4 files changed, 51 insertions, 1 deletions
diff --git a/dom/base/nsAttrValue.cpp b/dom/base/nsAttrValue.cpp
index ebddcb7ed..2418fb501 100644
--- a/dom/base/nsAttrValue.cpp
+++ b/dom/base/nsAttrValue.cpp
@@ -1526,6 +1526,40 @@ nsAttrValue::ParseIntWithFallback(const nsAString& aString, int32_t aDefault,
   SetIntValueAndType(val, eInteger, nonStrict ? &aString : nullptr);
 }
 
+void
+nsAttrValue::ParseClampedNonNegativeInt(const nsAString& aString,
+                                        int32_t aDefault, int32_t aMin,
+                                        int32_t aMax)
+{
+  ResetIfSet();
+
+  nsContentUtils::ParseHTMLIntegerResultFlags result;
+  int32_t val = nsContentUtils::ParseHTMLInteger(aString, &result);
+  bool nonStrict = (result & nsContentUtils::eParseHTMLInteger_IsPercent) ||
+                   (result & nsContentUtils::eParseHTMLInteger_NonStandard) ||
+                   (result & nsContentUtils::eParseHTMLInteger_DidNotConsumeAllInput);
+
+  if (result & nsContentUtils::eParseHTMLInteger_ErrorOverflow) {
+    if (result & nsContentUtils::eParseHTMLInteger_Negative) {
+      val = aDefault;
+    } else {
+      val = aMax;
+    }
+    nonStrict = true;
+  } else if ((result & nsContentUtils::eParseHTMLInteger_Error) || val < 0) {
+    val = aDefault;
+    nonStrict = true;
+  } else if (val < aMin) {
+    val = aMin;
+    nonStrict = true;
+  } else if (val > aMax) {
+    val = aMax;
+    nonStrict = true;
+  }
+
+  SetIntValueAndType(val, eInteger, nonStrict ? &aString : nullptr);
+}
+
 bool
 nsAttrValue::ParseNonNegativeIntValue(const nsAString& aString)
 {
diff --git a/dom/base/nsAttrValue.h b/dom/base/nsAttrValue.h
index 655e4ca61..23f61a614 100644
--- a/dom/base/nsAttrValue.h
+++ b/dom/base/nsAttrValue.h
@@ -362,6 +362,19 @@ public:
    */
   bool ParseNonNegativeIntValue(const nsAString& aString);
 
+   /**
+   * Parse a string value into a clamped non-negative integer.
+   * This method follows the rules for parsing non-negative integer from:
+   * https://html.spec.whatwg.org/multipage/infrastructure.html#clamped-to-the-range
+   *
+   * @param aString the string to parse
+   * @param aDefault value to return for negative or invalid values
+   * @param aMin minimum value
+   * @param aMax maximum value
+   */
+  void ParseClampedNonNegativeInt(const nsAString& aString, int32_t aDefault,
+                                  int32_t aMin, int32_t aMax);
+
   /**
    * Parse a string value into a positive integer.
    * This method follows the rules for parsing non-negative integer from:
diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index b6cbbbace..4f7b71b19 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -1088,6 +1088,7 @@ nsContentUtils::ParseHTMLInteger(const nsAString& aValue,
   int sign = 1;
   if (*iter == char16_t('-')) {
     sign = -1;
+    result |= eParseHTMLInteger_Negative;
     ++iter;
   } else if (*iter == char16_t('+')) {
     result |= eParseHTMLInteger_NonStandard;
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index bf6a59dcd..64f7485cb 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -445,7 +445,9 @@ public:
     // Set if one or more error flags were set.
     eParseHTMLInteger_Error                 = 1 << 3,
     eParseHTMLInteger_ErrorNoValue          = 1 << 4,
-    eParseHTMLInteger_ErrorOverflow         = 1 << 5
+    eParseHTMLInteger_ErrorOverflow         = 1 << 5,
+    // Use this flag to detect the difference between overflow and underflow
+    eParseHTMLInteger_Negative              = 1 << 6,
   };
   static int32_t ParseHTMLInteger(const nsAString& aValue,
                                   ParseHTMLIntegerResultFlags *aResult);