PSYC util lib: receiving/transmitting/logging PSYC messages

3 files changed, 1028 insertions, 125 deletions

diff --git a/src/psyc/Makefile.am b/src/psyc/Makefile.am
index 212c383ac..6a4f249a9 100644
--- a/src/psyc/Makefile.am
+++ b/src/psyc/Makefile.am
@@ -17,21 +17,35 @@ if USE_COVERAGE
   XLIB = -lgcov
 endif
 
-lib_LTLIBRARIES = libgnunetpsyc.la
+lib_LTLIBRARIES = libgnunetpsycutil.la libgnunetpsyc.la
+
+libgnunetpsycutil_la_SOURCES = \
+  psyc_util_lib.c
+libgnunetpsycutil_la_LIBADD = \
+  $(top_builddir)/src/util/libgnunetutil.la \
+  $(top_builddir)/src/env/libgnunetenv.la \
+  $(GN_LIBINTL) $(XLIB)
+libgnunetpsycutil_la_LDFLAGS = \
+  $(GN_LIB_LDFLAGS)  $(WINFLAGS) \
+  -version-info 0:0:0
+libgnunetpsycutil_la_DEPENDENCIES = \
+  $(top_builddir)/src/util/libgnunetutil.la \
+  $(top_builddir)/src/env/libgnunetenv.la
 
 libgnunetpsyc_la_SOURCES = \
-  psyc_api.c psyc.h \
-  psyc_common.c
+  psyc_api.c psyc.h
 libgnunetpsyc_la_LIBADD = \
   $(top_builddir)/src/util/libgnunetutil.la \
   $(top_builddir)/src/env/libgnunetenv.la \
+  $(top_builddir)/src/psyc/libgnunetpsycutil.la \
   $(GN_LIBINTL) $(XLIB)
 libgnunetpsyc_la_LDFLAGS = \
   $(GN_LIB_LDFLAGS)  $(WINFLAGS) \
   -version-info 0:0:0
 libgnunetpsyc_la_DEPENDENCIES = \
   $(top_builddir)/src/util/libgnunetutil.la \
-  $(top_builddir)/src/env/libgnunetenv.la
+  $(top_builddir)/src/env/libgnunetenv.la \
+  $(top_builddir)/src/psyc/libgnunetpsycutil.la
 
 bin_PROGRAMS =
 
@@ -39,19 +53,20 @@ libexec_PROGRAMS = \
  gnunet-service-psyc
 
 gnunet_service_psyc_SOURCES = \
- gnunet-service-psyc.c \
- psyc_common.c
+  gnunet-service-psyc.c
 gnunet_service_psyc_LDADD = \
   $(top_builddir)/src/util/libgnunetutil.la \
   $(top_builddir)/src/statistics/libgnunetstatistics.la \
   $(top_builddir)/src/multicast/libgnunetmulticast.la \
   $(top_builddir)/src/psycstore/libgnunetpsycstore.la \
+  $(top_builddir)/src/psyc/libgnunetpsycutil.la \
   $(GN_LIBINTL)
 gnunet_service_psyc_DEPENDENCIES = \
   $(top_builddir)/src/util/libgnunetutil.la \
   $(top_builddir)/src/statistics/libgnunetstatistics.la \
   $(top_builddir)/src/multicast/libgnunetmulticast.la \
-  $(top_builddir)/src/psycstore/libgnunetpsycstore.la
+  $(top_builddir)/src/psycstore/libgnunetpsycstore.la \
+  $(top_builddir)/src/psyc/libgnunetpsycutil.la
 gnunet_service_psyc_CFLAGS = $(AM_CFLAGS)
 
 
diff --git a/src/psyc/psyc_common.c b/src/psyc/psyc_common.c
deleted file mode 100644
index af9cc0c6f..000000000
--- a/src/psyc/psyc_common.c
+++ /dev/null
@@ -1,118 +0,0 @@
-/*
- * This file is part of GNUnet
- * (C) 2013 Christian Grothoff (and other contributing authors)
- *
- * GNUnet is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published
- * by the Free Software Foundation; either version 3, or (at your
- * option) any later version.
- *
- * GNUnet is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with GNUnet; see the file COPYING.  If not, write to the
- * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
- * Boston, MA 02111-1307, USA.
- */
-
-/**
- * @file psyc/psyc_common.c
- * @brief Common functions for PSYC
- * @author Gabor X Toth
- */
-
-#include <inttypes.h>
-#include "psyc.h"
-
-/**
- * Check if @a data contains a series of valid message parts.
- *
- * @param      data_size    Size of @a data.
- * @param      data         Data.
- * @param[out] first_ptype  Type of first message part.
- * @param[out] last_ptype   Type of last message part.
- *
- * @return Number of message parts found in @a data.
- *         or GNUNET_SYSERR if the message contains invalid parts.
