$Id$

Implementation notes:

  This is a true OS/400 implementation, not a PASE implementation (for PASE,
use AIX implementation).

  The biggest problem with OS/400 is EBCDIC. Libcurl implements an internal
conversion mechanism, but it has been designed for computers that have a
single native character set. OS/400 default native character set varies
depending on the country for which it has been localized. And more, a job
may dynamically alter its "native" character set.
  Several characters that do not have fixed code in EBCDIC variants are
used in libcurl strings. As a consequence, using the existing conversion
mechanism would have lead in a localized binary library - not portable across
countries.
  For this reason, and because libcurl was originally designed for ASCII based
operating systems, the current OS/400 implementation uses ASCII as internal
character set. This has been accomplished using the QADRT library and
include files, a C and system procedures ASCII wrapper library. See IBM QADRT
description for more information.
  This then results in libcurl being an ASCII library: any function string
argument is taken/returned in ASCII and a C/C++ calling program built around
QADRT may use libcurl functions as on any other platform.
  QADRT does not define ASCII wrappers for all C/system procedures: the
OS/400 configuration header file and an additional module (os400sys.c) define
some more of them, that are used by libcurl and that QADRT left out.
  To support all the different variants of EBCDIC, non-standard wrapper
procedures have been added to libcurl on OS/400: they provide an additional
CCSID (numeric Coded Character Set ID specific to OS/400) parameter for each
string argument. String values passed to callback procedures are NOT converted,
so text gathered this way is (probably !) ASCII.

  Another OS/400 problem comes from the fact that the last fixed argument of a
vararg procedure may not be of type char, unsigned char, short or unsigned
short. Enums that are internally implemented by the C compiler as one of these
types are also forbidden. Libcurl uses enums as vararg procedure tagfields...
Happily, there is a pragma forcing enums to type "int". The original libcurl
header files are thus altered during build process to use this pragma, in
order to force libcurl enums of being type int (the pragma disposition in use
before inclusion is restored before resuming the including unit compilation).

  Three SSL implementations were present in libcurl. Nevertheless, none of them
is available on OS/400. To support SSL on OS/400, a fourth implementation has
been added (qssl.[ch]). There is no way to have different certificate stores
for CAs and for personal/application certificates/key. More, the SSL context
may be defined as an application identifier in the main certificate store,
or as a keyring file. As a consequence, the meaning of some fields have been
slightly altered:
_ The "certificate identifier" is taken from CURLOPT_SSLCERT if defined, else
from CURLOPT_CAINFO.
_ The certificate identifier is then used as an application identifier in the
main certificate store. If successful, this context is used.
_ If the previous step failed, the certificate identifier is used as the file
name of a keyring. CURLOPT_KEYPASSWD is used here as the keyring password.
_ The default ca-bundle (CURLOPT_CAINFO) is set to the main certificate store's
keyring file name: this allows to use the system global CAs by default. (In that
case, the keyring password is safely recovered from the system... IBM dixit!)

  Non-standard EBCDIC wrapper prototypes are defined in an additional header
file: ccsidcurl.h. These should be self-explanatory to an OS/400-aware
designer. CCSID 0 can be used to select the current job's CCSID.
  Wrapper procedures with variable arguments are described below:

_ curl_easy_setopt_ccsid()
  Variable arguments are a string pointer and a CCSID (unsigned int) for
options:
        CURLOPT_CAINFO
        CURLOPT_CAPATH
        CURLOPT_COOKIE
        CURLOPT_COOKIEFILE
        CURLOPT_COOKIEJAR
        CURLOPT_COOKIELIST
        CURLOPT_CUSTOMREQUEST
        CURLOPT_EGDSOCKET
        CURLOPT_ENCODING
        CURLOPT_FTPPORT
        CURLOPT_FTP_ACCOUNT
        CURLOPT_FTP_ALTERNATIVE_TO_USER
        CURLOPT_INTERFACE
        CURLOPT_KEYPASSWD
        CURLOPT_KRBLEVEL
        CURLOPT_NETRC_FILE
        CURLOPT_POSTFIELDS
        CURLOPT_PROXY
        CURLOPT_PROXYUSERPWD
        CURLOPT_RANDOM_FILE
        CURLOPT_RANGE
        CURLOPT_REFERER
        CURLOPT_SSH_PRIVATE_KEYFILE
        CURLOPT_SSH_PUBLIC_KEYFILE
        CURLOPT_SSLCERT
        CURLOPT_SSLCERTTYPE
        CURLOPT_SSLENGINE
        CURLOPT_SSLKEY
        CURLOPT_SSLKEYTYPE
        CURLOPT_SSL_CIPHER_LIST
        CURLOPT_URL
        CURLOPT_USERAGENT
        CURLOPT_USERPWD
  Else it is the same as for curl_easy_setopt().
  Note that CURLOPT_ERRORBUFFER is not in the list above, since it gives the
address of an (empty) character buffer, not the address of a string.

_ curl_formadd_ccsid()
  In the variable argument list, string pointers should be followed by a (long)
CCSID for the following options:
        CURLFORM_FILENAME
        CURLFORM_CONTENTTYPE
        CURLFORM_BUFFER
        CURLFORM_FILE
        CURLFORM_FILECONTENT
        CURLFORM_COPYCONTENTS
        CURLFORM_COPYNAME
        CURLFORM_PTRNAME
  If taken from an argument array, an additional array entry must follow each
entry containing one of the above option. This additional entry holds the CCSID
in its value field, and the option field is meaningless.
  It is not possible to have a string pointer and its CCSID across a function
parameter/array boundary.
  Please note that CURLFORM_PTRCONTENTS and CURLFORM_BUFFERPTR are considered
unconvertible strings and thus are NOT followed by a CCSID.

