res_calendar_ews.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2008 - 2009, Digium, Inc.
 *
 * Jan Kalab <[email protected]>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 * \brief Resource for handling MS Exchange Web Service calendars
 */

/*** MODULEINFO
   <depend>res_calendar</depend>
   <depend>neon29</depend>
   <support_level>extended</support_level>
***/

#include "asterisk.h"

#include <ne_request.h>
#include <ne_session.h>
#include <ne_uri.h>
#include <ne_socket.h>
#include <ne_auth.h>
#include <ne_xml.h>
#include <ne_xmlreq.h>
#include <ne_utils.h>
#include <ne_redirect.h>

#include "asterisk/module.h"
#include "asterisk/channel.h"
#include "asterisk/calendar.h"
#include "asterisk/lock.h"
#include "asterisk/config.h"
#include "asterisk/astobj2.h"

static void *ewscal_load_calendar(void *data);
static void *unref_ewscal(void *obj);
static int ewscal_write_event(struct ast_calendar_event *event);

static struct ast_calendar_tech ewscal_tech = {
   .type = "ews",
   .description = "MS Exchange Web Service calendars",
   .module = AST_MODULE,
   .load_calendar = ewscal_load_calendar,
   .unref_calendar = unref_ewscal,
   .write_event = ewscal_write_event,
};

enum xml_op {
   XML_OP_FIND = 100,
   XML_OP_GET,
   XML_OP_CREATE,
};

struct calendar_id {
   struct ast_str *id;
   AST_LIST_ENTRY(calendar_id) next;
};

struct xml_context {
   ne_xml_parser *parser;
   struct ast_str *cdata;
   struct ast_calendar_event *event;
   enum xml_op op;
   struct ewscal_pvt *pvt;
   AST_LIST_HEAD_NOLOCK(ids, calendar_id) ids;
};

/* Important states of XML parsing */
enum {
   XML_EVENT_CALENDAR_ITEM = 9,
   XML_EVENT_NAME = 10,
   XML_EVENT_DESCRIPTION,
   XML_EVENT_START,
   XML_EVENT_END,
   XML_EVENT_BUSY,
   XML_EVENT_ORGANIZER,
   XML_EVENT_LOCATION,
   XML_EVENT_ATTENDEE_LIST,
   XML_EVENT_ATTENDEE,
   XML_EVENT_MAILBOX,
   XML_EVENT_EMAIL_ADDRESS,
   XML_EVENT_CATEGORIES,
   XML_EVENT_CATEGORY,
   XML_EVENT_IMPORTANCE,
};

struct ewscal_pvt {
   AST_DECLARE_STRING_FIELDS(
      AST_STRING_FIELD(url);
      AST_STRING_FIELD(user);
      AST_STRING_FIELD(secret);
   );
   struct ast_calendar *owner;
   ne_uri uri;
   ne_session *session;
   struct ao2_container *events;
   unsigned int items;
};

static void ewscal_destructor(void *obj)
{
   struct ewscal_pvt *pvt = obj;

   ast_debug(1, "Destroying pvt for Exchange Web Service calendar %s\n", "pvt->owner->name");
   if (pvt->session) {
      ne_session_destroy(pvt->session);
   }
   ne_uri_free(&pvt->uri);
   ast_string_field_free_memory(pvt);

   ao2_callback(pvt->events, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, NULL, NULL);

   ao2_ref(pvt->events, -1);
}

static void *unref_ewscal(void *obj)
{
   struct ewscal_pvt *pvt = obj;

   ast_debug(5, "EWS: unref_ewscal()\n");
   ao2_ref(pvt, -1);
   return NULL;
}

static int auth_credentials(void *userdata, const char *realm, int attempts, char *username, char *secret)
{
   struct ewscal_pvt *pvt = userdata;

   if (attempts > 1) {
      ast_log(LOG_WARNING, "Invalid username or password for Exchange Web Service calendar '%s'\n", pvt->owner->name);
      return -1;
   }

   ne_strnzcpy(username, pvt->user, NE_ABUFSIZ);
   ne_strnzcpy(secret, pvt->secret, NE_ABUFSIZ);

