Telephony: Distinguish GSM vs ETWS bc by message id

Per 3GPP TS 24.012 3.1 GSM CB can be less than 88 byes.
Fix to distinguish GSM vs ETWS broadcast format by checking message id field
rather than length of pdu.

Bug: 7417676
Change-Id: I6aeedcd531a89ded7901db33d89ed45baaabbaa7

1 files changed, 39 insertions, 36 deletions

diff --git a/src/java/com/android/internal/telephony/gsm/SmsCbHeader.java b/src/java/com/android/internal/telephony/gsm/SmsCbHeader.java
index 5692044..995f5b1 100644
--- a/src/java/com/android/internal/telephony/gsm/SmsCbHeader.java
+++ b/src/java/com/android/internal/telephony/gsm/SmsCbHeader.java
@@ -95,47 +95,50 @@ class SmsCbHeader {
             throw new IllegalArgumentException("Illegal PDU");
         }
 
-        if (pdu.length <= PDU_LENGTH_ETWS) {
-            format = FORMAT_ETWS_PRIMARY;
-            geographicalScope = (pdu[0] & 0xc0) >> 6;
+        if (pdu.length <= PDU_LENGTH_GSM) {
+            // can be ETWS or GSM format.
+            // Per TS23.041 9.4.1.2 and 9.4.1.3.2, GSM and ETWS format both
+            // contain serial number which contains GS, Message Code, and Update Number
+            // per 9.4.1.2.1, and message identifier in same octets
+            geographicalScope = (pdu[0] & 0xc0) >>> 6;
             serialNumber = ((pdu[0] & 0xff) << 8) | (pdu[1] & 0xff);
             messageIdentifier = ((pdu[2] & 0xff) << 8) | (pdu[3] & 0xff);
-            dataCodingScheme = -1;
-            pageIndex = -1;
-            nrOfPages = -1;
-            boolean emergencyUserAlert = (pdu[4] & 0x1) != 0;
-            boolean activatePopup = (pdu[5] & 0x80) != 0;
-            int warningType = (pdu[4] & 0xfe) >> 1;
-            byte[] warningSecurityInfo;
-            // copy the Warning-Security-Information, if present
-            if (pdu.length > PDU_HEADER_LENGTH) {
-                warningSecurityInfo = Arrays.copyOfRange(pdu, 6, pdu.length);
+            if (isEtwsMessage() && pdu.length <= PDU_LENGTH_ETWS) {
+                format = FORMAT_ETWS_PRIMARY;
+                dataCodingScheme = -1;
+                pageIndex = -1;
+                nrOfPages = -1;
+                boolean emergencyUserAlert = (pdu[4] & 0x1) != 0;
+                boolean activatePopup = (pdu[5] & 0x80) != 0;
+                int warningType = (pdu[4] & 0xfe) >>> 1;
+                byte[] warningSecurityInfo;
+                // copy the Warning-Security-Information, if present
+                if (pdu.length > PDU_HEADER_LENGTH) {
+                    warningSecurityInfo = Arrays.copyOfRange(pdu, 6, pdu.length);
+                } else {
+                    warningSecurityInfo = null;
+                }
+                mEtwsInfo = new SmsCbEtwsInfo(warningType, emergencyUserAlert, activatePopup,
+                        warningSecurityInfo);
+                mCmasInfo = null;
+                return;     // skip the ETWS/CMAS initialization code for regular notifications
             } else {
-                warningSecurityInfo = null;
-            }
-            mEtwsInfo = new SmsCbEtwsInfo(warningType, emergencyUserAlert, activatePopup,
-                    warningSecurityInfo);
-            mCmasInfo = null;
-            return;     // skip the ETWS/CMAS initialization code for regular notifications
-        } else if (pdu.length <= PDU_LENGTH_GSM) {
-            // GSM pdus are no more than 88 bytes
-            format = FORMAT_GSM;
-            geographicalScope = (pdu[0] & 0xc0) >> 6;
-            serialNumber = ((pdu[0] & 0xff) << 8) | (pdu[1] & 0xff);
-            messageIdentifier = ((pdu[2] & 0xff) << 8) | (pdu[3] & 0xff);
-            dataCodingScheme = pdu[4] & 0xff;
+                // GSM pdus are no more than 88 bytes
+                format = FORMAT_GSM;
+                dataCodingScheme = pdu[4] & 0xff;
 
-            // Check for invalid page parameter
-            int pageIndex = (pdu[5] & 0xf0) >> 4;
-            int nrOfPages = pdu[5] & 0x0f;
+                // Check for invalid page parameter
+                int pageIndex = (pdu[5] & 0xf0) >>> 4;
+                int nrOfPages = pdu[5] & 0x0f;
 
-            if (pageIndex == 0 || nrOfPages == 0 || pageIndex > nrOfPages) {
-                pageIndex = 1;
-                nrOfPages = 1;
-            }
+                if (pageIndex == 0 || nrOfPages == 0 || pageIndex > nrOfPages) {
+                    pageIndex = 1;
+                    nrOfPages = 1;
+                }
 
-            this.pageIndex = pageIndex;
-            this.nrOfPages = nrOfPages;
+                this.pageIndex = pageIndex;
+                this.nrOfPages = nrOfPages;
+            }
         } else {
             // UMTS pdus are always at least 90 bytes since the payload includes
             // a number-of-pages octet and also one length octet per page
@@ -148,7 +151,7 @@ class SmsCbHeader {
             }
 
             messageIdentifier = ((pdu[1] & 0xff) << 8) | pdu[2] & 0xff;
-            geographicalScope = (pdu[3] & 0xc0) >> 6;
+            geographicalScope = (pdu[3] & 0xc0) >>> 6;
             serialNumber = ((pdu[3] & 0xff) << 8) | (pdu[4] & 0xff);
             dataCodingScheme = pdu[5] & 0xff;