pontarius-xmpp/Documentation/Software Requirements Specification for Pontarius XMPP.lyx

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\begin_body

\begin_layout Title
Software Requirements Specification for Pontarius XMPP 0.1 (Third Draft)
\end_layout

\begin_layout Author
The Pontarius Project
\end_layout

\begin_layout Date
27th of July 2011
\end_layout

\begin_layout Standard
\begin_inset CommandInset toc
LatexCommand tableofcontents

\end_inset


\end_layout

\begin_layout Section
Introduction
\end_layout

\begin_layout Subsection
Purpose
\end_layout

\begin_layout Standard
The goal of this document is to clarify---for Pontarius
\begin_inset Foot
status open

\begin_layout Plain Layout
For more information about the Pontarius project, see http://www.pontarius.org/.
\end_layout

\end_inset

 developers, the XMPP community, and to some extent the Haskell community---what
 we are implementing.
 We hope that it will help us in the Pontarius project to keep track of
 functionality and requirements, provide a basis for scheduling, and help
 us with our validation and verification processes.
\end_layout

\begin_layout Subsection
Scope
\end_layout

\begin_layout Standard
Pontarius XMPP 0.1 will implement the client capabilities of RFC 6120: XMPP:
 Core and the depending specifications, such as RFC 6122: XMPP: Address
 Format, RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2,
 RFC 4422: Simple Authentication and Security Layer (SASL), RFC 5280: Internet
 X.509 Public Key Infrastructure Certificate and Certificate Revocation List
 (CRL) Profile, and Extensible Markup Language (XML) 1.0, among others.
\end_layout

\begin_layout Standard
Support for common extensions such as Instant Messaging, Data Forms, Service
 Discovery, etc.
 will 
\emph on
not
\emph default
 be included in the 0.1 version, but will be added in later (
\begin_inset Quotes eld
\end_inset

0.x
\begin_inset Quotes erd
\end_inset

) versions.
 Server components and XMPP server capabilities could also be added later.
\end_layout

\begin_layout Standard
While it is the goal of the Pontarius project to develop secure and privacy-awar
e 
\begin_inset Quotes eld
\end_inset

personal cloud
\begin_inset Quotes erd
\end_inset

 solutions on top of Pontarius XMPP, we want Pontarius XMPP to be a general-purp
ose---and the de facto---XMPP library for Haskell.
 It should be correct and efficient to work in.
\end_layout

\begin_layout Standard
We will not repeat the specifics of the requirements from the RFC 6120:
 XMPP Core specification and its depending specifications in this document
 unless we see any special reason to.
\end_layout

\begin_layout Subsection
Legal notice
\end_layout

\begin_layout Standard
Pontarius XMPP is a free and open source software project.
 
\begin_inset Quotes eld
\end_inset

The Pontarius project
\begin_inset Quotes erd
\end_inset

 is not a legal entity, but is like a synonym for Jon Kristensen.
 Jon Kristensen does DOES NOT TAKE ANY RESPONSIBILITY OR OFFER ANY GUARANTEES
 in regards to the software, its requirements or this document.
 Furthermore, the software is provided WITHOUT ANY WARRANTY; without even
 the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
\end_layout

\begin_layout Subsection
Definitions, acronyms, and abbrevations
\end_layout

\begin_layout Description
JID JabberID: An address for XMPP entities
\end_layout

\begin_layout Description
Pontarius A free and open source software project that aims to produce XMPP-base
d, uncentralized, and privacy-aware software solutions
\end_layout

\begin_layout Description
PX01 Pontarius XMPP 0.1
\end_layout

\begin_layout Description
REQ Requirement
\end_layout

\begin_layout Description
RFC Request for Comments: A memorandum published by the Internet Engineering
 Task Force; some of these, including XMPP: Core and XMPP: Address Format,
 are published as Internet standards
\end_layout

\begin_layout Description
TCP Transmission Control Protocol: A reliable network transport protocol
\end_layout

\begin_layout Description
TLS Transport Layer Security: A secure network protocol, a successor to
 Secure Sockets Layer (SSL)
\end_layout

\begin_layout Description
XMPP Extendable Messaging and Presence Protocol: An uncentralized, open,
 and near-real-time presence and messaging protocol
\end_layout