   return 0;
}

static int ssl_verify(void *userdata, int failures, const ne_ssl_certificate *cert)
{
   struct ewscal_pvt *pvt = userdata;
   if (failures & NE_SSL_UNTRUSTED) {
      ast_log(LOG_WARNING, "Untrusted SSL certificate for calendar %s!\n", pvt->owner->name);
      return 0;
   }
   return 1;   /* NE_SSL_NOTYETVALID, NE_SSL_EXPIRED, NE_SSL_IDMISMATCH */
}

static time_t mstime_to_time_t(char *mstime)
{
   struct ast_tm tm;
   struct timeval tv;

   if (ast_strptime(mstime, "%FT%TZ", &tm)) {
      tv = ast_mktime(&tm, "UTC");
      return tv.tv_sec;
   }
   return 0;
}

static int startelm(void *userdata, int parent, const char *nspace, const char *name, const char **atts)
{
   struct xml_context *ctx = userdata;

   ast_debug(5, "EWS: XML: Start: %s\n", name);
   if (ctx->op == XML_OP_CREATE) {
      return NE_XML_DECLINE;
   }

   /* Nodes needed for traversing until CalendarItem is found */
   if (!strcmp(name, "Envelope") ||
      (!strcmp(name, "Body") && parent != XML_EVENT_CALENDAR_ITEM) ||
      !strcmp(name, "FindItemResponse") ||
      !strcmp(name, "GetItemResponse") ||
      !strcmp(name, "CreateItemResponse") ||
      !strcmp(name, "ResponseMessages") ||
      !strcmp(name, "FindItemResponseMessage") || !strcmp(name, "GetItemResponseMessage") ||
      !strcmp(name, "Items")
   ) {
      return 1;
   } else if (!strcmp(name, "RootFolder")) {
      /* Get number of events */
      unsigned int items;

      ast_debug(3, "EWS: XML: <RootFolder>\n");
      if (sscanf(ne_xml_get_attr(ctx->parser, atts, NULL, "TotalItemsInView"), "%u", &items) != 1) {
         /* Couldn't read enything */
         ne_xml_set_error(ctx->parser, "Could't read number of events.");
         return NE_XML_ABORT;
      }

      ast_debug(3, "EWS: %u calendar items to load\n", items);
      ctx->pvt->items = items;
      if (items < 1) {
         /* Stop processing XML if there are no events */
         ast_calendar_merge_events(ctx->pvt->owner, ctx->pvt->events);
         return NE_XML_DECLINE;
      }
      return 1;
   } else if (!strcmp(name, "CalendarItem")) {
      /* Event start */
      ast_debug(3, "EWS: XML: <CalendarItem>\n");
      if (!(ctx->pvt && ctx->pvt->owner)) {
         ast_log(LOG_ERROR, "Require a private structure with an owner\n");
         return NE_XML_ABORT;
      }

      ctx->event = ast_calendar_event_alloc(ctx->pvt->owner);
      if (!ctx->event) {
         ast_log(LOG_ERROR, "Could not allocate an event!\n");
         return NE_XML_ABORT;
      }

      ctx->cdata = ast_str_create(64);
      if (!ctx->cdata) {
         ast_log(LOG_ERROR, "Could not allocate CDATA!\n");
         return NE_XML_ABORT;
      }

