > a:focus {
			color: black;
			color: var(--tocnav-hover-text);
			background: #f8f8f8;
			background: var(--tocnav-hover-bg);
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		#toc-nav > a:active {
			color: #c00;
			color: var(--tocnav-active-text);
			background: white;
			background: var(--tocnav-active-bg);
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		#toc-nav > #toc-jump {
			padding-bottom: 2em;
			margin-bottom: -1.9em;
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		/* statusbar gets in the way on keyboard focus; remove once browsers fix */
		#toc-nav > a[href="#toc"]:not(:hover):focus:last-child {
			padding-bottom: 1.5rem;
		}

		#toc-nav:not(:hover) > a:not(:focus) > span + span {
			/* Ideally this uses :focus-within on #toc-nav */
			display: none;
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		#toc-nav > a > span + span {
			padding-right: 0.2em;
		}
	}

/** ToC Sidebar ***************************************************************/

	/* Floating sidebar */
	@media screen {
		body.toc-sidebar #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			max-width: 80%;
			max-width: calc(100% - 2em - 26px);
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			color: black;
			color: var(--tocsidebar-text);
			background: inherit;
			background-color: #f7f8f9;
			background-color: var(--tocsidebar-bg);
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
			box-shadow: -.1em 0 .25em var(--tocsidebar-shadow) inset;
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		body.toc-sidebar #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
			color: var(--tocsidebar-heading-text);
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		body.toc-sidebar #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
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	/* Hide main scroller when only the ToC is visible anyway */
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	/* Sidebar with its own space */
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		body:not(.toc-inline) #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			color: black;
			color: var(--tocsidebar-text);
			background: inherit;
			background-color: #f7f8f9;
			background-color: var(--tocsidebar-bg);
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
			box-shadow: -.1em 0 .25em var(--tocsidebar-shadow) inset;
		}
		body:not(.toc-inline) #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
			color: var(--tocsidebar-heading-text);
		}

		body:not(.toc-inline) {
			padding-left: 29em;
		}
		/* See also Overflow section at the bottom */

		body:not(.toc-inline) #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) {
			margin: 0 4em;
		}
	}

/******************************************************************************/
/*                                Sectioning                                  */
/******************************************************************************/

/** Headings ******************************************************************/

	h1, h2, h3, h4, h5, h6, dt {
		page-break-after: avoid;
		page-break-inside: avoid;
		font: 100% sans-serif;   /* Reset all font styling to clear out UA styles */
		font-family: inherit;	/* Inherit the font family. */
		line-height: 1.2;		/* Keep wrapped headings compact */
		hyphens: manual;		/* Hyphenated headings look weird */
	}

	h2, h3, h4, h5, h6 {
		margin-top: 3rem;
	}

	h1, h2, h3 {
		color: #005A9C;
		color: var(--heading-text);
	}

	h1 { font-size: 170%; }
	h2 { font-size: 140%; }
	h3 { font-size: 120%; }
	h4 { font-weight: bold; }
	h5 { font-style: italic; }
	h6 { font-variant: small-caps; }
	dt { font-weight: bold; }

/** Subheadings ***************************************************************/

	h1 + h2,
	#profile-and-date {
		/* #profile-and-date is a subtitle in an H2 under the H1 */
		margin-top: 0;
	}
	h2 + h3,
	h3 + h4,
	h4 + h5,
	h5 + h6 {
		margin-top: 1.2em; /* = 1 x line-height */
	}

/** Section divider ***********************************************************/

	:not(.head) > :not(.head) + hr {
		font-size: 1.5em;
		text-align: center;
		margin: 1em auto;
		height: auto;
		color: black;
		color: var(--hr-text);
		border: transparent solid 0;
		background: transparent;
	}
	:not(.head) > hr::before {
		content: "\2727\2003\2003\2727\2003\2003\2727";
	}

/******************************************************************************/
/*                            Paragraphs and Lists                            */
/******************************************************************************/

	p {
		margin: 1em 0;
	}

	dd > p:first-child,
	li > p:first-child {
		margin-top: 0;
	}

	ul, ol {
		margin-left: 0;
		padding-left: 2em;
	}

	li {
		margin: 0.25em 0 0.5em;
		padding: 0;
	}

	dl dd {
		margin: 0 0 .5em 2em;
	}

	.head dd + dd { /* compact for header */
		margin-top: -.5em;
	}

	/* Style for algorithms */
	ol.algorithm ol:not(.algorithm),
	.algorithm > ol ol:not(.algorithm) {
	border-left: 0.5em solid #DEF;
	border-left: 0.5em solid var(--algo-border);
	}

	/* Put nice boxes around each algorithm. */
	[data-algorithm]:not(.heading) {
	 padding: .5em;
	 border: thin solid #ddd;
	 border: thin solid var(--algo-border);
	 border-radius: .5em;
	 margin: .5em calc(-0.5em - 1px);
	}
	[data-algorithm]:not(.heading) > :first-child {
	 margin-top: 0;
	}
	[data-algorithm]:not(.heading) > :last-child {
	 margin-bottom: 0;
	}

	/* Style for switch/case <dl>s */
	dl.switch > dd > ol.only,
	dl.switch > dd > .only > ol {
	margin-left: 0;
	}
	dl.switch > dd > ol.algorithm,
	dl.switch > dd > .algorithm > ol {
	margin-left: -2em;
	}
	dl.switch {
	padding-left: 2em;
	}
	dl.switch > dt {
	text-indent: -1.5em;
	margin-top: 1em;
	}
	dl.switch > dt + dt {
	margin-top: 0;
	}
	dl.switch > dt::before {
	content: '\21AA';
	padding: 0 0.5em 0 0;
	display: inline-block;
	width: 1em;
	text-align: right;
	line-height: 0.5em;
	}

/** Terminology Markup ********************************************************/


/******************************************************************************/
/*                                 Inline Markup                              */
/******************************************************************************/

/** Terminology Markup ********************************************************/
	dfn   { /* Defining instance */
		font-weight: bolder;
	}
	a > i { /* Instance of term */
		font-style: normal;
	}
	dt dfn code, code.idl {
		font-size: inherit;
	}
	dfn var {
		font-style: normal;
	}

/** Change Marking ************************************************************/

	del {
		color: #aa0000;
		color: var(--del-text);
		background: transparent;
		background: var(--del-bg);
		text-decoration: line-through;
	}
	ins {
		color: #006100;
		color: var(--ins-text);
		background: transparent;
		background: var(--ins-bg);
		text-decoration: underline;
	}

	/* for amendments (candidate/proposed changes) */

	.amendment ins, .correction ins, .addition ins,
	ins[class^=c] {
		text-decoration-style: dotted;
	}
	.amendment del, .correction del, .addition del,
	del[class^=c] {
		text-decoration-style: dotted;
	}
	.amendment.proposed ins, .correction.proposed ins, .addition.proposed ins,
	ins[class^=c].proposed {
		text-decoration-style: double;
	}
	.amendment.proposed del, .correction.proposed del, .addition.proposed del,
	del[class^=c].proposed {
		text-decoration-style: double;
	}

/** Miscellaneous improvements to inline formatting ***************************/

	sup {
		vertical-align: super;
		font-size: 80%
	}

/******************************************************************************/
/*                                    Code                                    */
/******************************************************************************/

/** General monospace/pre rules ***********************************************/

	pre, code, samp {
		font-family: Menlo, Consolas, "DejaVu Sans Mono", Monaco, monospace;
		font-size: .9em;
		hyphens: none;
		text-transform: none;
		text-align: left;
		text-align: start;
		font-variant: normal;
		orphans: 3;
		widows: 3;
		page-break-before: avoid;
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	pre code,
	code code {
		font-size: 100%;
	}

	pre {
		margin-top: 1em;
		margin-bottom: 1em;
		overflow: auto;
	}

/** Inline Code fragments *****************************************************/

	/* Do something nice. */

/******************************************************************************/
/*                                    Links                                   */
/******************************************************************************/

