Change reason-phrase to be optional but non-empty (instead of requrin…

…g it and allowing it to be empty). Also add a note about what the absence of reason-phrase means in practice (#197)

draft-ietf-httpbis-messaging-latest.xml

@@ -717,11 +717,11 @@ https://www.example.org
 <t>
    The first line of a response message is the status-line, consisting
    of the protocol version, a space (SP), the status code, another space,
-   a possibly empty textual phrase describing the status code, and
+   an &OPTIONAL; textual phrase describing the status code, and
    ending with CRLF.
 </t>
 <sourcecode type="abnf7230"><iref primary="true" item="Grammar" subitem="status-line"/>
-  <x:ref>status-line</x:ref> = <x:ref>HTTP-version</x:ref> <x:ref>SP</x:ref> <x:ref>status-code</x:ref> <x:ref>SP</x:ref> <x:ref>reason-phrase</x:ref> <x:ref>CRLF</x:ref>
+  <x:ref>status-line</x:ref> = <x:ref>HTTP-version</x:ref> <x:ref>SP</x:ref> <x:ref>status-code</x:ref> <x:ref>SP</x:ref> [<x:ref>reason-phrase</x:ref>] <x:ref>CRLF</x:ref>
 </sourcecode>
 <t>
    Although the status-line grammar rule requires that each of the component
@@ -759,8 +759,13 @@ https://www.example.org
    reliable channel for information (it might be discarded or overwritten by
    intermediaries, and it is not transmitted in other versions of HTTP).
 </t>
+<t>
+   Note that while the reason-phrase is optional, the preceding SP character
+   is not. In other words, absent a reason-phrase the status-line ends
+   with a trailing SP, followed by CRLF.
+</t>
 <sourcecode type="abnf7230"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
-  <x:ref>reason-phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
+  <x:ref>reason-phrase</x:ref>  = 1*( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
 </sourcecode>
 </section>
 
@@ -3030,14 +3035,14 @@ Upgrade: HTTP/2.0
 <x:ref>quoted-string</x:ref> = &lt;quoted-string, see <xref target="Semantics" x:fmt="," x:sec="4.2.3"/>&gt;
 
 <x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
-<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
+<x:ref>reason-phrase</x:ref> = 1*( HTAB / SP / VCHAR / obs-text )
 <x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
 <x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
  asterisk-form
 
 <x:ref>start-line</x:ref> = request-line / status-line
 <x:ref>status-code</x:ref> = 3DIGIT
-<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
+<x:ref>status-line</x:ref> = HTTP-version SP status-code SP [ reason-phrase ] CRLF
 
 <x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
 <x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
@@ -3379,6 +3384,7 @@ Upgrade: HTTP/2.0
 <section title="Since draft-ietf-httpbis-messaging-04" anchor="changes.since.04">
 <ul>
   <li>In <xref target="header.upgrade"/>, clarify that protocol-name is to be matched case-insensitively (<eref target="https://github.com/httpwg/http-core/issues/8"/>)</li>
+  <li>In <xref target="status.line"/>, add clarifications about empty reason phrases (<eref target="https://github.com/httpwg/http-core/issues/197"/>)</li>
 </ul>
 </section>
 

httpbis.abnf

@@ -187,7 +187,7 @@ quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
 qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
 range-unit = bytes-unit / other-range-unit
 rank = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
-reason-phrase = *( HTAB / SP / VCHAR / obs-text )
+reason-phrase = 1*( HTAB / SP / VCHAR / obs-text )
 received-by = ( uri-host [ ":" port ] ) / pseudonym
 received-protocol = [ protocol-name "/" ] protocol-version
 relative-part = <relative-part, see [RFC3986], Section 4.2>
@@ -198,7 +198,7 @@ second = 2DIGIT
 segment = <segment, see [RFC3986], Section 3.3>
 start-line = request-line / status-line
 status-code = 3DIGIT
-status-line = HTTP-version SP status-code SP reason-phrase CRLF
+status-line = HTTP-version SP status-code SP [ reason-phrase ] CRLF
 subtype = token
 suffix-byte-range-spec = "-" suffix-length
 suffix-length = 1*DIGIT