buffer: add buffer.transcode

Add buffer.transcode(source, from, to) method. Primarily uses ICU
to transcode a buffer's content from one of Node.js' supported
encodings to another.

Originally part of a proposal to add a new unicode module. Decided
to refactor the approach towrds individual PRs without a new module.

Refs: https://github.com/nodejs/node/pull/8075
PR-URL: https://github.com/nodejs/node/pull/9038
Reviewed-By: Anna Henningsen <anna@addaleax.net>

9 files changed, 437 insertions, 39 deletions

diff --git a/doc/api/buffer.md b/doc/api/buffer.md
index 6d06ae9ddd..3877cc5569 100644
--- a/doc/api/buffer.md
+++ b/doc/api/buffer.md
@@ -2302,6 +2302,33 @@ added: v3.0.0
 On 32-bit architectures, this value is `(2^30)-1` (~1GB).
 On 64-bit architectures, this value is `(2^31)-1` (~2GB).
 
+## buffer.transcode(source, fromEnc, toEnc)
+<!-- YAML
+added: REPLACEME
+-->
+
+* `source` {Buffer} A `Buffer` instance
+* `fromEnc` {String} The current encoding
+* `toEnc` {String} To target encoding
+
+Re-encodes the given `Buffer` instance from one character encoding to another.
+Returns a new `Buffer` instance.
+
+Throws if the `fromEnc` or `toEnc` specify invalid character encodings or if
+conversion from `fromEnc` to `toEnc` is not permitted.
+
+The transcoding process will use substitution characters if a given byte
+sequence cannot be adequately represented in the target encoding. For instance:
+
+```js
+const newBuf = buffer.transcode(Buffer.from('€'), 'utf8', 'ascii');
+console.log(newBuf.toString('ascii'));
+  // prints '?'
+```
+
+Because the Euro (`€`) sign is not representable in US-ASCII, it is replaced
+with `?` in the transcoded `Buffer`.
+
 ## Class: SlowBuffer
 <!-- YAML
 deprecated: v6.0.0
diff --git a/lib/buffer.js b/lib/buffer.js
index 667561c3db..4d11aa835f 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -1360,3 +1360,7 @@ Buffer.prototype.swap64 = function swap64() {
 };
 
 Buffer.prototype.toLocaleString = Buffer.prototype.toString;
+
+// Put this at the end because internal/buffer has a circular
+// dependency on Buffer.
+exports.transcode = require('internal/buffer').transcode;
diff --git a/lib/internal/buffer.js b/lib/internal/buffer.js
new file mode 100644
index 0000000000..fdb34b9efd
--- /dev/null
+++ b/lib/internal/buffer.js
@@ -0,0 +1,30 @@
+'use strict';
+
+if (!process.binding('config').hasIntl) {
+  return;
+}
+
+const normalizeEncoding = require('internal/util').normalizeEncoding;
+const Buffer = require('buffer').Buffer;
+
+const icu = process.binding('icu');
+
+// Transcodes the Buffer from one encoding to another, returning a new
+// Buffer instance.
+exports.transcode = function transcode(source, fromEncoding, toEncoding) {
+  if (!Buffer.isBuffer(source))
+    throw new TypeError('"source" argument must be a Buffer');
+  if (source.length === 0) return Buffer.alloc(0);
+
+  fromEncoding = normalizeEncoding(fromEncoding) || fromEncoding;
+  toEncoding = normalizeEncoding(toEncoding) || toEncoding;
+  const result = icu.transcode(source, fromEncoding, toEncoding);
+  if (Buffer.isBuffer(result))
+    return result;
+
+  const code = icu.icuErrName(result);
+  const err = new Error(`Unable to transcode Buffer [${code}]`);
+  err.code = code;
+  err.errno = result;
+  throw err;
+};
diff --git a/node.gyp b/node.gyp
index fa98547e09..59bdc0d3a7 100644
--- a/node.gyp
+++ b/node.gyp
@@ -74,6 +74,7 @@
       'lib/v8.js',
       'lib/vm.js',
       'lib/zlib.js',
+      'lib/internal/buffer.js',
       'lib/internal/child_process.js',
       'lib/internal/cluster.js',
       'lib/internal/freelist.js',
diff --git a/src/node_buffer.cc b/src/node_buffer.cc
index 07a4106642..540de1827f 100644
--- a/src/node_buffer.cc
+++ b/src/node_buffer.cc
@@ -22,23 +22,6 @@
     if (!(r)) return env->ThrowRangeError("out of range index");            \
   } while (0)
 
