Re: Gen-ART Last Call Review of draft-melnikov-imap-search-res-06.txt

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Hi Spencer,
I've updated my copy of the draft, so I am answering the remaining comments you've sent:

Spencer Dawkins wrote:

Abstract

  Many IMAP clients use the result of a SEARCH command as the input to
  perform another operation, for example fetching the found messages,
  deleting them or copying them to another mailbox.

  This can be achieved using standard IMAP operations described in RFC
  3501, however this would be suboptimal: the server will send the list
  of found messages to the client, after that the client will have to
  parse the list, reformat it and send it back to the server.  The
  client can't pipeline the SEARCH command with the subsequent command.

Spencer (readability) - in this paragraph, there are three ways that this extension improves normal operation - for bandwidth (because the list isn't sent in both directions when it doesn't have to be), for processing (since the list isn't parsed and reformatted when it doesn't have to be), and for serialization (since the two commands can now be pipelined). In the body of the document, a fourth improvement is also mentioned ("server optimization"), but isn't described at all. The two lists should be the same, and I wouldn't mind seeing some description of "server optimization" in the body of the document.

Done.

  This document proposes an IMAP extension that allows a client to tell
  a server to use the result of a SEARCH (or UID SEARCH) command as an
  input to any subsequent command.

2.   Introduction and Overview

Spencer (readability) - This section combines introduction/overview (not
normative) and protocol operation (normative). I'd suggest separating the
two. I'd also suggest using some of the abstract text as an actual
introduction - this section assumes that you've read the abstract, I think,
and not everyone will automatically do that.

Done.

  The SEARCH result reference extension defines a new SEARCH result
  option [IMAPABNF] "SAVE" that tells the server to remember the result
  of the SEARCH or UID SEARCH command (as well as any command based on
  SEARCH, e.g. SORT and THREAD [SORT]) and store it in an internal
  variable that we will reference as the "search result variable". The
  client can use the "$" marker to reference the content of this
  internal variable. The "$" marker can be used instead of message (or
  UID) sequence in order to indicate that the server should substitute

Spencer (nit) - "message" looks like a noun until you get past "(or UID)"
and discover it's an adjective. Suggest s/message (or UID) sequence/message
sequence or UID sequence/.

Changed.

  it with the list of messages from the search result variable.  Thus
  the client can use the result of the latest remembered SEARCH command
  as a parameter to another command.  The search result marker has
  several advantages:
   * it avoids wasted bandwidth and associated delay;
   * it allows the client to pipeline a SEARCH [IMAP4] command with a
     subsequent FETCH/STORE/COPY/SEARCH [IMAP4] or UID EXPUNGE
  [UIDPLUS] command;
   * the client doesn't need to spend time reformatting the
     result of a SEARCH command into a message set used in
     the subsequent command;
   * it allows the server to perform optimizations.

Spencer (readability) - in this list, there are FOUR advantages, not three as above... can you give any information about what optimizations a server can perform because this extension is being used?

I've added the following text:

  For example if the server
  can execute several pipelined commands in parallel (or out of order),
  presence of the search result marker can allow the server to decide
  which commands may or may not be executed out of order.

  In absence of any other SEARCH result option, the SAVE result option
  also suppresses any SEARCH response that would have been otherwise
  returned by the SEARCH command.

Spencer (readability) - somewhere around here, the actual protocol
specification section starts... :-)

I've split the section.
[...]

  command with the SAVE result option that caused the server to return
  NO tagged response sets the value of the search result variable to
  the empty sequence.

  When a message listed in the search result variable is EXPUNGEd, it
  is automatically removed from the list.  Implementors are reminded
  that if the server stores the list as a list of message numbers, it
  MUST automatically adjust them when notifying the client about

Spencer (readability) - is the meaning of "automatically adjust them"
obvious to everyone but me? Do you just remove the message number from the
list, or renumber the list, or ... ?

The latter. This is described in RFC 3501, section 7.4.1. I've added this reference to clarify.

  expunged messages.

  Note that even if the "$" marker contains the empty list of messages,
  it must be treated by all commands accepting message sets as
  parameters, as a valid, but non matching list of messages. For

Spencer (readability) - this is correct as written, but hard to parse.
Perhaps "treated as a valid but non matching list of messages, by all
commands that accept message sets as parameters"?