- */
-int
-GNUNET_PSYC_check_message_parts (uint16_t data_size, const char *data,
-                                 uint16_t *first_ptype, uint16_t *last_ptype)
-{
-  const struct GNUNET_MessageHeader *pmsg;
-  uint16_t parts = 0, ptype = 0, psize = 0, pos = 0;
-  if (NULL != first_ptype)
-    *first_ptype = 0;
-  if (NULL != last_ptype)
-    *last_ptype = 0;
-
-  for (pos = 0; pos < data_size; pos += psize, parts++)
-  {
-    pmsg = (const struct GNUNET_MessageHeader *) (data + pos);
-    psize = ntohs (pmsg->size);
-    ptype = ntohs (pmsg->type);
-    if (0 == parts && NULL != first_ptype)
-      *first_ptype = ptype;
-    if (NULL != last_ptype
-        && *last_ptype < GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_END)
-      *last_ptype = ptype;
-    if (psize < sizeof (*pmsg)
-        || pos + psize > data_size
-        || ptype < GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_METHOD
-        || GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_CANCEL < ptype)
-    {
-      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
-                  "Invalid message part of type %u and size %u.\n",
-                  ptype, psize);
-      return GNUNET_SYSERR;
-    }
-    /* FIXME: check message part order */
-  }
-  return parts;
-}
-
-
-void
-GNUNET_PSYC_log_message (enum GNUNET_ErrorType kind,
-                         const struct GNUNET_MessageHeader *msg)
-{
-  uint16_t size = ntohs (msg->size);
-  uint16_t type = ntohs (msg->type);
-  GNUNET_log (kind, "Message of type %d and size %u:\n", type, size);
-  switch (type)
-  {
-  case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE:
-  {
-    struct GNUNET_PSYC_MessageHeader *pmsg
-      = (struct GNUNET_PSYC_MessageHeader *) msg;
-    GNUNET_log (kind, "\tID: %" PRIu64 "\tflags: %x" PRIu32 "\n",
-                GNUNET_ntohll (pmsg->message_id), ntohl (pmsg->flags));
-    break;
-  }
-  case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_METHOD:
-  {
-    struct GNUNET_PSYC_MessageMethod *meth
-      = (struct GNUNET_PSYC_MessageMethod *) msg;
-    GNUNET_log (kind, "\t%.*s\n", size - sizeof (*meth), &meth[1]);
-    break;
-  }
-  case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_MODIFIER:
-  {
-    struct GNUNET_PSYC_MessageModifier *mod
-      = (struct GNUNET_PSYC_MessageModifier *) msg;
-    uint16_t name_size = ntohs (mod->name_size);
-    char oper = ' ' < mod->oper ? mod->oper : ' ';
-    GNUNET_log (kind, "\t%c%.*s\t%.*s\n", oper, name_size, &mod[1],
-                size - sizeof (*mod) - name_size - 1,
-                ((char *) &mod[1]) + name_size + 1);
-    break;
-  }
-  case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_MOD_CONT:
-  case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_DATA:
-    GNUNET_log (kind, "\t%.*s\n", size - sizeof (*msg), &msg[1]);
-    break;
-  }
-}
diff --git a/src/psyc/psyc_util_lib.c b/src/psyc/psyc_util_lib.c
new file mode 100644
index 000000000..6dd968190
--- /dev/null
+++ b/src/psyc/psyc_util_lib.c
@@ -0,0 +1,1006 @@
+/*
+ * This file is part of GNUnet
+ * (C) 2013 Christian Grothoff (and other contributing authors)
+ *
+ * GNUnet is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published
+ * by the Free Software Foundation; either version 3, or (at your
+ * option) any later version.
+ *
+ * GNUnet is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNUnet; see the file COPYING.  If not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+/**
+ * @file psyc/psyc_common.c
+ * @brief PSYC utilities; receiving/transmitting/logging PSYC messages.
+ * @author Gabor X Toth
+ */
+
+#include <inttypes.h>
+
+#include "platform.h"
+#include "gnunet_util_lib.h"
+#include "gnunet_psyc_service.h"
+#include "gnunet_psyc_util_lib.h"
+
+#define LOG(kind,...) GNUNET_log_from (kind, "psyc-util",__VA_ARGS__)
+
+/**
+ * Message receive states.
+ */
+enum GNUNET_PSYC_MessageState
+{
+  GNUNET_PSYC_MESSAGE_STATE_START    = 0,
+  GNUNET_PSYC_MESSAGE_STATE_HEADER   = 1,
+  GNUNET_PSYC_MESSAGE_STATE_METHOD   = 2,
+  GNUNET_PSYC_MESSAGE_STATE_MODIFIER = 3,
+  GNUNET_PSYC_MESSAGE_STATE_MOD_CONT = 4,
+  GNUNET_PSYC_MESSAGE_STATE_DATA     = 5,
+  GNUNET_PSYC_MESSAGE_STATE_END      = 6,
+  GNUNET_PSYC_MESSAGE_STATE_CANCEL   = 7,
+  GNUNET_PSYC_MESSAGE_STATE_ERROR    = 8,
+};
+
+
+struct GNUNET_PSYC_TransmitHandle
+{
+  /**
+   * Client connection to service.
+   */
+  struct GNUNET_CLIENT_MANAGER_Connection *client;
+
+  /**
+   * Message currently being received from the client.
+   */
+  struct GNUNET_MessageHeader *msg;
+
+  /**
+   * Callback to request next modifier from client.
+   */
+  GNUNET_PSYC_TransmitNotifyModifier notify_mod;
+
+  /**
+   * Closure for the notify callbacks.
+   */
+  void *notify_mod_cls;
+
+  /**
+   * Callback to request next data fragment from client.
+   */
+  GNUNET_PSYC_TransmitNotifyData notify_data;
+
+  /**
+   * Closure for the notify callbacks.
+   */
+  void *notify_data_cls;
+
+  /**
+   * Modifier of the environment that is currently being transmitted.