-#define THROW_AND_RETURN_UNLESS_BUFFER(env, obj)                            \
-  do {                                                                      \
-    if (!HasInstance(obj))                                                  \
-      return env->ThrowTypeError("argument should be a Buffer");            \
-  } while (0)
-
-#define SPREAD_ARG(val, name)                                                 \
-  CHECK((val)->IsUint8Array());                                               \
-  Local<Uint8Array> name = (val).As<Uint8Array>();                            \
-  ArrayBuffer::Contents name##_c = name->Buffer()->GetContents();             \
-  const size_t name##_offset = name->ByteOffset();                            \
-  const size_t name##_length = name->ByteLength();                            \
-  char* const name##_data =                                                   \
-      static_cast<char*>(name##_c.Data()) + name##_offset;                    \
-  if (name##_length > 0)                                                      \
-    CHECK_NE(name##_data, nullptr);
-
 #define SLICE_START_END(start_arg, end_arg, end_max)                        \
   size_t start;                                                             \
   size_t end;                                                               \
@@ -448,7 +431,7 @@ void StringSlice(const FunctionCallbackInfo<Value>& args) {
   Isolate* isolate = env->isolate();
 
   THROW_AND_RETURN_UNLESS_BUFFER(env, args.This());
-  SPREAD_ARG(args.This(), ts_obj);
+  SPREAD_BUFFER_ARG(args.This(), ts_obj);
 
   if (ts_obj_length == 0)
     return args.GetReturnValue().SetEmptyString();
@@ -465,7 +448,7 @@ void StringSlice<UCS2>(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
   THROW_AND_RETURN_UNLESS_BUFFER(env, args.This());
-  SPREAD_ARG(args.This(), ts_obj);
+  SPREAD_BUFFER_ARG(args.This(), ts_obj);
 
   if (ts_obj_length == 0)
     return args.GetReturnValue().SetEmptyString();
@@ -543,8 +526,8 @@ void Copy(const FunctionCallbackInfo<Value> &args) {
   THROW_AND_RETURN_UNLESS_BUFFER(env, args.This());
   THROW_AND_RETURN_UNLESS_BUFFER(env, args[0]);
   Local<Object> target_obj = args[0].As<Object>();
-  SPREAD_ARG(args.This(), ts_obj);
-  SPREAD_ARG(target_obj, target);
+  SPREAD_BUFFER_ARG(args.This(), ts_obj);
+  SPREAD_BUFFER_ARG(target_obj, target);
 
   size_t target_start;
   size_t source_start;
@@ -577,7 +560,7 @@ void Fill(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
   THROW_AND_RETURN_UNLESS_BUFFER(env, args[0]);
-  SPREAD_ARG(args[0], ts_obj);
+  SPREAD_BUFFER_ARG(args[0], ts_obj);
 
   size_t start = args[2]->Uint32Value();
   size_t end = args[3]->Uint32Value();
@@ -590,7 +573,7 @@ void Fill(const FunctionCallbackInfo<Value>& args) {
 
   // First check if Buffer has been passed.
   if (Buffer::HasInstance(args[1])) {
-    SPREAD_ARG(args[1], fill_obj);
+    SPREAD_BUFFER_ARG(args[1], fill_obj);
     str_length = fill_obj_length;
     memcpy(ts_obj_data + start, fill_obj_data, MIN(str_length, fill_length));
     goto start_fill;
@@ -669,7 +652,7 @@ void StringWrite(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
   THROW_AND_RETURN_UNLESS_BUFFER(env, args.This());
-  SPREAD_ARG(args.This(), ts_obj);
+  SPREAD_BUFFER_ARG(args.This(), ts_obj);
 
   if (!args[0]->IsString())
     return env->ThrowTypeError("Argument must be a string");
@@ -747,7 +730,7 @@ static inline void Swizzle(char* start, unsigned int len) {
 template <typename T, enum Endianness endianness>
 void ReadFloatGeneric(const FunctionCallbackInfo<Value>& args) {
   THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
-  SPREAD_ARG(args[0], ts_obj);
+  SPREAD_BUFFER_ARG(args[0], ts_obj);
 
   uint32_t offset = args[1]->Uint32Value();
   CHECK_LE(offset + sizeof(T), ts_obj_length);
@@ -881,8 +864,8 @@ void CompareOffset(const FunctionCallbackInfo<Value> &args) {
 
