/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 * SPDX-License-Identifier: curl
 *
 * RFC2195 CRAM-MD5 authentication
 * RFC2595 Using TLS with IMAP, POP3 and ACAP
 * RFC2831 DIGEST-MD5 authentication
 * RFC3501 IMAPv4 protocol
 * RFC4422 Simple Authentication and Security Layer (SASL)
 * RFC4616 PLAIN authentication
 * RFC4752 The Kerberos V5 ("GSSAPI") SASL Mechanism
 * RFC4959 IMAP Extension for SASL Initial Client Response
 * RFC5092 IMAP URL Scheme
 * RFC6749 OAuth 2.0 Authorization Framework
 * RFC8314 Use of TLS for Email Submission and Access
 * Draft   LOGIN SASL Mechanism <draft-murchison-sasl-login-00.txt>
 *
 ***************************************************************************/
#include "curl_setup.h"

#ifndef CURL_DISABLE_IMAP

#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#ifdef HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif
#ifdef HAVE_NETDB_H
#include <netdb.h>
#endif
#ifdef __VMS
#include <in.h>
#include <inet.h>
#endif

#include "curlx/dynbuf.h"
#include "urldata.h"
#include "sendf.h"
#include "curl_trc.h"
#include "hostip.h"
#include "progress.h"
#include "transfer.h"
#include "escape.h"
#include "pingpong.h"
#include "imap.h"
#include "mime.h"
#include "curlx/strparse.h"
#include "strcase.h"
#include "vtls/vtls.h"
#include "cfilters.h"
#include "connect.h"
#include "select.h"
#include "url.h"
#include "bufref.h"
#include "curl_sasl.h"
#include "curlx/strcopy.h"

/* meta key for storing protocol meta at easy handle */
#define CURL_META_IMAP_EASY   "meta:proto:imap:easy"
/* meta key for storing protocol meta at connection */
#define CURL_META_IMAP_CONN   "meta:proto:imap:conn"

typedef enum {
  IMAP_STOP,         /* do nothing state, stops the state machine */
  IMAP_SERVERGREET,  /* waiting for the initial greeting immediately after
                        a connect */
  IMAP_CAPABILITY,
  IMAP_STARTTLS,
  IMAP_UPGRADETLS,   /* asynchronously upgrade the connection to SSL/TLS
                       (multi mode only) */
  IMAP_AUTHENTICATE,
  IMAP_LOGIN,
  IMAP_LIST,
  IMAP_SELECT,
  IMAP_FETCH,
  IMAP_FETCH_FINAL,
  IMAP_APPEND,
  IMAP_APPEND_FINAL,
  IMAP_SEARCH,
  IMAP_LOGOUT,
  IMAP_LAST          /* never used */
} imapstate;

/* imap_conn is used for struct connection-oriented data */
struct imap_conn {
  struct pingpong pp;
  struct SASL sasl;           /* SASL-related parameters */
  struct dynbuf dyn;          /* for the IMAP commands */
  char *mailbox;              /* The last selected mailbox */
  imapstate state;            /* Always use imap.c:state() to change state! */
  unsigned int mb_uidvalidity; /* UIDVALIDITY parsed from select response */
  char resptag[5];            /* Response tag to wait for */
  unsigned char preftype;     /* Preferred authentication type */
  unsigned char cmdid;        /* Last used command ID */
  BIT(ssldone);               /* Is connect() over SSL done? */
  BIT(preauth);               /* Is this connection PREAUTH? */
  BIT(tls_supported);         /* StartTLS capability supported by server */
  BIT(login_disabled);        /* LOGIN command disabled by server */
  BIT(ir_supported);          /* Initial response supported by server */
  BIT(mb_uidvalidity_set);
};

/* This IMAP struct is used in the Curl_easy. All IMAP data that is
   connection-oriented must be in imap_conn to properly deal with the fact that
   perhaps the Curl_easy is changed between the times the connection is
   used. */
struct IMAP {
  curl_pp_transfer transfer;
  char *mailbox;          /* Mailbox to select */
  char *uid;              /* Message UID to fetch */
  char *mindex;           /* Index in mail box of mail to fetch */
  char *section;          /* Message SECTION to fetch */
  char *partial;          /* Message PARTIAL to fetch */
  char *query;            /* Query to search for */
  char *custom;           /* Custom request */
  char *custom_params;    /* Parameters for the custom request */
  unsigned int uidvalidity; /* UIDVALIDITY to check in select */
  BIT(uidvalidity_set);
};

/* Local API functions */
static CURLcode imap_regular_transfer(struct Curl_easy *data,
                                      struct IMAP *imap,
                                      bool *done);
static CURLcode imap_do(struct Curl_easy *data, bool *done);
static CURLcode imap_done(struct Curl_easy *data, CURLcode status,
                          bool premature);
static CURLcode imap_connect(struct Curl_easy *data, bool *done);
static CURLcode imap_disconnect(struct Curl_easy *data,
                                struct connectdata *conn, bool dead);
static CURLcode imap_multi_statemach(struct Curl_easy *data, bool *done);
static CURLcode imap_pollset(struct Curl_easy *data,
                             struct easy_pollset *ps);
static CURLcode imap_doing(struct Curl_easy *data, bool *dophase_done);
static CURLcode imap_setup_connection(struct Curl_easy *data,
                                      struct connectdata *conn);
static char *imap_atom(const char *str, bool escape_only);
static CURLcode imap_sendf(struct Curl_easy *data,
                           struct imap_conn *imapc,
                           const char *fmt, ...) CURL_PRINTF(3, 4);
static CURLcode imap_parse_url_options(struct connectdata *conn,
                                       struct imap_conn *imapc);
static CURLcode imap_parse_url_path(struct Curl_easy *data,
                                    struct IMAP *imap);
static CURLcode imap_parse_custom_request(struct Curl_easy *data,
                                          struct IMAP *imap);
static CURLcode imap_perform_authenticate(struct Curl_easy *data,
                                          const char *mech,
                                          const struct bufref *initresp);
static CURLcode imap_continue_authenticate(struct Curl_easy *data,
                                           const char *mech,
                                           const struct bufref *resp);
static CURLcode imap_cancel_authenticate(struct Curl_easy *data,
                                         const char *mech);
static CURLcode imap_get_message(struct Curl_easy *data, struct bufref *out);
static void imap_easy_reset(struct IMAP *imap);

/*
 * IMAP protocol handler.
 */

const struct Curl_handler Curl_handler_imap = {
  "imap",                           /* scheme */
  imap_setup_connection,            /* setup_connection */
  imap_do,                          /* do_it */
  imap_done,                        /* done */
  ZERO_NULL,                        /* do_more */
  imap_connect,                     /* connect_it */
  imap_multi_statemach,             /* connecting */
  imap_doing,                       /* doing */
  imap_pollset,                     /* proto_pollset */
  imap_pollset,                     /* doing_pollset */
  ZERO_NULL,                        /* domore_pollset */
  ZERO_NULL,                        /* perform_pollset */
  imap_disconnect,                  /* disconnect */
  ZERO_NULL,                        /* write_resp */
  ZERO_NULL,                        /* write_resp_hd */
  ZERO_NULL,                        /* connection_check */
  ZERO_NULL,                        /* attach connection */
  ZERO_NULL,                        /* follow */
  PORT_IMAP,                        /* defport */
  CURLPROTO_IMAP,                   /* protocol */
  CURLPROTO_IMAP,                   /* family */
  PROTOPT_CLOSEACTION |             /* flags */
  PROTOPT_URLOPTIONS | PROTOPT_SSL_REUSE |
  PROTOPT_CONN_REUSE
};

#ifdef USE_SSL
/*
 * IMAPS protocol handler.
 */

const struct Curl_handler Curl_handler_imaps = {
  "imaps",                          /* scheme */
  imap_setup_connection,            /* setup_connection */
  imap_do,                          /* do_it */
  imap_done,                        /* done */
  ZERO_NULL,                        /* do_more */
  imap_connect,                     /* connect_it */
  imap_multi_statemach,             /* connecting */
  imap_doing,                       /* doing */
  imap_pollset,                     /* proto_pollset */
  imap_pollset,                     /* doing_pollset */
  ZERO_NULL,                        /* domore_pollset */
  ZERO_NULL,                        /* perform_pollset */
  imap_disconnect,                  /* disconnect */
  ZERO_NULL,                        /* write_resp */
  ZERO_NULL,                        /* write_resp_hd */
  ZERO_NULL,                        /* connection_check */
  ZERO_NULL,                        /* attach connection */
  ZERO_NULL,                        /* follow */
  PORT_IMAPS,                       /* defport */
  CURLPROTO_IMAPS,                  /* protocol */
  CURLPROTO_IMAP,                   /* family */
  PROTOPT_CLOSEACTION | PROTOPT_SSL | /* flags */
  PROTOPT_URLOPTIONS | PROTOPT_CONN_REUSE
};
#endif

#define IMAP_RESP_OK       1
#define IMAP_RESP_NOT_OK   2
#define IMAP_RESP_PREAUTH  3