/** General Hyperlinks ********************************************************/

	/* We hyperlink a lot, so make it less intrusive */
	a[href] {
		color: #034575;
		color: var(--a-normal-text);
		text-decoration: underline #707070;
		text-decoration: underline var(--a-normal-underline);
		text-decoration-skip-ink: none;
	}
	a:visited {
		color: #034575;
		color: var(--a-visited-text);
		text-decoration-color: #bbb;
		text-decoration-color: var(--a-visited-underline);
	}

	/* Indicate interaction with the link */
	a[href]:focus,
	a[href]:hover {
		text-decoration-thickness: 2px;
	}
	a[href]:active {
		color: #c00;
		color: var(--a-active-text);
		text-decoration-color: #c00;
		text-decoration-color: var(--a-active-underline);
	}

	/* Backout above styling for W3C logo */
	.head .logo,
	.head .logo a {
		border: none;
		text-decoration: none;
		background: transparent;
	}

/******************************************************************************/
/*                                    Images                                  */
/******************************************************************************/

	img {
		border-style: none;
	}

	img, svg {
		/* Intentionally not color-scheme aware. */
		background: white;
	}

	/* For autogen numbers, add
	  .caption::before, figcaption::before { content: "Figure " counter(figure) ". "; }
	*/

	figure, .figure, .sidefigure {
		page-break-inside: avoid;
		text-align: center;
		margin: 2.5em 0;
	}
	.figure img,	.sidefigure img,	figure img,
	.figure object, .sidefigure object, figure object {
		max-width: 100%;
		margin: auto;
		height: auto;
	}
	.figure pre, .sidefigure pre, figure pre {
		text-align: left;
		display: table;
		margin: 1em auto;
	}
	.figure table, figure table {
		margin: auto;
	}
	@media screen and (min-width: 20em) {
		.sidefigure {
			float: right;
			width: 50%;
			margin: 0 0 0.5em 0.5em;
		}
	}
	.caption, figcaption, caption {
		font-style: italic;
		font-size: 90%;
	}
	.caption::before, figcaption::before, figcaption > .marker {
		font-weight: bold;
	}
	.caption, figcaption {
		counter-increment: figure;
	}

	/* DL list is indented 2em, but figure inside it is not */
	dd > .figure, dd > figure { margin-left: -2em; }

/******************************************************************************/
/*                             Colored Boxes                                  */
/******************************************************************************/

	.issue, .note, .example, .assertion, .advisement, blockquote,
	.amendment, .correction, .addition {
		margin: 1em auto;
		padding: .5em;
		border: .5em;
		border-left-style: solid;
		page-break-inside: avoid;
	}
	span.issue, span.note {
		padding: .1em .5em .15em;
		border-right-style: solid;
	}

	blockquote > :first-child,
	.note  > p:first-child,
	.issue > p:first-child,
	.amendment > p:first-child,
	.correction > p:first-child,
	.addition > p:first-child {
		margin-top: 0;
	}
	blockquote > :last-child,
	.note  > p:last-child,
	.issue > p:last-child,
	.amendment > p:last-child,
	.correction > p:last-child,
	.addition > p:last-child {
		margin-bottom: 0;
	}


	.issue::before, .issue > .marker,
	.example::before, .example > .marker,
	.note::before, .note > .marker,
	details.note > summary > .marker,
	.amendment::before, .amendment > .marker,
	details.amendment > summary > .marker,
	.addition::before, .addition > .marker,
	addition.amendment > summary > .marker,
	.correction::before, .correction > .marker,
	correction.amendment > summary > .marker
	{
		text-transform: uppercase;
		padding-right: 1em;
	}

	.example::before, .example > .marker {
		display: block;
		padding-right: 0em;
	}

/** Blockquotes ***************************************************************/

	blockquote {
		border-color: silver;
		border-color: var(--blockquote-border);
		background: transparent;
		background: var(--blockquote-bg);
		color: currentcolor;
		color: var(--blockquote-text);
	}

/** Open issue ****************************************************************/

	.issue {
		border-color: #e05252;
		border-color: var(--issue-border);
		background: #fbe9e9;
		background: var(--issue-bg);
		color: black;
		color: var(--issue-text);
		counter-increment: issue;
		overflow: auto;
	}
	.issue::before, .issue > .marker {
		color: #831616;
		color: var(--issueheading-text);
	}
	/* Add .issue::before { content: "Issue " counter(issue) " "; } for autogen numbers,
	  or use class="marker" to mark up the issue number in source. */

/** Example *******************************************************************/

	.example {
		border-color: #e0cb52;
		border-color: var(--example-border);
		background: #fcfaee;
		background: var(--example-bg);
		color: black;
		color: var(--example-text);
		counter-increment: example;
		overflow: auto;
		clear: both;
	}
	.example::before, .example > .marker {
		color: #574b0f;
		color: var(--exampleheading-text);
	}
	/* Add .example::before { content: "Example " counter(example) " "; } for autogen numbers,
	  or use class="marker" to mark up the example number in source. */

/** Non-normative Note ********************************************************/

	.note {
		border-color: #52e052;
		border-color: var(--note-border);
		background: #e9fbe9;
		background: var(--note-bg);
		color: black;
		color: var(--note-text);
		overflow: auto;
	}

	.note::before, .note > .marker,
	details.note > summary {
		color: hsl(120, 70%, 30%);
		color: var(--noteheading-text);
	}
	/* Add .note::before { content: "Note "; } for autogen label,
	  or use class="marker" to mark up the label in source. */

	details.note[open] > summary {
		border-bottom: 1px silver solid;
		border-bottom: 1px var(--notesummary-underline) solid;
	}

/** Assertion Box *************************************************************/
	/*  for assertions in algorithms */

	.assertion {
		border-color: #AAA;
		border-color: var(--assertion-border);
		background: #EEE;
		background: var(--assertion-bg);
		color: black;
		color: var(--assertion-text);
	}

/** Advisement Box ************************************************************/
	/*  for attention-grabbing normative statements */

	.advisement {
		border-color: orange;
		border-color: var(--advisement-border);
		border-style: none solid;
		background: #fec;
		background: var(--advisement-bg);
		color: black;
		color: var(--advisement-text);
	}
	strong.advisement {
		display: block;
		text-align: center;
	}
	.advisement::before, .advisement > .marker {
		color: #b35f00;
		color: var(--advisementheading-text);
	}

/** Amendment Box *************************************************************/

	.amendment, .correction, .addition {
		border-color: #330099;
		border-color: var(--amendment-border);
		background: #F5F0FF;
		background: var(--amendment-bg);
		color: black;
		color: var(--amendment-text);
	}
	.amendment.proposed, .correction.proposed, .addition.proposed {
		border-style: solid;
		border-block-width: 0.25em;
	}
	.amendment::before, .amendment > .marker,
	details.amendment > summary::before, details.amendment > summary > .marker,
	.correction::before, .correction > .marker,
	details.correction > summary::before, details.correction > summary > .marker,
	.addition::before, .addition > .marker,
	details.addition > summary::before, details.addition > summary > .marker {
		color: #220066;
		color: var(--amendmentheading-text);
	}
	.amendment.proposed::before, .amendment.proposed > .marker,
	details.amendment.proposed > summary::before, details.amendment.proposed > summary > .marker,
	.correction.proposed::before, .correction.proposed > .marker,
	details.correction.proposed > summary::before, details.correction.proposed > summary > .marker,
	.addition.proposed::before, .addition.proposed > .marker,
	details.addition.proposed > summary::before, details.addition.proposed > summary > .marker {
		font-weight: bold;
	}

/** Spec Obsoletion Notice ****************************************************/
	/* obnoxious obsoletion notice for older/abandoned specs. */

	details {
		display: block;
	}
	summary {
		font-weight: bolder;
	}

	.annoying-warning:not(details),
	details.annoying-warning:not([open]) > summary,
	details.annoying-warning[open] {
		background: hsla(40,100%,50%,0.95);
		background: var(--warning-bg);
		color: black;
		color: var(--warning-text);
		padding: .75em 1em;
		border: red;
		border: var(--warning-border);
		border-style: solid none;
		box-shadow: 0 2px 8px black;
		text-align: center;
	}
	.annoying-warning :last-child {
		margin-bottom: 0;
	}