\begin_layout Subsection
References
\end_layout

\begin_layout Itemize
Extensible Messaging and Presence Protocol (XMPP): Core, RFC 6120, March
 2011, Internet Engineering Task Force (see also its depending specifications)
\end_layout

\begin_layout Subsection
Overview
\end_layout

\begin_layout Standard
The second section provides an overall description of the requirements of
 PX01, going through the features in a non-strict fashion, talking shortly
 about the product functions, as well as some constraints and assumptions.
\end_layout

\begin_layout Standard
The third section simply lists the requirements, categorized by external
 interfaces, functions, performance requirements, design constraints, and
 software system (quality) attributes.
\end_layout

\begin_layout Section
Overall Description
\end_layout

\begin_layout Subsection
Product perspective
\end_layout

\begin_layout Standard
PX01 will be used by XMPP clients to manage presence and messaging in a
 uncentralized near-real-time environments.
 For this first milestone of the library, we have chosen to implement only
 the XMPP: Core specification, and only the client capabilities of it.
 The reason for this is that we want to get the library out quickly, and
 want to have the core functionality of the library particularly well tested.
 The X in XMPP stands for extendable, and Pontarius XMPP must be flexible
 in regards for extensions, such as RFCs and XEPs; we might end up implementing
 hundreds of them.
 This is one of the most important quality attribute of the software.
\end_layout

\begin_layout Standard
PX01 is designed to be used with Haskell.
\end_layout

\begin_layout Standard
PX01 must work on GNU/Linux, the main Free Software operating system.
 However, due to the platform support and high-level nature of Haskell,
 running it on other common operating systems is likely to work as well.
\end_layout

\begin_layout Standard
PX01 must work with (at least) the (estimated) most popular free and open
 source software XMPP server that works with the specifics of our implementation
 (such as SCRAM).
\end_layout

\begin_layout Standard
PX01 depends on the below (free and open source software) Haskell packages.
 I have omitted specification number [...].
 I have also omitted the source, as they are all available on Hackage.
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\begin_layout Standard
Every PX01 client will open up at most one TCP port on the system.
 PX01 in itself does not write anything to the file system storage of the
 operating system, with the exception of the optional logging facility,
 disabled by default, which may be configured to write to disk.
\end_layout

\begin_layout Standard
We will utilize 
\emph on
at least
\emph default
 Transport Layer Security to help protect clients using the library from
 attacks.
 PX01 will not provide any spam protection.
\end_layout

\begin_layout Standard
As we expect a very limited amount of concurrent XMPP clients, and a (relatively
) limited actitivity over XMPP streams--even when they are being fully active--w
e are not specifying any detailed memory or (process) performance requirements
 for PX01.
 However, we will stress test the library.
\end_layout

\begin_layout Standard
We see no hardware or user interfaces to take into account.
\end_layout

\begin_layout Subsection
Product functions
\end_layout

\begin_layout Standard
PX01 implements XMPP: Core and allow clients to do roughly the following:
 Open a TCP connection to a server, exchange XML information with the server
 to configure the (XML) stream, handle stream errors and encoding issues,
 have the connection secured by TLS, authenticate using a SASL mechanism
 and binding a resource to the stream, as well as sending and receiving
 so-called XMPP stanzas, certain 
\begin_inset Quotes eld
\end_inset

top level
\begin_inset Quotes erd
\end_inset

 XML elements in the stream for communicating messages and presence.
\end_layout

\begin_layout Subsection
User characteristics
\end_layout

\begin_layout Standard
We expect developers using PX01 to understand the XMPP: Core specification
 (and its depending specifications), Haskell, and monads, including the
 StateT monad transformer.
\end_layout

\begin_layout Subsection
Constraints
\end_layout

\begin_layout Standard
In addition to the requirements in XMPP: Core, XMPP applications should
 be reliable in that they should be able to be online (active or inactive)
 for a very long period of time, without problems of memory leaks, unnecessary
 CPU usage, or similar, arising.
\end_layout

\begin_layout Subsubsection
Assumptions and dependencies
\end_layout

\begin_layout Standard
We assume that the Glasgow Haskell Compiler (GHC) is available on the system
 where PX01 applications are built.
\end_layout

\begin_layout Section
Specific requirements
\end_layout

\begin_layout Subsection
External interfaces
\end_layout

\begin_layout Standard
The software is accessible from Haskell and may be configured to do logging.
\end_layout

