cbm: Add parsing bits for cell broadcast messages

This allows to parse the CBMs parameters like channel, part number and
message text. We parse uncompressed GSM7 and UCS2 encodings as
described in 3GPP TS 23.038.

Signed-off-by: Guido Günther <agx@sigxcpu.org>

1 files changed, 225 insertions, 0 deletions

diff --git a/src/mm-cbm-part.c b/src/mm-cbm-part.c
new file mode 100644
index 00000000..34bbfa55
--- /dev/null
+++ b/src/mm-cbm-part.c
@@ -0,0 +1,225 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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:
+ *
+ * Copyright (C) 2024 Guido Günther <agx@sigxcpu.org>
+ */
+
+#include <glib.h>
+
+#include <ModemManager.h>
+#define _LIBMM_INSIDE_MM
+#include <libmm-glib.h>
+
+#include "mm-common-helpers.h"
+#include "mm-helper-enums-types.h"
+#include "mm-cbm-part.h"
+#include "mm-charsets.h"
+#include "mm-log.h"
+#include "mm-sms-part-3gpp.h"
+
+#define CBS_DATA_CODING_GROUP_MASK           0b11110000
+#define CBS_DATA_CODING_LANG_GSM7            0b00000000
+#define CBS_DATA_CODING_GSM7                 0b00010000
+#define CBS_DATA_CODING_UCS2                 0b00010001
+#define CBS_DATA_CODING_GENERAL_NO_CLASS     0b01000000
+#define CBS_DATA_CODING_GENERAL_CLASS        0b01010000
+#define CBS_DATA_CODING_GENERAL_CHARSET_MASK 0b00001100
+#define CBS_DATA_CODING_GENERAL_GSM7         0b00000000
+#define CBS_DATA_CODING_GENERAL_8BIT         0b00000100
+#define CBS_DATA_CODING_GENERAL_UCS2         0b00001000
+#define CBS_DATA_CODING_UDH                  0b10010000
+
+struct _MMCbmPart {
+    guint16 serial;
+    guint16 channel;
+
+    guint8 num_parts;
+    guint8 part_num;
+
+    gchar *text;
+    MMSmsEncoding encoding;
+};
+
+
+MMCbmPart *
+mm_cbm_part_new_from_pdu (const gchar  *hexpdu,
+                          gpointer      log_object,
+                          GError      **error)
+{
+    g_autofree guint8 *pdu = NULL;
+    gsize              pdu_len;
+
+    /* Convert PDU from hex to binary */
+    pdu = mm_utils_hexstr2bin (hexpdu, -1, &pdu_len, error);
+    if (!pdu) {
+        g_prefix_error (error, "Couldn't convert 3GPP PDU from hex to binary: ");
+        return NULL;
+    }
+
+    return mm_cbm_part_new_from_binary_pdu (pdu, pdu_len, log_object, error);
+}
+
+MMCbmPart *
+mm_cbm_part_new_from_binary_pdu (const guint8  *pdu,
+                                 gsize          pdu_len,
+                                 gpointer       log_object,
+                                 GError       **error)
+{
+    MMCbmPart *cbm_part;
+    MMCbmGeoScope scope;
+    guint offset = 0;
+    guint16 serial, group;
+    int len;
+    g_autofree gchar *text = NULL;
+
+    cbm_part = mm_cbm_part_new ();
+
+    mm_obj_dbg (log_object, "parsing CBM...");
+
+#define PDU_SIZE_CHECK(required_size, check_descr_str)                 \
+    if (pdu_len < required_size) {                                     \
+        g_set_error (error,                                            \
+                     MM_CORE_ERROR,                                    \
+                     MM_CORE_ERROR_FAILED,                             \
+                     "PDU too short, %s: %" G_GSIZE_FORMAT " < %u",    \
+                     check_descr_str,                                  \
+                     pdu_len,                                          \
+                     required_size);                                   \
+        mm_cbm_part_free (cbm_part);                                   \
+        return NULL;                                                   \
+    }
+
+    /* Serial number (2 bytes) */
+    PDU_SIZE_CHECK (offset + 2, "cannot read serial number");
+    serial = pdu[offset] << 8 | pdu[offset+1];
+    scope = CBM_SERIAL_GEO_SCOPE (serial);
+    switch (scope) {
+    case MM_CBM_GEO_SCOPE_CELL_NORMAL:
+        mm_obj_dbg (log_object, "  normal cell cbm scope");
+        break;
+    case MM_CBM_GEO_SCOPE_PLMN:
