Errata

In (g) Response, the client make response to the server with "Authorization" header in which "nc=0000001"
According to RFC2617 and RFC 7616, nc should be a 8-hex-digit-nonce-count.
So, it should be "nc=00000001"

Errata ID: #zerustech-errata-2016-12-30-10-16
====================================

The pseudocode in example 7-1 conforms to the specifications till RFC 2616, which has been replaced by RFC 7234 in June, 2014. Unfortunately, the pseudocode is no longer suitable for describing the age calculation algorithm due to the changes in RFC 7234.

To keep the chapter of “Age Computation” updated with respect to the latest RFC, the following changes should be applied:

$apparent_age = max(0, $time_got_response - $Date_header_value);

--- $corrected_apparent_age = max($apparent_age, $Age_header_value);

$response_delay_estimate = ($time_got_response - $time_issued_request);

+++ $corrected_Age_header_value = $Age_header + $response_delay_estimate;

--- $age_when_document_arrived_at_our_cache = $corrected_apparent_age + $response_delay_estimate;

+++ $age_when_document_arrived_at_our_cache = max($apparent_age, $corrected_Age_header_value);

$age = $age_when_document_arrived_at_our_cache + $how_long_copy_has_been_in_our_cache;

Other corresponding parts in this chapter should also be updated accordingly.

Note: Figure 7-18 in page 192 should also be changed to reflect the new algorithm and variable names (I will provide the illustration in a separate email shortly).

However, please be advised that I submitted errata for “Figure 7-18” on Dec 29, 2016, but that was not for this issue (it was still based on the obsolete specification in RFC 2616). Therefore, if the author were to apply the changes above, the previous errata could be safely ignored.

Two issues were addressed:

1. "The label 'time_got_response' should be moved one node to the right,
and the currently labelled node should be removed from the Cache
timeline." This has been reported by someone else and has received feedback from the author or editor.

2. The illustrator didn't reflect the fact that the "corrected_apparent_age"—(time_got_response - date_value)— should have been counted twice when calculating the age of the cached document: age_when_document_arrived_at_our_cache = (request_delay_estimate + server_processing_time + response_delay_estimate) + response_delay_estimate. Therefore, to precisely illustrate the calculation algorithm, the timeline and age should be presented separately. I have created a new illustrator and I will send it in a separate email shortly.

> You can place multiple language tags in the Accept-Language header to enumerate all
supported languages and the order of preference (left to right).

The order does not matter to the client's preference. RFC 2616 says nothing about the order. And draft-ietf-httpbis-p2-semantics-26 [1] says a sender of the header cannot rely upon the recipient's behavior to accept the order as the sender's language preference, as follows:

Note that some recipients treat the order in which language tags are
listed as an indication of descending priority, particularly for tags
that are assigned equal quality values (no value is the same as q=1).
However, this behavior cannot be relied upon. For consistency and to
maximize interoperability, many user agents assign each language tag
a unique quality value while also listing them in order of decreasing
quality. Additional discussion of language priority lists can be
found in Section 2.3 of [RFC4647].

[1]: http://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-26#section-5.3.5

<meta http-equiv="Refresh" content="1;URL=index.html">

should be

<meta http-equiv="Refresh" content="1; URL=index.html">

(a space character added)

Because http://www.w3.org/TR/html-markup/meta.http-equiv.refresh.html says that one or more space characters are required between ";" and "url=".

In the case of having If-Match header with entity tags, the book says, "The resource is returned only if it has changed?that is, if the previously requested object?s entity tag does not match the entity tag of the current version on the server."

But I believe it is not correct because the resource is returned only if it has NOT changed. RFC 2616 says in 14.24 If-Match, "If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET request (without the If-Match header) on that resource."

In the description for Accept-Charset HTTP header in Appendix C, every "character set" should be changed to "charset".

Why:
1. The table 3-14 and table 17-2 says Accept-Charset header has charsets as its value, not character sets.
2. draft-ietf-httpbis-p2-semantics-22 says, "The "Accept-Charset" header field can be sent by a user agent to indicate what charsets are acceptable in textual response content.".

is:
Via = 1.1 cache.joes-hardware.com, 1.1 proxy.irenes-isp.net
should be:
Via: 1.1 proxy-62.irenes-isp.net, 1.0 cache.joes-hardware.com

is:
Via = "Via" ":" 1#( waypoint )
should be:
Via = "Via" ":" ( waypoint )[", " ( waypoint )...]

403 locked,

should be:

423 locked,