\begin_layout Description
REQ-1 The system shall be importable and fully functional from Haskell through
 a full import of the Network.XMPP namespace.
\end_layout

\begin_layout Description
REQ-2 The system shall be able to log information through arbitrary and
 flexible log handlers.
\end_layout

\begin_layout Description
REQ-3 The system shall run under GNU/Linux.
\end_layout

\begin_layout Description
REQ-4 The system shall work against (at least) the (estimated) most popular
 free and open source software XMPP server supporting the features that
 we require (such as SCRAM).
\end_layout

\begin_layout Subsection
Functions
\end_layout

\begin_layout Standard
If an error arises due to a bug in the software, the system shall throw
 a runtime exception and the process should exit.
 If an 
\begin_inset Quotes eld
\end_inset

acceptable
\begin_inset Quotes erd
\end_inset

 exception is possible to arise, such as the XMPP server times out, then
 the related functions should reflect that by being able to return values
 such as Nothing or null.
 This allows the XMPP clients to take the appropriate actions.
\end_layout

\begin_layout Description
REQ-5 The system shall be validating input from all functions exposed through
 any of the system's APIs.
 
\end_layout

\begin_layout Description
REQ-6 Each incoming stanza should move through a stack of (client) handlers,
 where each handler may block the stanza from being delivered to handlers
 further up in the stack.
 The exceptions to this rule is stanza errors and IQ result stanzas, which
 may be delivered directly to a callback provided when generating the stanza
 (and possibly surpressed there).
\end_layout

\begin_layout Standard
Rationale: We have so far found it useful to stack XMPP client handlers
 on top of each other, letting them all manage their particular responsibilities
 and surpress their messages to handlers further up the stack.
\end_layout

\begin_layout Description
REQ-7 When the client is disconnected, a 
\begin_inset Quotes eld
\end_inset

disconnect event
\begin_inset Quotes erd
\end_inset

 is generated in a way similar to in REQ-5.
 It is moved through the stack handlers; however, these events move down
 the stacks completely and can't be surpressed.
 The same thing applies for incoming stream errors, which can either be
 recoverable or unrecoverable.
 (?)
\end_layout

\begin_layout Standard
Rationale: We want the handlers to all do the appropriate clean-up activities.
\end_layout

\begin_layout Description
REQ-8 The API shall allow for opening a stream to a given IP or host name
 on a given port, returning either a success value or the reason for failing.
\end_layout

\begin_layout Description
REQ-9 The API shall allow for securing an opened stream with TLS, returning
 either a success value or the reason for failing.
\end_layout

\begin_layout Description
REQ-10 The API shall allow for authenticating an opened (possibly TLS secured)
 stream, returning either a success value of the reason for failing.
 If the credentials were wrong, the system shall allow the client to make
 as many retries as allowed by the server, without restarting the stream.
\end_layout

\begin_layout Description
REQ-11 The API shall allow for perform resource binding on an authenticated
 stream, either by trying to set a specific resource, or have the server
 generate one.
\end_layout

\begin_layout Standard
Rationale: Even though most clients wants to do REQ-8, REQ-9, REQ-10, and
 REQ-11 in one action, some uses of XMPP (such as In-Band Registration)
 demands more flexibility.
\end_layout

\begin_layout Description
REQ-12 The API shall provide a convenience function for opening a stream,
 securing the stream with TLS, authenticating an XMPP account, and perform
 resource binding in one function call, returning either a success value
 or the reason for failing.
\end_layout

\begin_layout Standard
Rationale: This makes the library easier and more efficient to use for most
 uses cases.
\end_layout

\begin_layout Description
REQ-13 The API shall provide the possibility for clients to close the stream.
\end_layout

\begin_layout Description
REQ-14 The API shall provide the possibility for clients to send stream
 errors.
\end_layout

\begin_layout Description
REQ-15 The API shall allow a convenient way for 
\begin_inset Quotes eld
\end_inset

standard disconnect
\begin_inset Quotes erd
\end_inset

 the client.
\end_layout

\begin_layout Description
REQ-16 The API shall provide a facility for convenient stanza (message,
 presence, info/query) creation, eliminating the risk of illegal stanzas
 where feasible.
\end_layout

