library/GSM_SystemInformation: add dec_SystemInformationSafe()
Some types of System Information (mostly the Rest Octets) are not
fully implemented, so calling the generic dec_SystemInformation()
may result in a DTE. Let's add dec_SystemInformationSafeBT() with
"prototype(backtrack)", so it would return a non-zero integer if
decoding fails. Let's add a wrapper dec_SystemInformationSafe()
that would additionally check the RR Protocol Discriminator.
Change-Id: Id4d73e0f3347e1d4c4c77aec75b767311d662292
Related: OS#4662
diff --git a/library/GSM_SystemInformation.ttcn b/library/GSM_SystemInformation.ttcn
index 3c3d96c..9113583 100644
--- a/library/GSM_SystemInformation.ttcn
+++ b/library/GSM_SystemInformation.ttcn
@@ -264,4 +264,29 @@
}
}
+ external function dec_SystemInformationSafeBT(in octetstring stream, out SystemInformation si)
+ return integer /* Decoding result: successful (0) or unsuccessful (1) */
+ with { extension "prototype(backtrack) decode(RAW)" };
+
+ /* Some types of System Information (mostly the Rest Octets) are not fully implemented,
+ * so calling the generic dec_SystemInformation() may result in a DTE. This function
+ * additionally checks RR Protocol Discriminator, and should be used in the most cases. */
+ function dec_SystemInformationSafe(in octetstring stream, out SystemInformation si)
+ return integer {
+ /* Try to decode a given octetstring as System Information */
+ if (dec_SystemInformationSafeBT(stream, si) != 0) {
+ log("Failed to decode (RR) System Information: ", stream);
+ return 1;
+ }
+
+ /* Check the protocol discriminator (we expect RR messages) */
+ if (si.header.rr_protocol_discriminator != bit2int('0110'B)) {
+ log("Protocol discriminator is not RR (!= '0110'B): ",
+ si.header.rr_protocol_discriminator);
+ return 1;
+ }
+
+ return 0;
+ }
+
} with { encode "RAW"; variant "FIELDORDER(msb)" }