Move internal `decodeUtf8` method from json.cpp to public util Unicode.h

Summary:
Moved decodeUtf8 -> folly::utf8ToCodePoint.
Implementation was not changed to make sure no bugs are introduced.

Reviewed By: yfeldblum

Differential Revision: D4372739

fbshipit-source-id: a015a9c47ece825e09e7c243fae454f21f99db80

folly/Unicode.cpp

@@ -15,6 +15,7 @@
  */
 
 #include <folly/Unicode.h>
+#include <folly/Conv.h>
 
 namespace folly {
 
@@ -48,6 +49,91 @@ std::string codePointToUtf8(char32_t cp) {
   return result;
 }
 
+
+char32_t utf8ToCodePoint(
+    const unsigned char*& p,
+    const unsigned char* const e,
+    bool skipOnError) {
+  /* The following encodings are valid, except for the 5 and 6 byte
+   * combinations:
+   * 0xxxxxxx
+   * 110xxxxx 10xxxxxx
+   * 1110xxxx 10xxxxxx 10xxxxxx
+   * 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
+   * 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
+   * 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
+   */
+
+  auto skip = [&] { ++p; return U'\ufffd'; };
+
+  if (p >= e) {
+    if (skipOnError) return skip();
+    throw std::runtime_error("folly::utf8ToCodePoint empty/invalid string");
+  }
+
+  unsigned char fst = *p;
+  if (!(fst & 0x80)) {
+    // trivial case
+    return *p++;
+  }
+
+  static const uint32_t bitMask[] = {
+    (1 << 7) - 1,
+    (1 << 11) - 1,
+    (1 << 16) - 1,
+    (1 << 21) - 1
+  };
+
+  // upper control bits are masked out later
+  uint32_t d = fst;
+
+  if ((fst & 0xC0) != 0xC0) {
+    if (skipOnError) return skip();
+    throw std::runtime_error(to<std::string>("folly::utf8ToCodePoint i=0 d=", d));
+  }
+
+  fst <<= 1;
+
+  for (unsigned int i = 1; i != 3 && p + i < e; ++i) {
+    unsigned char tmp = p[i];
+
+    if ((tmp & 0xC0) != 0x80) {
+      if (skipOnError) return skip();
+      throw std::runtime_error(
+        to<std::string>("folly::utf8ToCodePoint i=", i, " tmp=", (uint32_t)tmp));
+    }
+
+    d = (d << 6) | (tmp & 0x3F);
+    fst <<= 1;
+
+    if (!(fst & 0x80)) {
+      d &= bitMask[i];
+
+      // overlong, could have been encoded with i bytes
+      if ((d & ~bitMask[i - 1]) == 0) {
+        if (skipOnError) return skip();
+        throw std::runtime_error(
+          to<std::string>("folly::utf8ToCodePoint i=", i, " d=", d));
+      }
+
+      // check for surrogates only needed for 3 bytes
+      if (i == 2) {
+        if ((d >= 0xD800 && d <= 0xDFFF) || d > 0x10FFFF) {
+          if (skipOnError) return skip();
+          throw std::runtime_error(
+            to<std::string>("folly::utf8ToCodePoint i=", i, " d=", d));
+        }
+      }
+
+      p += i + 1;
+      return d;
+    }
+  }
+
+  if (skipOnError) return skip();
+  throw std::runtime_error("folly::utf8ToCodePoint encoding length maxed out");
+}
+
 //////////////////////////////////////////////////////////////////////
 
 }

folly/Unicode.h

@@ -31,6 +31,14 @@ namespace folly {
  */
 std::string codePointToUtf8(char32_t cp);
 
+/*
+ * Decode a single unicode code point from UTF-8 byte sequence.
+ */
+char32_t utf8ToCodePoint(
+    const unsigned char*& p,
+    const unsigned char* const e,
+    bool skipOnError);
+
 //////////////////////////////////////////////////////////////////////
 
