buffer: add Buffer.prototype.lastIndexOf()

* Remove unnecessary templating from SearchString

  SearchString used to have separate PatternChar and SubjectChar template type
  arguments, apparently to support things like searching for an 8-bit string
  inside a 16-bit string or vice versa. However, SearchString is only used from
  node_buffer.cc, where PatternChar and SubjectChar are always the same. Since
  this is extra complexity that's unused and untested (simplifying to a single
  Char template argument still compiles and didn't break any unit tests), I
  removed it.

* Use Boyer-Hoore[-Horspool] for both indexOf and lastIndexOf

  Add test cases for lastIndexOf. Test the fallback from BMH to
  Boyer-Moore, which looks like it was totally untested before.

* Extra bounds checks in node_buffer.cc

* Extra asserts in string_search.h

* Buffer.lastIndexOf: clean up, enforce consistency w/ String.lastIndexOf

* Polyfill memrchr(3) for non-GNU systems

PR-URL: #4846
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

doc/api/buffer.md

@@ -988,6 +988,46 @@ for (var key of buf.keys()) {
 //   5
 ```
 
+### buf.lastIndexOf(value[, byteOffset][, encoding])
+
+* `value` {String|Buffer|Number}
+* `byteOffset` {Number} Default: `buf.length`
+* `encoding` {String} Default: `'utf8'`
+* Return: {Number}
+
+Identical to [`Buffer#indexOf()`][], but searches the Buffer from back to front
+instead of front to back. Returns the starting index position of `value` in
+Buffer or `-1` if the Buffer does not contain `value`. The `value` can be a
+String, Buffer or Number. Strings are by default interpreted as UTF8. If
+`byteOffset` is provided, will return the last match that begins at or before
+`byteOffset`.
+
+```js
+const buf = new Buffer('this buffer is a buffer');
+
+buf.lastIndexOf('this');
+  // returns 0
+buf.lastIndexOf('buffer');
+  // returns 17
+buf.lastIndexOf(new Buffer('buffer'));
+  // returns 17
+buf.lastIndexOf(97); // ascii for 'a'
+  // returns 15
+buf.lastIndexOf(new Buffer('yolo'));
+  // returns -1
+buf.lastIndexOf('buffer', 5)
+  // returns 5
+buf.lastIndexOf('buffer', 4)
+  // returns -1
+
+const utf16Buffer = new Buffer('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
+
+utf16Buffer.lastIndexOf('\u03a3', null, 'ucs2');
+  // returns 6
+utf16Buffer.lastIndexOf('\u03a3', -5, 'ucs2');
+  // returns 4
+```
+
 ### buf.length
 
 * {Number}

lib/buffer.js

@@ -598,7 +598,48 @@ Buffer.prototype.compare = function compare(target,
   return binding.compareOffset(this, target, start, thisStart, end, thisEnd);
 };
 
-function slowIndexOf(buffer, val, byteOffset, encoding) {
+
+// Finds either the first index of `val` in `buffer` at offset >= `byteOffset`,
+// OR the last index of `val` in `buffer` at offset <= `byteOffset`.
+//
+// Arguments:
+// - buffer - a Buffer to search
+// - val - a string, Buffer, or number
+// - byteOffset - an index into `buffer`; will be clamped to an int32
+// - encoding - an optional encoding, relevant is val is a string
+// - dir - true for indexOf, false for lastIndexOf
+function bidirectionalIndexOf(buffer, val, byteOffset, encoding, dir) {
+  if (typeof byteOffset === 'string') {
+    encoding = byteOffset;
+    byteOffset = undefined;
+  } else if (byteOffset > 0x7fffffff) {
+    byteOffset = 0x7fffffff;
+  } else if (byteOffset < -0x80000000) {
+    byteOffset = -0x80000000;
+  }
+  byteOffset = +byteOffset;  // Coerce to Number.
+  if (isNaN(byteOffset)) {
+    // If the offset is undefined, null, NaN, "foo", etc, search whole buffer.
+    byteOffset = dir ? 0 : (buffer.length - 1);
