Make the boundary check less strict as per RFC2046

CHANGES

@@ -1,7 +1,8 @@
 v3.0.4 - YYYY-MMM-DD (to be released)
 -------------------------------------
 
-
+ - Make the boundary check less strict as per RFC2046
+   [Issue #1943 - @victorhora, @allanbomsft]
 
 
 v3.0.3 - 2018-Nov-05

src/request_body_processor/multipart.cc

@@ -158,41 +158,27 @@ int Multipart::boundary_characters_valid(const char *boundary) {
     }
 
     while ((c = *p) != '\0') {
-        /* Control characters and space not allowed. */
-        if (c < 32) {
+        // Check against allowed list defined in RFC2046 page 22
+        if (!(
+            ('0' <= c && c <= '9')
+            || ('A' <= c && c <= 'Z')
+            || ('a' <= c && c <= 'z')
+            || (c == ' ' && *(p + 1) != '\0') // space allowed, but not as last character
+            || c == '\''
+            || c == '('
+            || c == ')'
+            || c == '+'
+            || c == '_'
+            || c == ','
+            || c == '-'
+            || c == '.'
+            || c == '/'
+            || c == ':'
+            || c == '='
+            || c == '?'
+            )) {
             return 0;
         }
-
-        /* Non-ASCII characters not allowed. */
-        if (c > 126) {
-            return 0;
-        }
-
-        switch (c) {
-            /* Special characters not allowed. */
-            case '(' :
-            case ')' :
-            case '<' :
-            case '>' :
-            case '@' :
-            case ',' :
-            case ';' :
-            case ':' :
-            case '\\' :
-            case '"' :
-            case '/' :
-            case '[' :
-            case ']' :
-            case '?' :
-            case '=' :
-                return 0;
-                break;
-
-            default :
-                /* Do nothing. */
-                break;
-        }
-
         p++;
     }