Fixing ordering, reducing redundant iterations

src/web_app/js/sdputils.js

@@ -331,13 +331,21 @@ function maybePreferCodec(sdp, type, dir, codec) {
 
   // If the codec is available, set it as the default in m line.
   var payload = null;
-  for (var i = 0; i < sdpLines.length; i++) {
-    var index = findLineInRange(sdpLines, i, -1, 'a=rtpmap', codec);
+  // Iterate through rtpmap enumerations to find all matching codec entries
+  for (var i = sdpLines.length-1; i >= 0 ; --i) {
+    // Finds first match in rtpmap
+    var index = findLineInRange(sdpLines, i, 0, 'a=rtpmap', codec, 'desc');
     if (index !== null) {
+      // Skip all of the entries between i and index match
+      i = index;
       payload = getCodecPayloadTypeFromLine(sdpLines[index]);
       if (payload) {
+        // Move codec to top
         sdpLines[mLineIndex] = setDefaultCodec(sdpLines[mLineIndex], payload);
       }
+    } else {
+      // No match means we can break the loop
+      break;
     }
   }
 
@@ -456,13 +464,39 @@ function findLine(sdpLines, prefix, substr) {
 
 // Find the line in sdpLines[startLine...endLine - 1] that starts with |prefix|
 // and, if specified, contains |substr| (case-insensitive search).
-function findLineInRange(sdpLines, startLine, endLine, prefix, substr) {
-  var realEndLine = endLine !== -1 ? endLine : sdpLines.length;
-  for (var i = startLine; i < realEndLine; ++i) {
-    if (sdpLines[i].indexOf(prefix) === 0) {
-      if (!substr ||
-          sdpLines[i].toLowerCase().indexOf(substr.toLowerCase()) !== -1) {
-        return i;
+function findLineInRange(
+  sdpLines,
+  startLine,
+  endLine,
+  prefix,
+  substr,
+  direction
+) {
+  if (direction === undefined) {
+    direction = 'asc';
+  }
+  direction = direction | 'asc';
+
+  if (direction === 'asc') {
+    // Search beginning to end
+    var realEndLine = endLine !== -1 ? endLine : sdpLines.length;
+    for (var i = startLine; i < realEndLine; ++i) {
+      if (sdpLines[i].indexOf(prefix) === 0) {
+        if (!substr ||
+            sdpLines[i].toLowerCase().indexOf(substr.toLowerCase()) !== -1) {
+          return i;
+        }
+      }
+    }
+  } else {
+    // Search end to beginning
+    var realStartLine = startLine !== -1 ? startLine : sdpLines.length-1;
+    for (var j = realStartLine; j >= 0; --j) {
+      if (sdpLines[j].indexOf(prefix) === 0) {
+        if (!substr ||
+            sdpLines[j].toLowerCase().indexOf(substr.toLowerCase()) !== -1) {
+          return j;
+        }
       }
     }
   }