/* SASL parameters for the imap protocol */
static const struct SASLproto saslimap = {
  "imap",                     /* The service name */
  imap_perform_authenticate,  /* Send authentication command */
  imap_continue_authenticate, /* Send authentication continuation */
  imap_cancel_authenticate,   /* Send authentication cancellation */
  imap_get_message,           /* Get SASL response message */
  0,                          /* No maximum initial response length */
  '+',                        /* Code received when continuation is expected */
  IMAP_RESP_OK,               /* Code to receive upon authentication success */
  SASL_AUTH_DEFAULT,          /* Default mechanisms */
  SASL_FLAG_BASE64            /* Configuration flags */
};

struct ulbits {
  int bit;
  const char *flag;
};

/***********************************************************************
 *
 * imap_matchresp()
 *
 * Determines whether the untagged response is related to the specified
 * command by checking if it is in format "* <command-name> ..." or
 * "* <number> <command-name> ...".
 *
 * The "* " marker is assumed to have already been checked by the caller.
 */
static bool imap_matchresp(const char *line, size_t len, const char *cmd)
{
  const char *end = line + len;
  size_t cmd_len = strlen(cmd);

  /* Skip the untagged response marker */
  line += 2;

  /* Do we have a number after the marker? */
  if(line < end && ISDIGIT(*line)) {
    /* Skip the number */
    do
      line++;
    while(line < end && ISDIGIT(*line));

    /* Do we have the space character? */
    if(line == end || *line != ' ')
      return FALSE;

    line++;
  }

  /* Does the command name match and is it followed by a space character or at
     the end of line? */
  if(line + cmd_len <= end && curl_strnequal(line, cmd, cmd_len) &&
     (line[cmd_len] == ' ' || line + cmd_len + 2 == end))
    return TRUE;

  return FALSE;
}

/***********************************************************************
 *
 * imap_endofresp()
 *
 * Checks whether the given string is a valid tagged, untagged or continuation
 * response which can be processed by the response handler.
 */
static bool imap_endofresp(struct Curl_easy *data, struct connectdata *conn,
                           const char *line, size_t len, int *resp)
{
  struct imap_conn *imapc = Curl_conn_meta_get(conn, CURL_META_IMAP_CONN);
  struct IMAP *imap = Curl_meta_get(data, CURL_META_IMAP_EASY);
  const char *id;
  size_t id_len;

  DEBUGASSERT(imapc);
  DEBUGASSERT(imap);
  if(!imapc || !imap)
    return FALSE;

  /* Do we have a tagged command response? */
  id = imapc->resptag;
  id_len = strlen(id);
  if(len >= id_len + 1 && !memcmp(id, line, id_len) && line[id_len] == ' ') {
    line += id_len + 1;
    len -= id_len + 1;

    if(len >= 2 && !memcmp(line, "OK", 2))
      *resp = IMAP_RESP_OK;
    else if(len >= 7 && !memcmp(line, "PREAUTH", 7))
      *resp = IMAP_RESP_PREAUTH;
    else
      *resp = IMAP_RESP_NOT_OK;

    return TRUE;
  }

  /* Do we have an untagged command response? */
  if(len >= 2 && !memcmp("* ", line, 2)) {
    switch(imapc->state) {
    /* States which are interested in untagged responses */
    case IMAP_CAPABILITY:
      if(!imap_matchresp(line, len, "CAPABILITY"))
        return FALSE;
      break;

    case IMAP_LIST:
      if((!imap->custom && !imap_matchresp(line, len, "LIST")) ||
         (imap->custom && !imap_matchresp(line, len, imap->custom) &&
          (!curl_strequal(imap->custom, "STORE") ||
           !imap_matchresp(line, len, "FETCH")) &&
          !curl_strequal(imap->custom, "SELECT") &&
          !curl_strequal(imap->custom, "EXAMINE") &&
          !curl_strequal(imap->custom, "SEARCH") &&
          !curl_strequal(imap->custom, "EXPUNGE") &&
          !curl_strequal(imap->custom, "LSUB") &&
          !curl_strequal(imap->custom, "UID") &&
          !curl_strequal(imap->custom, "GETQUOTAROOT") &&
          !curl_strequal(imap->custom, "NOOP")))
        return FALSE;
      break;

    case IMAP_SELECT:
      /* SELECT is special in that its untagged responses do not have a
         common prefix so accept anything! */
      break;

    case IMAP_FETCH:
      if(!imap_matchresp(line, len, "FETCH"))
        return FALSE;
      break;

    case IMAP_SEARCH:
      if(!imap_matchresp(line, len, "SEARCH"))
        return FALSE;
      break;

    /* Ignore other untagged responses */
    default:
      return FALSE;
    }

    *resp = '*';
    return TRUE;
  }

  /* Do we have a continuation response? This should be a + symbol followed by
     a space and optionally some text as per RFC-3501 for the AUTHENTICATE and
     APPEND commands and as outlined in Section 4. Examples of RFC-4959 but
     some email servers ignore this and only send a single + instead. */
  if(!imap->custom && ((len == 3 && line[0] == '+') ||
                       (len >= 2 && !memcmp("+ ", line, 2)))) {
    switch(imapc->state) {
    /* States which are interested in continuation responses */
    case IMAP_AUTHENTICATE:
    case IMAP_APPEND:
      *resp = '+';
      break;

    default:
      failf(data, "Unexpected continuation response");
      *resp = -1;
      break;
    }

    return TRUE;
  }

  return FALSE; /* Nothing for us */
}

/***********************************************************************
 *
 * imap_get_message()
 *
 * Gets the authentication message from the response buffer.
 */
static CURLcode imap_get_message(struct Curl_easy *data, struct bufref *out)
{
  struct imap_conn *imapc =
    Curl_conn_meta_get(data->conn, CURL_META_IMAP_CONN);
  char *message;
  size_t len;

  if(!imapc)
    return CURLE_FAILED_INIT;

  message = curlx_dyn_ptr(&imapc->pp.recvbuf);
  len = imapc->pp.nfinal;
  if(len > 2) {
    /* Find the start of the message */
    len -= 2;
    for(message += 2; *message == ' ' || *message == '\t'; message++, len--)
      ;

    /* Find the end of the message */
    while(len--)
      if(message[len] != '\r' && message[len] != '\n' && message[len] != ' ' &&
         message[len] != '\t')
        break;

    /* Terminate the message */
    message[++len] = '\0';
    Curl_bufref_set(out, message, len, NULL);
  }
  else
    /* junk input => zero length output */
    Curl_bufref_set(out, "", 0, NULL);

  return CURLE_OK;
}

/***********************************************************************
 *
 * imap_state()
 *
 * This is the ONLY way to change IMAP state!
 */
static void imap_state(struct Curl_easy *data,
                       struct imap_conn *imapc,
                       imapstate newstate)
{
#if defined(DEBUGBUILD) && !defined(CURL_DISABLE_VERBOSE_STRINGS)
  /* for debug purposes */
  static const char * const names[] = {
    "STOP",
    "SERVERGREET",
    "CAPABILITY",
    "STARTTLS",
    "UPGRADETLS",
    "AUTHENTICATE",
    "LOGIN",
    "LIST",
    "SELECT",
    "FETCH",
    "FETCH_FINAL",
    "APPEND",
    "APPEND_FINAL",
    "SEARCH",
    "LOGOUT",
    /* LAST */
  };

  if(imapc->state != newstate)
    infof(data, "IMAP %p state change from %s to %s",
          (void *)imapc, names[imapc->state], names[newstate]);
#endif
  (void)data;
  imapc->state = newstate;
}

/***********************************************************************
 *
 * imap_perform_capability()
 *
 * Sends the CAPABILITY command in order to obtain a list of server side
 * supported capabilities.
 */
static CURLcode imap_perform_capability(struct Curl_easy *data,
                                        struct imap_conn *imapc)
{
  CURLcode result = CURLE_OK;

  imapc->sasl.authmechs = SASL_AUTH_NONE; /* No known auth. mechanisms yet */
  imapc->sasl.authused = SASL_AUTH_NONE;  /* Clear the auth. mechanism used */
  imapc->tls_supported = FALSE;           /* Clear the TLS capability */

  /* Send the CAPABILITY command */
  result = imap_sendf(data, imapc, "CAPABILITY");

  if(!result)
    imap_state(data, imapc, IMAP_CAPABILITY);

  return result;
}

/***********************************************************************
 *
 * imap_perform_starttls()
 *
 * Sends the STARTTLS command to start the upgrade to TLS.
 */
static CURLcode imap_perform_starttls(struct Curl_easy *data,
                                      struct imap_conn *imapc)
{
  /* Send the STARTTLS command */
  CURLcode result = imap_sendf(data, imapc, "STARTTLS");

  if(!result)
    imap_state(data, imapc, IMAP_STARTTLS);

  return result;
}

/***********************************************************************
 *
 * imap_perform_upgrade_tls()
 *
 * Performs the upgrade to TLS.
 */
static CURLcode imap_perform_upgrade_tls(struct Curl_easy *data,
                                         struct imap_conn *imapc,
                                         struct connectdata *conn)
{
#ifdef USE_SSL
  /* Start the SSL connection */
  CURLcode result;
  bool ssldone = FALSE;

  if(!Curl_conn_is_ssl(conn, FIRSTSOCKET)) {
    result = Curl_ssl_cfilter_add(data, conn, FIRSTSOCKET);
    if(result)
      goto out;
    /* Change the connection handler */
    conn->handler = &Curl_handler_imaps;
  }