   THROW_AND_RETURN_UNLESS_BUFFER(env, args[0]);
   THROW_AND_RETURN_UNLESS_BUFFER(env, args[1]);
-  SPREAD_ARG(args[0], ts_obj);
-  SPREAD_ARG(args[1], target);
+  SPREAD_BUFFER_ARG(args[0], ts_obj);
+  SPREAD_BUFFER_ARG(args[1], target);
 
   size_t target_start;
   size_t source_start;
@@ -921,8 +904,8 @@ void Compare(const FunctionCallbackInfo<Value> &args) {
 
   THROW_AND_RETURN_UNLESS_BUFFER(env, args[0]);
   THROW_AND_RETURN_UNLESS_BUFFER(env, args[1]);
-  SPREAD_ARG(args[0], obj_a);
-  SPREAD_ARG(args[1], obj_b);
+  SPREAD_BUFFER_ARG(args[0], obj_a);
+  SPREAD_BUFFER_ARG(args[1], obj_b);
 
   size_t cmp_length = MIN(obj_a_length, obj_b_length);
 
@@ -977,7 +960,7 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
                                     UTF8);
 
   THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
-  SPREAD_ARG(args[0], ts_obj);
+  SPREAD_BUFFER_ARG(args[0], ts_obj);
 
   Local<String> needle = args[1].As<String>();
   int64_t offset_i64 = args[2]->IntegerValue();
@@ -1084,8 +1067,8 @@ void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
 
   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);
+  SPREAD_BUFFER_ARG(args[0], ts_obj);
+  SPREAD_BUFFER_ARG(args[1], buf);
   int64_t offset_i64 = args[2]->IntegerValue();
   bool is_forward = args[4]->IsTrue();
 
@@ -1143,7 +1126,7 @@ void IndexOfNumber(const FunctionCallbackInfo<Value>& args) {
   ASSERT(args[3]->IsBoolean());
 
   THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
-  SPREAD_ARG(args[0], ts_obj);
+  SPREAD_BUFFER_ARG(args[0], ts_obj);
 
   uint32_t needle = args[1]->Uint32Value();
   int64_t offset_i64 = args[2]->IntegerValue();
@@ -1171,7 +1154,7 @@ void IndexOfNumber(const FunctionCallbackInfo<Value>& args) {
 void Swap16(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
   THROW_AND_RETURN_UNLESS_BUFFER(env, args[0]);
-  SPREAD_ARG(args[0], ts_obj);
+  SPREAD_BUFFER_ARG(args[0], ts_obj);
   SwapBytes16(ts_obj_data, ts_obj_length);
   args.GetReturnValue().Set(args[0]);
 }
@@ -1180,7 +1163,7 @@ void Swap16(const FunctionCallbackInfo<Value>& args) {
 void Swap32(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
   THROW_AND_RETURN_UNLESS_BUFFER(env, args[0]);
-  SPREAD_ARG(args[0], ts_obj);
+  SPREAD_BUFFER_ARG(args[0], ts_obj);
   SwapBytes32(ts_obj_data, ts_obj_length);
   args.GetReturnValue().Set(args[0]);
 }
@@ -1189,7 +1172,7 @@ void Swap32(const FunctionCallbackInfo<Value>& args) {
 void Swap64(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
   THROW_AND_RETURN_UNLESS_BUFFER(env, args[0]);
-  SPREAD_ARG(args[0], ts_obj);
+  SPREAD_BUFFER_ARG(args[0], ts_obj);
   SwapBytes64(ts_obj_data, ts_obj_length);
   args.GetReturnValue().Set(args[0]);
 }
diff --git a/src/node_i18n.cc b/src/node_i18n.cc
index e77591babf..7ac50423b2 100644
--- a/src/node_i18n.cc
+++ b/src/node_i18n.cc
@@ -24,6 +24,7 @@
 #if defined(NODE_HAVE_I18N_SUPPORT)
 