\begin_layout Description
REQ-17 The API shall allow for convenient construction of JabberIDs.
\end_layout

\begin_layout Description
REQ-18 The API shall provide utility functions to check whether or not a
 JID is full or bare.
\end_layout

\begin_layout Description
REQ-19 The API shall provide conversion functions to convert from a string
 to (
\begin_inset Quotes eld
\end_inset

Maybe
\begin_inset Quotes erd
\end_inset

) JID, and JID to string.
\end_layout

\begin_layout Description
REQ-20 The API shall provide an optional way for clients to receive time-out
 events on requests made, such as an IQ or connection attempt.
 The time-out interval should be customizable.
\end_layout

\begin_layout Description
REQ-21 The library should generate an internal infinite list of unique stanza
 IDs; the API should provide a way for application developers to acquire
 any amount of such IDs
\end_layout

\begin_layout Description
REQ-22 The system must offer timeout callbacks to be called if an asynchronous
 result is not guaranteed to be produced in a timely fashion.
\end_layout

\begin_layout Description
REQ-23 The system must a convenient API to deal with stanza and stream errors.
\end_layout

\begin_layout Subsection
Performance requirements
\end_layout

\begin_layout Standard
There is only one XMPP client per instance of the system.
\end_layout

\begin_layout Description
REQ-24 Regular desktop computers should be able to run hundreds of Pontarius
 XMPP 0.1 clients.
\end_layout

\begin_layout Description
REQ-25 Pontarius XMPP 0.1 should support virtually as many stanzas per second
 as (non-throttled) XMPP servers are able to route.
 This goes for both lightweight, heavy and mixed stanzas.
\end_layout

\begin_layout Description
REQ-26 Processing (parsing, generating, and firing the event) a received
 stanza should take at most 0.01 seconds.
\end_layout

\begin_layout Subsection
Design constraints
\end_layout

\begin_layout Subsubsection
RFC 6120: XMPP: Core
\end_layout

\begin_layout Description
REQ-27 The system shall support one persistant TCP stream/connection between
 the XMPP client and the XMPP server.
\end_layout

\begin_layout Description
REQ-28 The system shall implement (at least) the TLS_RSA_WITH_AES_128_CBC_SHA
 cipher suite for TLS.
\end_layout

\begin_layout Description
REQ-29 The system shall support (at least) the SHA-1 variant of SASL Salted
 Challenge Response Authentication Mechanism (SCRAM-SHA-1).
\end_layout

\begin_layout Description
REQ-30 XML namespaces for stanzas should always be known to the client.
\end_layout

\begin_layout Description
REQ-31 We must validate incoming XML (though not against the XML schemas).
\end_layout

\begin_layout Description
REQ-32 The system shall always check for the appropriate features before
 trying to use them.
\end_layout

\begin_layout Description
REQ-33 End-to-end presence or anything else presence-related defined outside
 of XMPP: Core (such as in XMPP: Instant Messaging) is 
\emph on
not
\emph default
 supported.
\end_layout

\begin_layout Subsubsection
RFC 6122: XMPP: Address Format
\end_layout

\begin_layout Description
REQ-34 JIDs should be validated, transformed, and internationalized in accordanc
e with the stringprep profiles Nodeprep, Nameprep, and Resourceprep.
\end_layout

\begin_layout Description
REQ-35 JIDs should be able to use hostnames, IPv4 addresses, and IPv6 addresses,
 as domainparts.
\end_layout

\begin_layout Subsubsection
Standards compliance
\end_layout

\begin_layout Description
REQ-36 The project and its source code shall adhere to the guidelines prestented
 in the guidelines found at http://www.haskell.org/haskellwiki/Programming_guideli
nes.
\end_layout

\begin_layout Subsection
Software system attributes
\end_layout

\begin_layout Description
REQ-37 The system shall be 
\emph on
extendable
\emph default
; it must be flexible in regards for extensions, such as RFCs and XEPs.
\end_layout

\begin_layout Description
REQ-38 The system shall be 
\emph on
reliable
\emph default
; it should produce not crash, lag behind, or get some data corruption under
 very heavy and lengthy use.
\end_layout

\begin_layout Description
REQ-39 The system shall be 
\emph on
secure
\emph default
; steps should be taken to protect the clients against man-in-the-middle
 attacks and the like.
\end_layout

\end_body
\end_document