support for %n in sscanf

2 files changed, 48 insertions, 5 deletions

diff --git a/src/library.js b/src/library.js
index 2855c33d..1164c81f 100644
--- a/src/library.js
+++ b/src/library.js
@@ -2437,6 +2437,20 @@ LibraryManager.library = {
     // Supports %x, %4x, %d.%d, %s, %f, %lf.
     // TODO: Support all format specifiers.
     format = Pointer_stringify(format);
+    var soFar = 0;
+    if (format.indexOf('%n') >= 0) {
+      // need to track soFar
+      var _get = get;
+      get = function() {
+        soFar++;
+        return _get();
+      }
+      var _unget = unget;
+      unget = function() {
+        soFar--;
+        return _unget();
+      }
+    }
     var formatIndex = 0;
     var argsi = 0;
     var fields = 0;
@@ -2450,6 +2464,7 @@ LibraryManager.library = {
     } 
     unget(next);
     next = 1;
+    mainLoop:
     for (var formatIndex = 0; formatIndex < format.length; formatIndex++) {
       if (next <= 0) return fields;
       var next = get();
@@ -2493,7 +2508,7 @@ LibraryManager.library = {
             unget(buffer.pop().charCodeAt(0));
           }
           next = get();
-        } else {
+        } else if (type != 'n') {
           var first = true;
           while ((curr < max_ || isNaN(max_)) && next > 0) {
             if (!(next in __scanString.whiteSpace) && // stop on whitespace
@@ -2513,7 +2528,7 @@ LibraryManager.library = {
             first = false;
           }
         }
-        if (buffer.length === 0) return 0;  // Failure.
+        if (buffer.length === 0 && type != 'n') return 0;  // Failure.
         var text = buffer.join('');
         var argPtr = {{{ makeGetValue('varargs', 'argIndex', 'void*') }}};
         argIndex += Runtime.getNativeFieldSize('void*');
@@ -2541,22 +2556,30 @@ LibraryManager.library = {
               {{{ makeSetValue('argPtr', 'j', 'array[j]', 'i8') }}}
             }
             break;
+          case 'n':
+            {{{ makeSetValue('argPtr', 0, 'soFar-1', 'i32') }}}
+            break;
         }
-        fields++;
+        if (type != 'n') fields++;
       } else if (format[formatIndex] in __scanString.whiteSpace) {
         while (next in __scanString.whiteSpace) {
           next = get();
-          if (next <= 0) return fields;  // End of input.
+          if (next <= 0) break mainLoop;  // End of input.
         }
         unget(next);
       } else {
         // Not a specifier.
         if (format[formatIndex].charCodeAt(0) !== next) {
           unget(next);
-          return fields;
+          break mainLoop;
         }
       }
     }
+    // 'n' is special in that it needs no input. so it can be at the end, even with nothing left to read
+    if (format[formatIndex-1] == '%' && format[formatIndex] == 'n') {
+      var argPtr = {{{ makeGetValue('varargs', 'argIndex', 'void*') }}};
+      {{{ makeSetValue('argPtr', 0, 'soFar-1', 'i32') }}}
+    }
     return fields;
   },
   // Performs prtinf-style formatting.
diff --git a/tests/runner.py b/tests/runner.py
index e3d5ac10..880e29a0 100755
--- a/tests/runner.py
+++ b/tests/runner.py
@@ -4341,6 +4341,26 @@ Pass: 123456.789000 123456.789000
 Pass: 0.000012 0.000012
 Pass: 0.000012 0.000012''')
 
+    def test_sscanf_n(self):
+      src = r'''
+        #include<stdio.h>
+        int main() {
+          char *line = "version 1.0";
+          int i, l, lineno;
+          char word[80];
+          if (sscanf(line, "%s%n", word, &l) != 1) {
+              printf("Header format error, line %d\n", lineno);
+          }
+          printf("[DEBUG] word 1: %s, l: %d\n", word, l);
+
+          int x = sscanf("one %n two", "%s %n", word, &l);
+          printf("%d,%s,%d\n", x, word, l);
+
+          return 0;
+        }
+      '''
+      self.do_run(src, '''[DEBUG] word 1: version, l: 7\n1,one,4''')
+
     def test_langinfo(self):
       src = open(path_from_root('tests', 'langinfo', 'test.c'), 'r').read()
       expected = open(path_from_root('tests', 'langinfo', 'output.txt'), 'r').read()