 #include "node.h"
+#include "node_buffer.h"
 #include "env.h"
 #include "env-inl.h"
 #include "util.h"
@@ -34,6 +35,10 @@
 #include <unicode/uchar.h>
 #include <unicode/udata.h>
 #include <unicode/uidna.h>
+#include <unicode/utypes.h>
+#include <unicode/ucnv.h>
+#include <unicode/utf8.h>
+#include <unicode/utf16.h>
 
 #ifdef NODE_HAVE_SMALL_ICU
 /* if this is defined, we have a 'secondary' entry point.
@@ -54,7 +59,9 @@ namespace node {
 
 using v8::Context;
 using v8::FunctionCallbackInfo;
+using v8::Isolate;
 using v8::Local;
+using v8::MaybeLocal;
 using v8::Object;
 using v8::String;
 using v8::Value;
@@ -63,6 +70,275 @@ bool flag_icu_data_dir = false;
 
 namespace i18n {
 
+const size_t kStorageSize = 1024;
+
+// TODO(jasnell): This could potentially become a member of MaybeStackBuffer
+// at some point in the future. Care would need to be taken with the
+// MaybeStackBuffer<UChar> variant below.
+MaybeLocal<Object> AsBuffer(Isolate* isolate,
+                            MaybeStackBuffer<char>* buf,
+                            size_t len) {
+  if (buf->IsAllocated()) {
+    MaybeLocal<Object> ret = Buffer::New(isolate, buf->out(), len);
+    if (!ret.IsEmpty()) buf->Release();
+    return ret;
+  }
+  return Buffer::Copy(isolate, buf->out(), len);
+}
+
+MaybeLocal<Object> AsBuffer(Isolate* isolate,
+                            MaybeStackBuffer<UChar>* buf,
+                            size_t len) {
+  char* dst = reinterpret_cast<char*>(**buf);
+  MaybeLocal<Object> ret;
+  if (buf->IsAllocated()) {
+    ret = Buffer::New(isolate, dst, len);
+    if (!ret.IsEmpty()) buf->Release();
+  } else {
+    ret = Buffer::Copy(isolate, dst, len);
+  }
+  if (!ret.IsEmpty() && IsBigEndian()) {
+    SPREAD_BUFFER_ARG(ret.ToLocalChecked(), buf);
+    SwapBytes16(buf_data, buf_length);
+  }
+  return ret;
+}
+
+struct Converter {
+  explicit Converter(const char* name, const char* sub = NULL)
+      : conv(nullptr) {
+    UErrorCode status = U_ZERO_ERROR;
+    conv = ucnv_open(name, &status);
+    CHECK(U_SUCCESS(status));
+    if (sub != NULL) {
+      ucnv_setSubstChars(conv, sub, strlen(sub), &status);
+    }
+  }
+
+  ~Converter() {
+    ucnv_close(conv);
+  }
+
+  UConverter* conv;
+};
+
+// One-Shot Converters
+
+void CopySourceBuffer(MaybeStackBuffer<UChar>* dest,
+                      const char* data,
+                      const size_t length,
+                      const size_t length_in_chars) {
+  dest->AllocateSufficientStorage(length_in_chars);
+  char* dst = reinterpret_cast<char*>(**dest);
+  memcpy(dst, data, length);
+  if (IsBigEndian()) {
+    SwapBytes16(dst, length);
+  }
+}
+
+typedef MaybeLocal<Object> (*TranscodeFunc)(Isolate* isolate,
+                                            const char* fromEncoding,
+                                            const char* toEncoding,
+                                            const char* source,
+                                            const size_t source_length,
+                                            UErrorCode* status);
+
+MaybeLocal<Object> Transcode(Isolate* isolate,
+                             const char* fromEncoding,
+                             const char* toEncoding,
+                             const char* source,
+                             const size_t source_length,
+                             UErrorCode* status) {
+  *status = U_ZERO_ERROR;
+  MaybeLocal<Object> ret;
+  MaybeStackBuffer<char> result;
+  Converter to(toEncoding, "?");
+  Converter from(fromEncoding);
+  const uint32_t limit = source_length * ucnv_getMaxCharSize(to.conv);
+  result.AllocateSufficientStorage(limit);