+  }
+  dir = !!dir;  // Cast to bool.
+
+  if (typeof val === 'string') {
+    if (encoding === undefined) {
+      return binding.indexOfString(buffer, val, byteOffset, encoding, dir);
+    }
+    return slowIndexOf(buffer, val, byteOffset, encoding, dir);
+  } else if (val instanceof Buffer) {
+    return binding.indexOfBuffer(buffer, val, byteOffset, encoding, dir);
+  } else if (typeof val === 'number') {
+    return binding.indexOfNumber(buffer, val, byteOffset, dir);
+  }
+
+  throw new TypeError('"val" argument must be string, number or Buffer');
+}
+
+
+function slowIndexOf(buffer, val, byteOffset, encoding, dir) {
   var loweredCase = false;
   for (;;) {
     switch (encoding) {
@@ -609,13 +650,13 @@ function slowIndexOf(buffer, val, byteOffset, encoding) {
       case 'utf16le':
       case 'utf-16le':
       case 'binary':
-        return binding.indexOfString(buffer, val, byteOffset, encoding);
+        return binding.indexOfString(buffer, val, byteOffset, encoding, dir);
 
       case 'base64':
       case 'ascii':
       case 'hex':
         return binding.indexOfBuffer(
-            buffer, Buffer.from(val, encoding), byteOffset, encoding);
+            buffer, Buffer.from(val, encoding), byteOffset, encoding, dir);
 
       default:
         if (loweredCase) {
@@ -628,29 +669,14 @@ function slowIndexOf(buffer, val, byteOffset, encoding) {
   }
 }
 
+
 Buffer.prototype.indexOf = function indexOf(val, byteOffset, encoding) {
-  if (typeof byteOffset === 'string') {
-    encoding = byteOffset;
-    byteOffset = 0;
-  } else if (byteOffset > 0x7fffffff) {
-    byteOffset = 0x7fffffff;
-  } else if (byteOffset < -0x80000000) {
-    byteOffset = -0x80000000;
-  }
-  byteOffset >>= 0;
+  return bidirectionalIndexOf(this, val, byteOffset, encoding, true);
+};
 
-  if (typeof val === 'string') {
-    if (encoding === undefined) {
-      return binding.indexOfString(this, val, byteOffset, encoding);
-    }
-    return slowIndexOf(this, val, byteOffset, encoding);
-  } else if (val instanceof Buffer) {
-    return binding.indexOfBuffer(this, val, byteOffset, encoding);
-  } else if (typeof val === 'number') {
-    return binding.indexOfNumber(this, val, byteOffset);
-  }
 
-  throw new TypeError('"val" argument must be string, number or Buffer');
+Buffer.prototype.lastIndexOf = function lastIndexOf(val, byteOffset, encoding) {
+  return bidirectionalIndexOf(this, val, byteOffset, encoding, false);
 };
 
 

src/node_buffer.cc

@@ -943,9 +943,44 @@ void Compare(const FunctionCallbackInfo<Value> &args) {
 }
 
 
+// Computes the offset for starting an indexOf or lastIndexOf search.
+// Returns either a valid offset in [0...<length - 1>], ie inside the Buffer,
+// or -1 to signal that there is no possible match.
+int64_t IndexOfOffset(size_t length, int64_t offset_i64, bool is_forward) {
+  int64_t length_i64 = static_cast<int64_t>(length);
+  if (length_i64 == 0) {
+    // Empty buffer, no match.
+    return -1;
+  }
+  if (offset_i64 < 0) {
+    if (offset_i64 + length_i64 >= 0) {
+      // Negative offsets count backwards from the end of the buffer.
+      return length_i64 + offset_i64;
+    } else if (is_forward) {
+      // indexOf from before the start of the buffer: search the whole buffer.
+      return 0;
+    } else {
+      // lastIndexOf from before the start of the buffer: no match.
+      return -1;
+    }
+  } else {
+    if (offset_i64 < length_i64) {
+      // Valid positive offset.
+      return offset_i64;
+    } else if (is_forward) {
+      // indexOf from past the end of the buffer: no match.