+   */
+  struct GNUNET_ENV_Modifier *mod;
+
+  /**
+   * 
+   */
+  const char *mod_value;
+  size_t mod_value_size;
+
+  /**
+   * State of the current message being received from client.
+   */
+  enum GNUNET_PSYC_MessageState state;
+
+  /**
+   * Number of PSYC_TRANSMIT_ACK messages we are still waiting for.
+   */
+  uint8_t acks_pending;
+
+  /**
+   * Is transmission paused?
+   */
+  uint8_t paused;
+
+  /**
+   * Are we currently transmitting a message?
+   */
+  uint8_t in_transmit;
+};
+
+
+
+struct GNUNET_PSYC_ReceiveHandle
+{
+  /**
+   * Message part callback.
+   */
+  GNUNET_PSYC_MessageCallback message_cb;
+
+  /**
+   * Message part callback for historic message.
+   */
+  GNUNET_PSYC_MessageCallback hist_message_cb;
+
+  /**
+   * Closure for the callbacks.
+   */
+  void *cb_cls;
+
+  /**
+   * ID of the message being received from the PSYC service.
+   */
+  uint64_t message_id;
+
+  /**
+   * Public key of the slave from which a message is being received.
+   */
+  struct GNUNET_CRYPTO_EddsaPublicKey slave_key;
+
+  /**
+   * State of the currently being received message from the PSYC service.
+   */
+  enum GNUNET_PSYC_MessageState state;
+
+  /**
+   * Flags for the currently being received message from the PSYC service.
+   */
+  enum GNUNET_PSYC_MessageFlags flags;
+
+  /**
+   * Expected value size for the modifier being received from the PSYC service.
+   */
+  uint32_t mod_value_size_expected;
+
+  /**
+   * Actual value size for the modifier being received from the PSYC service.
+   */
+  uint32_t mod_value_size;
+};
+
+
+void
+GNUNET_PSYC_log_message (enum GNUNET_ErrorType kind,
+                         const struct GNUNET_MessageHeader *msg)
+{
+  uint16_t size = ntohs (msg->size);
+  uint16_t type = ntohs (msg->type);
+  GNUNET_log (kind, "Message of type %d and size %u:\n", type, size);
+  switch (type)
+  {
+  case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE:
+  {
+    struct GNUNET_PSYC_MessageHeader *pmsg
+      = (struct GNUNET_PSYC_MessageHeader *) msg;
+    GNUNET_log (kind, "\tID: %" PRIu64 "\tflags: %x" PRIu32 "\n",
+                GNUNET_ntohll (pmsg->message_id), ntohl (pmsg->flags));
+    break;
+  }
+  case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_METHOD:
+  {
+    struct GNUNET_PSYC_MessageMethod *meth
+      = (struct GNUNET_PSYC_MessageMethod *) msg;
+    GNUNET_log (kind, "\t%.*s\n", size - sizeof (*meth), &meth[1]);
+    break;
+  }
+  case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_MODIFIER:
+  {
+    struct GNUNET_PSYC_MessageModifier *mod
+      = (struct GNUNET_PSYC_MessageModifier *) msg;
+    uint16_t name_size = ntohs (mod->name_size);
+    char oper = ' ' < mod->oper ? mod->oper : ' ';
+    GNUNET_log (kind, "\t%c%.*s\t%.*s\n", oper, name_size, &mod[1],
+                size - sizeof (*mod) - name_size - 1,
+                ((char *) &mod[1]) + name_size + 1);
+    break;
+  }
+  case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_MOD_CONT:
+  case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_DATA:
+    GNUNET_log (kind, "\t%.*s\n", size - sizeof (*msg), &msg[1]);
+    break;
+  }
+}
+
+
+/**** Transmitting messages ****/
+
+
+/**
+ * Create a transmission handle.
+ */
+struct GNUNET_PSYC_TransmitHandle *
+GNUNET_PSYC_transmit_create (struct GNUNET_CLIENT_MANAGER_Connection *client)
+{
+  struct GNUNET_PSYC_TransmitHandle *tmit = GNUNET_malloc (sizeof (*tmit));
+  tmit->client = client;
+  return tmit;
+}
+
+
+/**
+ * Destroy a transmission handle.
+ */
+void
+GNUNET_PSYC_transmit_destroy (struct GNUNET_PSYC_TransmitHandle *tmit)
+{
+  GNUNET_free (tmit);
+}
+
+
+/**
+ * Queue a message part for transmission.
+ *
+ * The message part is added to the current message buffer.
+ * When this buffer is full, it is added to the transmission queue.
+ *
+ * @param tmit  Transmission handle.
+ * @param msg  Message part, or NULL.
+ * @param end  End of message? #GNUNET_YES or #GNUNET_NO.