      return XML_EVENT_CALENDAR_ITEM;
   } else if (!strcmp(name, "ItemId")) {
      /* Event UID */
      if (ctx->op == XML_OP_FIND) {
         struct calendar_id *id;
         if (!(id = ast_calloc(1, sizeof(*id)))) {
            return NE_XML_ABORT;
         }
         if (!(id->id = ast_str_create(256))) {
            ast_free(id);
            return NE_XML_ABORT;
         }
         ast_str_set(&id->id, 0, "%s", ne_xml_get_attr(ctx->parser, atts, NULL, "Id"));
         AST_LIST_INSERT_TAIL(&ctx->ids, id, next);
         ast_debug(3, "EWS_FIND: XML: UID: %s\n", ast_str_buffer(id->id));
      } else {
         ast_debug(3, "EWS_GET: XML: UID: %s\n", ne_xml_get_attr(ctx->parser, atts, NULL, "Id"));
         ast_string_field_set(ctx->event, uid, ne_xml_get_attr(ctx->parser, atts, NULL, "Id"));
      }
      return XML_EVENT_NAME;
   } else if (!strcmp(name, "Subject")) {
      /* Event name */
      if (!ctx->cdata) {
         return NE_XML_ABORT;
      }
      ast_str_reset(ctx->cdata);
      return XML_EVENT_NAME;
   } else if (!strcmp(name, "Body") && parent == XML_EVENT_CALENDAR_ITEM) {
      /* Event body/description */
      if (!ctx->cdata) {
         return NE_XML_ABORT;
      }
      ast_str_reset(ctx->cdata);
      return XML_EVENT_DESCRIPTION;
   } else if (!strcmp(name, "Start")) {
      /* Event start time */
      return XML_EVENT_START;
   } else if (!strcmp(name, "End")) {
      /* Event end time */
      return XML_EVENT_END;
   } else if (!strcmp(name, "LegacyFreeBusyStatus")) {
      /* Event busy state */
      return XML_EVENT_BUSY;
   } else if (!strcmp(name, "Organizer") ||
         (parent == XML_EVENT_ORGANIZER && (!strcmp(name, "Mailbox") ||
         !strcmp(name, "Name")))) {
      /* Event organizer */
      if (!ctx->cdata) {
         return NE_XML_ABORT;
      }
      ast_str_reset(ctx->cdata);
      return XML_EVENT_ORGANIZER;
   } else if (!strcmp(name, "Location")) {
      /* Event location */
      if (!ctx->cdata) {
         return NE_XML_ABORT;
      }
      ast_str_reset(ctx->cdata);
      return XML_EVENT_LOCATION;
   } else if (!strcmp(name, "Categories")) {
      /* Event categories */
      if (!ctx->cdata) {
         return NE_XML_ABORT;
      }
      ast_str_reset(ctx->cdata);
      return XML_EVENT_CATEGORIES;
   } else if (parent == XML_EVENT_CATEGORIES && !strcmp(name, "String")) {
      /* Event category */
      return XML_EVENT_CATEGORY;
   } else if (!strcmp(name, "Importance")) {
      /* Event importance (priority) */
      if (!ctx->cdata) {
         return NE_XML_ABORT;
      }
      ast_str_reset(ctx->cdata);
      return XML_EVENT_IMPORTANCE;
   } else if (!strcmp(name, "RequiredAttendees") || !strcmp(name, "OptionalAttendees")) {
      return XML_EVENT_ATTENDEE_LIST;
   } else if (!strcmp(name, "Attendee") && parent == XML_EVENT_ATTENDEE_LIST) {
      return XML_EVENT_ATTENDEE;
   } else if (!strcmp(name, "Mailbox") && parent == XML_EVENT_ATTENDEE) {
      return XML_EVENT_MAILBOX;
   } else if (!strcmp(name, "EmailAddress") && parent == XML_EVENT_MAILBOX) {
      if (!ctx->cdata) {
         return NE_XML_ABORT;
      }
      ast_str_reset(ctx->cdata);
      return XML_EVENT_EMAIL_ADDRESS;
   }

   return NE_XML_DECLINE;
}

static int cdata(void *userdata, int state, const char *cdata, size_t len)
{
   struct xml_context *ctx = userdata;
   char data[len + 1];

   /* !!! DON'T USE AST_STRING_FIELD FUNCTIONS HERE, JUST COLLECT CTX->CDATA !!! */
   if (state < XML_EVENT_NAME || ctx->op == XML_OP_CREATE) {
      return 0;
   }

   if (!ctx->event) {
      ast_log(LOG_ERROR, "Parsing event data, but event object does not exist!\n");
      return 1;
   }

   if (!ctx->cdata) {
      ast_log(LOG_ERROR, "String for storing CDATA is unitialized!\n");
      return 1;
   }

   ast_copy_string(data, cdata, len + 1);

   switch (state) {
   case XML_EVENT_START:
      ctx->event->start = mstime_to_time_t(data);
      break;
   case XML_EVENT_END:
      ctx->event->end = mstime_to_time_t(data);
      break;
   case XML_EVENT_BUSY:
      if (!strcmp(data, "Busy") || !strcmp(data, "OOF")) {
         ast_debug(3, "EWS: XML: Busy: yes\n");
         ctx->event->busy_state = AST_CALENDAR_BS_BUSY;
      }
      else if (!strcmp(data, "Tentative")) {
         ast_debug(3, "EWS: XML: Busy: tentative\n");
         ctx->event->busy_state = AST_CALENDAR_BS_BUSY_TENTATIVE;
      }
      else {
         ast_debug(3, "EWS: XML: Busy: no\n");
         ctx->event->busy_state = AST_CALENDAR_BS_FREE;
      }
      break;
   case XML_EVENT_CATEGORY:
      if (ast_str_strlen(ctx->cdata) == 0) {
         ast_str_set(&ctx->cdata, 0, "%s", data);
      } else {
         ast_str_append(&ctx->cdata, 0, ",%s", data);
      }
      break;
   default:
      ast_str_append(&ctx->cdata, 0, "%s", data);
   }

