modem-helpers: implement less strict APN comparison

u-blox modems will append a string showing the MCC and MNC info to the access
point name listed in AT+CGDCONT? responses. We will try to detect when that
happens, and we just accept the match.

The logic doesn't just look for a string prefix; it also looks for the special
MCC + MNC suffix, which is much more restrictive, to try to avoid false
positives.

src/mm-broadband-bearer.c

@@ -891,13 +891,14 @@ parse_pdp_list (MMBaseModem             *modem,
                 const gchar *apn;
 
                 apn = mm_bearer_properties_get_apn (mm_base_bearer_peek_config (MM_BASE_BEARER (ctx->self)));
-                if (apn && !g_ascii_strcasecmp (pdp->apn, apn)) {
+                /* First requested, then existing */
+                if (mm_3gpp_cmp_apn_name (apn, pdp->apn)) {
                     gchar *ip_family_str;
 
-                    /* Found a PDP context with the same CID and PDP type, we'll use it. */
+                    /* Found a PDP context with the same APN and PDP type, we'll use it. */
                     ip_family_str = mm_bearer_ip_family_build_string_from_mask (pdp->pdp_type);
                     mm_dbg ("Found PDP context with CID %u and PDP type %s for APN '%s'",
-                            pdp->cid, ip_family_str, pdp->apn);
+                            pdp->cid, ip_family_str, apn);
                     cid = pdp->cid;
                     ctx->use_existing_cid = TRUE;
                     g_free (ip_family_str);

src/mm-modem-helpers.c

@@ -1030,6 +1030,50 @@ out:
     return TRUE;
 }
 
+/*************************************************************************/
+/* Logic to compare two APN names */
+
+gboolean
+mm_3gpp_cmp_apn_name (const gchar *requested,
+                      const gchar *existing)
+{
+    size_t requested_len;
+    size_t existing_len;
+
+    /* Both must be given to compare properly */
+    if (!existing || !existing[0] || !requested || !requested[0])
+        return FALSE;
+
+    requested_len = strlen (requested);
+
+    /*
+     * 1) The requested APN should be at least the prefix of the existing one.
+     */
+    if (g_ascii_strncasecmp (existing, requested, requested_len) != 0)
+        return FALSE;
+
+    /*
+     * 2) If the existing one is actually the same as the requested one (i.e.
+     *    there are no more different chars in the existing one), we're done.
+     */
+    if (existing[requested_len] == '\0')
+        return TRUE;
+
+    existing_len = strlen (existing);
+
+    /* 3) Special handling for PDP contexts reported by u-blox modems once the
+     *    contexts have been activated at least once:
+     *      "ac.vodafone.es.MNC001.MCC214.GPRS" should match "ac.vodafone.es"
+     */
+    if ((existing_len > (requested_len + 14)) &&
+        g_ascii_strncasecmp (&existing[requested_len], ".mnc", 4) == 0 &&
+        g_ascii_strncasecmp (&existing[requested_len + 7], ".mcc", 4) == 0)
+        return TRUE;
+
+    /* No match */
+    return FALSE;
+}
+
 /*************************************************************************/
 
 static void

src/mm-modem-helpers.h

@@ -127,6 +127,10 @@ gboolean mm_3gpp_parse_cops_read_response (const gchar              *response,
                                            MMModemAccessTechnology  *out_act,
                                            GError                  **error);
 
+/* Logic to compare two APN names */
+gboolean mm_3gpp_cmp_apn_name (const gchar *requested,
+                               const gchar *existing);
+
 /* AT+CGDCONT=? (PDP context format) test parser */
 typedef struct {
     guint min_cid;

src/tests/test-modem-helpers.c

@@ -1821,6 +1821,43 @@ test_iccid_parse_unquoted_invalid_mii (void *f, gpointer d)
     g_error_free (error);
 }
 
+/*****************************************************************************/
+/* Test APN cmp */
+
+typedef struct {
+    const gchar *existing;
+    const gchar *requested;
+    gboolean     match_expected;
+} TestApnCmp;
+
+static const TestApnCmp test_apn_cmp[] = {
+    { "m2m.com.attz",                      "m2m.com.attz",                      TRUE  },
+    { "m2m.com.attz",                      "M2M.COM.ATTZ",                      TRUE  },
+    { "M2M.COM.ATTZ",                      "m2m.com.attz",                      TRUE  },
+    { "m2m.com.attz.mnc170.mcc310.gprs",   "m2m.com.attz",                      TRUE  },
+    { "ac.vodafone.es.MNC001.MCC214.GPRS", "ac.vodafone.es",                    TRUE  },
+    { "m2m.com.attz",                      "m2m.com.attz.mnc170.mcc310.gprs",   FALSE },
+    { "ac.vodafone.es",                    "ac.vodafone.es.MNC001.MCC214.GPRS", FALSE },
+    { "internet.test",                     "internet",                          FALSE },
+    { "internet.test",                     "INTERNET",                          FALSE },
+    { "internet.test",                     "internet.tes",                      FALSE },
+    { "",                                  "",                                  FALSE },
+};
+
+static void
+test_cmp_apn_name (void)
+{
+    guint i;
+
+    for (i = 0; i < G_N_ELEMENTS (test_apn_cmp); i++) {
+        g_debug ("Comparing requested '%s' vs existing '%s': %s match",
+                 test_apn_cmp[i].requested,
+                 test_apn_cmp[i].existing,
+                 test_apn_cmp[i].match_expected ? "should" : "shouldn't");
+        g_assert (mm_3gpp_cmp_apn_name (test_apn_cmp[i].requested, test_apn_cmp[i].existing) == test_apn_cmp[i].match_expected);
+    }
+}
+
 /*****************************************************************************/
 /* Test CGDCONT test responses */
 
@@ -3456,6 +3493,8 @@ int main (int argc, char **argv)
     g_test_suite_add (suite, TESTCASE (test_cpms_response_empty_fields, NULL));
     g_test_suite_add (suite, TESTCASE (test_cpms_query_response,        NULL));
 
+    g_test_suite_add (suite, TESTCASE (test_cmp_apn_name, NULL));
+
     g_test_suite_add (suite, TESTCASE (test_cgdcont_test_response_single, NULL));
     g_test_suite_add (suite, TESTCASE (test_cgdcont_test_response_multiple, NULL));
     g_test_suite_add (suite, TESTCASE (test_cgdcont_test_response_multiple_and_ignore, NULL));