+      return -1;
+    } else {
+      // lastIndexOf from past the end of the buffer: search the whole buffer.
+      return length_i64 - 1;
+    }
+  }
+}
+
 void IndexOfString(const FunctionCallbackInfo<Value>& args) {
   ASSERT(args[1]->IsString());
   ASSERT(args[2]->IsNumber());
+  ASSERT(args[4]->IsBoolean());
 
   enum encoding enc = ParseEncoding(args.GetIsolate(),
                                     args[3],
@@ -955,31 +990,26 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
   SPREAD_ARG(args[0], ts_obj);
 
   Local<String> needle = args[1].As<String>();
+  int64_t offset_i64 = args[2]->IntegerValue();
+  bool is_forward = args[4]->IsTrue();
+
   const char* haystack = ts_obj_data;
   const size_t haystack_length = ts_obj_length;
   // Extended latin-1 characters are 2 bytes in Utf8.
   const size_t needle_length =
       enc == BINARY ? needle->Length() : needle->Utf8Length();
 
-
   if (needle_length == 0 || haystack_length == 0) {
     return args.GetReturnValue().Set(-1);
   }
 
-  int64_t offset_i64 = args[2]->IntegerValue();
-  size_t offset = 0;
-
-  if (offset_i64 < 0) {
-    if (offset_i64 + static_cast<int64_t>(haystack_length) < 0) {
-      offset = 0;
-    } else {
-      offset = static_cast<size_t>(haystack_length + offset_i64);
-    }
-  } else {
-    offset = static_cast<size_t>(offset_i64);
+  int64_t opt_offset = IndexOfOffset(haystack_length, offset_i64, is_forward);
+  if (opt_offset <= -1) {
+    return args.GetReturnValue().Set(-1);
   }
-
-  if (haystack_length < offset || needle_length + offset > haystack_length) {
+  size_t offset = static_cast<size_t>(opt_offset);
+  CHECK_LT(offset, haystack_length);
+  if (is_forward && needle_length + offset > haystack_length) {
     return args.GetReturnValue().Set(-1);
   }
 
@@ -1007,13 +1037,15 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
                             haystack_length / 2,
                             decoded_string,
                             decoder.size() / 2,
-                            offset / 2);
+                            offset / 2,
+                            is_forward);
     } else {
       result = SearchString(reinterpret_cast<const uint16_t*>(haystack),
                             haystack_length / 2,
                             reinterpret_cast<const uint16_t*>(*needle_value),
                             needle_value.length(),
-                            offset / 2);
+                            offset / 2,
+                            is_forward);
     }
     result *= 2;
   } else if (enc == UTF8) {
@@ -1025,7 +1057,8 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
                           haystack_length,
                           reinterpret_cast<const uint8_t*>(*needle_value),
                           needle_length,
-                          offset);
+                          offset,
+                          is_forward);
   } else if (enc == BINARY) {
     uint8_t* needle_data = static_cast<uint8_t*>(malloc(needle_length));
     if (needle_data == nullptr) {
@@ -1038,7 +1071,8 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
                           haystack_length,
                           needle_data,
                           needle_length,
-                          offset);
+                          offset,
+                          is_forward);
     free(needle_data);
   }
 
@@ -1049,17 +1083,18 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
 void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
   ASSERT(args[1]->IsObject());
