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From jdca...@apache.org
Subject cvs commit: maven-components/maven-core/src/site/apt offline-mode.apt
Date Fri, 08 Apr 2005 16:28:58 GMT
jdcasey     2005/04/08 09:28:58

  Added:       maven-core/src/site/apt offline-mode.apt
  Log:
  First pass at documenting the design needed to add offline mode.
  
  Revision  Changes    Path
  1.1                  maven-components/maven-core/src/site/apt/offline-mode.apt
  
  Index: offline-mode.apt
  ===================================================================
  * Assumptions: What is Offline?
  
    For the purposes of determining the areas sensitive to offline status,
    it is definitely useful to define what the offline state really means.
  
    [[1]] This is obvious, but the network/internet is unavailable.
  
    [[2]] Localhost (127.0.0.1) may also be unavailable if the whole
          network stack is offline.
  
    [[3]] "Remote" repositories referenced using the file:// protocol may
          be available. However, if that file:// url references a
          file-share, as in the case of an NFS or SMB mount, that will
          be unavailable.
  
    So, offline mode has several implications, some of which may not be
    altogether obvious:
  
    * Localhost may be unavailable. Therefore, even locally installed
      server processes which work by conversing over a port may fail.
  
    * Not all "remote" repositories will fail. Specifically, if the remote
      repo uses the file:// protocol, and it doesn't refer to a shared
      filesystem, it will continue to be available.
  
  
  * Implications for Resolution
  
  ** Dependency Resolution
  
    This one is obvious...we only have access to the repositories using
    the file:// protocol and living on a truly local filesystem when
    offline.
  
  ** Plugin Resolution
  
    This is similar to dependency resolution. Plugin repositories not
    using file:// or not residing on a local (not shared) filesystem will
    be unavailable.
  
  
  * Implications for Mojo Execution
  
  ** Deployment mojos
  
    The concept of deployment is dependent on the availability of a some
    remote repository. Just as above, if that repository is not using
    file:// (which is highly likely to be the case), or the repository is
    not on a local filesystem, deployment will fail when offline.
  
  ** Testing mojos
  
    This can be a problem if the tests are more than simple unit tests;
    that is, if they require configuration of a server process, and
    subsequent testing in-container.
  
  ** SCM mojos
  
    See below for discussion on SCM-related operations. Any mojo which
    carries out some analysis or other interaction with a SCM system
    will likely be unavailable when in offline mode.
  
  
  * Implications for Subsystems
  
  ** Maven-Wagon
  
    Parts of Wagon will continue to function normally. These include:
  
    * The file wagon, provided the referenced location is on a local
      filesystem.
  
      It is not possible to determine whether a file-based location will
      be available except on a case-by-case basis (or a root-url by
      root-url basis).
  
    * If not otherwise specified, all other wagons are assumed to be
      remote-only, and are therefore sensitive to offline mode.
  
  ** Maven-Artifact
  
    This is wholly dependent on Maven-Wagon, above.
  
  ** Maven-SCM
  
    In all but trivial examples, SCM operations cannot complete without
    having access to the versioning server. Therefore, it is assumed that
    any SCM-related activity will be unavailable when m2 is in offline
    mode.
    
  ** Maven-Core
  
    We'll examine the different parts of maven-core on a case-by-case
    basis, below:
  
  *** DefaultLifecycleExecutor
  
    When binding goals to the project's configured lifecycle, each mojo
    descriptor should declare whether it requires online/offline status.
    This value should be a java.lang.Boolean, so it can implement 3VL
    (three value logic: yes, no, don't-care). The requiredConnectivity
    field in the mojo descriptor has the following semantics:
  
    [Boolean.TRUE] Online status is required for this mojo to function
                   correctly.
  
    [Boolean.FALSE] Offline status is required for this mojo to function
                    correctly.
  
    [null] Either status is acceptable for the mojo to execute. It doesn't
           care.
  
    The majority of mojos will leave the requiredConnectivity == null,
    since online/offline status will be irrelevant, provided they have
    access to their required artifacts and other classpath elements.
  
  
  * Implementation Notes
  
  ** Accessibility of offline status
  
    Offline status should be indicated in the MavenSettings instance, since it
    can conceivably be set from either the settings.xml or the command-line.
  
    In the event the '-o' switch is the impetus for setting offline mode, this
    should result in modification of the active profile in the MavenSettings
    instance, just as definition of the active profile from the command-line
    should result in similar modification. This object is not meant to be
    static within the build process, but rather to be setup as an aggregation of
    all settings-related information passed into the system.
  
  ** Control over downloads
  
    Find the control point for m2 using maven-wagon. At this point, inject
    a offline status parameter which is used when retrieving the specific Wagon.
  
    If <<<offline == true>>>:
    
    * If the wagon is not bound to "file://", then ignore the request and print
      a debug message.
  
    * If the wagon is bound to "file://" then:
  
      Retrieve the file or base-url file to be "downloaded".
      
      * If the file (or more usefully, the base-url file) exists, proceed.
  
      * If the file (or base-url file) doesn't exist, assume that this location
        is part of a file-share. Ignore the request and print a debug message 
        as above.
  
  ** Control over mojos in the lifecycle
  
    When binding a mojo to the project's lifecycle instance, check the mojo 
    descriptor's requiredConnectivity field.
  
    * If <<<(offline == true) && (Boolean.TRUE != requiredConnectivity)>>>,
bind
      the mojo to the lifecycle. 
      
      In this case, the client is <<offline>>, and the mojo either requires <<offline>>
      status, or else doesn't care.
  
    * If <<<(offline == false) && (Boolean.FALSE != requiredConnectivity)>>>,
bind
      the mojo to the lifecycle.
  
      In this case, the client is <<online>>, and the mojo either requires <<online>>
      status, or else doesn't care.
  
    * Otherwise, don't bind the mojo. Log a debug message to indicate that it is
      sensitive the the online state of the application, and that this state is
      currently wrong for execution.
  
    <<NOTE:>> Do we want to fail when we cannot bind a mojo to the lifecycle because
    of offline/online status? That would probably indicate that the user was trying to
    do something they cannot succeed at for now...so we probably should throw an
    exception in this case.
  
   
  
  
  

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