@media not print {
	details.annoying-warning[open] {
		position: fixed;
		left: 0;
		right: 0;
		bottom: 2em;
		z-index: 1000;
	}
}

	details.annoying-warning:not([open]) > summary {
		text-align: center;
	}

/** Entity Definition Boxes ***************************************************/

	.def {
		padding: .5em 1em;
		background: #def;
		background: var(--def-bg);
		margin: 1.2em 0;
		border-left: 0.5em solid #8ccbf2;
		border-left: 0.5em solid var(--def-border);
		color: black;
		color: var(--def-text);
	}

/******************************************************************************/
/*                                    Tables                                  */
/******************************************************************************/

	th, td {
		text-align: left;
		text-align: start;
	}

/** Property/Descriptor Definition Tables *************************************/

	table.def {
		/* inherits .def box styling, see above */
		width: 100%;
		border-spacing: 0;
	}

	table.def td,
	table.def th {
		padding: 0.5em;
		vertical-align: baseline;
		border-bottom: 1px solid #bbd7e9;
		border-bottom: 1px solid var(--defrow-border);
	}

	table.def > tbody > tr:last-child th,
	table.def > tbody > tr:last-child td {
		border-bottom: 0;
	}

	table.def th {
		font-style: italic;
		font-weight: normal;
		padding-left: 1em;
		width: 3em;
	}

	/* For when values are extra-complex and need formatting for readability */
	table td.pre {
		white-space: pre-wrap;
	}

	/* A footnote at the bottom of a def table */
	table.def td.footnote {
		padding-top: 0.6em;
	}
	table.def td.footnote::before {
		content: " ";
		display: block;
		height: 0.6em;
		width: 4em;
		border-top: thin solid;
	}

/** Data tables (and properly marked-up index tables) *************************/
	/*
		<table class="data"> highlights structural relationships in a table
		when correct markup is used (e.g. thead/tbody, th vs. td, scope attribute)

		Use class="complex data" for particularly complicated tables --
		(This will draw more lines: busier, but clearer.)

		Use class="long" on table cells with paragraph-like contents
		(This will adjust text alignment accordingly.)
		Alternately use class="longlastcol" on tables, to have the last column assume "long".
	*/

	table {
		word-wrap: normal;
		overflow-wrap: normal;
		hyphens: manual;
	}

	table.data,
	table.index {
		margin: 1em auto;
		border-collapse: collapse;
		border: hidden;
		width: 100%;
	}
	table.data caption,
	table.index caption {
		max-width: 50em;
		margin: 0 auto 1em;
	}

	table.data td,  table.data th,
	table.index td, table.index th {
		padding: 0.5em 1em;
		border-width: 1px;
		border-color: silver;
		border-color: var(--datacell-border);
		border-top-style: solid;
	}

	table.data thead td:empty {
		padding: 0;
		border: 0;
	}

	table.data  thead,
	table.index thead,
	table.data  tbody,
	table.index tbody {
		border-bottom: 2px solid;
	}

	table.data colgroup,
	table.index colgroup {
		border-left: 2px solid;
	}

	table.data  tbody th:first-child,
	table.index tbody th:first-child  {
		border-right: 2px solid;
		border-top: 1px solid silver;
		border-top: 1px solid var(--datacell-border);
		padding-right: 1em;
	}

	table.data th[colspan],
	table.data td[colspan] {
		text-align: center;
	}

	table.complex.data th,
	table.complex.data td {
		border: 1px solid silver;
		border: 1px solid var(--datacell-border);
		text-align: center;
	}

	table.data.longlastcol td:last-child,
	table.data td.long {
		vertical-align: baseline;
		text-align: left;
	}

	table.data img {
		vertical-align: middle;
	}


/*
Alternate table alignment rules

	table.data,
	table.index {
		text-align: center;
	}

	table.data  thead th[scope="row"],
	table.index thead th[scope="row"] {
		text-align: right;
	}

	table.data  tbody th:first-child,
	table.index tbody th:first-child  {
		text-align: right;
	}

Possible extra rowspan handling

	table.data  tbody th[rowspan]:not([rowspan='1']),
	table.index tbody th[rowspan]:not([rowspan='1']),
	table.data  tbody td[rowspan]:not([rowspan='1']),
	table.index tbody td[rowspan]:not([rowspan='1']) {
		border-left: 1px solid silver;
	}

	table.data  tbody th[rowspan]:first-child,
	table.index tbody th[rowspan]:first-child,
	table.data  tbody td[rowspan]:first-child,
	table.index tbody td[rowspan]:first-child{
		border-left: 0;
		border-right: 1px solid silver;
	}
*/

/******************************************************************************/
/*                                  Indices                                   */
/******************************************************************************/


/** Table of Contents *********************************************************/

	.toc a {
		/* More spacing; use padding to make it part of the click target. */
		padding: 0.1rem 1px 0;
		/* Larger, more consistently-sized click target */
		display: block;
		/* Switch to using border-bottom for underlines */
		text-decoration: none;
		border-bottom: 1px solid;
		/* Reverse color scheme */
		color: black;
		color: var(--toclink-text);
		border-color: #3980b5;
		border-color: var(--toclink-underline);
	}
	.toc a:visited {
		color: black;
		color: var(--toclink-visited-text);
		border-color: #054572;
		border-color: var(--toclink-visited-underline);
	}
	.toc a:focus,
	.toc a:hover {
		background: rgba(75%, 75%, 75%, .25);
		background: var(--a-hover-bg);
		border-bottom-width: 3px;
		margin-bottom: -2px;
	}
	.toc a:not(:focus):not(:hover) {
		/* Allow colors to cascade through from link styling */
		border-bottom-color: transparent;
	}

	.toc, .toc ol, .toc ul, .toc li {
		list-style: none; /* Numbers must be inlined into source */
		/* because generated content isn't search/selectable and markers can't do multilevel yet */
		margin:  0;
		padding: 0;
	}
	.toc {
		line-height: 1.1em;
	}

	/* ToC not indented until third level, but font style & margins show hierarchy */
	.toc > li			{ font-weight: bold;   }
	.toc > li li		 { font-weight: normal; }
	.toc > li li li	  { font-size:   95%;	}
	.toc > li li li li	{ font-size:   90%;	}
	.toc > li li li li li { font-size:   85%;	}

	/* @supports not (display:grid) { */
		.toc > li			{ margin: 1.5rem 0;	}
		.toc > li li		 { margin: 0.3rem 0;	}
		.toc > li li li	  { margin-left: 2rem;   }

		/* Section numbers in a column of their own */
		.toc .secno {
			float: left;
			width: 4rem;
			white-space: nowrap;
		}
		.toc > li li li li .secno { font-size: 85%; }
		.toc > li li li li li .secno { font-size: 100%; }

		.toc li {
			clear: both;
		}

		:not(li) > .toc			 { margin-left:  5rem; }
		.toc .secno				 { margin-left: -5rem; }
		.toc > li li li .secno	  { margin-left: -7rem; }
		.toc > li li li li .secno	{ margin-left: -9rem; }
		.toc > li li li li li .secno { margin-left: -11rem; }

		/* Tighten up indentation in narrow ToCs */
		@media (max-width: 30em) {
			:not(li) > .toc			 { margin-left:  4rem; }
			.toc .secno				 { margin-left: -4rem; }
			.toc > li li li			 { margin-left:  1rem; }
			.toc > li li li .secno	  { margin-left: -5rem; }
			.toc > li li li li .secno	{ margin-left: -6rem; }
			.toc > li li li li li .secno { margin-left: -7rem; }
		}
		/* Loosen it on wide screens */
		@media screen and (min-width: 78em) {
			body:not(.toc-inline) :not(li) > .toc			 { margin-left:  4rem; }
			body:not(.toc-inline) .toc .secno				 { margin-left: -4rem; }
			body:not(.toc-inline) .toc > li li li			 { margin-left:  1rem; }
			body:not(.toc-inline) .toc > li li li .secno	  { margin-left: -5rem; }
			body:not(.toc-inline) .toc > li li li li .secno	{ margin-left: -6rem; }
			body:not(.toc-inline) .toc > li li li li li .secno { margin-left: -7rem; }
	}
	/* } */