   ast_debug(5, "EWS: XML: CDATA: %s\n", ast_str_buffer(ctx->cdata));

   return 0;
}

static int endelm(void *userdata, int state, const char *nspace, const char *name)
{
   struct xml_context *ctx = userdata;

   ast_debug(5, "EWS: XML: End:   %s\n", name);
   if (ctx->op == XML_OP_FIND || ctx->op == XML_OP_CREATE) {
      return NE_XML_DECLINE;
   }

   if (!strcmp(name, "Subject")) {
      /* Event name end*/
      ast_string_field_set(ctx->event, summary, ast_str_buffer(ctx->cdata));
      ast_debug(3, "EWS: XML: Summary: %s\n", ctx->event->summary);
      ast_str_reset(ctx->cdata);
   } else if (!strcmp(name, "Body") && state == XML_EVENT_DESCRIPTION) {
      /* Event body/description end */
      ast_string_field_set(ctx->event, description, ast_str_buffer(ctx->cdata));
      ast_debug(3, "EWS: XML: Description: %s\n", ctx->event->description);
      ast_str_reset(ctx->cdata);
   } else if (!strcmp(name, "Organizer")) {
      /* Event organizer end */
      ast_string_field_set(ctx->event, organizer, ast_str_buffer(ctx->cdata));
      ast_debug(3, "EWS: XML: Organizer: %s\n", ctx->event->organizer);
      ast_str_reset(ctx->cdata);
   } else if (!strcmp(name, "Location")) {
      /* Event location end */
      ast_string_field_set(ctx->event, location, ast_str_buffer(ctx->cdata));
      ast_debug(3, "EWS: XML: Location: %s\n", ctx->event->location);
      ast_str_reset(ctx->cdata);
   } else if (!strcmp(name, "Categories")) {
      /* Event categories end */
      ast_string_field_set(ctx->event, categories, ast_str_buffer(ctx->cdata));
      ast_debug(3, "EWS: XML: Categories: %s\n", ctx->event->categories);
      ast_str_reset(ctx->cdata);
   } else if (!strcmp(name, "Importance")) {
      /* Event importance end */
      if (!strcmp(ast_str_buffer(ctx->cdata), "Low")) {
         ctx->event->priority = 9;
      } else if (!strcmp(ast_str_buffer(ctx->cdata), "Normal")) {
         ctx->event->priority = 5;
      } else if (!strcmp(ast_str_buffer(ctx->cdata), "High")) {
         ctx->event->priority = 1;
      }
      ast_debug(3, "EWS: XML: Importance: %s (%d)\n", ast_str_buffer(ctx->cdata), ctx->event->priority);
      ast_str_reset(ctx->cdata);
   } else if (state == XML_EVENT_EMAIL_ADDRESS) {
      struct ast_calendar_attendee *attendee;

      if (!(attendee = ast_calloc(1, sizeof(*attendee)))) {
         ctx->event = ast_calendar_unref_event(ctx->event);
         return  1;
      }

      if (ast_str_strlen(ctx->cdata)) {
         attendee->data = ast_strdup(ast_str_buffer(ctx->cdata));
         AST_LIST_INSERT_TAIL(&ctx->event->attendees, attendee, next);
      } else {
         ast_free(attendee);
      }
      ast_debug(3, "EWS: XML: attendee address '%s'\n", ast_str_buffer(ctx->cdata));
      ast_str_reset(ctx->cdata);
   } else if (!strcmp(name, "CalendarItem")) {
      /* Event end */
      ast_debug(3, "EWS: XML: </CalendarItem>\n");
      ast_free(ctx->cdata);
      if (ctx->event) {
         ao2_link(ctx->pvt->events, ctx->event);
         ctx->event = ast_calendar_unref_event(ctx->event);
      } else {
         ast_log(LOG_ERROR, "Event data ended in XML, but event object does not exist!\n");
         return 1;
      }
   } else if (!strcmp(name, "Envelope")) {
      /* Events end */
      ast_debug(3, "EWS: XML: %d of %u event(s) has been parsed…\n", ao2_container_count(ctx->pvt->events), ctx->pvt->items);
      if (ao2_container_count(ctx->pvt->events) >= ctx->pvt->items) {
         ast_debug(3, "EWS: XML: All events has been parsed, merging…\n");
         ast_calendar_merge_events(ctx->pvt->owner, ctx->pvt->events);
      }
   }