_ curl_easy_getinfo_ccsid
  The following options are followed by a 'char * *' and a CCSID. Unlike
curl_easy_getinfo(), the value returned in the pointer should be freed after
use:
        CURLINFO_EFFECTIVE_URL
        CURLINFO_CONTENT_TYPE
        CURLINFO_FTP_ENTRY_PATH
  Other options are processed like in curl_easy_getinfo().

  Standard compilation environment does support neither autotools nor make;
in fact, very few common utilities are available. As a consequence, the
config-os400.h has been coded manually and the compilation scripts are
a set of shell scripts stored in subdirectory packages/OS400.

  The "curl" command and the test environment are currently not supported on
OS/400.


Protocols currently implemented on OS/400:
_ HTTP
_ HTTPS
_ FTP
_ FTPS
_ FTP with secure transmission.
_ LDAP
_ DICT
_ TELNET



Compiling on OS/400:

  These instructions targets people who knows about OS/400, compiling, IFS and
archive extraction. Do not ask questions about these subjects if you're not
familiar with.

_ As a prerequisite, QADRT development environment must be installed.
_ Install the curl source directory in IFS.
_ Enter shell (QSH)
_ Change current directory to the curl installation directory
_ Change current directory to ./packages/OS400
_ Edit file iniscript.sh. You may want to change tunable configuration
  parameters, like debug info generation, optimisation level, listing option,
  target library, etc.
_ Copy any file in the current directory to makelog (i.e.:
  cp initscript.sh makelog): this is intended to create the makelog file with
  an ASCII CCSID!
_ Enter the command "sh makefile.sh > makelog 2>&1'
_ Examine the makelog file to check for compilation errors.

  Leaving file initscript.sh unchanged, this will produce the following OS/400
objects:
_ Library CURL. All other objects will be stored in this library.
_ Modules for all libcurl units.
_ Binding directory CURL_A, to be used at calling program link time for
  statically binding the modules (specify BNDSRVPGM(QADRTTS) when creating a
  program using CURL_A).
_ Service program CURL, to be used at calling program run-time when this program
  has dynamically bound curl at link time.
_ Binding directory CURL. To be used to dynamically bind libcurl when linking a
  calling program.
_ Source file H. It contains all the include members needed to compile a C/C++
  module using libcurl, and an ILE/RPG /copy member for support in this
  language.
_ Standard C/C++ libcurl include members in file H.
_ CCSIDCURL member in file H. This defines the non-standard EBCDIC wrappers for
  C and C++.
_ CURL.INC member in file H. This defines everything needed by an ILE/RPG
  program using libcurl.
_ LIBxxx modules and programs. Although the test environment is not supported
  on OS/400, the libcurl test programs are compiled for manual tests.



Special programming consideration:

QADRT being used, the following points must be considered:
_ If static binding is used, service program QADRTTS must be linked too.
_ The EBCDIC CCSID used by QADRT is 37 by default, NOT THE JOB'S CCSID. If
  another EBCDIC CCSID is required, it must be set via a locale through a call
  to setlocale_a (QADRT's setlocale() ASCII wrapper) with category LC_ALL or
  LC_CTYPE, or by setting environment variable QADRT_ENV_LOCALE to the locale
  object path before executing the program.
_ Do not use original source include files unless you know what you are doing.
  Use the installed members instead (in /QSYS.LIB/CURL.LIB/H.FILE).



ILE/RPG support:

  Since 95% of the OS/400 programmers use ILE/RPG exclusively, a definition
  /COPY member is provided for this language. To include all libcurl
  definitions in an ILE/RPG module, line

     h bnddir('CURL/CURL')

must figure in the program header, and line

     d/copy curl/h,curl.inc

in the global data section of the module's source code.

  No vararg procedure support exists in ILE/RPG: for this reason, the following
considerations apply:
_ Procedures curl_easy_setopt_long(), curl_easy_setopt_object(),
  curl_easy_setopt_function() and curl_easy_setopt_offset() are all alias
  prototypes to curl_easy_setopt(), but with different parameter lists.
_ Procedures curl_easy_getinfo_string(), curl_easy_getinfo_long(),
  curl_easy_getinfo_double() and curl_easy_getinfo_slist() are all alias
  prototypes to curl_easy_getinfo(), but with different parameter lists.
_ Procedures curl_multi_setopt_long(), curl_multi_setopt_object(),
  curl_multi_setopt_function() and curl_multi_setopt_offset() are all alias
  prototypes to curl_multi_setopt(), but with different parameter lists.
_ The prototype of procedure curl_formadd() allows specifying a pointer option
  and the CURLFORM_END option. This makes possible to use an option array
  without any additional definition. If some specific incompatible argument
  list is used in the ILE/RPG program, the latter must define a specialised
  alias. The same applies to curl_formadd_ccsid() too.

  Since RPG cannot cast a long to a pointer, procedure curl_form_long_value()
is provided for that purpose: this allows storing a long value in the curl_forms
array.