   ASSERT(args[2]->IsNumber());
+  ASSERT(args[4]->IsBoolean());
 
   enum encoding enc = ParseEncoding(args.GetIsolate(),
                                     args[3],
                                     UTF8);
 
   THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[1]);
   SPREAD_ARG(args[0], ts_obj);
   SPREAD_ARG(args[1], buf);
-
-  if (buf_length > 0)
-    CHECK_NE(buf_data, nullptr);
+  int64_t offset_i64 = args[2]->IntegerValue();
+  bool is_forward = args[4]->IsTrue();
 
   const char* haystack = ts_obj_data;
   const size_t haystack_length = ts_obj_length;
@@ -1070,19 +1105,13 @@ void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
     return args.GetReturnValue().Set(-1);
   }
 
-  int64_t offset_i64 = args[2]->IntegerValue();
-  size_t offset = 0;
-
-  if (offset_i64 < 0) {
-    if (offset_i64 + static_cast<int64_t>(haystack_length) < 0)
-      offset = 0;
-    else
-      offset = static_cast<size_t>(haystack_length + offset_i64);
-  } else {
-    offset = static_cast<size_t>(offset_i64);
+  int64_t opt_offset = IndexOfOffset(haystack_length, offset_i64, is_forward);
+  if (opt_offset <= -1) {
+    return args.GetReturnValue().Set(-1);
   }
-
-  if (haystack_length < offset || needle_length + offset > haystack_length) {
+  size_t offset = static_cast<size_t>(opt_offset);
+  CHECK_LT(offset, haystack_length);
+  if (is_forward && needle_length + offset > haystack_length) {
     return args.GetReturnValue().Set(-1);
   }
 
@@ -1097,15 +1126,17 @@ void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
         haystack_length / 2,
         reinterpret_cast<const uint16_t*>(needle),
         needle_length / 2,
-        offset / 2);
+        offset / 2,
+        is_forward);
     result *= 2;
   } else {
     result = SearchString(
         reinterpret_cast<const uint8_t*>(haystack),
         haystack_length,
         reinterpret_cast<const uint8_t*>(needle),
         needle_length,
-        offset);
+        offset,
+        is_forward);
   }
 
   args.GetReturnValue().Set(
@@ -1115,28 +1146,29 @@ void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
 void IndexOfNumber(const FunctionCallbackInfo<Value>& args) {
   ASSERT(args[1]->IsNumber());
   ASSERT(args[2]->IsNumber());
+  ASSERT(args[3]->IsBoolean());
 
   THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   SPREAD_ARG(args[0], ts_obj);
 
   uint32_t needle = args[1]->Uint32Value();
   int64_t offset_i64 = args[2]->IntegerValue();
-  size_t offset;
-
-  if (offset_i64 < 0) {
-    if (offset_i64 + static_cast<int64_t>(ts_obj_length) < 0)
-      offset = 0;
-    else
-      offset = static_cast<size_t>(ts_obj_length + offset_i64);
-  } else {
-    offset = static_cast<size_t>(offset_i64);
-  }
+  bool is_forward = args[3]->IsTrue();
 
-  if (ts_obj_length == 0 || offset + 1 > ts_obj_length)
+  int64_t opt_offset = IndexOfOffset(ts_obj_length, offset_i64, is_forward);
+  if (opt_offset <= -1) {
     return args.GetReturnValue().Set(-1);
+  }
+  size_t offset = static_cast<size_t>(opt_offset);
+  CHECK_LT(offset, ts_obj_length);
 
-  void* ptr = memchr(ts_obj_data + offset, needle, ts_obj_length - offset);
-  char* ptr_char = static_cast<char*>(ptr);
+  const void* ptr;
+  if (is_forward) {
+    ptr = memchr(ts_obj_data + offset, needle, ts_obj_length - offset);
+  } else {
+    ptr = node::stringsearch::MemrchrFill(ts_obj_data, needle, offset + 1);
+  }
+  const char* ptr_char = static_cast<const char*>(ptr);
   args.GetReturnValue().Set(ptr ? static_cast<int>(ptr_char - ts_obj_data)
                                 : -1);
 }