	@supports (display:grid) and (display:contents) {
		/* Use #toc over .toc to override non-@supports rules. */
		#toc {
			display: grid;
			align-content: start;
			grid-template-columns: auto 1fr;
			grid-column-gap: 1rem;
			column-gap: 1rem;
			grid-row-gap: .6rem;
			row-gap: .6rem;
		}
		#toc h2 {
			grid-column: 1 / -1;
			margin-bottom: 0;
		}
		#toc ol,
		#toc li,
		#toc a {
			display: contents;
			/* Switch <a> to subgrid when supported */
		}
		#toc span {
			margin: 0;
		}
		#toc > .toc > li > a > span {
			/* The spans of the top-level list,
			  comprising the first items of each top-level section. */
			margin-top: 1.1rem;
		}
		#toc#toc .secno { /* Ugh, need more specificity to override base.css */
			grid-column: 1;
			width: auto;
			margin-left: 0;
		}
		#toc .content {
			grid-column: 2;
			width: auto;
			margin-right: 1rem;
			border-bottom: 3px solid transparent;
			margin-bottom: -3px;
		}
		#toc .content:hover,
		#toc .content:focus {
			background: rgba(75%, 75%, 75%, .25);
			background: var(--a-hover-bg);
			border-bottom-color: #054572;
			border-bottom-color: var(--toclink-underline);
		}
		#toc li li li .content {
			margin-left: 1rem;
		}
		#toc li li li li .content {
			margin-left: 2rem;
		}
	}


/** Index *********************************************************************/

	/* Index Lists: Layout */
	ul.index	  { margin-left: 0; columns: 15em; text-indent: 1em hanging; }
	ul.index li	{ margin-left: 0; list-style: none; break-inside: avoid; }
	ul.index li li { margin-left: 1em; }
	ul.index dl	{ margin-top: 0; }
	ul.index dt	{ margin: .2em 0 .2em 20px;}
	ul.index dd	{ margin: .2em 0 .2em 40px;}
	/* Index Lists: Typography */
	ul.index ul,
	ul.index dl { font-size: smaller; }
	@media not print {
		ul.index li a + span {
			white-space: nowrap;
			color: transparent; }
		ul.index li a:hover + span,
		ul.index li a:focus + span {
			color: #707070;
			color: var(--indexinfo-text);
		}
	}

/** Index Tables *****************************************************/
	/* See also the data table styling section, which this effectively subclasses */

	table.index {
		font-size: small;
		border-collapse: collapse;
		border-spacing: 0;
		text-align: left;
		margin: 1em 0;
	}

	table.index td,
	table.index th {
		padding: 0.4em;
	}

	table.index tr:hover td:not([rowspan]),
	table.index tr:hover th:not([rowspan]) {
		color: black;
		color: var(--indextable-hover-text);
		background: #f7f8f9;
		background: var(--indextable-hover-bg);
	}

	/* The link in the first column in the property table (formerly a TD) */
	table.index th:first-child a {
		font-weight: bold;
	}

/** Outdated warning **********************************************************/

.outdated-spec {
	color: black;
	color: var(--outdatedspec-text);
	background-color: rgba(0,0,0,0.5);
	background-color: var(--outdatedspec-bg);
}

.outdated-warning {
	position: fixed;
	bottom: 50%;
	left: 0;
	right: 0;
	margin: 0 auto;
	width: 50%;
	background: maroon;
	background: var(--outdated-bg);
	color: white;
	color: var(--outdated-text);
	border-radius: 1em;
	box-shadow: 0 0 1em red;
	box-shadow: 0 0 1em var(--outdated-shadow);
	padding: 2em;
	text-align: center;
	z-index: 2;
}

.outdated-warning a {
	color: currentcolor;
	background: transparent;
}

.edited-rec-warning {
	background: darkorange;
	background: var(--editedrec-bg);
	box-shadow: 0 0 1em;
}

.outdated-warning button {
	color: var(--outdated-text);
	border-radius: 1em;
	box-shadow: 0 0 1em red;
	box-shadow: 0 0 1em var(--outdated-shadow);
	padding: 2em;
	text-align: center;
	z-index: 2;
}

.outdated-warning a {
	color: currentcolor;
	background: transparent;
}

.edited-rec-warning {
	background: darkorange;
	background: var(--editedrec-bg);
	box-shadow: 0 0 1em;
}

.outdated-warning button {
	position: absolute;
	top: 0;
	right:0;
	margin: 0;
	border: 0;
	padding: 0.25em 0.5em;
	background: transparent;
	color: white;
	color: var(--outdated-text);
	font:1em sans-serif;
	text-align:center;
}

.outdated-warning span {
	display: block;
}

.outdated-collapsed {
	bottom: 0;
	border-radius: 0;
	width: 100%;
	padding: 0;
}

/******************************************************************************/
/*                                    Print                                   */
/******************************************************************************/

	@media print {
		/* Pages have their own margins. */
		html {
			margin: 0;
		}
		/* Serif for print. */
		body {
			font-family: serif;
		}

		.outdated-warning {
			position: absolute;
			border-style: solid;
			border-color: red;
		}

		.outdated-warning input {
			display: none;
		}
	}
	@page {
		margin: 1.5cm 1.1cm;
	}



/******************************************************************************/
/*                             Overflow Control                               */
/******************************************************************************/

	.figure .caption, .sidefigure .caption, figcaption {
		/* in case figure is overlarge, limit caption to 50em */
		max-width: 50rem;
		margin-left: auto;
		margin-right: auto;
	}
	.overlarge {
		/* Magic to create good item positioning:
		  "content column" is 50ems wide at max; less on smaller screens.
		  Extra space (after ToC + content) is empty on the right.

		  1. When item < content column, centers item in column.
		  2. When content < item < available, left-aligns.
		  3. When item > available, fills available + scroll bar.
		*/
		display: grid;
		grid-template-columns: minmax(0, 50em);
	}
	.overlarge > table {
		/* limit preferred width of table */
		max-width: 50em;
		margin-left: auto;
		margin-right: auto;
	}

	@media (min-width: 55em) {
		.overlarge {
			margin-right: calc(13px + 26.5rem - 50vw);
			max-width: none;
		}
	}
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) .overlarge {
			/* 30.5em body padding 50em content area */
			margin-right: calc(40em - 50vw) !important;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) .overlarge {
			/* 4em html margin 30.5em body padding 50em content area */
			margin-right: calc(84.5em - 100vw) !important;
		}
	}

