The Apache EBCDIC Port - Apache HTTP Server Version 2.4








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Apache HTTP Server Version 2.4



Apache > HTTP Server > Documentation > Version 2.4 > Platform Specific NotesThe Apache EBCDIC Port

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    Warning: This document
    has not been updated to take into account changes made in
    the 2.0 version of the Apache HTTP Server. Some of the
    information may still be relevant, but please use it with care.
    

  
 Overview of the Apache EBCDIC Port
 Design Goals
 Technical Solution
 Porting Notes
 Document Storage Notes
 Apache Modules' Status
 Third Party Modules' Status
See alsoComments


Overview of the Apache EBCDIC Port

    

    Version 1.3 of the Apache HTTP Server was the first version
    which included a port to a (non-ASCII) mainframe machine which
    uses the EBCDIC character set as its native codeset.

    (It is the SIEMENS family of mainframes running the BS2000/OSD
    operating system. This mainframe OS nowadays features a
    SVR4-derived POSIX subsystem).

    The port was started initially to

    
      prove the feasibility of porting the Apache HTTP server to
      this platform

      find a "worthy and capable" successor for the venerable
      CERN-3.0 daemon
      (which was ported a couple of years ago), and to

      prove that Apache's preforking process model can on this
      platform easily outperform the accept-fork-serve model used
      by CERN by a factor of 5 or more.
    

    This document serves as a rationale to describe some of the
    design decisions of the port to this machine.

  

Design Goals

    

    One objective of the EBCDIC port was to maintain enough
    backwards compatibility with the (EBCDIC) CERN server to make
    the transition to the new server attractive and easy. This
    required the addition of a configurable method to define
    whether a HTML document was stored in ASCII (the only format
    accepted by the old server) or in EBCDIC (the native document
    format in the POSIX subsystem, and therefore the only realistic
    format in which the other POSIX tools like grep or
    sed could operate on the documents). The current
    solution to this is a "pseudo-MIME-format" which is intercepted
    and interpreted by the Apache server (see below). Future versions
    might solve the problem by defining an "ebcdic-handler" for all
    documents which must be converted.

  

Technical Solution

    

    Since all Apache input and output is based upon the BUFF
    data type and its methods, the easiest solution was to add the
    conversion to the BUFF handling routines. The conversion must
    be settable at any time, so a BUFF flag was added which defines
    whether a BUFF object has currently enabled conversion or not.
    This flag is modified at several points in the HTTP
    protocol:

    
      set before a request is received
      (because the request and the request header lines are always
      in ASCII format)

      set/unset when the request body is
      received - depending on the content type of the request body
      (because the request body may contain ASCII text or a binary
      file)

      set before a reply header is sent
      (because the response header lines are always in ASCII
      format)

      set/unset when the response body is sent
      - depending on the content type of the response body (because
      the response body may contain text or a binary file)
    

  

Porting Notes

    

    
      
        The relevant changes in the source are #ifdef'ed
        into two categories:

        
          #ifdef
          CHARSET_EBCDIC

          
            Code which is needed for any EBCDIC based machine.
            This includes character translations, differences in
            contiguity of the two character sets, flags which
            indicate which part of the HTTP protocol has to be
            converted and which part doesn't etc.
          

          #ifdef _OSD_POSIX

          
            Code which is needed for the SIEMENS BS2000/OSD
            mainframe platform only. This deals with include file
            differences and socket implementation topics which are
            only required on the BS2000/OSD platform.
          
        
      

      
        The possibility to translate between ASCII and EBCDIC at
        the socket level (on BS2000 POSIX, there is a socket option
        which supports this) was intentionally not chosen,
        because the byte stream at the HTTP protocol level consists
        of a mixture of protocol related strings and non-protocol
        related raw file data. HTTP protocol strings are always
        encoded in ASCII (the GET request, any Header: lines,
        the chunking information etc.) whereas the file transfer
        parts (i.e., GIF images, CGI output etc.)
        should usually be just "passed through" by the server. This
        separation between "protocol string" and "raw data" is
        reflected in the server code by functions like bgets()
        or rvputs() for strings, and functions like
        bwrite() for binary data. A global translation
        of everything would therefore be inadequate.

        (In the case of text files of course, provisions must be
        made so that EBCDIC documents are always served in
        ASCII)
      

      
        This port therefore features a built-in protocol level
        conversion for the server-internal strings (which the
        compiler translated to EBCDIC strings) and thus for all
        server-generated documents. The hard coded ASCII escapes
        \012 and \015 which are ubiquitous
        in the server code are an exception: they are already the binary
        encoding of the ASCII \n and \r and
        must not be converted to ASCII a second time.
        This exception is only relevant for server-generated strings;
        and external EBCDIC documents are not expected to
        contain ASCII newline characters.
      

