Complete.

Library-conneg.md

@@ -58,17 +58,131 @@ Now we are in a position to do some negotiating. At the beginning of your handle
 
     local
 			l_media_variants: MEDIA_TYPE_VARIANT_RESULTS
+                        l_is_head: BOOLEAN
+                        h: HTTP_HEADER
+                        l_msg: STRING
 		do
+                        l_is_head := False -- or `True' if this is for a HEAD handler
 			l_media_variants:= conneg.media_type_preference (mime_types_supported, a_req.http_accept)
 			if not l_media_variants.is_acceptable then
-				send_unacceptable_media_type (a_res)
+				send_unacceptable_media_type (a_res, l_is_head)
 		 	elseif not conneg.charset_preference (charsets_supported, a_req.http_accept_charset).is_acceptable then
- 				send_unacceptable_charset (a_res)
+ 				send_unacceptable_charset (a_res, l_is_head)
  			elseif not conneg.encoding_preference (encodings_supported, a_req.http_accept_encoding).is_acceptable then
- 				send_unacceptable_encoding (a_res)
+ 				send_unacceptable_encoding (a_res, l_is_head)
  			elseif not conneg.language_preference (languages_supported, a_req.http_accept_language).is_acceptable then
  				send_unacceptable_encoding (a_res)
 			else
                           -- We have agreed a representation, let's go and serve it to the client
 `
 
+Now for those `send_unnacceptable_...` routines. They are fairly simple:
+
+    	send_unacceptable_media_type (a_res: WSF_RESPONSE; a_is_head: BOOLEAN) is
+			-- Send error result as text/plain that the media type is unnacceptable.
+		require
+			a_res_not_void: a_res /= Void
+			status_not_set: not a_res.status_is_set
+			header_not_committed: not a_res.header_committed
+		local
+			l_error_text: STRING
+		do
+			l_error_text := "The requested media type(s) is/are not supported by this server."
+			send_unacceptable (a_res, a_is_head, l_error_text)
+		end
+
+	send_unacceptable_charset (a_res: WSF_RESPONSE; a_is_head: BOOLEAN) is
+			-- Send error result as text/plain that the character set is unnacceptable.
+		require
+			a_res_not_void: a_res /= Void
+			status_not_set: not a_res.status_is_set
+			header_not_committed: not a_res.header_committed
+		local
+			l_error_text: STRING
+		do
+			l_error_text := "The requested character set(s) is/are not supported by this server. Only UTF-8 is supported."
+			send_unacceptable (a_res, a_is_head, l_error_text)
+		end
+
+	send_unacceptable_encoding (a_res: WSF_RESPONSE; a_is_head: BOOLEAN) is
+			-- Send error result as text/plain that the encoding is unnacceptable.
+		require
+			a_res_not_void: a_res /= Void
+			status_not_set: not a_res.status_is_set
+			header_not_committed: not a_res.header_committed
+		local
+			l_error_text: STRING
+		do
+			l_error_text := "The requested encoding(s) is/are not supported by this server. Only identity is supported."
+			send_unacceptable (a_res, a_is_head, l_error_text)
+		end
+
+	send_unacceptable_language (a_res: WSF_RESPONSE; a_is_head: BOOLEAN) is
+			-- Send error result as text/plain that the language unnacceptable.
+		require
+			a_res_not_void: a_res /= Void
+			status_not_set: not a_res.status_is_set
+			header_not_committed: not a_res.header_committed
+		local
+			l_error_text: STRING
+		do
+			l_error_text := "The requested language(s) is/are not supported by this server. Only en (English) is supported."
+			send_unacceptable (a_res, a_is_head, l_error_text)
+		end
+	
+	send_unacceptable (a_res: WSF_RESPONSE; a_is_head: BOOLEAN; a_error_text: STRING) is
+			-- Send a_error_text as text/plain that a header is unnacceptable.
+		require
+			a_res_not_void: a_res /= Void
+			status_not_set: not a_res.status_is_set
+			header_not_committed: not a_res.header_committed
+			a_error_text_not_void: a_error_text /= Void
+		local
+			h: HTTP_HEADER
+		do
+			create h.make
+			set_content_type (h, Void)
+			h.put_content_length (a_error_text.count)
+			h.put_current_date
+			a_res.set_status_code ({HTTP_STATUS_CODE}.not_acceptable)
+			a_res.put_header_text (h.string)
+			if not a_is_head then
+				a_res.put_string (a_error_text)
+			end
+		end
+
+We'll see that `set_content_type` routine in a bit. But for now, we just have to generate the response. Let's go back to that `else ...` bit:
+
+    else
+                       -- We have agreed a representation, let's go and serve it to the client
+	create h.make
+	set_content_type (h, a_media_variants)
+       	if a_media_variants.media_type ~ {HTTP_MIME_TYPES}.application_xml then
+		l_msg := "<?xml version='1.0' encoding='UTF-8' ?><my-tag>etc."
+	else
+		l_msg := json.value (<some-value>).representation
+	end
+	h.put_content_length (l_msg.count)
+	h.put_current_date
+	a_res.set_status_code ({HTTP_STATUS_CODE}.ok)
+	a_res.put_header_text (h.string)
+	if not a_is_head then
+	   a_res.put_string (l_msg)
+	end
+
+There's that `set_content_type` again. Finally, we will take a look at it:
+
+    	set_content_type (a_h: HTTP_HEADER; a_media_variants: MEDIA_TYPE_VARIANT_RESULTS) is
+			-- Set the content=type header in `a_h' according to `a_media_variants'.
+		require
+			a_h_not_void: a_h /= Void
+		do
+			if a_media_variants = Void or else not a_media_variants.is_acceptable then
+				a_h.put_content_type ({HTTP_MIME_TYPES}.text_plain)
+			else
+				a_h.put_content_type (a_media_variants.media_type)
+			end
+			a_h.put_header_key_value ({HTTP_HEADER_NAMES}.header_vary, {HTTP_HEADER_NAMES}.header_accept)
+		end
+
+Firstly, if we haven't agreed a media-type, then we send our (negative) response as `plain/text`. Otherwise we will send the response in the agreed media-type. But in each case we add a `Vary:Accept` header. This tells proxy caches that they have to check the media-type before returning a cached result, as there may be a different representation available. Since we do not vary our representation by language, charset or encoding, we don't add `Vary:Accept-Language,Accept-Charset,Accept-Encoding`. But if we were to negotiate different representations on those dimensions also, we would need to list the appropriate headers in the `Vary` header.