	@media not print {
		.overlarge {
			overflow-x: auto;
			/* See Lea Verou's explanation background-attachment:
			* http://lea.verou.me/2012/04/background-attachment-local/
			*
			background: top left  / 4em 100% linear-gradient(to right,  #ffffff, rgba(255, 255, 255, 0)) local,
						top right / 4em 100% linear-gradient(to left, #ffffff, rgba(255, 255, 255, 0)) local,
						top left  / 1em 100% linear-gradient(to right,  #c3c3c5, rgba(195, 195, 197, 0)) scroll,
						top right / 1em 100% linear-gradient(to left, #c3c3c5, rgba(195, 195, 197, 0)) scroll,
						white;
			background-repeat: no-repeat;
			*/
		}
	}
</style>
<style>
    table, th, td {
      border: 1px solid black;
      border-collapse: collapse;
      vertical-align: top;
    }
    th, td {
      border-left: none;
      border-right: none;
      padding: 0px 10px;
    }
    th {
      text-align: center;
    }

    del { background: #fcc; color: #000; text-decoration: line-through; }
    ins { background: #cfc; color: #000; }
    blockquote .highlight:not(.idl) { background: initial; margin: initial; padding: 0.5em }
    blockquote ul { background: inherit; }
    blockquote code.highlight:not(.idl) { padding: initial; }
    blockquote c-[a] { color: inherit; } /* Keyword.Declaration */
    blockquote c-[b] { color: inherit; } /* Keyword.Type */
    blockquote c-[c] { color: inherit; } /* Comment */
    blockquote c-[d] { color: inherit; } /* Comment.Multiline */
    blockquote c-[e] { color: inherit; } /* Name.Attribute */
    blockquote c-[f] { color: inherit; } /* Name.Tag */
    blockquote c-[g] { color: inherit; } /* Name.Variable */
    blockquote c-[k] { color: inherit; } /* Keyword */
    blockquote c-[l] { color: inherit; } /* Literal */
    blockquote c-[m] { color: inherit; } /* Literal.Number */
    blockquote c-[n] { color: inherit; } /* Name */
    blockquote c-[o] { color: inherit; } /* Operator */
    blockquote c-[p] { color: inherit; } /* Punctuation */
    blockquote c-[s] { color: inherit; } /* Literal.String */
    blockquote c-[t] { color: inherit; } /* Literal.String.Single */
    blockquote c-[u] { color: inherit; } /* Literal.String.Double */
    blockquote c-[cp] { color: inherit; } /* Comment.Preproc */
    blockquote c-[c1] { color: inherit; } /* Comment.Single */
    blockquote c-[cs] { color: inherit; } /* Comment.Special */
    blockquote c-[kc] { color: inherit; } /* Keyword.Constant */
    blockquote c-[kn] { color: inherit; } /* Keyword.Namespace */
    blockquote c-[kp] { color: inherit; } /* Keyword.Pseudo */
    blockquote c-[kr] { color: inherit; } /* Keyword.Reserved */
    blockquote c-[ld] { color: inherit; } /* Literal.Date */
    blockquote c-[nc] { color: inherit; } /* Name.Class */
    blockquote c-[no] { color: inherit; } /* Name.Constant */
    blockquote c-[nd] { color: inherit; } /* Name.Decorator */
    blockquote c-[ni] { color: inherit; } /* Name.Entity */
    blockquote c-[ne] { color: inherit; } /* Name.Exception */
    blockquote c-[nf] { color: inherit; } /* Name.Function */
    blockquote c-[nl] { color: inherit; } /* Name.Label */
    blockquote c-[nn] { color: inherit; } /* Name.Namespace */
    blockquote c-[py] { color: inherit; } /* Name.Property */
    blockquote c-[ow] { color: inherit; } /* Operator.Word */
    blockquote c-[mb] { color: inherit; } /* Literal.Number.Bin */
    blockquote c-[mf] { color: inherit; } /* Literal.Number.Float */
    blockquote c-[mh] { color: inherit; } /* Literal.Number.Hex */
    blockquote c-[mi] { color: inherit; } /* Literal.Number.Integer */
    blockquote c-[mo] { color: inherit; } /* Literal.Number.Oct */
    blockquote c-[sb] { color: inherit; } /* Literal.String.Backtick */
    blockquote c-[sc] { color: inherit; } /* Literal.String.Char */
    blockquote c-[sd] { color: inherit; } /* Literal.String.Doc */
    blockquote c-[se] { color: inherit; } /* Literal.String.Escape */
    blockquote c-[sh] { color: inherit; } /* Literal.String.Heredoc */
    blockquote c-[si] { color: inherit; } /* Literal.String.Interpol */
    blockquote c-[sx] { color: inherit; } /* Literal.String.Other */
    blockquote c-[sr] { color: inherit; } /* Literal.String.Regex */
    blockquote c-[ss] { color: inherit; } /* Literal.String.Symbol */
    blockquote c-[vc] { color: inherit; } /* Name.Variable.Class */
    blockquote c-[vg] { color: inherit; } /* Name.Variable.Global */
    blockquote c-[vi] { color: inherit; } /* Name.Variable.Instance */
    blockquote c-[il] { color: inherit; } /* Literal.Number.Integer.Long */
  </style>
  <meta content="Bikeshed version d5d58a306, updated Fri Jan 26 16:12:28 2024 -0800" name="generator">
  <link href="http://wg21.link/Pxxxx" rel="canonical">
  <link href="https://isocpp.org/favicon.ico" rel="icon">
  <meta content="964d3c9c729550f60df6f52db78246c7fa58a691" name="revision">
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 <body class="h-entry">
  <div class="head">
   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">P3185R0<br>A proposed direction for C++ Standard Networking based on IETF TAPS</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="profile-and-date"><span class="content">Draft Proposal, <time class="dt-updated" datetime="2024-03-13">2024-03-13</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt>This version:
     <dd><a class="u-url" href="http://wg21.link/Pxxxx">http://wg21.link/Pxxxx</a>
     <dt class="editor">Author:
     <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:thomas.rodgers@woven-planet.global">Thomas Rodgers</a> (<span class="p-org org">Woven By Toyota</span>)
     <dt>Audience:
     <dd>SG4
     <dt>Project:
     <dd>ISO/IEC 14882 Programming Languages — C++, ISO/IEC JTC1/SC22/WG21
     <dt>Source:
     <dd><a href="https://github.com/rodgert/papers/blob/master/source/p3185r0.bs">https://github.com/rodgert/papers/blob/master/source/p3185r0.bs</a>
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p>A proposal align C++ Standard Networking with IETF’s TAPS initiative</p>
  </div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li><a href="#background"><span class="secno">1</span> <span class="content">Background</span></a>
    <li>
     <a href="#what-is-transport-services-application-programming-interface-taps"><span class="secno">2</span> <span class="content">What is Transport Services Application Programming Interface (TAPS)?</span></a>
     <ol class="toc">
      <li><a href="#why-taps"><span class="secno">2.1</span> <span class="content">Why TAPS?</span></a>
      <li><a href="#api-model"><span class="secno">2.2</span> <span class="content">API Model</span></a>
      <li><a href="#taps-concepts"><span class="secno">2.3</span> <span class="content">TAPS Concepts</span></a>
      <li><a href="#all-data-transfer-is-by-messages"><span class="secno">2.4</span> <span class="content">All data transfer is by Messages</span></a>
      <li><a href="#flexible-connection-establishment"><span class="secno">2.5</span> <span class="content">Flexible Connection establishment</span></a>
     </ol>
    <li><a href="#architecture"><span class="secno">3</span> <span class="content">Architecture</span></a>
    <li><a href="#open-question-s"><span class="secno">4</span> <span class="content">Open Question(s)</span></a>
    <li><a href="#conclusion"><span class="secno">5</span> <span class="content">Conclusion</span></a>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
     </ol>
   </ol>
  </nav>
  <main>
   <h2 class="heading settled" data-level="1" id="background"><span class="secno">1. </span><span class="content">Background</span><a class="self-link" href="#background"></a></h2>
    In 2014, the C++ committee made a decision to "adopt existing practice" for a
standard networking proposal, specifically to adopt a proposal based on the
widely used <a data-link-type="biblio" href="#biblio-asio" title="Asio C++ Library">[Asio]</a> library. The NetworkingTS <a data-link-type="biblio" href="#biblio-netts" title="Working Draft, C++ Extensions for Networking">[netts]</a> was the result of years