  DEBUGASSERT(!imapc->ssldone);
  result = Curl_conn_connect(data, FIRSTSOCKET, FALSE, &ssldone);
  DEBUGF(infof(data, "imap_perform_upgrade_tls, connect -> %d, %d",
         result, ssldone));
  if(!result && ssldone) {
    imapc->ssldone = ssldone;
    /* perform CAPA now, changes imapc->state out of IMAP_UPGRADETLS */
    result = imap_perform_capability(data, imapc);
  }
out:
  return result;
#else
  (void)data;
  (void)imapc;
  (void)conn;
  return CURLE_NOT_BUILT_IN;
#endif
}

/***********************************************************************
 *
 * imap_perform_login()
 *
 * Sends a clear text LOGIN command to authenticate with.
 */
static CURLcode imap_perform_login(struct Curl_easy *data,
                                   struct imap_conn *imapc,
                                   struct connectdata *conn)
{
  CURLcode result = CURLE_OK;
  char *user;
  char *passwd;

  /* Check we have a username and password to authenticate with and end the
     connect phase if we do not */
  if(!data->state.aptr.user) {
    imap_state(data, imapc, IMAP_STOP);

    return result;
  }

  /* Make sure the username and password are in the correct atom format */
  user = imap_atom(conn->user, FALSE);
  passwd = imap_atom(conn->passwd, FALSE);

  /* Send the LOGIN command */
  result = imap_sendf(data, imapc, "LOGIN %s %s", user ? user : "",
                      passwd ? passwd : "");

  curlx_free(user);
  curlx_free(passwd);

  if(!result)
    imap_state(data, imapc, IMAP_LOGIN);

  return result;
}

/***********************************************************************
 *
 * imap_perform_authenticate()
 *
 * Sends an AUTHENTICATE command allowing the client to login with the given
 * SASL authentication mechanism.
 */
static CURLcode imap_perform_authenticate(struct Curl_easy *data,
                                          const char *mech,
                                          const struct bufref *initresp)
{
  struct imap_conn *imapc =
    Curl_conn_meta_get(data->conn, CURL_META_IMAP_CONN);
  CURLcode result = CURLE_OK;
  const char *ir = Curl_bufref_ptr(initresp);

  if(!imapc)
    return CURLE_FAILED_INIT;
  if(ir) {
    /* Send the AUTHENTICATE command with the initial response */
    result = imap_sendf(data, imapc, "AUTHENTICATE %s %s", mech, ir);
  }
  else {
    /* Send the AUTHENTICATE command */
    result = imap_sendf(data, imapc, "AUTHENTICATE %s", mech);
  }

  return result;
}

/***********************************************************************
 *
 * imap_continue_authenticate()
 *
 * Sends SASL continuation data.
 */
static CURLcode imap_continue_authenticate(struct Curl_easy *data,
                                           const char *mech,
                                           const struct bufref *resp)
{
  struct imap_conn *imapc =
    Curl_conn_meta_get(data->conn, CURL_META_IMAP_CONN);

  (void)mech;
  if(!imapc)
    return CURLE_FAILED_INIT;
  return Curl_pp_sendf(data, &imapc->pp, "%s", Curl_bufref_ptr(resp));
}

/***********************************************************************
 *
 * imap_cancel_authenticate()
 *
 * Sends SASL cancellation.
 */
static CURLcode imap_cancel_authenticate(struct Curl_easy *data,
                                         const char *mech)
{
  struct imap_conn *imapc =
    Curl_conn_meta_get(data->conn, CURL_META_IMAP_CONN);

  (void)mech;
  if(!imapc)
    return CURLE_FAILED_INIT;
  return Curl_pp_sendf(data, &imapc->pp, "*");
}

/***********************************************************************
 *
 * imap_perform_authentication()
 *
 * Initiates the authentication sequence, with the appropriate SASL
 * authentication mechanism, falling back to clear text should a common
 * mechanism not be available between the client and server.
 */
static CURLcode imap_perform_authentication(struct Curl_easy *data,
                                            struct imap_conn *imapc)
{
  CURLcode result = CURLE_OK;
  saslprogress progress;

  /* Check if already authenticated OR if there is enough data to authenticate
     with and end the connect phase if we do not */
  if(imapc->preauth ||
     !Curl_sasl_can_authenticate(&imapc->sasl, data)) {
    imap_state(data, imapc, IMAP_STOP);
    return result;
  }

  /* Calculate the SASL login details */
  result = Curl_sasl_start(&imapc->sasl, data, imapc->ir_supported, &progress);

  if(!result) {
    if(progress == SASL_INPROGRESS)
      imap_state(data, imapc, IMAP_AUTHENTICATE);
    else if(!imapc->login_disabled && (imapc->preftype & IMAP_TYPE_CLEARTEXT))
      /* Perform clear text authentication */
      result = imap_perform_login(data, imapc, data->conn);
    else
      result = Curl_sasl_is_blocked(&imapc->sasl, data);
  }

  return result;
}

/***********************************************************************
 *
 * imap_perform_list()
 *
 * Sends a LIST command or an alternative custom request.
 */
static CURLcode imap_perform_list(struct Curl_easy *data,
                                  struct imap_conn *imapc,
                                  struct IMAP *imap)
{
  CURLcode result = CURLE_OK;

  if(imap->custom)
    /* Send the custom request */
    result = imap_sendf(data, imapc, "%s%s", imap->custom,
                        imap->custom_params ? imap->custom_params : "");
  else {
    /* Make sure the mailbox is in the correct atom format if necessary */
    char *mailbox = imap->mailbox ? imap_atom(imap->mailbox, TRUE)
                                  : curlx_strdup("");
    if(!mailbox)
      return CURLE_OUT_OF_MEMORY;

    /* Send the LIST command */
    result = imap_sendf(data, imapc, "LIST \"%s\" *", mailbox);

    curlx_free(mailbox);
  }

  if(!result)
    imap_state(data, imapc, IMAP_LIST);

  return result;
}

/***********************************************************************
 *
 * imap_perform_select()
 *
 * Sends a SELECT command to ask the server to change the selected mailbox.
 */
static CURLcode imap_perform_select(struct Curl_easy *data,
                                    struct imap_conn *imapc,
                                    struct IMAP *imap)
{
  CURLcode result = CURLE_OK;
  char *mailbox;

  /* Invalidate old information as we are switching mailboxes */
  Curl_safefree(imapc->mailbox);

  /* Check we have a mailbox */
  if(!imap->mailbox) {
    failf(data, "Cannot SELECT without a mailbox.");
    return CURLE_URL_MALFORMAT;
  }

  /* Make sure the mailbox is in the correct atom format */
  mailbox = imap_atom(imap->mailbox, FALSE);
  if(!mailbox)
    return CURLE_OUT_OF_MEMORY;

  /* Send the SELECT command */
  result = imap_sendf(data, imapc, "SELECT %s", mailbox);

  curlx_free(mailbox);

  if(!result)
    imap_state(data, imapc, IMAP_SELECT);

  return result;
}

/***********************************************************************
 *
 * imap_perform_fetch()
 *
 * Sends a FETCH command to initiate the download of a message.
 */
static CURLcode imap_perform_fetch(struct Curl_easy *data,
                                   struct imap_conn *imapc,
                                   struct IMAP *imap)
{
  CURLcode result = CURLE_OK;
  /* Check we have a UID */
  if(imap->uid) {

    /* Send the FETCH command */
    if(imap->partial)
      result = imap_sendf(data, imapc, "UID FETCH %s BODY[%s]<%s>",
                          imap->uid, imap->section ? imap->section : "",
                          imap->partial);
    else
      result = imap_sendf(data, imapc, "UID FETCH %s BODY[%s]",
                          imap->uid, imap->section ? imap->section : "");
  }
  else if(imap->mindex) {
    /* Send the FETCH command */
    if(imap->partial)
      result = imap_sendf(data, imapc, "FETCH %s BODY[%s]<%s>",
                          imap->mindex, imap->section ? imap->section : "",
                          imap->partial);
    else
      result = imap_sendf(data, imapc, "FETCH %s BODY[%s]",
                          imap->mindex, imap->section ? imap->section : "");
  }
  else {
    failf(data, "Cannot FETCH without a UID.");
    return CURLE_URL_MALFORMAT;
  }
  if(!result)
    imap_state(data, imapc, IMAP_FETCH);

  return result;
}

/***********************************************************************
 *
 * imap_perform_append()
 *
 * Sends an APPEND command to initiate the upload of a message.
 */
static CURLcode imap_perform_append(struct Curl_easy *data,
                                    struct imap_conn *imapc,
                                    struct IMAP *imap)
{
  CURLcode result = CURLE_OK;
  char *mailbox;
  struct dynbuf flags;

  /* Check we have a mailbox */
  if(!imap->mailbox) {
    failf(data, "Cannot APPEND without a mailbox.");
    return CURLE_URL_MALFORMAT;
  }