      
        By examining the call hierarchy for the BUFF management
        routines, I added an "ebcdic/ascii conversion layer" which
        would be crossed on every puts/write/get/gets, and a
        conversion flag which allowed enabling/disabling the
        conversions on-the-fly. Usually, a document crosses this
        layer twice from its origin source (a file or CGI output) to
        its destination (the requesting client): file ->
        Apache, and Apache -> client.

        The server can now read the header lines of a CGI-script
        output in EBCDIC format, and then find out that the remainder
        of the script's output is in ASCII (like in the case of the
        output of a WWW Counter program: the document body contains a
        GIF image). All header processing is done in the native
        EBCDIC format; the server then determines, based on the type
        of document being served, whether the document body (except
        for the chunking information, of course) is in ASCII already
        or must be converted from EBCDIC.
      

      
        For Text documents (MIME types text/plain, text/html
        etc.), an implicit translation to ASCII can be
        used, or (if the users prefer to store some documents in
        raw ASCII form for faster serving, or because the files
        reside on a NFS-mounted directory tree) can be served
        without conversion.

        Example:

        to serve files with the suffix .ahtml as a
        raw ASCII text/html document without implicit
        conversion (and suffix .ascii as ASCII
        text/plain), use the directives:

        
          AddType  text/x-ascii-html  .ahtml 
          AddType  text/x-ascii-plain .ascii
        

        Similarly, any text/foo MIME type can be
        served as "raw ASCII" by configuring a MIME type
        "text/x-ascii-foo" for it using
        AddType.
      

      
        Non-text documents are always served "binary" without
        conversion. This seems to be the most sensible choice for,
        .e.g., GIF/ZIP/AU file types. This of course
        requires the user to copy them to the mainframe host using
        the "rcp -b" binary switch.
      

      
        Server parsed files are always assumed to be in native
        (i.e., EBCDIC) format as used on the machine, and
        are converted after processing.
      

      
        For CGI output, the CGI script determines whether a
        conversion is needed or not: by setting the appropriate
        Content-Type, text files can be converted, or GIF output can
        be passed through unmodified. An example for the latter case
        is the wwwcount program which we ported as well.
      

    

  

Document Storage Notes

    

    Binary Files

      

      All files with a Content-Type: which does not
      start with text/ are regarded as binary
      files by the server and are not subject to any conversion.
      Examples for binary files are GIF images, gzip-compressed files
      and the like.

      When exchanging binary files between the mainframe host and
      a Unix machine or Windows PC, be sure to use the ftp "binary"
      (TYPE I) command, or use the
      rcp -b command from the mainframe host (the
      -b switch is not supported in unix
      rcp's).

    

    Text Documents

      

      The default assumption of the server is that Text Files
      (i.e., all files whose Content-Type:
      starts with text/) are stored in the native
      character set of the host, EBCDIC.

    

    Server Side Included Documents

      

      SSI documents must currently be stored in EBCDIC only.
      No provision is made to convert it from ASCII before
      processing.

    

  

Apache Modules' Status

    

    
      
        Module
        Status
        Notes
      

      
        core
        +
        
      

      
        mod_access
        +
        
      

      
        mod_actions
        +
        
      

      
        mod_alias
        +
        
      

      
        mod_asis
        +
        
      

      
        mod_auth
        +
        
      

      
        mod_authn_anon
        +
        
      

      
        mod_authn_dbm
        ?
        with own libdb.a
      

      
        mod_authz_dbm
        ?
        with own libdb.a
      

      
        mod_autoindex
        +
        
      

      
        mod_cern_meta
        ?
        
      

      
        mod_cgi
        +
        
      

      
        mod_digest
        +
        
      

      
        mod_dir
        +
        
      

      
        mod_so
        -
        no shared libs
      

      
        mod_env
        +
        
      

      
        mod_example
        -
        (test bed only)
      

      
        mod_expires
        +
        
      

      
        mod_headers
        +
        
      

      
        mod_imagemap
        +
        
      

      
        mod_include
        +
        
      

      
        mod_info
        +
        
      

      
        mod_log_agent
        +
        
      

      
        mod_log_config
        +
        
      

      
        mod_log_referer
        +
        
      

      
        mod_mime
        +
        
      

      
        mod_mime_magic
        ?
        not ported yet
      

      
        mod_negotiation
        +
        
      

      
        mod_proxy
        +
        
      

      
        mod_rewrite
        +
        untested
      

      
        mod_setenvif
        +
        
      

      
        mod_speling
        +
        
      

      
        mod_status
        +
        
      

      
        mod_unique_id
        +
        
      

      
        mod_userdir
        +
        
      

      
        mod_usertrack
        ?
        untested
      
    

  

Third Party Modules' Status

    

    
      
        Module
        Status
        Notes
      

      
        JK (Formerly mod_jserv)
        
        -
        JAVA still being ported.
      

      
        mod_php3
        +
        mod_php3 runs fine, with LDAP and GD
        and FreeType libraries.
      

      
        mod_put
        ?
        untested
      

      
        mod_session
        -
        untested
      
    

  

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