of effort to meet that guidance from the direction setting groups within WG21.
The resulting proposal didn’t support various common requirements for many modern
networking use cases, such as secure-by-default <a data-link-type="biblio" href="#biblio-p1861" title="Secure Networking in C++">[p1861]</a> networking. Somewhat
independently a decision was made to adopt the Sender/Receiver <a data-link-type="biblio" href="#biblio-p2300" title="std::execution">[p2300]</a> model
for asynchrony. The NetworkingTS asynchrony model is not currently harmonized
with the adopted direction of <a data-link-type="biblio" href="#biblio-p2300" title="std::execution">[p2300]</a>, which is something that <a data-link-type="biblio" href="#biblio-p2762" title="Sender/Receiver Interface For Networking">[p2762]</a> seeks
to address. Recent SG4 discussion <a data-link-type="biblio" href="#biblio-p2762_kona" title="Minutes - SG4 Nov 8, 2023 -- p2762: Presenting - Dietmar Kuhl">[p2762_kona]</a> revived discussion around the
desire to support connection-by-name which would necessitate the addition of a
proposal for name resolution, parsing of string based interface paths, etc.
The Kona discussion suggested that perhaps SG4 could look to the Internet
Engineering Task Force’s (IETF) Transport Services Application Programming
Interface (TAPS) for the industry expert’s current thinking on approaching this
expanded feature set. 
   <h2 class="heading settled" data-level="2" id="what-is-transport-services-application-programming-interface-taps"><span class="secno">2. </span><span class="content">What is Transport Services Application Programming Interface (TAPS)?</span><a class="self-link" href="#what-is-transport-services-application-programming-interface-taps"></a></h2>
    TAPS is a Standards Track initiative of the Internet Engineering Task Force (IETF)
to describe a language agnostic abstract architecture for exposing transport protocol
features to applications for network communication <a data-link-type="biblio" href="#biblio-taps_arch" title="Architecture and Requirements for Transport Services">[TAPS_arch]</a>. The IETF has also
published a language agnostic abstract interface <a data-link-type="biblio" href="#biblio-taps_iface" title="Architecture and Requirements for Transport Services">[TAPS_iface]</a> and implementation
guidance <a data-link-type="biblio" href="#biblio-taps_impl" title="Architecture and Requirements for Transport Services">[TAPS_impl]</a>. 
   <h3 class="heading settled" data-level="2.1" id="why-taps"><span class="secno">2.1. </span><span class="content">Why TAPS?</span><a class="self-link" href="#why-taps"></a></h3>
   <ul>
    <li data-md>
     <p>TAPS is an IETF initiative to shape future networking API design based on lessons learned from building networking systems on Berkeley Sockets based designs.</p>
    <li data-md>
     <p>TAPS proposes a language agnostic API that covers areas that have been raised as shortcomings of the current Networking TS:</p>
     <ul>
      <li data-md>
       <p>Named connections, including DNS resolution</p>
      <li data-md>
       <p>Transport Layer Security</p>
     </ul>
    <li data-md>
     <p>TAPS seeks to address the inconsistent concepts and naming of existing networking APIs (often derived from Berkeley Sockets) where names and concepts often vary as a pure quirk of the history of "how we got to here" and based on the protocol being used.</p>
    <li data-md>
     <p>The TAPS architecture aims to redefine the interface between applications and transports in a way that allows the transport layer to evolve without fundamentally changing the contract with the application.</p>
    <li data-md>
     <p>The TAPS recommendations aim to make common use cases simple and consistent while still providing more fine grained control over the transport layer for those applications that require it.</p>
   </ul>
   <h3 class="heading settled" data-level="2.2" id="api-model"><span class="secno">2.2. </span><span class="content">API Model</span><a class="self-link" href="#api-model"></a></h3>
    The traditional model, including that outlined in the Networking TS <a data-link-type="biblio" href="#biblio-netts" title="Working Draft, C++ Extensions for Networking">[netts]</a>, can
be described as follows: 
   <ul>
    <li data-md>
     <p>Create connections and transfer data using a Sockets API.</p>
    <li data-md>
     <p>The Socket API provides the interface to implementations of the TCP and UDP protocols (typically provided by the system’s kernel, or e.g. lwIP <a data-link-type="biblio" href="#biblio-lwip" title="lwIP - A Lightweight TCP/IP stack">[lwip]</a> in embedded systems).</p>
    <li data-md>
     <p>The TCP and UDP implementation send and receive data over the network layer interfaces.</p>
    <li data-md>
     <p>Sockets are bound directly to transport-layer and network-layer addresses, obtained via a separate resolution step, usually performed by a system-provided DNS stub resolver.</p>
   </ul>
<pre class="highlight"><c- o>+-----------------------------------------------------+</c->
<c- o>|</c->                    <c- n>Application</c->                      <c- o>|</c->
<c- o>+-----------------------------------------------------+</c->
        <c- o>|</c->                 <c- o>|</c->                  <c- o>|</c->
  <c- o>+------------+</c->     <c- o>+------------+</c->    <c- o>+--------------+</c->
  <c- o>|</c->  <c- n>DNS</c-> <c- n>stub</c->  <c- o>|</c->     <c- o>|</c-> <c- n>Stream</c-> <c- n>API</c-> <c- o>|</c->    <c- o>|</c-> <c- n>Datagram</c-> <c- n>API</c-> <c- o>|</c->
  <c- o>|</c->  <c- n>resolver</c->  <c- o>|</c->     <c- o>+------------+</c->    <c- o>+--------------+</c->
  <c- o>+------------+</c->          <c- o>|</c->                  <c- o>|</c->
                    <c- o>+---------------------------------+</c->
                    <c- o>|</c->    <c- n>TCP</c->                <c- n>UDP</c->       <c- o>|</c->
                    <c- o>|</c->    <c- n>Kernel</c-> <c- n>Networking</c-> <c- n>Stack</c->      <c- o>|</c->
                    <c- o>+---------------------------------+</c->
                                    <c- o>|</c->
<c- o>+-----------------------------------------------------+</c->
<c- o>|</c->               <c- n>Network</c-> <c- n>Layer</c-> <c- n>Interface</c->               <c- o>|</c->
<c- o>+-----------------------------------------------------+</c->
</pre>
   <p>TAPS simplifies and modernizes this API structure to -</p>
<pre class="highlight"><c- o>+-----------------------------------------------------+</c->
<c- o>|</c->                    <c- n>Application</c->                      <c- o>|</c->
<c- o>+-----------------------------------------------------+</c->
                          <c- o>|</c->
<c- o>+-----------------------------------------------------+</c->
<c- o>|</c->              <c- n>Transport</c-> <c- n>Services</c-> <c- n>API</c->                 <c- o>|</c->
<c- o>+-----------------------------------------------------+</c->
                          <c- o>|</c->
<c- o>+-----------------------------------------------------+</c->
<c- o>|</c->          <c- n>Transport</c-> <c- n>Services</c-> <c- n>Implementation</c->          <c- o>|</c->
<c- o>|</c->  <c- p>(</c-><c- n>Using</c-><c- o>:</c-> <c- n>DNS</c-><c- p>,</c-> <c- n>UDP</c-><c- p>,</c-> <c- n>TCP</c-><c- p>,</c-> <c- n>SCTP</c-><c- p>,</c-> <c- n>DCCP</c-><c- p>,</c-> <c- n>TLS</c-><c- p>,</c-> <c- n>QUIC</c-><c- p>,</c-> <c- n>etc</c-><c- p>)</c-> <c- o>|</c->
<c- o>+-----------------------------------------------------+</c->
                          <c- o>|</c->
<c- o>+-----------------------------------------------------+</c->
<c- o>|</c->               <c- n>Network</c-> <c- n>Layer</c-> <c- n>Interface</c->               <c- o>|</c->
<c- o>+-----------------------------------------------------+</c->
</pre>
   <p>The API defines an interface for creating connections and transferring data,
