SkUTF8_CountUnichars(s,l) and SkUTF8_NextUnichar(s,l) now safe.

Theory:  We will accept blobs of data as utf-8 text without validation,
but when it comes time to process it: count code poits or convert to
code points, be careful to check for errors.

TODO: SkTypeface::charsToGlyphs() needs to take a length.

Change-Id: Id8110ab43dbffce96faffdda1e0bdaa39cad40e4
Reviewed-on: https://skia-review.googlesource.com/6849
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Herb Derby <herb@google.com>

1 files changed, 26 insertions, 2 deletions

diff --git a/src/core/SkUtils.h b/src/core/SkUtils.h
index 26f19e6906..e24dd52f45 100644
--- a/src/core/SkUtils.h
+++ b/src/core/SkUtils.h
@@ -9,6 +9,7 @@
 #define SkUtils_DEFINED
 
 #include "SkTypes.h"
+#include "SkMath.h"
 
 /** Similar to memset(), but it assigns a 16bit value into the buffer.
     @param buffer   The memory to have value copied into it
@@ -58,7 +59,31 @@ inline int SkUTF8_CountUTF8Bytes(const char utf8[]) {
 }
 
 int         SkUTF8_CountUnichars(const char utf8[]);
-int         SkUTF8_CountUnichars(const char utf8[], size_t byteLength);
+
+/** This function is safe: invalid UTF8 sequences will return -1; */
+int         SkUTF8_CountUnicharsWithError(const char utf8[], size_t byteLength);
+
+/** This function is safe: invalid UTF8 sequences will return 0; */
+inline int  SkUTF8_CountUnichars(const char utf8[], size_t byteLength) {
+    return SkClampPos(SkUTF8_CountUnicharsWithError(utf8, byteLength));
+}
+
+/** This function is safe: invalid UTF8 sequences will return -1
+ *  When -1 is returned, ptr is unchanged.
+ *  Precondition: *ptr < end;
+ */
+SkUnichar SkUTF8_NextUnicharWithError(const char** ptr, const char* end);
+
+/** this version replaces invalid utf-8 sequences with code point U+FFFD. */
+inline SkUnichar SkUTF8_NextUnichar(const char** ptr, const char* end) {
+    SkUnichar val = SkUTF8_NextUnicharWithError(ptr, end);
+    if (val < 0) {
+        *ptr = end;
+        return 0xFFFD;  // REPLACEMENT CHARACTER
+    }
+    return val;
+}
+
 SkUnichar   SkUTF8_ToUnichar(const char utf8[]);
 SkUnichar   SkUTF8_NextUnichar(const char**);
 SkUnichar   SkUTF8_PrevUnichar(const char**);
@@ -99,5 +124,4 @@ inline bool SkUnichar_IsVariationSelector(SkUnichar uni) {
     }
     return true;
 }
-
 #endif