+ */
+static void
+transmit_queue_insert (struct GNUNET_PSYC_TransmitHandle *tmit,
+                       const struct GNUNET_MessageHeader *msg,
+                       uint8_t end)
+{
+  uint16_t size = (NULL != msg) ? ntohs (msg->size) : 0;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Queueing message of type %u and size %u (end: %u)).\n",
+       ntohs (msg->type), size, end);
+
+  if (NULL != tmit->msg)
+  {
+    if (NULL == msg
+        || GNUNET_MULTICAST_FRAGMENT_MAX_PAYLOAD < tmit->msg->size + size)
+    {
+      /* End of message or buffer is full, add it to transmission queue
+       * and start with empty buffer */
+      tmit->msg->type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE);
+      tmit->msg->size = htons (tmit->msg->size);
+      GNUNET_CLIENT_MANAGER_transmit (tmit->client, tmit->msg);
+      tmit->msg = NULL;
+      tmit->acks_pending++;
+    }
+    else
+    {
+      /* Message fits in current buffer, append */
+      tmit->msg = GNUNET_realloc (tmit->msg, tmit->msg->size + size);
+      memcpy ((char *) tmit->msg + tmit->msg->size, msg, size);
+      tmit->msg->size += size;
+    }
+  }
+
+  if (NULL == tmit->msg && NULL != msg)
+  {
+    /* Empty buffer, copy over message. */
+    tmit->msg = GNUNET_malloc (sizeof (*tmit->msg) + size);
+    tmit->msg->size = sizeof (*tmit->msg) + size;
+    memcpy (&tmit->msg[1], msg, size);
+  }
+
+  if (NULL != tmit->msg
+      && (GNUNET_YES == end
+          || (GNUNET_MULTICAST_FRAGMENT_MAX_PAYLOAD
+              < tmit->msg->size + sizeof (struct GNUNET_MessageHeader))))
+  {
+    /* End of message or buffer is full, add it to transmission queue. */
+    tmit->msg->type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE);
+    tmit->msg->size = htons (tmit->msg->size);
+    GNUNET_CLIENT_MANAGER_transmit (tmit->client, tmit->msg);
+    tmit->msg = NULL;
+    tmit->acks_pending++;
+  }
+
+  if (GNUNET_YES == end)
+    tmit->in_transmit = GNUNET_NO;
+}
+
+
+/**
+ * Request data from client to transmit.
+ *
+ * @param tmit  Transmission handle.
+ */
+static void
+transmit_data (struct GNUNET_PSYC_TransmitHandle *tmit)
+{
+  uint16_t data_size = GNUNET_PSYC_DATA_MAX_PAYLOAD;
+  char data[GNUNET_MULTICAST_FRAGMENT_MAX_PAYLOAD] = "";
+  struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) data;
+  msg->type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_DATA);
+
+  int notify_ret = tmit->notify_data (tmit->notify_data_cls, &data_size, &msg[1]);
+  switch (notify_ret)
+  {
+  case GNUNET_NO:
+    if (0 == data_size)
+    {
+      /* Transmission paused, nothing to send. */
+      tmit->paused = GNUNET_YES;
+      return;
+    }
+    break;
+
+  case GNUNET_YES:
+    tmit->state = GNUNET_PSYC_MESSAGE_STATE_END;
+    break;
+
+  default:
+    LOG (GNUNET_ERROR_TYPE_ERROR,
+         "TransmitNotifyData callback returned error when requesting data.\n");
+
+    tmit->state = GNUNET_PSYC_MESSAGE_STATE_CANCEL;
+    msg->type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_CANCEL);
+    msg->size = htons (sizeof (*msg));
+    transmit_queue_insert (tmit, msg, GNUNET_YES);
+    return;
+  }
+
+  if (0 < data_size)
+  {
+    GNUNET_assert (data_size <= GNUNET_PSYC_DATA_MAX_PAYLOAD);
+    msg->size = htons (sizeof (*msg) + data_size);
+    transmit_queue_insert (tmit, msg, !notify_ret);
+  }
+
+  /* End of message. */
+  if (GNUNET_YES == notify_ret)
+  {
+    msg->type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_END);
+    msg->size = htons (sizeof (*msg));
+    transmit_queue_insert (tmit, msg, GNUNET_YES);
+  }
+}
+
+
+/**
+ * Request a modifier from a client to transmit.
+ *
+ * @param tmit  Transmission handle.