combining interfaces for multiple interaction patterns into a unified whole.
The API offers generic support for protocols as protocol specific mappings
for, e.g. TCP, UDP, etc. These protocol mappings are extensible to future
protocol definitions, e.g. QUIC <a data-link-type="biblio" href="#biblio-rfc9000" title="QUIC: A UDP-Based Multiplexed and Secure Transport">[rfc9000]</a> or perhaps even the Binary Lexical
Octet Ad-Hoc Transport <a data-link-type="biblio" href="#biblio-rfc3252" title="Binary Lexical Octet Ad-hoc Transport">[rfc3252]</a>.</p>
   <p>By combining name resolution with connection establishment and data transfer,
the API allows for more flexible implementations (a library QoI decision) to
provide path and transport protocol agility on the application’s behalf.</p>
   <p>Key differences exist between the architecture of the TAPS design and the
architecture of the Socket API: the TAPS API is asynchronous and event-driven;
it uses messages to represent data transfer to applications; and it describes
how an application can resolve Endpoint Identifiers to use multiple IP addresses,
multiple protocols, multiple paths, and provide multiple application streams.</p>
   <h3 class="heading settled" data-level="2.3" id="taps-concepts"><span class="secno">2.3. </span><span class="content">TAPS Concepts</span><a class="self-link" href="#taps-concepts"></a></h3>
    Event driven API - Originally, the Socket API presented a blocking interface
for establishing connections and transferring data.  However, most modern
applications interact with the network asynchronously. Various strategies are
employed to implement this interface over the blocking sockets API, and the <a data-link-type="biblio" href="#biblio-netts" title="Working Draft, C++ Extensions for Networking">[netts]</a> provides such an abstraction, while also exposing the blocking
synchronous API of the underlying socket library. 
   <p>In contrast to this model, all interactions with TAPS are expected to be
asynchronous and the API is defined around an event driven model. For example,
when an application uses the TAPS API to receive data, it issues an
asynchronous call to receive new data (a value) from the Connection.  When
delivered data becomes available, this data (value) is delivered to the
application using asynchronous events (receiver::set_value) that contain the
data (a complete framed message value). Error handling is also asynchronous,
resulting in asynchronous error events (receiver::set_error). In a design that
meshes well with the sort of asynchronous programming model envisioned by <a data-link-type="biblio" href="#biblio-p2300" title="std::execution">[p2300]</a>.</p>
   <p>Additional events are delivered asynchronously to the application regarding the
lifetime of a connection and changes in network availability, which were not
previously made explicit in the Socket API.</p>
   <p>Separate from events, callbacks are also provided for interactions with the TAPS
API that are not directly related to events on the network or network interfaces,
typically for negotiating transport layer security.</p>
   <h3 class="heading settled" data-level="2.4" id="all-data-transfer-is-by-messages"><span class="secno">2.4. </span><span class="content">All data transfer is by Messages</span><a class="self-link" href="#all-data-transfer-is-by-messages"></a></h3>
    The Socket API provides a message interface for datagram protocols like UDP,
but provides an unstructured stream abstraction for TCP.  While TCP has the
ability to send and receive data as a byte-stream, most applications need to
interpret structure within this byte-stream. For example, HTTP/1.1 uses character
delimiters to segment messages over a byte-stream <a data-link-type="biblio" href="#biblio-rfc9112" title="HTTP/1.1">[RFC9112]</a>; TLS <a data-link-type="biblio" href="#biblio-rfc8446" title="The Transport Layer Security (TLS) Protocol Version 1.3">[RFC8446]</a> record headers carry a version, content type, and length [[RFC8446][; and HTTP/2
uses frames to segment its headers and bodies <a data-link-type="biblio" href="#biblio-rfc9113" title="HTTP/2">[RFC9113]</a>. It is common for other
protocols, e.g. <a data-link-type="biblio" href="#biblio-zeromq" title="ZeroMQ Message Transport Protocol">[ZeroMQ]</a> to use an embedded framing preamble that specifies the
number of octets in the TCP stream which comprise a message. 
   <p>TAPS represents data as messages, which more closely matches the way applications
use the network. There are additional benefits to this message-oriented approach:</p>
   <ul>
    <li data-md>
     <p>Provide additional information to the protocol stack and application (e.g. a structured header type, separate from the message body).</p>
    <li data-md>
     <p>Ability to associate deadlines with messages, for applications that care about timing</p>
    <li data-md>
     <p>Ability to control reliability, which messages to retransmit when there is packet loss, and how best to make use of the data that arrived</p>
    <li data-md>
     <p>Ability to automatically assign messages and connections to underlying transport connections to utilize multi-streaming and pooled connections.</p>
   </ul>
   <p>This message oriented approach is generally backwards compatible with existing
usages where application code would have previously provided the framing of
messages, while giving more information to the protocol stack in a consistent
fashion that allows the application to adapt to transport level changes in 
a consistent manner. For protocols that inherently use streaming, or where
applications use a non-standard or custom message framing, Framers bridge the
gap between abstractions.</p>
   <h3 class="heading settled" data-level="2.5" id="flexible-connection-establishment"><span class="secno">2.5. </span><span class="content">Flexible Connection establishment</span><a class="self-link" href="#flexible-connection-establishment"></a></h3>
    The Socket API for protocols like TCP and UDP is generally limited to connecting
a single address over a single interface. It also presents a single stream to the
application. Software layers built atop this abstraction frequently propagate this
single-address single-stream model. The TAPS architecture provides: 
   <ul>
    <li data-md>
     <p>Handling multiple candidate endpoints, protocols, and paths</p>
    <li data-md>
     <p>Support for candidate protocol racing to select the most optimal stack in each situation</p>
    <li data-md>
     <p>Support multipath and multistreaming protocols</p>
    <li data-md>
     <p>State caching and application control over it.</p>
   </ul>
   <p>A TAPS implementation is intended to be flexible at connection establishment time,
considering many different options to select the most optimal connection that meets
the requested criteria, with appropriate fallback strategies.</p>
   <p>Information used in connection establishment (e.g. cryptographic resumption tokens,
information about usability of certain protocols on the path, results of racing in
previous connections) are cached by the implementation and applications have control
over whether this information is used for a specific establishment, in order to allow
trade offs between efficiency and link capability.</p>
   <p>TAPS also allows for flexibility after connection reestablishment, for instance
migration between multiple network-layer interfaces, allowing the application to react
to interface changes, quality of service, etc.</p>
   <h2 class="heading settled" data-level="3" id="architecture"><span class="secno">3. </span><span class="content">Architecture</span><a class="self-link" href="#architecture"></a></h2>
    Connections are described by properties: 
   <ul>
    <li data-md>
     <p>Flexible</p>
    <li data-md>
     <p>Fallback Handling</p>
   </ul>
   Connections are asynchronous: 
   <ul>
    <li data-md>
     <p>Sending</p>
    <li data-md>
     <p>Receiving</p>
   </ul>
   Message definition is flexible: 