+  char* target = *result;
+  ucnv_convertEx(to.conv, from.conv, &target, target + limit,
+                 &source, source + source_length, nullptr, nullptr,
+                 nullptr, nullptr, true, true, status);
+  if (U_SUCCESS(*status))
+    ret = AsBuffer(isolate, &result, target - &result[0]);
+  return ret;
+}
+
+MaybeLocal<Object> TranscodeToUcs2(Isolate* isolate,
+                                   const char* fromEncoding,
+                                   const char* toEncoding,
+                                   const char* source,
+                                   const size_t source_length,
+                                   UErrorCode* status) {
+  *status = U_ZERO_ERROR;
+  MaybeLocal<Object> ret;
+  MaybeStackBuffer<UChar> destbuf(source_length);
+  Converter from(fromEncoding);
+  const size_t length_in_chars = source_length * sizeof(*destbuf);
+  ucnv_toUChars(from.conv, *destbuf, length_in_chars,
+                source, source_length, status);
+  if (U_SUCCESS(*status))
+    ret = AsBuffer(isolate, &destbuf, length_in_chars);
+  return ret;
+}
+
+MaybeLocal<Object> TranscodeFromUcs2(Isolate* isolate,
+                                     const char* fromEncoding,
+                                     const char* toEncoding,
+                                     const char* source,
+                                     const size_t source_length,
+                                     UErrorCode* status) {
+  *status = U_ZERO_ERROR;
+  MaybeStackBuffer<UChar> sourcebuf;
+  MaybeLocal<Object> ret;
+  Converter to(toEncoding, "?");
+  const size_t length_in_chars = source_length / sizeof(UChar);
+  CopySourceBuffer(&sourcebuf, source, source_length, length_in_chars);
+  MaybeStackBuffer<char> destbuf(length_in_chars);
+  const uint32_t len = ucnv_fromUChars(to.conv, *destbuf, length_in_chars,
+                                       *sourcebuf, length_in_chars, status);
+  if (U_SUCCESS(*status))
+    ret = AsBuffer(isolate, &destbuf, len);
+  return ret;
+}
+
+MaybeLocal<Object> TranscodeUcs2FromUtf8(Isolate* isolate,
+                                         const char* fromEncoding,
+                                         const char* toEncoding,
+                                         const char* source,
+                                         const size_t source_length,
+                                         UErrorCode* status) {
+  *status = U_ZERO_ERROR;
+  MaybeStackBuffer<UChar, kStorageSize> destbuf;
+  int32_t result_length;
+  u_strFromUTF8(*destbuf, kStorageSize, &result_length,
+                source, source_length, status);
+  MaybeLocal<Object> ret;
+  if (U_SUCCESS(*status)) {
+    ret = AsBuffer(isolate, &destbuf, result_length * sizeof(**destbuf));
+  } else if (*status == U_BUFFER_OVERFLOW_ERROR) {
+    *status = U_ZERO_ERROR;
+    destbuf.AllocateSufficientStorage(result_length);
+    u_strFromUTF8(*destbuf, result_length, &result_length,
+                  source, source_length, status);
+    if (U_SUCCESS(*status))
+      ret = AsBuffer(isolate, &destbuf, result_length * sizeof(**destbuf));
+  }
+  return ret;
+}
+
+MaybeLocal<Object> TranscodeUtf8FromUcs2(Isolate* isolate,
+                                         const char* fromEncoding,
+                                         const char* toEncoding,
+                                         const char* source,
+                                         const size_t source_length,
+                                         UErrorCode* status) {
+  *status = U_ZERO_ERROR;
+  MaybeLocal<Object> ret;
+  const size_t length_in_chars = source_length / sizeof(UChar);