   return 0;
}

static const char *mstime(time_t t, char *buf, size_t buflen)
{
   struct timeval tv = {
      .tv_sec = t,
   };
   struct ast_tm tm;

   ast_localtime(&tv, &tm, "utc");
   ast_strftime(buf, buflen, "%FT%TZ", &tm);

   return S_OR(buf, "");
}

static const char *msstatus(enum ast_calendar_busy_state state)
{
   switch (state) {
   case AST_CALENDAR_BS_BUSY_TENTATIVE:
      return "Tentative";
   case AST_CALENDAR_BS_BUSY:
      return "Busy";
   case AST_CALENDAR_BS_FREE:
      return "Free";
   default:
      return "";
   }
}

static const char *get_soap_action(enum xml_op op)
{
   switch (op) {
   case XML_OP_FIND:
      return "\"http://schemas.microsoft.com/exchange/services/2006/messages/FindItem\"";
   case XML_OP_GET:
      return "\"http://schemas.microsoft.com/exchange/services/2006/messages/GetItem\"";
   case XML_OP_CREATE:
      return "\"http://schemas.microsoft.com/exchange/services/2006/messages/CreateItem\"";
   }

   return "";
}

static int send_ews_request_and_parse(struct ast_str *request, struct xml_context *ctx)
{
   int ret;
   ne_request *req;
   ne_xml_parser *parser;

   ast_debug(3, "EWS: HTTP request...\n");
   if (!(ctx && ctx->pvt)) {
      ast_log(LOG_ERROR, "There is no private!\n");
      return -1;
   }

   if (!ast_str_strlen(request)) {
      ast_log(LOG_ERROR, "No request to send!\n");
      return -1;
   }

   ast_debug(3, "%s\n", ast_str_buffer(request));

   /* Prepare HTTP POST request */
   req = ne_request_create(ctx->pvt->session, "POST", ctx->pvt->uri.path);
   ne_set_request_flag(req, NE_REQFLAG_IDEMPOTENT, 0);

   /* Set headers--should be application/soap+xml, but MS… :/ */
   ne_add_request_header(req, "Content-Type", "text/xml; charset=utf-8");
   ne_add_request_header(req, "SOAPAction", get_soap_action(ctx->op));

   /* Set body to SOAP request */
   ne_set_request_body_buffer(req, ast_str_buffer(request), ast_str_strlen(request));

   /* Prepare XML parser */
   parser = ne_xml_create();
   ctx->parser = parser;
   ne_xml_push_handler(parser, startelm, cdata, endelm, ctx);  /* Callbacks */

   /* Dispatch request and parse response as XML */
   ret = ne_xml_dispatch_request(req, parser);
   if (ret != NE_OK) { /* Error handling */
      ast_log(LOG_WARNING, "Unable to communicate with Exchange Web Service at '%s': %s\n", ctx->pvt->url, ne_get_error(ctx->pvt->session));
      ne_request_destroy(req);
      ne_xml_destroy(parser);
      return -1;
   }

   /* Cleanup */
   ne_request_destroy(req);
   ne_xml_destroy(parser);

   return 0;
}

static int ewscal_write_event(struct ast_calendar_event *event)
{
   struct ast_str *request;
   struct ewscal_pvt *pvt = event->owner->tech_pvt;
   char start[21], end[21];
   struct xml_context ctx = {
      .op = XML_OP_CREATE,
      .pvt = pvt,
   };
   int ret;
   char *category, *categories;

