Bug 1034627 part 1 - Add some new string APIs. r=terrence

js/src/jsapi.cpp

@@ -5384,6 +5384,49 @@ JS_GetTwoByteStringCharsAndLength(JSContext *cx, const JS::AutoCheckCannotGC &no
     return linear->twoByteChars(nogc);
 }
 
+JS_PUBLIC_API(const jschar *)
+JS_GetTwoByteExternalStringChars(JSString *str)
+{
+    return str->asExternal().twoByteChars();
+}
+
+JS_PUBLIC_API(bool)
+JS_GetStringCharAt(JSContext *cx, JSString *str, size_t index, jschar *res)
+{
+    AssertHeapIsIdleOrStringIsFlat(cx, str);
+    CHECK_REQUEST(cx);
+    assertSameCompartment(cx, str);
+
+    JSLinearString *linear = str->ensureLinear(cx);
+    if (!linear)
+        return false;
+
+    *res = linear->latin1OrTwoByteChar(index);
+    return true;
+}
+
+JS_PUBLIC_API(jschar)
+JS_GetFlatStringCharAt(JSFlatString *str, size_t index)
+{
+    return str->latin1OrTwoByteChar(index);
+}
+
+JS_PUBLIC_API(bool)
+JS_CopyStringChars(JSContext *cx, mozilla::Range<jschar> dest, JSString *str)
+{
+    AssertHeapIsIdleOrStringIsFlat(cx, str);
+    CHECK_REQUEST(cx);
+    assertSameCompartment(cx, str);
+
+    JSLinearString *linear = str->ensureLinear(cx);
+    if (!linear)
+        return false;
+
+    MOZ_ASSERT(linear->length() <= dest.length());
+    CopyChars(dest.start().get(), *linear);
+    return true;
+}
+
 JS_PUBLIC_API(const jschar *)
 JS_GetInternedStringChars(JSString *str)
 {

js/src/jsapi.h

@@ -11,6 +11,7 @@
 
 #include "mozilla/FloatingPoint.h"
 #include "mozilla/MemoryReporting.h"
+#include "mozilla/Range.h"
 #include "mozilla/RangedPtr.h"
 #include "mozilla/TypedEnum.h"
 
@@ -4181,6 +4182,18 @@ extern JS_PUBLIC_API(const jschar *)
 JS_GetTwoByteStringCharsAndLength(JSContext *cx, const JS::AutoCheckCannotGC &nogc, JSString *str,
                                   size_t *length);
 
+extern JS_PUBLIC_API(bool)
+JS_GetStringCharAt(JSContext *cx, JSString *str, size_t index, jschar *res);
+
+extern JS_PUBLIC_API(jschar)
+JS_GetFlatStringCharAt(JSFlatString *str, size_t index);
+
+extern JS_PUBLIC_API(const jschar *)
+JS_GetTwoByteExternalStringChars(JSString *str);
+
+extern JS_PUBLIC_API(bool)
+JS_CopyStringChars(JSContext *cx, mozilla::Range<jschar> dest, JSString *str);
+
 extern JS_PUBLIC_API(const jschar *)
 JS_GetInternedStringChars(JSString *str);
 

js/src/vm/String.h

@@ -953,6 +953,14 @@ class JSExternalString : public JSFlatString
         return d.s.u3.externalFinalizer;
     }
 
+    /*
+     * External chars are never allocated inline or in the nursery, so we can
+     * safely expose this without requiring an AutoCheckCannotGC argument.
+     */
+    const jschar *twoByteChars() const {
+        return rawTwoByteChars();
+    }
+
     /* Only called by the GC for strings with the FINALIZE_EXTERNAL_STRING kind. */
 
     inline void finalize(js::FreeOp *fop);