   <ul>
    <li data-md>
     <p>Custom framing</p>
     <ul>
      <li data-md>
       <p><a data-link-type="biblio" href="#biblio-zeromq" title="ZeroMQ Message Transport Protocol">[zeromq]</a></p>
      <li data-md>
       <p><a data-link-type="biblio" href="#biblio-rfc3252" title="Binary Lexical Octet Ad-hoc Transport">[rfc3252]</a></p>
     </ul>
   </ul>
   <h2 class="heading settled" data-level="4" id="open-question-s"><span class="secno">4. </span><span class="content">Open Question(s)</span><a class="self-link" href="#open-question-s"></a></h2>
   <ul>
    <li data-md>
     <p>Should a C++ Networking Standard provide a high level interface, e.g. TAPS, or should it provide low level facilities, sufficient to build higher level application interfaces?</p>
    <li data-md>
     <p>Should a C++ Networking Standard admit the possibility to support more "interesting" transports, e.g.  InfiniBand, RDMA, etc.?</p>
     <ul>
      <li data-md>
       <p>If so, how does a more primitive networking standard’s surface area support that? How does a TAPS based interface?</p>
     </ul>
    <li data-md>
     <p>TAPS has significant implementation complexity. Can the stdlib implementers adopt a proposal of this complexity?</p>
     <ul>
      <li data-md>
       <p>I would argue it is an equivalent "lift" to what has already been proposed by the Networking TS along with enhancements to support Sender/Receiver, connection-by-name, and secure-by-default proposals.</p>
      <li data-md>
       <p>A donated reference implementation would be helpful but not required, many of TAPS facilities are provided by existing libraries and operating systems. Standard libraries could choose to base their implementations on these libraries.</p>
      <li data-md>
       <p>Any donated implementation would require something akin to the standard libraries adopting <a data-link-type="biblio" href="#biblio-range_v3" title="range-v3">[range_v3]</a>, <a data-link-type="biblio" href="#biblio-stdpar" title="Parallel STL">[stdpar]</a>, <a data-link-type="biblio" href="#biblio-p2300" title="std::execution">[p2300]</a>, etc.</p>
      <li data-md>
       <p>If we adopt TAPS, we could finally foreclose on SG4 (circa 2012)'s most pressing concern, "What to do about IPv8"; with TAPS, this is simple, we approve an IPv8 transport and property set which is supported by the generic TransportProperties type. One could only dream of this job stability.</p>
     </ul>
   </ul>
   <h2 class="heading settled" data-level="5" id="conclusion"><span class="secno">5. </span><span class="content">Conclusion</span><a class="self-link" href="#conclusion"></a></h2>
    Remember the <a data-link-type="biblio" href="#biblio-r101" title="R101 - Wikipedia">[R101]</a> - Should SG4 spend it’s resources to design large scale changes to the NetworkingTS to support - 
   <ul>
    <li data-md>
     <p>A new async model</p>
    <li data-md>
     <p>Connection-by-name, endpoint resolvers, etc.</p>
    <li data-md>
     <p>Transport security</p>
    <li data-md>
     <p>etc.</p>
   </ul>
   <p>Would such an effort yield a similarly cohesive result as the IETF’s TAPS initiative?</p>
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  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
  <dl>
   <dt id="biblio-asio">[Asio]
   <dd>Chris Kohlhoff. <a href="https://think-async.com/Asio"><cite>Asio C++ Library</cite></a>. URL: <a href="https://think-async.com/Asio">https://think-async.com/Asio</a>
   <dt id="biblio-lwip">[LWIP]
   <dd><a href="https://savannah.nongnu.org/projects/lwip"><cite>lwIP - A Lightweight TCP/IP stack</cite></a>. 2002-10-17. URL: <a href="https://savannah.nongnu.org/projects/lwip">https://savannah.nongnu.org/projects/lwip</a>
   <dt id="biblio-netts">[NETTS]
   <dd><a href="https://wg21.link/n4734"><cite>Working Draft, C++ Extensions for Networking</cite></a>. 2018-04-04. URL: <a href="https://wg21.link/n4734">https://wg21.link/n4734</a>
   <dt id="biblio-p1861">[P1861]
   <dd><cite>Secure Networking in C++</cite>. 2020-05-11. 
   <dt id="biblio-p2300">[P2300]
   <dd><a href="https://wg21.link/p2300"><cite>std::execution</cite></a>. 2023-04-21. URL: <a href="https://wg21.link/p2300">https://wg21.link/p2300</a>
   <dt id="biblio-p2762">[P2762]
   <dd><a href="https://wg21.link/p2762"><cite>Sender/Receiver Interface For Networking</cite></a>. 2023-10-12. URL: <a href="https://wg21.link/p2762">https://wg21.link/p2762</a>
   <dt id="biblio-p2762_kona">[P2762_KONA]
   <dd><a href="https://wiki.edg.com/bin/view/Wg21kona2023/SG4"><cite>Minutes - SG4 Nov 8, 2023 -- p2762: Presenting - Dietmar Kuhl</cite></a>. 2023-11-08. URL: <a href="https://wiki.edg.com/bin/view/Wg21kona2023/SG4">https://wiki.edg.com/bin/view/Wg21kona2023/SG4</a>
   <dt id="biblio-r101">[R101]
   <dd><a href="https://en.wikipedia.org/wiki/R101"><cite>R101 - Wikipedia</cite></a>. 1930-10-05. URL: <a href="https://en.wikipedia.org/wiki/R101">https://en.wikipedia.org/wiki/R101</a>
   <dt id="biblio-range_v3">[RANGE_V3]
   <dd>Eric Niebler. <a href="https://github.com/ericniebler/range-v3"><cite>range-v3</cite></a>. URL: <a href="https://github.com/ericniebler/range-v3">https://github.com/ericniebler/range-v3</a>
   <dt id="biblio-rfc3252">[RFC3252]
   <dd><a href="https://www.ietf.org/rfc/rfc3252.txt"><cite>Binary Lexical Octet Ad-hoc Transport</cite></a>. 2002-04-01. URL: <a href="https://www.ietf.org/rfc/rfc3252.txt">https://www.ietf.org/rfc/rfc3252.txt</a>
   <dt id="biblio-rfc8446">[RFC8446]
   <dd><a href="https://datatracker.ietf.org/doc/html/rfc8446"><cite>The Transport Layer Security (TLS) Protocol Version 1.3</cite></a>. 2018-08-01. URL: <a href="https://datatracker.ietf.org/doc/html/rfc8446">https://datatracker.ietf.org/doc/html/rfc8446</a>
   <dt id="biblio-rfc9000">[RFC9000]
   <dd><a href="https://datatracker.ietf.org/doc/html/rfc9000"><cite>QUIC: A UDP-Based Multiplexed and Secure Transport</cite></a>. 2021-05-01. URL: <a href="https://datatracker.ietf.org/doc/html/rfc9000">https://datatracker.ietf.org/doc/html/rfc9000</a>
   <dt id="biblio-rfc9112">[RFC9112]
   <dd><a href="https://datatracker.ietf.org/doc/html/rfc9112"><cite>HTTP/1.1</cite></a>. 2022-06-01. URL: <a href="https://datatracker.ietf.org/doc/html/rfc9112">https://datatracker.ietf.org/doc/html/rfc9112</a>
   <dt id="biblio-rfc9113">[RFC9113]
   <dd><a href="https://datatracker.ietf.org/doc/html/rfc9113"><cite>HTTP/2</cite></a>. 2022-06-01. URL: <a href="https://datatracker.ietf.org/doc/html/rfc9113">https://datatracker.ietf.org/doc/html/rfc9113</a>
   <dt id="biblio-stdpar">[STDPAR]
   <dd><a href="https://github.com/llvm/llvm-project/tree/main/pstl"><cite>Parallel STL</cite></a>. URL: <a href="https://github.com/llvm/llvm-project/tree/main/pstl">https://github.com/llvm/llvm-project/tree/main/pstl</a>
   <dt id="biblio-taps_arch">[TAPS_arch]
   <dd><a href="https://datatracker.ietf.org/doc/draft-ietf-taps-arch/"><cite>Architecture and Requirements for Transport Services</cite></a>. 2023-11-09. URL: <a href="https://datatracker.ietf.org/doc/draft-ietf-taps-arch/">https://datatracker.ietf.org/doc/draft-ietf-taps-arch/</a>
   <dt id="biblio-taps_iface">[TAPS_iface]
   <dd><a href="https://datatracker.ietf.org/doc/draft-ietf-taps-interface/"><cite>Architecture and Requirements for Transport Services</cite></a>. 2023-11-09. URL: <a href="https://datatracker.ietf.org/doc/draft-ietf-taps-interface/">https://datatracker.ietf.org/doc/draft-ietf-taps-interface/</a>
   <dt id="biblio-taps_impl">[TAPS_impl]
   <dd><a href="https://datatracker.ietf.org/doc/draft-ietf-taps-impl/"><cite>Architecture and Requirements for Transport Services</cite></a>. 2023-11-09. URL: <a href="https://datatracker.ietf.org/doc/draft-ietf-taps-impl/">https://datatracker.ietf.org/doc/draft-ietf-taps-impl/</a>
   <dt id="biblio-zeromq">[ZEROMQ]
   <dd><a href="https://rfc.zeromq.org/spec/23/"><cite>ZeroMQ Message Transport Protocol</cite></a>. URL: <a href="https://rfc.zeromq.org/spec/23/">https://rfc.zeromq.org/spec/23/</a>
  </dl>