+  int32_t result_length;
+  MaybeStackBuffer<UChar> sourcebuf;
+  MaybeStackBuffer<char, kStorageSize> destbuf;
+  CopySourceBuffer(&sourcebuf, source, source_length, length_in_chars);
+  u_strToUTF8(*destbuf, kStorageSize, &result_length,
+              *sourcebuf, length_in_chars, status);
+  if (U_SUCCESS(*status)) {
+    ret = AsBuffer(isolate, &destbuf, result_length);
+  } else if (*status == U_BUFFER_OVERFLOW_ERROR) {
+    *status = U_ZERO_ERROR;
+    destbuf.AllocateSufficientStorage(result_length);
+    u_strToUTF8(*destbuf, result_length, &result_length, *sourcebuf,
+                length_in_chars, status);
+    if (U_SUCCESS(*status)) {
+      ret = Buffer::New(isolate, *destbuf, result_length);
+      destbuf.Release();
+    }
+  }
+  return ret;
+}
+
+const char* EncodingName(const enum encoding encoding) {
+  switch (encoding) {
+    case ASCII: return "us-ascii";
+    case LATIN1: return "iso8859-1";
+    case UCS2: return "utf16le";
+    case UTF8: return "utf-8";
+    default: return NULL;
+  }
+}
+
+bool SupportedEncoding(const enum encoding encoding) {
+  switch (encoding) {
+    case ASCII:
+    case LATIN1:
+    case UCS2:
+    case UTF8: return true;
+    default: return false;
+  }
+}
+
+void Transcode(const FunctionCallbackInfo<Value>&args) {
+  Environment* env = Environment::GetCurrent(args);
+  Isolate* isolate = env->isolate();
+  UErrorCode status = U_ZERO_ERROR;
+  MaybeLocal<Object> result;
+
+  THROW_AND_RETURN_UNLESS_BUFFER(env, args[0]);
+  SPREAD_BUFFER_ARG(args[0], ts_obj);
+  const enum encoding fromEncoding = ParseEncoding(isolate, args[1], BUFFER);
+  const enum encoding toEncoding = ParseEncoding(isolate, args[2], BUFFER);
+
+  if (SupportedEncoding(fromEncoding) && SupportedEncoding(toEncoding)) {
+    TranscodeFunc tfn = &Transcode;
+    switch (fromEncoding) {
+      case ASCII:
+      case LATIN1:
+        if (toEncoding == UCS2)
+          tfn = &TranscodeToUcs2;
+        break;
+      case UTF8:
+        if (toEncoding == UCS2)
+          tfn = &TranscodeUcs2FromUtf8;
+        break;
+      case UCS2:
+        switch (toEncoding) {
+          case UCS2:
+            tfn = &Transcode;
+            break;
+          case UTF8:
+            tfn = &TranscodeUtf8FromUcs2;
+            break;
+          default:
+            tfn = TranscodeFromUcs2;
+        }
+        break;
+      default:
+        // This should not happen because of the SupportedEncoding checks
+        ABORT();
+    }
+
+    result = tfn(isolate, EncodingName(fromEncoding), EncodingName(toEncoding),
+                 ts_obj_data, ts_obj_length, &status);
+  } else {
+    status = U_ILLEGAL_ARGUMENT_ERROR;
+  }
+
+  if (result.IsEmpty())
+    return args.GetReturnValue().Set(status);
+
+  return args.GetReturnValue().Set(result.ToLocalChecked());
+}
+
+static void ICUErrorName(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+  UErrorCode status = static_cast<UErrorCode>(args[0]->Int32Value());
+  args.GetReturnValue().Set(
+      String::NewFromUtf8(env->isolate(),
+                          u_errorName(status),
+                          v8::NewStringType::kNormal).ToLocalChecked());
+}
+
 bool InitializeICUDirectory(const char* icu_data_path) {
   if (icu_data_path != nullptr) {
     flag_icu_data_dir = true;
@@ -282,6 +558,10 @@ void Init(Local<Object> target,
   env->SetMethod(target, "toUnicode", ToUnicode);
   env->SetMethod(target, "toASCII", ToASCII);
   env->SetMethod(target, "getStringWidth", GetStringWidth);
+
+  // One-shot converters
+  env->SetMethod(target, "icuErrName", ICUErrorName);
+  env->SetMethod(target, "transcode", Transcode);
 }
 