 }

folly/json.cpp

@@ -33,90 +33,6 @@ namespace folly {
 namespace json {
 namespace {
 
-char32_t decodeUtf8(
-    const unsigned char*& p,
-    const unsigned char* const e,
-    bool skipOnError) {
-  /* The following encodings are valid, except for the 5 and 6 byte
-   * combinations:
-   * 0xxxxxxx
-   * 110xxxxx 10xxxxxx
-   * 1110xxxx 10xxxxxx 10xxxxxx
-   * 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
-   * 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
-   * 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
-   */
-
-  auto skip = [&] { ++p; return U'\ufffd'; };
-
-  if (p >= e) {
-    if (skipOnError) return skip();
-    throw std::runtime_error("folly::decodeUtf8 empty/invalid string");
-  }
-
-  unsigned char fst = *p;
-  if (!(fst & 0x80)) {
-    // trivial case
-    return *p++;
-  }
-
-  static const uint32_t bitMask[] = {
-    (1 << 7) - 1,
-    (1 << 11) - 1,
-    (1 << 16) - 1,
-    (1 << 21) - 1
-  };
-
-  // upper control bits are masked out later
-  uint32_t d = fst;
-
-  if ((fst & 0xC0) != 0xC0) {
-    if (skipOnError) return skip();
-    throw std::runtime_error(to<std::string>("folly::decodeUtf8 i=0 d=", d));
-  }
-
-  fst <<= 1;
-
-  for (unsigned int i = 1; i != 3 && p + i < e; ++i) {
-    unsigned char tmp = p[i];
-
-    if ((tmp & 0xC0) != 0x80) {
-      if (skipOnError) return skip();
-      throw std::runtime_error(
-        to<std::string>("folly::decodeUtf8 i=", i, " tmp=", (uint32_t)tmp));
-    }
-
-    d = (d << 6) | (tmp & 0x3F);
-    fst <<= 1;
-
-    if (!(fst & 0x80)) {
-      d &= bitMask[i];
-
-      // overlong, could have been encoded with i bytes
-      if ((d & ~bitMask[i - 1]) == 0) {
-        if (skipOnError) return skip();
-        throw std::runtime_error(
-          to<std::string>("folly::decodeUtf8 i=", i, " d=", d));
-      }
-
-      // check for surrogates only needed for 3 bytes
-      if (i == 2) {
-        if ((d >= 0xD800 && d <= 0xDFFF) || d > 0x10FFFF) {
-          if (skipOnError) return skip();
-          throw std::runtime_error(
-            to<std::string>("folly::decodeUtf8 i=", i, " d=", d));
-        }
-      }
-
-      p += i + 1;
-      return d;
-    }
-  }
-
-  if (skipOnError) return skip();
-  throw std::runtime_error("folly::decodeUtf8 encoding length maxed out");
-}
-
 struct Printer {
   explicit Printer(
       std::string& out,
@@ -716,7 +632,7 @@ void escapeString(
       if (q == p) {
         // calling utf8_decode has the side effect of
         // checking that utf8 encodings are valid
-        char32_t v = decodeUtf8(q, e, opts.skip_invalid_utf8);
+        char32_t v = utf8ToCodePoint(q, e, opts.skip_invalid_utf8);
         if (opts.skip_invalid_utf8 && v == U'\ufffd') {
           out.append(u8"\ufffd");
           p = q;
@@ -727,7 +643,7 @@ void escapeString(
     if (opts.encode_non_ascii && (*p & 0x80)) {
       // note that this if condition captures utf8 chars
       // with value > 127, so size > 1 byte
-      char32_t v = decodeUtf8(p, e, opts.skip_invalid_utf8);
+      char32_t v = utf8ToCodePoint(p, e, opts.skip_invalid_utf8);
       out.append("\\u");
       out.push_back(hexDigit(uint8_t(v >> 12)));
       out.push_back(hexDigit((v >> 8) & 0x0f));