Bug 387522. Native JSON support. r=crowder/jst, sr=brendan

content/base/public/nsContentUtils.h

@@ -472,6 +472,19 @@ public:
                                            const nsACString& aInput,
                                            nsAString& aOutput);
 
+  /**
+   * Determine whether a buffer begins with a BOM for UTF-8, UTF-16LE,
+   * UTF-16BE, UTF-32LE, UTF-32BE.
+   *
+   * @param aBuffer the buffer to check
+   * @param aLength the length of the buffer
+   * @param aCharset empty if not found
+   * @return boolean indicating whether a BOM was detected.
+   */
+  static PRBool CheckForBOM(const unsigned char* aBuffer, PRUint32 aLength,
+                            nsACString& aCharset);
+
+
   /**
    * Determine whether aContent is in some way associated with aForm.  If the
    * form is a container the only elements that are considered to be associated

content/base/src/nsContentUtils.cpp

@@ -2874,6 +2874,47 @@ nsContentUtils::ConvertStringFromCharset(const nsACString& aCharset,
   return rv;
 }
 
+/* static */
+PRBool
+nsContentUtils::CheckForBOM(const unsigned char* aBuffer, PRUint32 aLength,
+                            nsACString& aCharset)
+{
+  PRBool found = PR_TRUE;
+  aCharset.Truncate();
+  if (aLength >= 3 &&
+      aBuffer[0] == 0xEF &&
+      aBuffer[1] == 0xBB &&
+      aBuffer[2] == 0xBF) {
+    aCharset = "UTF-8";
+  }
+  else if (aLength >= 4 &&
+           aBuffer[0] == 0x00 &&
+           aBuffer[1] == 0x00 &&
+           aBuffer[2] == 0xFE &&
+           aBuffer[3] == 0xFF) {
+    aCharset = "UTF-32BE";
+  }
+  else if (aLength >= 4 &&
+           aBuffer[0] == 0xFF &&
+           aBuffer[1] == 0xFE &&
+           aBuffer[2] == 0x00 &&
+           aBuffer[3] == 0x00) {
+    aCharset = "UTF-32LE";
+  }
+  else if (aLength >= 2 &&
+           aBuffer[0] == 0xFE && aBuffer[1] == 0xFF) {
+    aCharset = "UTF-16BE";
+  }
+  else if (aLength >= 2 &&
+           aBuffer[0] == 0xFF && aBuffer[1] == 0xFE) {
+    aCharset = "UTF-16LE";
+  } else {
+    found = PR_FALSE;
+  }
+
+  return found;
+}
+
 static PRBool EqualExceptRef(nsIURL* aURL1, nsIURL* aURL2)
 {
   nsCOMPtr<nsIURI> u1;