+ */
+static void
+transmit_mod (struct GNUNET_PSYC_TransmitHandle *tmit)
+{
+  uint16_t max_data_size, data_size;
+  char data[GNUNET_MULTICAST_FRAGMENT_MAX_PAYLOAD] = "";
+  struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) data;
+  int notify_ret;
+
+  switch (tmit->state)
+  {
+  case GNUNET_PSYC_MESSAGE_STATE_MODIFIER:
+  {
+    struct GNUNET_PSYC_MessageModifier *mod
+      = (struct GNUNET_PSYC_MessageModifier *) msg;
+    max_data_size = data_size = GNUNET_PSYC_MODIFIER_MAX_PAYLOAD;
+    msg->type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_MODIFIER);
+    msg->size = sizeof (struct GNUNET_PSYC_MessageModifier);
+    notify_ret = tmit->notify_mod (tmit->notify_mod_cls, &data_size, &mod[1],
+                                   &mod->oper, &mod->value_size);
+    mod->name_size = strnlen ((char *) &mod[1], data_size);
+    if (mod->name_size < data_size)
+    {
+      mod->value_size = htonl (mod->value_size);
+      mod->name_size = htons (mod->name_size);
+    }
+    else if (0 < data_size)
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Got invalid modifier name.\n");
+      notify_ret = GNUNET_SYSERR;
+    }
+    break;
+  }
+  case GNUNET_PSYC_MESSAGE_STATE_MOD_CONT:
+  {
+    max_data_size = data_size = GNUNET_PSYC_MOD_CONT_MAX_PAYLOAD;
+    msg->type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_MOD_CONT);
+    msg->size = sizeof (struct GNUNET_MessageHeader);
+    notify_ret = tmit->notify_mod (tmit->notify_mod_cls,
+                                   &data_size, &msg[1], NULL, NULL);
+    break;
+  }
+  default:
+    GNUNET_assert (0);
+  }
+
+  switch (notify_ret)
+  {
+  case GNUNET_NO:
+    if (0 == data_size)
+    { /* Transmission paused, nothing to send. */
+      tmit->paused = GNUNET_YES;
+      return;
+    }
+    tmit->state = GNUNET_PSYC_MESSAGE_STATE_MOD_CONT;
+    break;
+
+  case GNUNET_YES:
+    if (0 == data_size)
+    {
+      /* End of modifiers. */
+      tmit->state = GNUNET_PSYC_MESSAGE_STATE_DATA;
+      if (0 == tmit->acks_pending)
+        transmit_data (tmit);
+
+      return;
+    }
+    tmit->state = GNUNET_PSYC_MESSAGE_STATE_MODIFIER;
+    break;
+
+  default:
+    LOG (GNUNET_ERROR_TYPE_ERROR,
+         "TransmitNotifyModifier callback returned error "
+         "when requesting a modifier.\n");
+
+    tmit->state = GNUNET_PSYC_MESSAGE_STATE_CANCEL;
+    msg->type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_CANCEL);
+    msg->size = htons (sizeof (*msg));
+
+    transmit_queue_insert (tmit, msg, GNUNET_YES);
+    return;
+  }
+
+  if (0 < data_size)
+  {
+    GNUNET_assert (data_size <= max_data_size);
+    msg->size = htons (msg->size + data_size);
+    transmit_queue_insert (tmit, msg, GNUNET_NO);
+  }
+
+  transmit_mod (tmit);
+}
+
+
+int
+transmit_notify_env (void *cls, uint16_t *data_size, void *data, uint8_t *oper,
+                     uint32_t *full_value_size)
+
+{
+  struct GNUNET_PSYC_TransmitHandle *tmit = cls;
+  uint16_t name_size = 0;
+  size_t value_size = 0;
+  const char *value = NULL;
+
+  if (NULL != oper && NULL != tmit->mod)
+  { /* New modifier */
+    tmit->mod = tmit->mod->next;
+    if (NULL == tmit->mod)
+    { /* No more modifiers, continue with data */
+      *data_size = 0;
+      return GNUNET_YES;
+    }
+
+    GNUNET_assert (tmit->mod->value_size < UINT32_MAX);
+    *full_value_size = tmit->mod->value_size;
+    *oper = tmit->mod->oper;
+    name_size = strlen (tmit->mod->name);
+
+    if (name_size + 1 + tmit->mod->value_size <= *data_size)
+    {
+      *data_size = name_size + 1 + tmit->mod->value_size;
+    }
+    else
+    {
+      tmit->mod_value_size = tmit->mod->value_size;
+      value_size = *data_size - name_size - 1;
+      tmit->mod_value_size -= value_size;
+      tmit->mod_value = tmit->mod->value + value_size;
+    }
+
+    memcpy (data, tmit->mod->name, name_size);
+    ((char *)data)[name_size] = '\0';
+    memcpy ((char *)data + name_size + 1, tmit->mod->value, value_size);
+  }
+  else if (NULL != tmit->mod_value && 0 < tmit->mod_value_size)
+  { /* Modifier continuation */
+    value = tmit->mod_value;
+    if (tmit->mod_value_size <= *data_size)
+    {
+      value_size = tmit->mod_value_size;
+      tmit->mod_value = NULL;
+    }
+    else
+    {
+      value_size = *data_size;
+      tmit->mod_value += value_size;
+    }
+    tmit->mod_value_size -= value_size;
+
+    if (*data_size < value_size)
+    {
+      LOG (GNUNET_ERROR_TYPE_DEBUG,
+           "Value in environment larger than buffer: %u < %zu\n",
+           *data_size, value_size);
+      *data_size = 0;
+      return GNUNET_NO;
+    }
+
+    *data_size = value_size;
+    memcpy (data, value, value_size);
+  }
+
+  return 0 == tmit->mod_value_size ? GNUNET_YES : GNUNET_NO;
+}
+
+
+/**
+ * Transmit a message.
+ *
+ * @param tmit         Transmission handle.
+ * @param method_name  Which method should be invoked.
+ * @param env          Environment for the message.
+ *   Should stay available until the first call to notify_data.
+ *   Can be NULL if there are no modifiers or @a notify_mod is provided instead.
+ * @param notify_mod   Function to call to obtain modifiers.
+ *   Can be NULL if there are no modifiers or @a env is provided instead.
+ * @param notify_data  Function to call to obtain fragments of the data.
+ * @param notify_cls   Closure for @a notify_mod and @a notify_data.
+ * @param flags        Flags for the message being transmitted.
+ *
+ * @return #GNUNET_OK if the transmission was started.
+ *         #GNUNET_SYSERR if another transmission is already going on.