   if (!pvt) {
      return -1;
   }

   if (!(request = ast_str_create(1024))) {
      return -1;
   }

   ast_str_set(&request, 0,
      "<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" "
         "xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" "
         "xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\" "
         "xmlns:t=\"http://schemas.microsoft.com/exchange/services/2006/types\">"
         "<soap:Body>"
         "<CreateItem xmlns=\"http://schemas.microsoft.com/exchange/services/2006/messages\" "
            "xmlns:t=\"http://schemas.microsoft.com/exchange/services/2006/types\" "
            "SendMeetingInvitations=\"SendToNone\" >"
            "<SavedItemFolderId>"
               "<t:DistinguishedFolderId Id=\"calendar\"/>"
            "</SavedItemFolderId>"
            "<Items>"
               "<t:CalendarItem xmlns=\"http://schemas.microsoft.com/exchange/services/2006/types\">"
                  "<Subject>%s</Subject>"
                  "<Body BodyType=\"Text\">%s</Body>"
                  "<ReminderIsSet>false</ReminderIsSet>"
                  "<Start>%s</Start>"
                  "<End>%s</End>"
                  "<IsAllDayEvent>false</IsAllDayEvent>"
                  "<LegacyFreeBusyStatus>%s</LegacyFreeBusyStatus>"
                  "<Location>%s</Location>",
      event->summary,
      event->description,
      mstime(event->start, start, sizeof(start)),
      mstime(event->end, end, sizeof(end)),
      msstatus(event->busy_state),
      event->location
   );
   /* Event priority */
   switch (event->priority) {
   case 1:
   case 2:
   case 3:
   case 4:
      ast_str_append(&request, 0, "<Importance>High</Importance>");
      break;
   case 5:
      ast_str_append(&request, 0, "<Importance>Normal</Importance>");
      break;
   case 6:
   case 7:
   case 8:
   case 9:
      ast_str_append(&request, 0, "<Importance>Low</Importance>");
      break;
   }
   /* Event categories*/
   if (strlen(event->categories) > 0) {
      ast_str_append(&request, 0, "<Categories>");
      categories = ast_strdupa(event->categories); /* Duplicate string, since strsep() is destructive */
      category = strsep(&categories, ",");
      while (category != NULL) {
         ast_str_append(&request, 0, "<String>%s</String>", category);
         category = strsep(&categories, ",");
      }
      ast_str_append(&request, 0, "</Categories>");
   }
   /* Finish request */
   ast_str_append(&request, 0, "</t:CalendarItem></Items></CreateItem></soap:Body></soap:Envelope>");

   ret = send_ews_request_and_parse(request, &ctx);

   ast_free(request);

   return ret;
}

static struct calendar_id *get_ewscal_ids_for(struct ewscal_pvt *pvt)
{
   char start[21], end[21];
   struct ast_tm tm;
   struct timeval tv;
   struct ast_str *request;
   struct xml_context ctx = {
      .op = XML_OP_FIND,
      .pvt = pvt,
   };

   ast_debug(5, "EWS: get_ewscal_ids_for()\n");

   if (!pvt) {
      ast_log(LOG_ERROR, "There is no private!\n");
      return NULL;
   }

   /* Prepare timeframe strings */
   tv = ast_tvnow();
   ast_localtime(&tv, &tm, "UTC");
   ast_strftime(start, sizeof(start), "%FT%TZ", &tm);
   tv.tv_sec += 60 * pvt->owner->timeframe;
   ast_localtime(&tv, &tm, "UTC");
   ast_strftime(end, sizeof(end), "%FT%TZ", &tm);

   /* Prepare SOAP request */
   if (!(request = ast_str_create(512))) {
      return NULL;
   }

   ast_str_set(&request, 0,
      "<SOAP-ENV:Envelope xmlns:SOAP-ENV=\"http://schemas.xmlsoap.org/soap/envelope/\" "
      "xmlns:ns1=\"http://schemas.microsoft.com/exchange/services/2006/types\" "
      "xmlns:ns2=\"http://schemas.microsoft.com/exchange/services/2006/messages\">"
         "<SOAP-ENV:Body>"
            "<ns2:FindItem Traversal=\"Shallow\">"
               "<ns2:ItemShape>"
                  "<ns1:BaseShape>IdOnly</ns1:BaseShape>"
               "</ns2:ItemShape>"
               "<ns2:CalendarView StartDate=\"%s\" EndDate=\"%s\"/>" /* Timeframe */
               "<ns2:ParentFolderIds>"
                  "<ns1:DistinguishedFolderId Id=\"calendar\"/>"
               "</ns2:ParentFolderIds>"
            "</ns2:FindItem>"
         "</SOAP-ENV:Body>"
      "</SOAP-ENV:Envelope>",
      start, end  /* Timeframe */
   );