 }  // namespace i18n
diff --git a/src/util.h b/src/util.h
index e2f9df02bc..d1c5ac0285 100644
--- a/src/util.h
+++ b/src/util.h
@@ -343,6 +343,15 @@ class MaybeStackBuffer {
     buf_ = nullptr;
   }
 
+  bool IsAllocated() {
+    return buf_ != buf_st_;
+  }
+
+  void Release() {
+    buf_ = buf_st_;
+    length_ = 0;
+  }
+
   MaybeStackBuffer() : length_(0), buf_(buf_st_) {
     // Default to a zero-length, null-terminated buffer.
     buf_[0] = T();
@@ -378,6 +387,24 @@ class BufferValue : public MaybeStackBuffer<char> {
   explicit BufferValue(v8::Isolate* isolate, v8::Local<v8::Value> value);
 };
 
+#define THROW_AND_RETURN_UNLESS_BUFFER(env, obj)                            \
+  do {                                                                      \
+    if (!Buffer::HasInstance(obj))                                          \
+      return env->ThrowTypeError("argument should be a Buffer");            \
+  } while (0)
+
+#define SPREAD_BUFFER_ARG(val, name)                                          \
+  CHECK((val)->IsUint8Array());                                               \
+  Local<v8::Uint8Array> name = (val).As<v8::Uint8Array>();                    \
+  v8::ArrayBuffer::Contents name##_c = name->Buffer()->GetContents();         \
+  const size_t name##_offset = name->ByteOffset();                            \
+  const size_t name##_length = name->ByteLength();                            \
+  char* const name##_data =                                                   \
+      static_cast<char*>(name##_c.Data()) + name##_offset;                    \
+  if (name##_length > 0)                                                      \
+    CHECK_NE(name##_data, nullptr);
+
+
 }  // namespace node
 
 #endif  // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
diff --git a/test/parallel/test-icu-transcode.js b/test/parallel/test-icu-transcode.js
new file mode 100644
index 0000000000..f45b997436
--- /dev/null
+++ b/test/parallel/test-icu-transcode.js
@@ -0,0 +1,48 @@
+'use strict';
+
+require('../common');
+const buffer = require('buffer');
+const assert = require('assert');
+
+const orig = Buffer.from('tést €', 'utf8');
+
+// Test Transcoding
+const tests = {
+  'latin1': [0x74, 0xe9, 0x73, 0x74, 0x20, 0x3f],
+  'ascii': [0x74, 0x3f, 0x73, 0x74, 0x20, 0x3f],
+  'ucs2': [0x74, 0x00, 0xe9, 0x00, 0x73,
+           0x00, 0x74, 0x00, 0x20, 0x00,
+           0xac, 0x20]
+};
+
+for (const test in tests) {
+  const dest = buffer.transcode(orig, 'utf8', test);
+  assert.strictEqual(dest.length, tests[test].length);
+  for (var n = 0; n < tests[test].length; n++)
+    assert.strictEqual(dest[n], tests[test][n]);
+}
+
+{
+  const dest = buffer.transcode(Buffer.from(tests.ucs2), 'ucs2', 'utf8');
+  assert.strictEqual(dest.toString(), orig.toString());
+}
+
+{
+  const utf8 = Buffer.from('€'.repeat(4000), 'utf8');
+  const ucs2 = Buffer.from('€'.repeat(4000), 'ucs2');
+  const utf8_to_ucs2 = buffer.transcode(utf8, 'utf8', 'ucs2');
+  const ucs2_to_utf8 = buffer.transcode(ucs2, 'ucs2', 'utf8');
+  assert.deepStrictEqual(utf8, ucs2_to_utf8);
+  assert.deepStrictEqual(ucs2, utf8_to_ucs2);
+  assert.strictEqual(ucs2_to_utf8.toString('utf8'),
+                     utf8_to_ucs2.toString('ucs2'));
+}
+
+assert.throws(
+  () => buffer.transcode(Buffer.from('a'), 'b', 'utf8'),
+  /Unable to transcode Buffer \[U_ILLEGAL_ARGUMENT_ERROR\]/
+);
+assert.throws(
+  () => buffer.transcode(Buffer.from('a'), 'uf8', 'b'),
+  /Unable to transcode Buffer \[U_ILLEGAL_ARGUMENT_ERROR\]/
+);
diff --git a/tools/icu/icu-generic.gyp b/tools/icu/icu-generic.gyp
index 3a284461d8..cf615717e8 100644
--- a/tools/icu/icu-generic.gyp
+++ b/tools/icu/icu-generic.gyp
@@ -20,9 +20,7 @@
       'type': 'none',
       'toolsets': [ 'target' ],
       'direct_dependent_settings': {
-        'defines': [
-          'UCONFIG_NO_CONVERSION=1',
-        ]
+        'defines': []
       },
     },
     {