I like that. Thanks.

  example, the "FETCH $" command would return tagged OK response and no
  FETCH responses.  See also the Example # 5 below.

[...]

  2) The following example demonstrates that the result of one SEARCH
     command can be used to subset the result of another SEARCH
     command:

  Example 3:
              C: A300 SEARCH RETURN (SAVE) SINCE 1-Jan-2004
                  NOT FROM "Smith"
              S: A300 OK SEARCH completed
              C: A301 UID SEARCH UID $ SMALLER 4096
              S: * SEARCH 17 900 901
              S: A301 OK completed

  Note that the second command in Example 3 can be replaced with:
              C: A301 UID SEARCH $ SMALLER 4096
  and the result of the command would be the same.

Spencer (readability) - I didn't quite follow this. I think what confused me is the introductory text - isn't this example demonstrating "that the result
of one SEARCH command can be used as input to a second SEARCH command"?
"Subset" as written seemed to say that the first result was taking an action
("subset"), but it's just input to the second SEARCH...

I've changed the text as you've suggested.

2.2.   Multiple Commands in Progress

Spencer (readability) - could you insert a sentence that introduces Example
7 and explains what you illustrate in this example? (Is it only what the
//comment says?) (same for Example 8)

       Example 7:
                   C: G282 SEARCH RETURN (SAVE) KEYWORD $Junk
                   C: G283 SEARCH RETURN (ALL) SINCE 28-Oct-2006
                       FROM "Eric"
                   //The server can execute the two SEARCH commands
                   //in any order, as the don't have any dependency.

Spencer (nit) - s/the/they/

Fixed.

                   //Note that the second command is making use of
                   //the [ESEARCH] extension.
                   S: * ESEARCH (TAG "G283") ALL 3:15,27,29:103
                   S: G283 OK SEARCH completed
                   S: G282 OK SEARCH completed

       Example 8:
                   C: H282 SEARCH RETURN (SAVE) KEYWORD $Junk
                   C: H283 SEARCH RETURN (SAVE) SINCE 28-Oct-2006
                       FROM "Eric"
                   //The result of the second SEARCH overrides the
                   //result of the first.
                   S: H283 OK SEARCH completed
                   S: H282 OK SEARCH completed


2.3.   Interaction with ESEARCH extension

       When the SAVE result option is combined with the MIN or MAX
       [ESEARCH] result option, and none of the other ESEARCH result
       options are present, the corresponding MIN/MAX is returned (if
       the search result is not empty) but the "$" marker would contain
       a single message as returned in the MIN/MAX return item. If the
       SAVE result option is combined with both MIN and MAX result
       options, and none of the other ESEARCH result options are
       present, the "$" marker would contain one or two messages as
       returned in the MIN/MAX return items.  If the SAVE result option
       is combined with ALL and/or COUNT result option, the "$" marker
       would always contain all messages found by the SEARCH or UID
       SEARCH command.  (Note that the last rule might affect ESEARCH
       implementations that optimize how COUNT result is constructed.)

Spencer (readability) - is it obvious to everyone except me *how* the last
rule might affect these implementations?

Spencer (nit) - the previous paragraph is pretty dense. It might be more
readable as a bulleted list (one bullet per case).

I've split the paragraph into multiples. I hope this is more readable.

  3.   Formal Syntax

4.   Security Considerations

  This extension requires the server to keep additional state, that may
  be used to simplify Deny of Service attacks. In order to minimize
  damage from such attacks server implementations MAY limit the number
  of saved searches they allow across all connections at any given time
  and return the tagged NO response to a SEARCH RETURN (SAVE) command
  when this limit is exceeded.

Spencer (readability) - I'm guessing there is no way for a client to
discover this is the reason for the tagged NO response?

I've added a new IMAP response code to allow the server to signal that its limit is exceeded.

but it might be nice
to say so explicitly. Just curious - is this what an IMAP server would do
today, when it detects a DoS attack (by an attacker who's just working harder)? If so, it might be nice to point that out, too.

5.  IANA Considerations

  This document defines the "X-DRAFT-I05-SEARCHRES" <<Fix upon
  publication>> IMAP capability.  IANA is requested to add it to the
  IMAP4 Capabilities Registry, which is currently located at:

     http://www.iana.org/assignments/imap4-capabilities

Spencer (nit) - IANA has suggested "search-res" as the permanent name for this capability. You might add it here, just for completeness.




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