+ */
+int
+GNUNET_PSYC_transmit_message (struct GNUNET_PSYC_TransmitHandle *tmit,
+                              const char *method_name,
+                              const struct GNUNET_ENV_Environment *env,
+                              GNUNET_PSYC_TransmitNotifyModifier notify_mod,
+                              GNUNET_PSYC_TransmitNotifyData notify_data,
+                              void *notify_cls,
+                              uint32_t flags)
+{
+  if (GNUNET_NO != tmit->in_transmit)
+    return GNUNET_SYSERR;
+  tmit->in_transmit = GNUNET_YES;
+
+  size_t size = strlen (method_name) + 1;
+  struct GNUNET_PSYC_MessageMethod *pmeth;
+  tmit->msg = GNUNET_malloc (sizeof (*tmit->msg) + sizeof (*pmeth) + size);
+  tmit->msg->size = sizeof (*tmit->msg) + sizeof (*pmeth) + size;
+
+  pmeth = (struct GNUNET_PSYC_MessageMethod *) &tmit->msg[1];
+  pmeth->header.type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_METHOD);
+  pmeth->header.size = htons (sizeof (*pmeth) + size);
+  pmeth->flags = htonl (flags);
+  memcpy (&pmeth[1], method_name, size);
+
+  tmit->state = GNUNET_PSYC_MESSAGE_STATE_MODIFIER;
+  tmit->notify_data = notify_data;
+  tmit->notify_data_cls = notify_cls;
+
+  if (NULL != notify_mod)
+  {
+    tmit->notify_mod = notify_mod;
+    tmit->notify_mod_cls = notify_cls;
+  }
+  else
+  {
+    tmit->notify_mod = &transmit_notify_env;
+    tmit->notify_mod_cls = tmit;
+    tmit->mod
+      = (NULL != env)
+      ? GNUNET_ENV_environment_head (env)
+      : NULL;
+  }
+
+  transmit_mod (tmit);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Resume transmission.
+ *
+ * @param tmit  Transmission handle.
+ */
+void
+GNUNET_PSYC_transmit_resume (struct GNUNET_PSYC_TransmitHandle *tmit)
+{
+  if (0 == tmit->acks_pending)
+  {
+    tmit->paused = GNUNET_NO;
+    transmit_data (tmit);
+  }
+}
+
+
+/**
+ * Abort transmission request.
+ *
+ * @param tmit  Transmission handle.
+ */
+void
+GNUNET_PSYC_transmit_cancel (struct GNUNET_PSYC_TransmitHandle *tmit)
+{
+  if (GNUNET_NO == tmit->in_transmit)
+    return;
+
+  tmit->state = GNUNET_PSYC_MESSAGE_STATE_CANCEL;
+  tmit->in_transmit = GNUNET_NO;
+  tmit->paused = GNUNET_NO;
+
+  /* FIXME */
+  struct GNUNET_MessageHeader msg;
+  msg.type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_DATA);
+  msg.type = htons (GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_CANCEL);
+  msg.size = htons (sizeof (msg));
+  transmit_queue_insert (tmit, &msg, GNUNET_YES);
+}
+
+
+/**
+ * Got acknowledgement of a transmitted message part, continue transmission.
+ *
+ * @param tmit  Transmission handle.
+ */
+void
+GNUNET_PSYC_transmit_got_ack (struct GNUNET_PSYC_TransmitHandle *tmit)
+{
+  if (0 == tmit->acks_pending)
+  {
+    LOG (GNUNET_ERROR_TYPE_WARNING, "Ignoring extraneous message ACK\n");
+    GNUNET_break (0);
+    return;
+  }
+  tmit->acks_pending--;
+
+  switch (tmit->state)
+  {
+  case GNUNET_PSYC_MESSAGE_STATE_MODIFIER:
+  case GNUNET_PSYC_MESSAGE_STATE_MOD_CONT:
+    if (GNUNET_NO == tmit->paused)
+      transmit_mod (tmit);
+    break;
+
+  case GNUNET_PSYC_MESSAGE_STATE_DATA:
+    if (GNUNET_NO == tmit->paused)
+      transmit_data (tmit);
+    break;
+
+  case GNUNET_PSYC_MESSAGE_STATE_END:
+  case GNUNET_PSYC_MESSAGE_STATE_CANCEL:
+    break;
+
+  default:
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "Ignoring message ACK in state %u.\n", tmit->state);
+  }
+}
+
+
+/**** Receiving messages ****/
+
+
+/**
+ * Create handle for receiving messages.
+ */
+struct GNUNET_PSYC_ReceiveHandle *
+GNUNET_PSYC_receive_create (GNUNET_PSYC_MessageCallback message_cb,
+                            GNUNET_PSYC_MessageCallback hist_message_cb,
+                            void *cb_cls)
+{
+  struct GNUNET_PSYC_ReceiveHandle *recv = GNUNET_malloc (sizeof (*recv));
+  recv->message_cb = message_cb;
+  recv->hist_message_cb = hist_message_cb;
+  recv->cb_cls = cb_cls;
+  return recv;
+}
+
+
+/**
+ * Destroy handle for receiving messages.
+ */
+void
+GNUNET_PSYC_receive_destroy (struct GNUNET_PSYC_ReceiveHandle *recv)
+{
+  GNUNET_free (recv);
+}
+
+
+/**
+ * Reset stored data related to the last received message.