#ifndef CURL_DISABLE_MIME
  /* Prepare the mime data if some. */
  if(data->set.mimepost.kind != MIMEKIND_NONE) {
    /* Use the whole structure as data. */
    data->set.mimepost.flags &= ~(unsigned int)MIME_BODY_ONLY;

    /* Add external headers and mime version. */
    curl_mime_headers(&data->set.mimepost, data->set.headers, 0);
    result = Curl_mime_prepare_headers(data, &data->set.mimepost, NULL,
                                       NULL, MIMESTRATEGY_MAIL);

    if(!result)
      if(!Curl_checkheaders(data, STRCONST("Mime-Version")))
        result = Curl_mime_add_header(&data->set.mimepost.curlheaders,
                                      "Mime-Version: 1.0");

    if(!result)
      result = Curl_creader_set_mime(data, &data->set.mimepost);
    if(result)
      return result;
    data->state.infilesize = Curl_creader_client_length(data);
  }
  else
#endif
  {
    result = Curl_creader_set_fread(data, data->state.infilesize);
    if(result)
      return result;
  }

  /* Check we know the size of the upload */
  if(data->state.infilesize < 0) {
    failf(data, "Cannot APPEND with unknown input file size");
    return CURLE_UPLOAD_FAILED;
  }

  /* Make sure the mailbox is in the correct atom format */
  mailbox = imap_atom(imap->mailbox, FALSE);
  if(!mailbox)
    return CURLE_OUT_OF_MEMORY;

  /* Generate flags string and send the APPEND command */
  curlx_dyn_init(&flags, 100);
  if(data->set.upload_flags) {
    int i;
    struct ulbits ulflag[] = {
      {CURLULFLAG_ANSWERED, "Answered"},
      {CURLULFLAG_DELETED, "Deleted"},
      {CURLULFLAG_DRAFT, "Draft"},
      {CURLULFLAG_FLAGGED, "Flagged"},
      {CURLULFLAG_SEEN, "Seen"},
      {0, NULL}
    };

    result = CURLE_OUT_OF_MEMORY;
    if(curlx_dyn_add(&flags, " (")) {
      goto cleanup;
    }

    for(i = 0; ulflag[i].bit; i++) {
      if(data->set.upload_flags & ulflag[i].bit) {
        if((curlx_dyn_len(&flags) > 2 && curlx_dyn_add(&flags, " ")) ||
           curlx_dyn_add(&flags, "\\") ||
           curlx_dyn_add(&flags, ulflag[i].flag))
          goto cleanup;
      }
    }

    if(curlx_dyn_add(&flags, ")"))
      goto cleanup;
  }
  else if(curlx_dyn_add(&flags, ""))
    goto cleanup;

  result = imap_sendf(data, imapc, "APPEND %s%s {%" FMT_OFF_T "}",
                      mailbox, curlx_dyn_ptr(&flags), data->state.infilesize);

cleanup:
  curlx_dyn_free(&flags);
  curlx_free(mailbox);

  if(!result)
    imap_state(data, imapc, IMAP_APPEND);

  return result;
}

/***********************************************************************
 *
 * imap_perform_search()
 *
 * Sends a SEARCH command.
 */
static CURLcode imap_perform_search(struct Curl_easy *data,
                                    struct imap_conn *imapc,
                                    struct IMAP *imap)
{
  CURLcode result = CURLE_OK;

  /* Check we have a query string */
  if(!imap->query) {
    failf(data, "Cannot SEARCH without a query string.");
    return CURLE_URL_MALFORMAT;
  }

  /* Send the SEARCH command */
  result = imap_sendf(data, imapc, "SEARCH %s", imap->query);

  if(!result)
    imap_state(data, imapc, IMAP_SEARCH);

  return result;
}

/***********************************************************************
 *
 * imap_perform_logout()
 *
 * Performs the logout action prior to sclose() being called.
 */
static CURLcode imap_perform_logout(struct Curl_easy *data,
                                    struct imap_conn *imapc)
{
  /* Send the LOGOUT command */
  CURLcode result = imap_sendf(data, imapc, "LOGOUT");

  if(!result)
    imap_state(data, imapc, IMAP_LOGOUT);

  return result;
}

/* For the initial server greeting */
static CURLcode imap_state_servergreet_resp(struct Curl_easy *data,
                                            struct imap_conn *imapc,
                                            int imapcode,
                                            imapstate instate)
{
  (void)instate;

  if(imapcode == IMAP_RESP_PREAUTH) {
    /* PREAUTH */
    imapc->preauth = TRUE;
    infof(data, "PREAUTH connection, already authenticated");
  }
  else if(imapcode != IMAP_RESP_OK) {
    failf(data, "Got unexpected imap-server response");
    return CURLE_WEIRD_SERVER_REPLY;
  }

  return imap_perform_capability(data, imapc);
}

/* For CAPABILITY responses */
static CURLcode imap_state_capability_resp(struct Curl_easy *data,
                                           struct imap_conn *imapc,
                                           int imapcode,
                                           imapstate instate)
{
  CURLcode result = CURLE_OK;
  struct connectdata *conn = data->conn;
  const char *line = curlx_dyn_ptr(&imapc->pp.recvbuf);

  (void)instate;

  /* Do we have an untagged response? */
  if(imapcode == '*') {
    line += 2;

    /* Loop through the data line */
    for(;;) {
      size_t wordlen;
      while(*line &&
            (*line == ' ' || *line == '\t' ||
              *line == '\r' || *line == '\n')) {

        line++;
      }

      if(!*line)
        break;

      /* Extract the word */
      for(wordlen = 0; line[wordlen] && line[wordlen] != ' ' &&
                       line[wordlen] != '\t' && line[wordlen] != '\r' &&
                       line[wordlen] != '\n';)
        wordlen++;

      /* Does the server support the STARTTLS capability? */
      if(wordlen == 8 && curl_strnequal(line, "STARTTLS", 8))
        imapc->tls_supported = TRUE;

      /* Has the server explicitly disabled clear text authentication? */
      else if(wordlen == 13 && curl_strnequal(line, "LOGINDISABLED", 13))
        imapc->login_disabled = TRUE;

      /* Does the server support the SASL-IR capability? */
      else if(wordlen == 7 && curl_strnequal(line, "SASL-IR", 7))
        imapc->ir_supported = TRUE;

      /* Do we have a SASL based authentication mechanism? */
      else if(wordlen > 5 && curl_strnequal(line, "AUTH=", 5)) {
        size_t llen;
        unsigned short mechbit;

        line += 5;
        wordlen -= 5;

        /* Test the word for a matching authentication mechanism */
        mechbit = Curl_sasl_decode_mech(line, wordlen, &llen);
        if(mechbit && llen == wordlen)
          imapc->sasl.authmechs |= mechbit;
      }

      line += wordlen;
    }
  }
  else if(data->set.use_ssl && !Curl_conn_is_ssl(conn, FIRSTSOCKET)) {
    /* PREAUTH is not compatible with STARTTLS. */
    if(imapcode == IMAP_RESP_OK && imapc->tls_supported && !imapc->preauth) {
      /* Switch to TLS connection now */
      result = imap_perform_starttls(data, imapc);
    }
    else if(data->set.use_ssl <= CURLUSESSL_TRY)
      result = imap_perform_authentication(data, imapc);
    else {
      failf(data, "STARTTLS not available.");
      result = CURLE_USE_SSL_FAILED;
    }
  }
  else
    result = imap_perform_authentication(data, imapc);

  return result;
}

/* For STARTTLS responses */
static CURLcode imap_state_starttls_resp(struct Curl_easy *data,
                                         struct imap_conn *imapc,
                                         int imapcode,
                                         imapstate instate)
{
  CURLcode result = CURLE_OK;

  (void)instate;

  /* Pipelining in response is forbidden. */
  if(imapc->pp.overflow)
    return CURLE_WEIRD_SERVER_REPLY;

  if(imapcode != IMAP_RESP_OK) {
    if(data->set.use_ssl != CURLUSESSL_TRY) {
      failf(data, "STARTTLS denied");
      result = CURLE_USE_SSL_FAILED;
    }
    else
      result = imap_perform_authentication(data, imapc);
  }
  else
    imap_state(data, imapc, IMAP_UPGRADETLS);

  return result;
}

/* For SASL authentication responses */
static CURLcode imap_state_auth_resp(struct Curl_easy *data,
                                     struct imap_conn *imapc,
                                     int imapcode,
                                     imapstate instate)
{
  CURLcode result = CURLE_OK;
  saslprogress progress;

