**imclient** library
********************

Authenticating callback interface to IMAP servers


Synopsis
========

   #include <cyrus/imclient.h>

   **int imclient_connect(struct imclient *****imclient* **, const char ****host* **,
       const char ****port***);**

   **void imclient_close (struct imclient ****imclient***);**
   **void imclient_setflags(struct imclient ****imclient* **, int** *flags***);**
   **void imclient_clearflags (struct imclient ****imclient* **, int** *flags***);**
   **char* imclient_servername (struct imclient ****imclient***);**
   **void imclient_addcallback (struct imclient ****imclient*,...**);**
   **void imclient_send (struct imclient ****imclient***, void (****finishproc***)(),
       void ****finishrock***, const char ****fmt*,...**);**
   **void imclient_getselectinfo (struct imclient ****imclient***, int *** *fd***,
       int *** *wanttowrite***);**
   **void imclient_processoneevent (struct imclient ****imclient***);**
   **int imclient_authenticate (struct imclient ****imclient***,
       struct sasl_client *****availmech***, const char ****service***,
       const char ****user***, int** *protallowed***);**
   **int imclient_havetls ();**
   **int imclient_starttls (struct imclient ****imclient***, char ****cert_file***,
       char ****key_file***, char ****CAfile***, char ****CApath***);**


Description
===========

The imclient library functions are distributed with Cyrus IMAP. These
functions are used for building IMAP client software. These functions
handle Kerberos authentication and can set callbacks based on the
keyword in untagged replies or based on the command tag at the end of
command replies.

Users must link with the -lcyrus switch, and must supply a function
called *fatal* to be called in case of any error within *libcyrus.la*.

All of the **imclient** functions begin with the prefix *imclient* and
take  an  argument of type **struct imclient *** as the first argument
which is  initialized by **imclient_connect** and freed by
**imclient_close**.

See below for a description of each function.

**imclient_connect()**
   Connects the client server to the host. If successful, it returns 0
   and sets the imclient argument to a pointer to an **imclient**
   struct.  The **imclient** struct represents the current connection,
   flags, and callbacks.  On failure, the current **errno** is
   returned if a system call failed, -1 is returned if the host name
   was not found, and -2 is returned if the service name was not
   found.

**imclient_close()**
   Closes and frees the **imclient** connection.

**imclient_setflags()**
   Sets the flags specified by the *flags* argument on the
   **imclient** connection. Currently the only  flag allowed is
   **IMCLIENT_CONN_NONSYNCLITERAL** (this flag indicates that the
   server supports non-synchronizing literals described by the
   LITERAL+ extension).

**imclient_clearflags()**
   Clears the flags specified by the *flags* argument on the
   **imclient** connection.

**imclient_servername()**
   Returns a char * pointer to the name of the server connected to by
   **imclient**.

**imclient_addcallback()**
   Adds an untagged data callback to the **imclient** connection. The
   function **imclient_addcallback** takes callbacks of the type
   **imclient_proc_t** which is defined to be:

         typedef void imclient_proc_t (struct imclient *imclient, void *rock, struct imclient_reply *reply);

   and **struct imclient_reply *** is defined to be:

         struct imclient_reply {
             char *keyword;
             long msgno;
             char *text;
         };

   After the first argument, *imclient*, there can be zero or more
   instances of the set of *keyword*, *flags*, *proc*, and *rock*,
   each adding or changing a single callback.  Each instance adds or
   changes the callback for *keyword*.  The argument *flags* specifies
   information about the parsing of the untagged data.  *proc* and
   *rock* specify the callback function and rock to invoke when the
   untagged data is received.  *proc* may be a null pointer, in which
   case no function is invoked.  The callback function may not call
   the functions **imclient_close(), imclient_send(), imclient_eof(),
   imclient_processoneevent()**, or **imclient_authenticate()** on the
   connection. The callback function may overwrite  the text of
   untagged data.

**imclient_send()**
   Sends a new command to the **imclient** connection.  *finishproc*
   and *finishrock* are the function and rock called when the command
   completes.  *functionproc* may be a null pointer, in which case no
   callback is made. The callback function may not call the functions
   **imclient_close(), imclient_send(), imclient_eof(),
   imclient_processoneevent()**, or **imclient_authenticate()** on the
   connection.  The argument *fmt* is a *printf(3)* like specification
   of the command. It must not include the tag as the tag is
   automatically added by **imclient_send()**.

