http-notes: proof read

1 files changed, 34 insertions, 39 deletions

diff --git a/public/http-notes.md b/public/http-notes.md
index 5f8021b..520639d 100644
--- a/public/http-notes.md
+++ b/public/http-notes.md
@@ -43,42 +43,38 @@ protocol.
 >     requests and Date on responses, so that implementations can decide
 >     when not to handle a message as early as possible.
 
-I took that as a notice that I can use the first Host or similar
-header to quickly route along to my sub-component before I've parsed
-the entire header field set.
+Which is great!  We can make an optimization!
 
-However, it later states in [§5.4][RFC7230§5.4]:
+This is only a valid optimization for deciding to *not handle* a
+message.  You cannot use it to decide to route to a backend early
+based on this.  Part of the reason is that [§5.4][RFC7230§5.4] tells
+us we must inspect the entire header field set to know if we need to
+respond with a 400 status code:
 
 >     A server MUST respond with a 400 (Bad Request) status code to any
 >     HTTP/1.1 request message that lacks a Host header field and to any
 >     request message that contains more than one Host header field or a
 >     Host header field with an invalid field-value.
 
-Which means that I must parse the entire header field set.
-
-However, if I look a bit closer at §3.2.2, I see that this short-cut
-is only valid for deciding to *not handle* a message; if I am handling
-it, I cannot use this short-cut.
-
-Except that if I decide not to handle a request based on the Host
-header field, the correct thing to do is to send a 404 status code.
-Which implies that I have parsed the remainder of the header field set
-to validate the message syntax.  Oh no, what do I do?
+However, if I decide not to handle a request based on the Host header
+field, the correct thing to do is to send a 404 status code.  Which
+implies that I have parsed the remainder of the header field set to
+validate the message syntax.  We need to parse the entire field-set to
+know if we need to send a 400 or a 404.  Did this just kill the
+possibility of using the optimization?
 
 Well, there are a number of "A server MUST respond with a XXX code if"
 rules that can all be triggered on the same request.  So we get to
-choose which to use.
-
-And fortunately for optimizing implementations,
+choose which to use.  And fortunately for optimizing implementations,
 [§3.2.5][RFC7230§3.2.5] gave us:
 
 >     A server that receives a            ...           set of fields,
 >     larger than it wishes to process MUST respond with an appropriate 4xx
 >     (Client Error) status code.
 
-And since the header field set is longer than we want to process
-(since we want to short-cut processing), we are free to respond with
-whichever 4XX status code we like!
+Since the header field set is longer than we want to process (since we
+want to short-cut processing), we are free to respond with whichever
+4XX status code we like!
 
 # On normalizing target URIs
 
@@ -86,40 +82,39 @@ An implementer is tempted to normalize URIs all over the place, just
 for safety and sanitation.  After all,
 [RFC3986§6.1][] says it's safe!
 
-Unfortunately, most URI normalizers implementations will normalize an
-empty path to "/".  Which is not always save;
-[RFC7230§2.7.3][], which defines this
-"equivalence", actually says:
+Unfortunately, most URI normalization implementations will normalize an
+empty path to "/".  Which is not always safe; [RFC7230§2.7.3][], which
+defines this "equivalence", actually says:
 
 >                                             When not being used in
 >     absolute form as the request target of an OPTIONS request, an empty
 >     path component is equivalent to an absolute path of "/", so the
 >     normal form is to provide a path of "/" instead.
 
-Which means we can't use the usual normalizer implementation if we are
-making an OPTIONS request!
+Which means we can't use the usual normalization implementation if we
+are making an OPTIONS request!
 
-Why is that?  Well, if we turn to [§5.3.4][RFC7230§5.3.4], we
-find the answer.  One of the special cases for when the request target
-is not a URI, is that we may use "\*" as the target for an OPTIONS
-request to request information about the origin server itself, rather
-than a resource on that server.
+Why is that?  Well, if we turn to [§5.3.4][RFC7230§5.3.4], we find the
+answer.  One of the special cases for when the request target is not a
+URI, is that we may use "\*" as the target for an OPTIONS request to
+request information about the origin server itself, rather than a
+resource on that server.
 
 However, as discussed above, the target in a request to a proxy must
-be an absolute URI (and [§5.3.2][RFC7230§5.3.2] says that the
-origin server must also understand this syntax).  So, we must define a
-way to map "\*" to an absolute URI.
+be an absolute URI (and [§5.3.2][RFC7230§5.3.2] says that the origin
+server must also understand this syntax).  So, we must define a way to
+map "\*" to an absolute URI.
 
 Naively, one might be tempted to use "/\*" as the path.  But that
 would make it impossible to have a resource actually named "/\*".  So,
 we must define a special case in the URI syntax that doesn't obstruct
 a real path.
 
-If we didn't have this special case in the URI normalizer, and we
-handled the "/" path as the same as empty in the OPTIONS handler of
-the last proxy server, then it would be impossible to request OPTIONS
-for the "/" resources, as it would get translated into "\*" and
-treated as OPTIONS for the entire server.
+If we didn't have this special case in the URI normalization rules,
+and we handled the "/" path as the same as empty in the OPTIONS
+handler of the last proxy server, then it would be impossible to
+request OPTIONS for the "/" resources, as it would get translated into
+"\*" and treated as OPTIONS for the entire server.
 
 [RFC3986§6.1]: https://tools.ietf.org/html/rfc3986#section-6.1
 [RFC7230§2.7.3]: https://tools.ietf.org/html/rfc7230#section-2.7.3