  (void)instate;

  result = Curl_sasl_continue(&imapc->sasl, data, imapcode, &progress);
  if(!result)
    switch(progress) {
    case SASL_DONE:
      imap_state(data, imapc, IMAP_STOP);  /* Authenticated */
      break;
    case SASL_IDLE:            /* No mechanism left after cancellation */
      if((!imapc->login_disabled) && (imapc->preftype & IMAP_TYPE_CLEARTEXT))
        /* Perform clear text authentication */
        result = imap_perform_login(data, imapc, data->conn);
      else {
        failf(data, "Authentication cancelled");
        result = CURLE_LOGIN_DENIED;
      }
      break;
    default:
      break;
    }

  return result;
}

/* For LOGIN responses */
static CURLcode imap_state_login_resp(struct Curl_easy *data,
                                      struct imap_conn *imapc,
                                      int imapcode,
                                      imapstate instate)
{
  CURLcode result = CURLE_OK;
  (void)instate;

  if(imapcode != IMAP_RESP_OK) {
    failf(data, "Access denied. %c", imapcode);
    result = CURLE_LOGIN_DENIED;
  }
  else
    /* End of connect phase */
    imap_state(data, imapc, IMAP_STOP);

  return result;
}

/* For LIST and SEARCH responses */
static CURLcode imap_state_listsearch_resp(struct Curl_easy *data,
                                           struct imap_conn *imapc,
                                           int imapcode,
                                           imapstate instate)
{
  CURLcode result = CURLE_OK;
  char *line = curlx_dyn_ptr(&imapc->pp.recvbuf);
  size_t len = imapc->pp.nfinal;

  (void)instate;

  if(imapcode == '*') {
    /* Check if this response contains a literal (e.g. FETCH responses with
       body data). Literal syntax is {size}\r\n */
    const char *cr = memchr(line, '\r', len);
    size_t line_len = cr ? (size_t)(cr - line) : len;
    const char *ptr = memchr(line, '{', line_len);
    if(ptr) {
      curl_off_t size = 0;
      bool parsed = FALSE;
      ptr++;
      if(!curlx_str_number(&ptr, &size, CURL_OFF_T_MAX) &&
         !curlx_str_single(&ptr, '}'))
        parsed = TRUE;

      if(parsed) {
        struct pingpong *pp = &imapc->pp;
        size_t buffer_len = curlx_dyn_len(&pp->recvbuf);
        size_t after_header = buffer_len - pp->nfinal;

        /* This is a literal response, setup to receive the body data */
        infof(data, "Found %" FMT_OFF_T " bytes to download", size);

        /* First write the header line */
        result = Curl_client_write(data, CLIENTWRITE_BODY, line, len);
        if(result)
          return result;

        /* Handle data already in buffer after the header line */
        if(after_header > 0) {
          /* There is already data in the buffer that is part of the literal
             body or subsequent responses */
          size_t chunk = after_header;

          /* Keep only the data after the header line */
          curlx_dyn_tail(&pp->recvbuf, chunk);
          pp->nfinal = 0; /* done */

          /* Limit chunk to the literal size */
          if(chunk > (size_t)size)
            chunk = (size_t)size;

          if(chunk) {
            /* Write the literal body data */
            result = Curl_client_write(data, CLIENTWRITE_BODY,
                                       curlx_dyn_ptr(&pp->recvbuf), chunk);
            if(result)
              return result;
          }

          /* Handle remaining data in buffer (either more literal data or
             subsequent responses) */
          if(after_header > chunk) {
            /* Keep the data after the literal body */
            pp->overflow = after_header - chunk;
            curlx_dyn_tail(&pp->recvbuf, pp->overflow);
          }
          else {
            pp->overflow = 0;
            curlx_dyn_reset(&pp->recvbuf);
          }
        }
        else {
          /* No data in buffer yet, reset overflow */
          pp->overflow = 0;
        }

        if((CURL_OFF_T_MAX - size) < (curl_off_t)len)
          /* unlikely to actually be a transfer this big, but avoid integer
             overflow */
          size = CURL_OFF_T_MAX;
        else
          size += len;

        /* Progress size includes both header line and literal body */
        Curl_pgrsSetDownloadSize(data, size);

        if(data->req.bytecount == size)
          /* All data already transferred (header + literal body) */
          Curl_xfer_setup_nop(data);
        else {
          /* Setup to receive the literal body data.
             maxdownload and transfer size include both header line and
             literal body */
          data->req.maxdownload = size;
          Curl_xfer_setup_recv(data, FIRSTSOCKET, size);
        }
        /* End of DO phase */
        imap_state(data, imapc, IMAP_STOP);
      }
      else {
        /* Failed to parse literal, just write the line */
        result = Curl_client_write(data, CLIENTWRITE_BODY, line, len);
      }
    }
    else {
      /* No literal, just write the line as-is */
      result = Curl_client_write(data, CLIENTWRITE_BODY, line, len);
    }
  }
  else if(imapcode != IMAP_RESP_OK)
    result = CURLE_QUOTE_ERROR;
  else
    /* End of DO phase */
    imap_state(data, imapc, IMAP_STOP);

  return result;
}

/* For SELECT responses */
static CURLcode imap_state_select_resp(struct Curl_easy *data,
                                       struct imap_conn *imapc,
                                       struct IMAP *imap,
                                       int imapcode,
                                       imapstate instate)
{
  CURLcode result = CURLE_OK;
  (void)instate;

  if(imapcode == '*') {
    /* See if this is an UIDVALIDITY response */
    const char *line = curlx_dyn_ptr(&imapc->pp.recvbuf);
    size_t len = curlx_dyn_len(&imapc->pp.recvbuf);
    if((len >= 18) && checkprefix("OK [UIDVALIDITY ", &line[2])) {
      curl_off_t value;
      const char *p = &line[2] + strlen("OK [UIDVALIDITY ");
      if(!curlx_str_number(&p, &value, UINT_MAX)) {
        imapc->mb_uidvalidity = (unsigned int)value;
        imapc->mb_uidvalidity_set = TRUE;
      }
    }
  }
  else if(imapcode == IMAP_RESP_OK) {
    /* Check if the UIDVALIDITY has been specified and matches */
    if(imap->uidvalidity_set && imapc->mb_uidvalidity_set &&
       (imap->uidvalidity != imapc->mb_uidvalidity)) {
      failf(data, "Mailbox UIDVALIDITY has changed");
      result = CURLE_REMOTE_FILE_NOT_FOUND;
    }
    else {
      /* Note the currently opened mailbox on this connection */
      DEBUGASSERT(!imapc->mailbox);
      imapc->mailbox = curlx_strdup(imap->mailbox);
      if(!imapc->mailbox)
        return CURLE_OUT_OF_MEMORY;

      if(imap->custom)
        result = imap_perform_list(data, imapc, imap);
      else if(imap->query)
        result = imap_perform_search(data, imapc, imap);
      else
        result = imap_perform_fetch(data, imapc, imap);
    }
  }
  else {
    failf(data, "Select failed");
    result = CURLE_LOGIN_DENIED;
  }

  return result;
}

/* For the (first line of the) FETCH responses */
static CURLcode imap_state_fetch_resp(struct Curl_easy *data,
                                      struct imap_conn *imapc,
                                      int imapcode,
                                      imapstate instate)
{
  CURLcode result = CURLE_OK;
  struct pingpong *pp = &imapc->pp;
  const char *ptr = curlx_dyn_ptr(&imapc->pp.recvbuf);
  size_t len = imapc->pp.nfinal;
  bool parsed = FALSE;
  curl_off_t size = 0;

  (void)instate;

  if(imapcode != '*') {
    Curl_pgrsSetDownloadSize(data, -1);
    imap_state(data, imapc, IMAP_STOP);
    return CURLE_REMOTE_FILE_NOT_FOUND;
  }

  /* Something like this is received "* 1 FETCH (BODY[TEXT] {2021}\r" so parse
     the continuation data contained within the curly brackets */
  ptr = memchr(ptr, '{', len);
  if(ptr) {
    ptr++;
    if(!curlx_str_number(&ptr, &size, CURL_OFF_T_MAX) &&
       !curlx_str_single(&ptr, '}'))
      parsed = TRUE;
  }

  if(parsed) {
    infof(data, "Found %" FMT_OFF_T " bytes to download", size);
    Curl_pgrsSetDownloadSize(data, size);

    if(pp->overflow) {
      /* At this point there is a data in the receive buffer that is body
         content, send it as body and then skip it. Do note that there may
         even be additional "headers" after the body. */
      size_t chunk = pp->overflow;

      /* keep only the overflow */
      curlx_dyn_tail(&pp->recvbuf, chunk);
      pp->nfinal = 0; /* done */

      if(chunk > (size_t)size)
        /* The conversion from curl_off_t to size_t is always fine here */
        chunk = (size_t)size;

      if(!chunk) {
        /* no size, we are done with the data */
        imap_state(data, imapc, IMAP_STOP);
        return CURLE_OK;
      }
      result = Curl_client_write(data, CLIENTWRITE_BODY,
                                 curlx_dyn_ptr(&pp->recvbuf), chunk);
      if(result)
        return result;

      infof(data, "Written %zu bytes, %" FMT_OFF_TU
            " bytes are left for transfer", chunk, size - chunk);

      /* Have we used the entire overflow or just part of it?*/
      if(pp->overflow > chunk) {
        /* remember the remaining trailing overflow data */
        pp->overflow -= chunk;
        curlx_dyn_tail(&pp->recvbuf, pp->overflow);
      }
      else {
        pp->overflow = 0; /* handled */
        /* Free the cache */
        curlx_dyn_reset(&pp->recvbuf);
      }
    }

    if(data->req.bytecount == size)
      /* The entire data is already transferred! */
      Curl_xfer_setup_nop(data);
    else {
      /* IMAP download */
      data->req.maxdownload = size;
      Curl_xfer_setup_recv(data, FIRSTSOCKET, size);
    }
  }
  else {
    /* We do not know how to parse this line */
    failf(data, "Failed to parse FETCH response.");
    result = CURLE_WEIRD_SERVER_REPLY;
  }