   The defined %-sequences are:

         %% for %
         %a for an IMAP atom
         %s for an astring (which will be quoted or literalized as needed)
         %d for a decimal
         %u for an unsigned decimal
         %v for #astring (argument is a null-terminated array of char *
         which are written as space separated astrings)

**imclient_getselectinfo()**
   Gets the information for calling *select(2)*.  *fd* is filled in
   with the file descriptor to *select(2)* for read. *wanttowrite* is
   filled in with a nonzero value if **select** should be used for
   write as well.

**imclient_processoneevent()**
   Processes one input or output event on the **imclient** connection.

**imclient_authenticate()**
   Authenticates the **imclient** connection using one of the
   mechanisms in *availmech*.  The argument *user*, if not NULL,
   specifies the user to authenticate as. If the user is NULL, the
   current user is used. The argument *protallowed* is a bitmask of
   permissible protection mechanisms. On success, 0 is returned.  On
   failure (i.e., "BAD" keyboard, or no authentication mechanisms
   worked), 1 is returned. On extreme failure (premature "OK"), 2 is
   returned.

**imclient_havetls()**
   Returns a Boolean indicating whether the **imclient** library was
   compiled with TLS (SSL) support.  If so, **imclient_starttls()**
   may be used to secure the IMAP connection.

**imclient_starttls()**
   Issues a STARTTLS command on an existing IMAP connection and
   negotiates the secure link.  The *cert_file* and *key_file*
   arguments specify the client certificate and secret key to use to
   authenticate ourselves to the server.  If client authentication is
   not needed, set both of these arguments to NULL.

   The *CAfile* and *CApath* arguments specify a file or directory,
   respectively, of CA certificates for validating server
   certificates. (See *SSL_CTX_load_verify_locations(3)* for details.)
   If both of these are NULL, the client will be unable to validate
   the server's certificate, in which case the connection may succeed
   but a warning will be printed to stdout.


Examples
========

The following code is a possible skeleton of **imclient** that relies
on Kerberos to do authentication.  This code performs an IMAP
CAPABILITY request and prints out the result.

      #include <cyrus/xmalloc.h> /* example uses xstrdup */
      #include <cyrus/sasl.h>
      #include <cyrus/imclient.h>
      #include <stdio.h>

      extern struct sasl_client krb_sasl_client;

      struct sasl_client *login_sasl_client[] = {
          &krb_sasl_client,
          NULL
      };
      struct imclient *imclient;
      char server[] = "cyrus.andrew.cmu.edu" ;
      char port[] = "imap";

      void fatal(char* message, int rc) {
          fprintf(stderr, "fatal error: %s\en", message);
          exit(rc);
      }

      static void callback_capability(struct imclient *imclient,
                                      void *rock,
                                      struct imclient_reply *reply) {
          if (reply->text != NULL) {
              *((char**)rock) = xstrdup( reply->text );
          }
      }

      static void end_command(struct imclient *connection, void*
                              rock,  struct imclient_reply *inmsg) {
          (*(int*)rock)--;
      }

      main() {
          char* capability_string;
          int nc;

          if (imclient_connect(&imclient, server, port)) {
              fprintf(stderr,
                      "error: Couldn't connect to %s %s\en",
                      server, port);
              exit(1);
          }

          if (imclient_authenticate(imclient, login_sasl_client, "imap"
                                    /* service */,
                                    NULL /* user */, SASL_PROT_ANY)) {
              exit(1);
          }

          imclient_addcallback(imclient, "CAPABILITY",
                               CALLBACK_NOLITERAL,
                               callback_capability,
                               &capability_string,
                               NULL);

          nc = 1;

          imclient_send(imclient, end_command,
                        (void*) &nc, "CAPABILITY");

          while(nc > 0) {
              imclient_processoneevent(imclient);
          }

          if (strstr("LITERAL+", capability_string)) {
              imclient_setflags(imclient, IMCLIENT_CONN_NONSYNCLITERAL);
          }

          imclient_send(imclient, NULL, NULL, "LOGOUT");
          imclient_close(imclient);

          printf("capability text is: %s\en", capability_string);

          free(capability_string);
      }


Bugs
====

No known bugs.


See Also
========

cyradm(8), imapd(8), **RFC 2033** (IMAP LITERAL+ extension), **RFC
2060** (IMAP4rev1 specification), and *select(2)*


Keywords
========

IMAP, ACAP, Kerberos, Authentication