+ */
+void
+GNUNET_PSYC_receive_reset (struct GNUNET_PSYC_ReceiveHandle *recv)
+{
+  recv->state = GNUNET_PSYC_MESSAGE_STATE_START;
+  recv->flags = 0;
+  recv->message_id = 0;
+  recv->mod_value_size = 0;
+  recv->mod_value_size_expected = 0;
+}
+
+
+static void
+recv_error (struct GNUNET_PSYC_ReceiveHandle *recv)
+{
+  GNUNET_PSYC_MessageCallback message_cb
+    = recv->flags & GNUNET_PSYC_MESSAGE_HISTORIC
+    ? recv->hist_message_cb
+    : recv->message_cb;
+
+  if (NULL != message_cb)
+    message_cb (recv->cb_cls, recv->message_id, recv->flags, NULL);
+
+  GNUNET_PSYC_receive_reset (recv);
+}
+
+
+/**
+ * Handle incoming PSYC message.
+ *
+ * @param recv  Receive handle.
+ * @param msg   The message.
+ *
+ * @return #GNUNET_OK on success,
+ *         #GNUNET_SYSERR on receive error.
+ */
+int
+GNUNET_PSYC_receive_message (struct GNUNET_PSYC_ReceiveHandle *recv,
+                             const struct GNUNET_PSYC_MessageHeader *msg)
+{
+  uint16_t size = ntohs (msg->header.size);
+  uint32_t flags = ntohl (msg->flags);
+
+  GNUNET_PSYC_log_message (GNUNET_ERROR_TYPE_DEBUG,
+                           (struct GNUNET_MessageHeader *) msg);
+
+  if (GNUNET_PSYC_MESSAGE_STATE_START == recv->state)
+  {
+    recv->message_id = GNUNET_ntohll (msg->message_id);
+    recv->flags = flags;
+    recv->slave_key = msg->slave_key;
+    recv->mod_value_size = 0;
+    recv->mod_value_size_expected = 0;
+  }
+  else if (GNUNET_ntohll (msg->message_id) != recv->message_id)
+  {
+    // FIXME
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         "Unexpected message ID. Got: %" PRIu64 ", expected: %" PRIu64 "\n",
+         GNUNET_ntohll (msg->message_id), recv->message_id);
+    GNUNET_break_op (0);
+    recv_error (recv);
+    return GNUNET_SYSERR;
+  }
+  else if (flags != recv->flags)
+  {
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         "Unexpected message flags. Got: %lu, expected: %lu\n",
+         flags, recv->flags);
+    GNUNET_break_op (0);
+    recv_error (recv);
+    return GNUNET_SYSERR;
+  }
+
+  uint16_t pos = 0, psize = 0, ptype, size_eq, size_min;
+
+  for (pos = 0; sizeof (*msg) + pos < size; pos += psize)
+  {
+    const struct GNUNET_MessageHeader *pmsg
+      = (const struct GNUNET_MessageHeader *) ((char *) &msg[1] + pos);
+    psize = ntohs (pmsg->size);
+    ptype = ntohs (pmsg->type);
+    size_eq = size_min = 0;
+
+    if (psize < sizeof (*pmsg) || sizeof (*msg) + pos + psize > size)
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                  "Dropping message of type %u with invalid size %u.\n",
+                  ptype, psize);
+      recv_error (recv);
+      return GNUNET_SYSERR;
+    }
+
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Received message part from PSYC.\n");
+    GNUNET_PSYC_log_message (GNUNET_ERROR_TYPE_DEBUG, pmsg);
+
+    switch (ptype)
+    {
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_METHOD:
+      size_min = sizeof (struct GNUNET_PSYC_MessageMethod);
+      break;
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_MODIFIER:
+      size_min = sizeof (struct GNUNET_PSYC_MessageModifier);
+      break;
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_MOD_CONT:
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_DATA:
+      size_min = sizeof (struct GNUNET_MessageHeader);
+      break;
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_END:
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_CANCEL:
+      size_eq = sizeof (struct GNUNET_MessageHeader);
+      break;
+    default:
+      GNUNET_break_op (0);
+      recv_error (recv);
+      return GNUNET_SYSERR;
+    }
+
+    if (! ((0 < size_eq && psize == size_eq)
+           || (0 < size_min && size_min <= psize)))
+    {
+      GNUNET_break_op (0);
+      recv_error (recv);
+      return GNUNET_SYSERR;
+    }
+
+    switch (ptype)
+    {
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_METHOD:
+    {
+      struct GNUNET_PSYC_MessageMethod *meth
+        = (struct GNUNET_PSYC_MessageMethod *) pmsg;
+
+      if (GNUNET_PSYC_MESSAGE_STATE_START != recv->state)
+      {
+        LOG (GNUNET_ERROR_TYPE_WARNING,
+             "Dropping out of order message method (%u).\n",
+             recv->state);
+        /* It is normal to receive an incomplete message right after connecting,
+         * but should not happen later.
+         * FIXME: add a check for this condition.