  /* End of DO phase */
  imap_state(data, imapc, IMAP_STOP);

  return result;
}

/* For final FETCH responses performed after the download */
static CURLcode imap_state_fetch_final_resp(struct Curl_easy *data,
                                            struct imap_conn *imapc,
                                            int imapcode,
                                            imapstate instate)
{
  CURLcode result = CURLE_OK;

  (void)instate;

  if(imapcode != IMAP_RESP_OK)
    result = CURLE_WEIRD_SERVER_REPLY;
  else
    /* End of DONE phase */
    imap_state(data, imapc, IMAP_STOP);

  return result;
}

/* For APPEND responses */
static CURLcode imap_state_append_resp(struct Curl_easy *data,
                                       struct imap_conn *imapc,
                                       int imapcode,
                                       imapstate instate)
{
  CURLcode result = CURLE_OK;
  (void)instate;

  if(imapcode != '+') {
    result = CURLE_UPLOAD_FAILED;
  }
  else {
    /* Set the progress upload size */
    Curl_pgrsSetUploadSize(data, data->state.infilesize);

    /* IMAP upload */
    Curl_xfer_setup_send(data, FIRSTSOCKET);

    /* End of DO phase */
    imap_state(data, imapc, IMAP_STOP);
  }

  return result;
}

/* For final APPEND responses performed after the upload */
static CURLcode imap_state_append_final_resp(struct Curl_easy *data,
                                             struct imap_conn *imapc,
                                             int imapcode,
                                             imapstate instate)
{
  CURLcode result = CURLE_OK;

  (void)instate;

  if(imapcode != IMAP_RESP_OK)
    result = CURLE_UPLOAD_FAILED;
  else
    /* End of DONE phase */
    imap_state(data, imapc, IMAP_STOP);

  return result;
}

static CURLcode imap_pp_statemachine(struct Curl_easy *data,
                                     struct connectdata *conn)
{
  CURLcode result = CURLE_OK;
  int imapcode;
  struct imap_conn *imapc = Curl_conn_meta_get(conn, CURL_META_IMAP_CONN);
  struct IMAP *imap = Curl_meta_get(data, CURL_META_IMAP_EASY);
  struct pingpong *pp;
  size_t nread = 0;

  (void)data;
  if(!imapc || !imap)
    return CURLE_FAILED_INIT;
  pp = &imapc->pp;
  /* Busy upgrading the connection; right now all I/O is SSL/TLS, not IMAP */
upgrade_tls:
  if(imapc->state == IMAP_UPGRADETLS) {
    result = imap_perform_upgrade_tls(data, imapc, conn);
    if(result || (imapc->state == IMAP_UPGRADETLS))
      return result;
  }

  /* Flush any data that needs to be sent */
  if(pp->sendleft)
    return Curl_pp_flushsend(data, pp);

  do {
    /* Read the response from the server */
    result = Curl_pp_readresp(data, FIRSTSOCKET, pp, &imapcode, &nread);
    if(result)
      return result;

    /* Was there an error parsing the response line? */
    if(imapcode == -1)
      return CURLE_WEIRD_SERVER_REPLY;

    if(!imapcode)
      break;

    /* We have now received a full IMAP server response */
    switch(imapc->state) {
    case IMAP_SERVERGREET:
      result = imap_state_servergreet_resp(data, imapc,
                                           imapcode, imapc->state);
      break;

    case IMAP_CAPABILITY:
      result = imap_state_capability_resp(data, imapc, imapcode, imapc->state);
      break;

    case IMAP_STARTTLS:
      result = imap_state_starttls_resp(data, imapc, imapcode, imapc->state);
      /* During UPGRADETLS, leave the read loop as we need to connect
       * (e.g. TLS handshake) before we continue sending/receiving. */
      if(!result && (imapc->state == IMAP_UPGRADETLS))
        goto upgrade_tls;
      break;

    case IMAP_AUTHENTICATE:
      result = imap_state_auth_resp(data, imapc, imapcode, imapc->state);
      break;

    case IMAP_LOGIN:
      result = imap_state_login_resp(data, imapc, imapcode, imapc->state);
      break;

    case IMAP_LIST:
    case IMAP_SEARCH:
      result = imap_state_listsearch_resp(data, imapc, imapcode, imapc->state);
      break;

    case IMAP_SELECT:
      result = imap_state_select_resp(data, imapc, imap,
                                      imapcode, imapc->state);
      break;

    case IMAP_FETCH:
      result = imap_state_fetch_resp(data, imapc, imapcode, imapc->state);
      break;

    case IMAP_FETCH_FINAL:
      result = imap_state_fetch_final_resp(data, imapc,
                                           imapcode, imapc->state);
      break;

    case IMAP_APPEND:
      result = imap_state_append_resp(data, imapc, imapcode, imapc->state);
      break;

    case IMAP_APPEND_FINAL:
      result = imap_state_append_final_resp(data, imapc,
                                            imapcode, imapc->state);
      break;

    case IMAP_LOGOUT:
    default:
      /* internal error */
      imap_state(data, imapc, IMAP_STOP);
      break;
    }
  } while(!result && imapc->state != IMAP_STOP && Curl_pp_moredata(pp));

  return result;
}

/* Called repeatedly until done from multi.c */
static CURLcode imap_multi_statemach(struct Curl_easy *data, bool *done)
{
  CURLcode result = CURLE_OK;
  struct imap_conn *imapc =
    Curl_conn_meta_get(data->conn, CURL_META_IMAP_CONN);

  *done = FALSE;
  if(!imapc)
    return CURLE_FAILED_INIT;
  result = Curl_pp_statemach(data, &imapc->pp, FALSE, FALSE);
  *done = (imapc->state == IMAP_STOP);

  return result;
}

static CURLcode imap_block_statemach(struct Curl_easy *data,
                                     struct imap_conn *imapc,
                                     bool disconnecting)
{
  CURLcode result = CURLE_OK;

  while(imapc->state != IMAP_STOP && !result)
    result = Curl_pp_statemach(data, &imapc->pp, TRUE, disconnecting);

  return result;
}

/* For the IMAP "protocol connect" and "doing" phases only */
static CURLcode imap_pollset(struct Curl_easy *data,
                             struct easy_pollset *ps)
{
  struct imap_conn *imapc =
    Curl_conn_meta_get(data->conn, CURL_META_IMAP_CONN);
  return imapc ? Curl_pp_pollset(data, &imapc->pp, ps) : CURLE_OK;
}

/***********************************************************************
 *
 * imap_connect()
 *
 * This function should do everything that is to be considered a part of the
 * connection phase.
 *
 * The variable 'done' points to will be TRUE if the protocol-layer connect
 * phase is done when this function returns, or FALSE if not.
 */
static CURLcode imap_connect(struct Curl_easy *data, bool *done)
{
  struct imap_conn *imapc =
    Curl_conn_meta_get(data->conn, CURL_META_IMAP_CONN);
  CURLcode result = CURLE_OK;

  *done = FALSE; /* default to not done yet */
  if(!imapc)
    return CURLE_FAILED_INIT;

  /* Parse the URL options */
  result = imap_parse_url_options(data->conn, imapc);
  if(result)
    return result;

  /* Start off waiting for the server greeting response */
  imap_state(data, imapc, IMAP_SERVERGREET);

  /* Start off with an response id of '*' */
  curlx_strcopy(imapc->resptag, sizeof(imapc->resptag), "*", 1);

  result = imap_multi_statemach(data, done);

  return result;
}

/***********************************************************************
 *
 * imap_done()
 *
 * The DONE function. This does what needs to be done after a single DO has
 * performed.
 *
 * Input argument is already checked for validity.
 */
static CURLcode imap_done(struct Curl_easy *data, CURLcode status,
                          bool premature)
{
  CURLcode result = CURLE_OK;
  struct connectdata *conn = data->conn;
  struct imap_conn *imapc = Curl_conn_meta_get(conn, CURL_META_IMAP_CONN);
  struct IMAP *imap = Curl_meta_get(data, CURL_META_IMAP_EASY);

  (void)premature;

  if(!imapc)
    return CURLE_FAILED_INIT;
  if(!imap)
    return CURLE_OK;

  if(status) {
    connclose(conn, "IMAP done with bad status"); /* marked for closure */
    result = status;         /* use the already set error code */
  }
  else if(!data->set.connect_only &&
          ((!imap->custom && (imap->uid || imap->mindex)) ||
           (imap->custom && data->req.maxdownload > 0) ||
           data->state.upload || IS_MIME_POST(data))) {
    /* Handle responses after FETCH or APPEND transfer has finished.
       For custom commands, check if we set up a download which indicates
       a FETCH-like command with literal data. */

    if(!data->state.upload && !IS_MIME_POST(data))
      imap_state(data, imapc, IMAP_FETCH_FINAL);
    else {
      /* End the APPEND command first by sending an empty line */
      result = Curl_pp_sendf(data, &imapc->pp, "%s", "");
      if(!result)
        imap_state(data, imapc, IMAP_APPEND_FINAL);
    }