   AST_LIST_HEAD_INIT_NOLOCK(&ctx.ids);

   /* Dispatch request and parse response as XML */
   if (send_ews_request_and_parse(request, &ctx)) {
      ast_free(request);
      return NULL;
   }

   /* Cleanup */
   ast_free(request);

   return AST_LIST_FIRST(&ctx.ids);
}

static int parse_ewscal_id(struct ewscal_pvt *pvt, const char *id) {
   struct ast_str *request;
   struct xml_context ctx = {
      .pvt = pvt,
      .op = XML_OP_GET,
   };

   if (!(request = ast_str_create(512))) {
      return -1;
   }

   ast_str_set(&request, 0,
      "<?xml version=\"1.0\" encoding=\"utf-8\"?>"
      "<soap:Envelope xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\" "
      "xmlns:t=\"http://schemas.microsoft.com/exchange/services/2006/types\">"
      "<soap:Body>"
         "<GetItem xmlns=\"http://schemas.microsoft.com/exchange/services/2006/messages\">"
            "<ItemShape>"
               "<t:BaseShape>AllProperties</t:BaseShape>"
            "</ItemShape>"
            "<ItemIds>"
               "<t:ItemId Id=\"%s\"/>"
            "</ItemIds>"
         "</GetItem>"
      "</soap:Body>"
      "</soap:Envelope>", id
   );

   if (send_ews_request_and_parse(request, &ctx)) {
      ast_free(request);
      return -1;
   }

   ast_free(request);

   return 0;
}

static int update_ewscal(struct ewscal_pvt *pvt)
{
   struct calendar_id *id_head;
   struct calendar_id *iter;

   if (!(id_head = get_ewscal_ids_for(pvt))) {
      return 0;
   }

   for (iter = id_head; iter; iter = AST_LIST_NEXT(iter, next)) {
      parse_ewscal_id(pvt, ast_str_buffer(iter->id));
      ast_free(iter->id);
      ast_free(iter);
   }

   return 0;
}

static void *ewscal_load_calendar(void *void_data)
{
   struct ewscal_pvt *pvt;
   const struct ast_config *cfg;
   struct ast_variable *v;
   struct ast_calendar *cal = void_data;
   ast_mutex_t refreshlock;

   ast_debug(5, "EWS: ewscal_load_calendar()\n");

   if (!(cal && (cfg = ast_calendar_config_acquire()))) {
      ast_log(LOG_ERROR, "You must enable calendar support for res_ewscal to load\n");
      return NULL;
   }

   if (ao2_trylock(cal)) {
      if (cal->unloading) {
         ast_log(LOG_WARNING, "Unloading module, load_calendar cancelled.\n");
      } else {
         ast_log(LOG_WARNING, "Could not lock calendar, aborting!\n");
      }
      ast_calendar_config_release();
      return NULL;
   }

   if (!(pvt = ao2_alloc(sizeof(*pvt), ewscal_destructor))) {
      ast_log(LOG_ERROR, "Could not allocate ewscal_pvt structure for calendar: %s\n", cal->name);
      ast_calendar_config_release();
      return NULL;
   }

   pvt->owner = cal;

   if (!(pvt->events = ast_calendar_event_container_alloc())) {
      ast_log(LOG_ERROR, "Could not allocate space for fetching events for calendar: %s\n", cal->name);
      pvt = unref_ewscal(pvt);
      ao2_unlock(cal);
      ast_calendar_config_release();
      return NULL;
   }

   if (ast_string_field_init(pvt, 32)) {
      ast_log(LOG_ERROR, "Couldn't allocate string field space for calendar: %s\n", cal->name);
      pvt = unref_ewscal(pvt);
      ao2_unlock(cal);
      ast_calendar_config_release();
      return NULL;
   }

   for (v = ast_variable_browse(cfg, cal->name); v; v = v->next) {
      if (!strcasecmp(v->name, "url")) {
         ast_string_field_set(pvt, url, v->value);
      } else if (!strcasecmp(v->name, "user")) {
         ast_string_field_set(pvt, user, v->value);
      } else if (!strcasecmp(v->name, "secret")) {
         ast_string_field_set(pvt, secret, v->value);
      }
   }

   ast_calendar_config_release();