+        mm_obj_dbg (log_object, "  plmn cbm scope");
+        break;
+    case MM_CBM_GEO_SCOPE_AREA:
+        mm_obj_dbg (log_object, "  area cbm scope");
+        break;
+    case MM_CBM_GEO_SCOPE_CELL_IMMEDIATE:
+        mm_obj_dbg (log_object, "  immediate cell cbm scope");
+        break;
+    default:
+        mm_cbm_part_free (cbm_part);
+        g_set_error (error,
+                     MM_CORE_ERROR,
+                     MM_CORE_ERROR_FAILED,
+                     "Unhandled cbm message scope: 0x%02x",
+                     scope);
+        return NULL;
+    }
+    cbm_part->serial = serial;
+    offset+=2;
+
+    /* Channel / Message identifier */
+    PDU_SIZE_CHECK (offset + 2, "cannot read channel");
+    cbm_part->channel = pdu[offset] << 8 | pdu[offset+1];
+    offset+=2;
+
+    PDU_SIZE_CHECK (offset + 1, "cannot read encoding scheme");
+    group = pdu[offset] & CBS_DATA_CODING_GROUP_MASK;
+    /* Order matches 3GPP TS 23.038 Chapter 5 */
+    if (group == CBS_DATA_CODING_LANG_GSM7) {
+        cbm_part->encoding = MM_SMS_ENCODING_GSM7;
+    } else if (pdu[offset] == CBS_DATA_CODING_GSM7) {
+        PDU_SIZE_CHECK (offset + 4, "cannot skip lang");
+        offset+=3;
+        cbm_part->encoding = MM_SMS_ENCODING_GSM7;
+    } else if (pdu[offset] == CBS_DATA_CODING_UCS2) {
+        PDU_SIZE_CHECK (offset + 3, "cannot skip lang");
+        offset+=2;
+        cbm_part->encoding = MM_SMS_ENCODING_UCS2;
+    } else if ((group == CBS_DATA_CODING_GENERAL_CLASS) ||
+               (group == CBS_DATA_CODING_GENERAL_NO_CLASS) ||
+               (group == CBS_DATA_CODING_UDH)) {
+        guint16 charset = pdu[offset] & CBS_DATA_CODING_GENERAL_CHARSET_MASK;
+        /* We don't handle compression or 8 bit data */
+        if (charset == CBS_DATA_CODING_GENERAL_GSM7)
+            cbm_part->encoding = MM_SMS_ENCODING_GSM7;
+        else if (charset == CBS_DATA_CODING_GENERAL_UCS2)
+            cbm_part->encoding = MM_SMS_ENCODING_UCS2;
+    } else {
+        mm_cbm_part_free (cbm_part);
+        g_set_error (error,
+                     MM_CORE_ERROR,
+                     MM_CORE_ERROR_FAILED,
+                     "Unhandled cbm message encoding: 0x%02x",
+                     pdu[offset]);
+        return NULL;
+    }
+    offset++;
+
+    PDU_SIZE_CHECK (offset + 1, "cannot read page parameter");
+    cbm_part->num_parts = (pdu[offset] & 0x0F);
+    cbm_part->part_num = (pdu[offset] & 0xF0) >> 4;
+    offset++;
+
+    switch (cbm_part->encoding) {
+    case MM_SMS_ENCODING_GSM7:
+        len = ((pdu_len - offset) * 8) / 7;
+        break;
+    case MM_SMS_ENCODING_UCS2:
+        len = pdu_len - offset;
+        break;
+    case MM_SMS_ENCODING_8BIT:
+    case MM_SMS_ENCODING_UNKNOWN:
+    default:
+        g_assert_not_reached ();
+    }
+    PDU_SIZE_CHECK (offset + 1, "cannot read message text");
+    text = mm_sms_decode_text (&pdu[offset],
+                               len,
+                               cbm_part->encoding,
+                               0,
+                               log_object,
+                               error);
+    if (!text) {
+        mm_cbm_part_free (cbm_part);
+        return NULL;
+    }
+    cbm_part->text = g_steal_pointer (&text);
+
+    return cbm_part;
+}
+
+MMCbmPart *
+mm_cbm_part_new (void)
+{
+    return g_slice_new0 (MMCbmPart);
+}
+
+void
+mm_cbm_part_free (MMCbmPart *part)
+{
+  g_clear_pointer (&part->text, g_free);
+  g_slice_free (MMCbmPart, part);
+}
+
+#define PART_GET_FUNC(type, name)             \
+    type                                      \
+    mm_cbm_part_get_##name (MMCbmPart *self)  \
+    {                                         \
+        return self->name;                    \
+    }
+
+PART_GET_FUNC (guint, part_num)
+PART_GET_FUNC (guint, num_parts)
+PART_GET_FUNC (const char *, text)
+PART_GET_FUNC (guint16, channel)
+PART_GET_FUNC (guint16, serial)