    /* Run the state-machine */
    if(!result)
      result = imap_block_statemach(data, imapc, FALSE);
  }

  imap_easy_reset(imap);
  return result;
}

/***********************************************************************
 *
 * imap_perform()
 *
 * This is the actual DO function for IMAP. Fetch or append a message, or do
 * other things according to the options previously setup.
 */
static CURLcode imap_perform(struct Curl_easy *data, bool *connected,
                             bool *dophase_done)
{
  /* This is IMAP and no proxy */
  CURLcode result = CURLE_OK;
  struct connectdata *conn = data->conn;
  struct imap_conn *imapc = Curl_conn_meta_get(conn, CURL_META_IMAP_CONN);
  struct IMAP *imap = Curl_meta_get(data, CURL_META_IMAP_EASY);
  bool selected = FALSE;

  DEBUGF(infof(data, "DO phase starts"));
  if(!imapc || !imap)
    return CURLE_FAILED_INIT;

  if(data->req.no_body) {
    /* Requested no body means no transfer */
    imap->transfer = PPTRANSFER_INFO;
  }

  *dophase_done = FALSE; /* not done yet */

  /* Determine if the requested mailbox (with the same UIDVALIDITY if set)
     has already been selected on this connection */
  if(imap->mailbox && imapc->mailbox &&
     curl_strequal(imap->mailbox, imapc->mailbox) &&
     (!imap->uidvalidity_set || !imapc->mb_uidvalidity_set ||
      (imap->uidvalidity == imapc->mb_uidvalidity)))
    selected = TRUE;

  /* Start the first command in the DO phase */
  if(data->state.upload || IS_MIME_POST(data))
    /* APPEND can be executed directly */
    result = imap_perform_append(data, imapc, imap);
  else if(imap->custom && (selected || !imap->mailbox))
    /* Custom command using the same mailbox or no mailbox */
    result = imap_perform_list(data, imapc, imap);
  else if(!imap->custom && selected && (imap->uid || imap->mindex))
    /* FETCH from the same mailbox */
    result = imap_perform_fetch(data, imapc, imap);
  else if(!imap->custom && selected && imap->query)
    /* SEARCH the current mailbox */
    result = imap_perform_search(data, imapc, imap);
  else if(imap->mailbox && !selected &&
          (imap->custom || imap->uid || imap->mindex || imap->query))
    /* SELECT the mailbox */
    result = imap_perform_select(data, imapc, imap);
  else
    /* LIST */
    result = imap_perform_list(data, imapc, imap);

  if(result)
    return result;

  /* Run the state-machine */
  result = imap_multi_statemach(data, dophase_done);

  *connected = Curl_conn_is_connected(conn, FIRSTSOCKET);

  if(*dophase_done)
    DEBUGF(infof(data, "DO phase is complete"));

  return result;
}

/***********************************************************************
 *
 * imap_do()
 *
 * This function is registered as 'curl_do' function. It decodes the path
 * parts etc as a wrapper to the actual DO function (imap_perform).
 *
 * The input argument is already checked for validity.
 */
static CURLcode imap_do(struct Curl_easy *data, bool *done)
{
  struct IMAP *imap = Curl_meta_get(data, CURL_META_IMAP_EASY);
  CURLcode result = CURLE_OK;
  *done = FALSE; /* default to false */

  if(!imap)
    return CURLE_FAILED_INIT;
  /* Parse the URL path */
  result = imap_parse_url_path(data, imap);
  if(result)
    return result;

  /* Parse the custom request */
  result = imap_parse_custom_request(data, imap);
  if(result)
    return result;

  result = imap_regular_transfer(data, imap, done);

  return result;
}

/***********************************************************************
 *
 * imap_disconnect()
 *
 * Disconnect from an IMAP server. Cleanup protocol-specific per-connection
 * resources. BLOCKING.
 */
static CURLcode imap_disconnect(struct Curl_easy *data,
                                struct connectdata *conn, bool dead_connection)
{
  struct imap_conn *imapc = Curl_conn_meta_get(conn, CURL_META_IMAP_CONN);

  (void)data;
  if(imapc) {
    /* We cannot send quit unconditionally. If this connection is stale or
       bad in any way (pingpong has pending data to send),
       sending quit and waiting around here will make the
       disconnect wait in vain and cause more problems than we need to. */
    if(!dead_connection && conn->bits.protoconnstart &&
       !Curl_pp_needs_flush(data, &imapc->pp)) {
      if(!imap_perform_logout(data, imapc))
        (void)imap_block_statemach(data, imapc, TRUE); /* ignore errors */
    }
  }
  return CURLE_OK;
}

/* Call this when the DO phase has completed */
static CURLcode imap_dophase_done(struct Curl_easy *data,
                                  struct IMAP *imap,
                                  bool connected)
{
  (void)connected;

  if(imap->transfer != PPTRANSFER_BODY)
    /* no data to transfer */
    Curl_xfer_setup_nop(data);

  return CURLE_OK;
}

/* Called from multi.c while DOing */
static CURLcode imap_doing(struct Curl_easy *data, bool *dophase_done)
{
  struct IMAP *imap = Curl_meta_get(data, CURL_META_IMAP_EASY);
  CURLcode result;

  if(!imap)
    return CURLE_FAILED_INIT;

  result = imap_multi_statemach(data, dophase_done);
  if(result)
    DEBUGF(infof(data, "DO phase failed"));
  else if(*dophase_done) {
    result = imap_dophase_done(data, imap, FALSE /* not connected */);

    DEBUGF(infof(data, "DO phase is complete"));
  }

  return result;
}

/***********************************************************************
 *
 * imap_regular_transfer()
 *
 * The input argument is already checked for validity.
 *
 * Performs all commands done before a regular transfer between a local and a
 * remote host.
 */
static CURLcode imap_regular_transfer(struct Curl_easy *data,
                                      struct IMAP *imap,
                                      bool *dophase_done)
{
  CURLcode result = CURLE_OK;
  bool connected = FALSE;

  /* Make sure size is unknown at this point */
  data->req.size = -1;

  /* Set the progress data */
  Curl_pgrsReset(data);

  /* Carry out the perform */
  result = imap_perform(data, &connected, dophase_done);

  /* Perform post DO phase operations if necessary */
  if(!result && *dophase_done)
    result = imap_dophase_done(data, imap, connected);

  return result;
}

static void imap_easy_reset(struct IMAP *imap)
{
  Curl_safefree(imap->mailbox);
  Curl_safefree(imap->uid);
  Curl_safefree(imap->mindex);
  Curl_safefree(imap->section);
  Curl_safefree(imap->partial);
  Curl_safefree(imap->query);
  Curl_safefree(imap->custom);
  Curl_safefree(imap->custom_params);
  /* Clear the transfer mode for the next request */
  imap->transfer = PPTRANSFER_BODY;
}

static void imap_easy_dtor(void *key, size_t klen, void *entry)
{
  struct IMAP *imap = entry;
  (void)key;
  (void)klen;
  imap_easy_reset(imap);
  curlx_free(imap);
}

static void imap_conn_dtor(void *key, size_t klen, void *entry)
{
  struct imap_conn *imapc = entry;
  (void)key;
  (void)klen;
  Curl_pp_disconnect(&imapc->pp);
  curlx_dyn_free(&imapc->dyn);
  Curl_safefree(imapc->mailbox);
  curlx_free(imapc);
}

static CURLcode imap_setup_connection(struct Curl_easy *data,
                                      struct connectdata *conn)
{
  struct imap_conn *imapc;
  struct pingpong *pp;
  struct IMAP *imap;

  imapc = curlx_calloc(1, sizeof(*imapc));
  if(!imapc)
    return CURLE_OUT_OF_MEMORY;

  pp = &imapc->pp;
  PINGPONG_SETUP(pp, imap_pp_statemachine, imap_endofresp);

  /* Set the default preferred authentication type and mechanism */
  imapc->preftype = IMAP_TYPE_ANY;
  Curl_sasl_init(&imapc->sasl, data, &saslimap);

  curlx_dyn_init(&imapc->dyn, DYN_IMAP_CMD);
  Curl_pp_init(pp, Curl_pgrs_now(data));

  if(Curl_conn_meta_set(conn, CURL_META_IMAP_CONN, imapc, imap_conn_dtor))
    return CURLE_OUT_OF_MEMORY;

  imap = curlx_calloc(1, sizeof(struct IMAP));
  if(!imap ||
     Curl_meta_set(data, CURL_META_IMAP_EASY, imap, imap_easy_dtor))
    return CURLE_OUT_OF_MEMORY;

  return CURLE_OK;
}

/***********************************************************************
 *
 * imap_sendf()
 *
 * Sends the formatted string as an IMAP command to the server.
 *
 * Designed to never block.
 */
static CURLcode imap_sendf(struct Curl_easy *data,
                           struct imap_conn *imapc,
                           const char *fmt, ...)
{
  CURLcode result = CURLE_OK;

  DEBUGASSERT(fmt);

  /* Calculate the tag based on the connection ID and command ID */
  curl_msnprintf(imapc->resptag, sizeof(imapc->resptag), "%c%03d",
                 'A' + curlx_sltosi((long)(data->conn->connection_id % 26)),
                 ++imapc->cmdid);