+         */
+        GNUNET_break_op (0);
+        recv_error (recv);
+        return GNUNET_SYSERR;
+      }
+
+      if ('\0' != *((char *) meth + psize - 1))
+      {
+        LOG (GNUNET_ERROR_TYPE_WARNING,
+             "Dropping message with malformed method. "
+             "Message ID: %" PRIu64 "\n", recv->message_id);
+        GNUNET_break_op (0);
+        recv_error (recv);
+        return GNUNET_SYSERR;
+      }
+      recv->state = GNUNET_PSYC_MESSAGE_STATE_METHOD;
+      break;
+    }
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_MODIFIER:
+    {
+      if (!(GNUNET_PSYC_MESSAGE_STATE_METHOD == recv->state
+            || GNUNET_PSYC_MESSAGE_STATE_MODIFIER == recv->state
+            || GNUNET_PSYC_MESSAGE_STATE_MOD_CONT == recv->state))
+      {
+        LOG (GNUNET_ERROR_TYPE_WARNING,
+             "Dropping out of order message modifier (%u).\n",
+             recv->state);
+        GNUNET_break_op (0);
+        recv_error (recv);
+        return GNUNET_SYSERR;
+      }
+
+      struct GNUNET_PSYC_MessageModifier *mod
+        = (struct GNUNET_PSYC_MessageModifier *) pmsg;
+
+      uint16_t name_size = ntohs (mod->name_size);
+      recv->mod_value_size_expected = ntohl (mod->value_size);
+      recv->mod_value_size = psize - sizeof (*mod) - name_size - 1;
+
+      if (psize < sizeof (*mod) + name_size + 1
+          || '\0' != *((char *) &mod[1] + name_size)
+          || recv->mod_value_size_expected < recv->mod_value_size)
+      {
+        LOG (GNUNET_ERROR_TYPE_WARNING, "Dropping malformed modifier.\n");
+        GNUNET_break_op (0);
+        recv_error (recv);
+        return GNUNET_SYSERR;
+      }
+      recv->state = GNUNET_PSYC_MESSAGE_STATE_MODIFIER;
+      break;
+    }
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_MOD_CONT:
+    {
+      recv->mod_value_size += psize - sizeof (*pmsg);
+
+      if (!(GNUNET_PSYC_MESSAGE_STATE_MODIFIER == recv->state
+            || GNUNET_PSYC_MESSAGE_STATE_MOD_CONT == recv->state)
+          || recv->mod_value_size_expected < recv->mod_value_size)
+      {
+        LOG (GNUNET_ERROR_TYPE_WARNING,
+             "Dropping out of order message modifier continuation "
+             "!(%u == %u || %u == %u) || %lu < %lu.\n",
+             GNUNET_PSYC_MESSAGE_STATE_MODIFIER, recv->state,
+             GNUNET_PSYC_MESSAGE_STATE_MOD_CONT, recv->state,
+             recv->mod_value_size_expected, recv->mod_value_size);
+        GNUNET_break_op (0);
+        recv_error (recv);
+        return GNUNET_SYSERR;
+      }
+      break;
+    }
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_DATA:
+    {
+      if (recv->state < GNUNET_PSYC_MESSAGE_STATE_METHOD
+          || recv->mod_value_size_expected != recv->mod_value_size)
+      {
+        LOG (GNUNET_ERROR_TYPE_WARNING,
+             "Dropping out of order message data fragment "
+             "(%u < %u || %lu != %lu).\n",
+             recv->state, GNUNET_PSYC_MESSAGE_STATE_METHOD,
+             recv->mod_value_size_expected, recv->mod_value_size);
+
+        GNUNET_break_op (0);
+        recv_error (recv);
+        return GNUNET_SYSERR;
+      }
+      recv->state = GNUNET_PSYC_MESSAGE_STATE_DATA;
+      break;
+    }
+    }
+
+    GNUNET_PSYC_MessageCallback message_cb
+      = recv->flags & GNUNET_PSYC_MESSAGE_HISTORIC
+      ? recv->hist_message_cb
+      : recv->message_cb;
+
+    if (NULL != message_cb)
+      message_cb (recv->cb_cls, recv->message_id, recv->flags, pmsg);
+
+    switch (ptype)
+    {
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_END:
+    case GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_CANCEL:
+      GNUNET_PSYC_receive_reset (recv);
+      break;
+    }
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Check if @a data contains a series of valid message parts.
+ *
+ * @param      data_size    Size of @a data.
+ * @param      data         Data.
+ * @param[out] first_ptype  Type of first message part.
+ * @param[out] last_ptype   Type of last message part.
+ *
+ * @return Number of message parts found in @a data.
+ *         or GNUNET_SYSERR if the message contains invalid parts.
+ */
+int
+GNUNET_PSYC_receive_check_parts (uint16_t data_size, const char *data,
+                                 uint16_t *first_ptype, uint16_t *last_ptype)
+{
+  const struct GNUNET_MessageHeader *pmsg;
+  uint16_t parts = 0, ptype = 0, psize = 0, pos = 0;
+  if (NULL != first_ptype)
+    *first_ptype = 0;
+  if (NULL != last_ptype)
+    *last_ptype = 0;
+
+  for (pos = 0; pos < data_size; pos += psize, parts++)
+  {
+    pmsg = (const struct GNUNET_MessageHeader *) (data + pos);
+    psize = ntohs (pmsg->size);
+    ptype = ntohs (pmsg->type);
+    if (0 == parts && NULL != first_ptype)
+      *first_ptype = ptype;
+    if (NULL != last_ptype
+        && *last_ptype < GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_END)
+      *last_ptype = ptype;
+    if (psize < sizeof (*pmsg)
+        || pos + psize > data_size
+        || ptype < GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_METHOD
+        || GNUNET_MESSAGE_TYPE_PSYC_MESSAGE_CANCEL < ptype)
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                  "Invalid message part of type %u and size %u.\n",
+                  ptype, psize);
+      return GNUNET_SYSERR;
+    }
+    /* FIXME: check message part order */
+  }
+  return parts;
+}