   if (ast_strlen_zero(pvt->url)) {
      ast_log(LOG_WARNING, "No URL was specified for Exchange Web Service calendar '%s' - skipping.\n", cal->name);
      pvt = unref_ewscal(pvt);
      ao2_unlock(cal);
      return NULL;
   }

   if (ne_uri_parse(pvt->url, &pvt->uri) || pvt->uri.host == NULL || pvt->uri.path == NULL) {
      ast_log(LOG_WARNING, "Could not parse url '%s' for Exchange Web Service calendar '%s' - skipping.\n", pvt->url, cal->name);
      pvt = unref_ewscal(pvt);
      ao2_unlock(cal);
      return NULL;
   }

   if (pvt->uri.scheme == NULL) {
      pvt->uri.scheme = "http";
   }

   if (pvt->uri.port == 0) {
      pvt->uri.port = ne_uri_defaultport(pvt->uri.scheme);
   }

   ast_debug(3, "ne_uri.scheme   = %s\n", pvt->uri.scheme);
   ast_debug(3, "ne_uri.host  = %s\n", pvt->uri.host);
   ast_debug(3, "ne_uri.port  = %u\n", pvt->uri.port);
   ast_debug(3, "ne_uri.path  = %s\n", pvt->uri.path);
   ast_debug(3, "user      = %s\n", pvt->user);
   ast_debug(3, "secret    = %s\n", pvt->secret);

   pvt->session = ne_session_create(pvt->uri.scheme, pvt->uri.host, pvt->uri.port);
   ne_redirect_register(pvt->session);
   ne_set_server_auth(pvt->session, auth_credentials, pvt);
   ne_set_useragent(pvt->session, "Asterisk");

   if (!strcasecmp(pvt->uri.scheme, "https")) {
      ne_ssl_trust_default_ca(pvt->session);
      ne_ssl_set_verify(pvt->session, ssl_verify, pvt);
   }

   cal->tech_pvt = pvt;

   ast_mutex_init(&refreshlock);

   /* Load it the first time */
   update_ewscal(pvt);

   ao2_unlock(cal);

   /* The only writing from another thread will be if unload is true */
   for (;;) {
      struct timeval tv = ast_tvnow();
      struct timespec ts = {0,};

      ts.tv_sec = tv.tv_sec + (60 * pvt->owner->refresh);

      ast_mutex_lock(&refreshlock);
      while (!pvt->owner->unloading) {
         if (ast_cond_timedwait(&pvt->owner->unload, &refreshlock, &ts) == ETIMEDOUT) {
            break;
         }
      }
      ast_mutex_unlock(&refreshlock);

      if (pvt->owner->unloading) {
         ast_debug(10, "Skipping refresh since we got a shutdown signal\n");
         return NULL;
      }

      ast_debug(10, "Refreshing after %d minute timeout\n", pvt->owner->refresh);

      update_ewscal(pvt);
   }

   return NULL;
}

static int load_module(void)
{
   /* Actualy, 0.29.1 is required (because of NTLM authentication), but this
    * function does not support matching patch version.
    *
    * The ne_version_match function returns non-zero if the library
    * version is not of major version major, or the minor version
    * is less than minor. For neon versions 0.x, every minor
    * version is assumed to be incompatible with every other minor
    * version.
    *
    * I.e. for version 1.2..1.9 we would do ne_version_match(1, 2)
    * but for version 0.29 and 0.30 we need two checks. */
   if (ne_version_match(0, 29) && ne_version_match(0, 30)) {
      ast_log(LOG_ERROR, "Exchange Web Service calendar module require neon >= 0.29.1, but %s is installed.\n", ne_version_string());
      return AST_MODULE_LOAD_DECLINE;
   }

   if (ast_calendar_register(&ewscal_tech) && (ne_sock_init() == 0)) {
      return AST_MODULE_LOAD_DECLINE;
   }

   return AST_MODULE_LOAD_SUCCESS;
}

static int unload_module(void)
{
   ne_sock_exit();
   ast_calendar_unregister(&ewscal_tech);

   return 0;
}

AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_LOAD_ORDER, "Asterisk MS Exchange Web Service Calendar Integration",
   .support_level = AST_MODULE_SUPPORT_EXTENDED,
   .load = load_module,
   .unload = unload_module,
   .load_pri = AST_MODPRI_DEVSTATE_PLUGIN,
   .requires = "res_calendar",
);