  /* start with a blank buffer */
  curlx_dyn_reset(&imapc->dyn);

  /* append tag + space + fmt */
  result = curlx_dyn_addf(&imapc->dyn, "%s %s", imapc->resptag, fmt);
  if(!result) {
    va_list ap;
    va_start(ap, fmt);
#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wformat-nonliteral"
#endif
    result = Curl_pp_vsendf(data, &imapc->pp, curlx_dyn_ptr(&imapc->dyn), ap);
#ifdef __clang__
#pragma clang diagnostic pop
#endif
    va_end(ap);
  }
  return result;
}

/***********************************************************************
 *
 * imap_atom()
 *
 * Checks the input string for characters that need escaping and returns an
 * atom ready for sending to the server.
 *
 * The returned string needs to be freed.
 *
 */
static char *imap_atom(const char *str, bool escape_only)
{
  struct dynbuf line;
  size_t nclean;
  size_t len;

  if(!str)
    return NULL;

  len = strlen(str);
  nclean = strcspn(str, "() {%*]\\\"");
  if(len == nclean)
    /* nothing to escape, return a strdup */
    return curlx_strdup(str);

  curlx_dyn_init(&line, 2000);

  if(!escape_only && curlx_dyn_addn(&line, "\"", 1))
    return NULL;

  while(*str) {
    if((*str == '\\' || *str == '"') &&
       curlx_dyn_addn(&line, "\\", 1))
      return NULL;
    if(curlx_dyn_addn(&line, str, 1))
      return NULL;
    str++;
  }

  if(!escape_only && curlx_dyn_addn(&line, "\"", 1))
    return NULL;

  return curlx_dyn_ptr(&line);
}

/***********************************************************************
 *
 * imap_is_bchar()
 *
 * Portable test of whether the specified char is a "bchar" as defined in the
 * grammar of RFC-5092.
 */
static bool imap_is_bchar(char ch)
{
  /* Performing the alnum check with this macro is faster because of ASCII
     arithmetic */
  if(ISALNUM(ch))
    return TRUE;

  switch(ch) {
  /* bchar */
  case ':':
  case '@':
  case '/':
  /* bchar -> achar */
  case '&':
  case '=':
  /* bchar -> achar -> uchar -> unreserved (without alphanumeric) */
  case '-':
  case '.':
  case '_':
  case '~':
  /* bchar -> achar -> uchar -> sub-delims-sh */
  case '!':
  case '$':
  case '\'':
  case '(':
  case ')':
  case '*':
  case '+':
  case ',':
  /* bchar -> achar -> uchar -> pct-encoded */
  case '%': /* HEXDIG chars are already included above */
    return TRUE;

  default:
    return FALSE;
  }
}

/***********************************************************************
 *
 * imap_parse_url_options()
 *
 * Parse the URL login options.
 */
static CURLcode imap_parse_url_options(struct connectdata *conn,
                                       struct imap_conn *imapc)
{
  CURLcode result = CURLE_OK;
  const char *ptr = conn->options;
  bool prefer_login = FALSE;

  while(!result && ptr && *ptr) {
    const char *key = ptr;
    const char *value;

    while(*ptr && *ptr != '=')
      ptr++;

    value = ptr + 1;

    while(*ptr && *ptr != ';')
      ptr++;

    if(curl_strnequal(key, "AUTH=+LOGIN", 11)) {
      /* User prefers plaintext LOGIN over any SASL, including SASL LOGIN */
      prefer_login = TRUE;
      imapc->sasl.prefmech = SASL_AUTH_NONE;
    }
    else if(curl_strnequal(key, "AUTH=", 5)) {
      prefer_login = FALSE;
      result = Curl_sasl_parse_url_auth_option(&imapc->sasl,
                                               value, ptr - value);
    }
    else {
      prefer_login = FALSE;
      result = CURLE_URL_MALFORMAT;
    }

    if(*ptr == ';')
      ptr++;
  }

  if(prefer_login)
    imapc->preftype = IMAP_TYPE_CLEARTEXT;
  else {
    switch(imapc->sasl.prefmech) {
    case SASL_AUTH_NONE:
      imapc->preftype = IMAP_TYPE_NONE;
      break;
    case SASL_AUTH_DEFAULT:
      imapc->preftype = IMAP_TYPE_ANY;
      break;
    default:
      imapc->preftype = IMAP_TYPE_SASL;
      break;
    }
  }

  return result;
}

/***********************************************************************
 *
 * imap_parse_url_path()
 *
 * Parse the URL path into separate path components.
 *
 */
static CURLcode imap_parse_url_path(struct Curl_easy *data,
                                    struct IMAP *imap)
{
  /* The imap struct is already initialised in imap_connect() */
  CURLcode result = CURLE_OK;
  const char *begin = &data->state.up.path[1]; /* skip leading slash */
  const char *ptr = begin;

  /* See how much of the URL is a valid path and decode it */
  while(imap_is_bchar(*ptr))
    ptr++;

  if(ptr != begin) {
    /* Remove the trailing slash if present */
    const char *end = ptr;
    if(end > begin && end[-1] == '/')
      end--;

    result = Curl_urldecode(begin, end - begin, &imap->mailbox, NULL,
                            REJECT_CTRL);
    if(result)
      return result;
  }
  else
    imap->mailbox = NULL;

  /* There can be any number of parameters in the form ";NAME=VALUE" */
  while(*ptr == ';') {
    char *name;
    char *value;
    size_t valuelen;

    /* Find the length of the name parameter */
    begin = ++ptr;
    while(*ptr && *ptr != '=')
      ptr++;

    if(!*ptr)
      return CURLE_URL_MALFORMAT;

    /* Decode the name parameter */
    result = Curl_urldecode(begin, ptr - begin, &name, NULL,
                            REJECT_CTRL);
    if(result)
      return result;

    /* Find the length of the value parameter */
    begin = ++ptr;
    while(imap_is_bchar(*ptr))
      ptr++;

    /* Decode the value parameter */
    result = Curl_urldecode(begin, ptr - begin, &value, &valuelen,
                            REJECT_CTRL);
    if(result) {
      curlx_free(name);
      return result;
    }

    DEBUGF(infof(data, "IMAP URL parameter '%s' = '%s'", name, value));

    /* Process the known hierarchical parameters (UIDVALIDITY, UID, SECTION
       and PARTIAL) stripping of the trailing slash character if it is
       present.

       Note: Unknown parameters trigger a URL_MALFORMAT error. */
    if(valuelen > 0 && value[valuelen - 1] == '/')
      value[valuelen - 1] = '\0';
    if(valuelen) {
      if(curl_strequal(name, "UIDVALIDITY") && !imap->uidvalidity_set) {
        curl_off_t num;
        const char *p = (const char *)value;
        if(!curlx_str_number(&p, &num, UINT_MAX)) {
          imap->uidvalidity = (unsigned int)num;
          imap->uidvalidity_set = TRUE;
        }
        curlx_free(value);
      }
      else if(curl_strequal(name, "UID") && !imap->uid) {
        imap->uid = value;
      }
      else if(curl_strequal(name, "MAILINDEX") && !imap->mindex) {
        imap->mindex = value;
      }
      else if(curl_strequal(name, "SECTION") && !imap->section) {
        imap->section = value;
      }
      else if(curl_strequal(name, "PARTIAL") && !imap->partial) {
        imap->partial = value;
      }
      else {
        curlx_free(name);
        curlx_free(value);
        return CURLE_URL_MALFORMAT;
      }
    }
    else
      /* blank? */
      curlx_free(value);
    curlx_free(name);
  }

  /* Does the URL contain a query parameter? Only valid when we have a mailbox
     and no UID as per RFC-5092 */
  if(imap->mailbox && !imap->uid && !imap->mindex) {
    /* Get the query parameter, URL decoded */
    CURLUcode uc = curl_url_get(data->state.uh, CURLUPART_QUERY, &imap->query,
                                CURLU_URLDECODE);
    if(uc == CURLUE_OUT_OF_MEMORY)
      return CURLE_OUT_OF_MEMORY;
  }

  /* Any extra stuff at the end of the URL is an error */
  if(*ptr)
    return CURLE_URL_MALFORMAT;

  return CURLE_OK;
}

/***********************************************************************
 *
 * imap_parse_custom_request()
 *
 * Parse the custom request.
 */
static CURLcode imap_parse_custom_request(struct Curl_easy *data,
                                          struct IMAP *imap)
{
  CURLcode result = CURLE_OK;
  const char *custom = data->set.str[STRING_CUSTOMREQUEST];

  if(custom) {
    /* URL decode the custom request */
    result = Curl_urldecode(custom, 0, &imap->custom, NULL, REJECT_CTRL);

    /* Extract the parameters if specified */
    if(!result) {
      const char *params = imap->custom;

      while(*params && *params != ' ')
        params++;

      if(*params) {
        imap->custom_params = curlx_strdup(params);
        imap->custom[params - imap->custom] = '\0';

        if(!imap->custom_params)
          result = CURLE_OUT_OF_MEMORY;
      }
    }
  }

  return result;
}

#endif /* CURL_DISABLE_IMAP */
