Rework Reader and Writer

* add tests that cover same behaviors as Convert and ConvertString
 * align read and write behaviors with bufio to play nice
 * add methods that allow to customize buffer size
 * add methods to reset, allowing reuse

converter.go

@@ -6,6 +6,7 @@ package iconv
 #cgo windows LDFLAGS: -liconv
 #include <stdlib.h>
 #include <iconv.h>
+#include <locale.h>
 
 // As of GO 1.6 passing a pointer to Go pointer, will lead to panic
 // Therofore we use this wrapper function, to avoid passing **char directly from go
@@ -20,47 +21,40 @@ import "unsafe"
 
 type Converter struct {
 	context C.iconv_t
-	open    bool
 }
 
 // Initialize a new Converter. If fromEncoding or toEncoding are not supported by
 // iconv then an EINVAL error will be returned. An ENOMEM error maybe returned if
 // there is not enough memory to initialize an iconv descriptor
-func NewConverter(fromEncoding string, toEncoding string) (converter *Converter, err error) {
-	converter = new(Converter)
-
+func NewConverter(fromEncoding string, toEncoding string) (*Converter, error) {
 	// convert to C strings
 	toEncodingC := C.CString(toEncoding)
 	fromEncodingC := C.CString(fromEncoding)
 
 	// open an iconv descriptor
-	converter.context, err = C.iconv_open(toEncodingC, fromEncodingC)
+	context, err := C.iconv_open(toEncodingC, fromEncodingC)
 
 	// free the C Strings
 	C.free(unsafe.Pointer(toEncodingC))
 	C.free(unsafe.Pointer(fromEncodingC))
 
-	// check err
-	if err == nil {
-		// no error, mark the context as open
-		converter.open = true
+	if err != nil {
+		return nil, err
 	}
 
-	return
+	return &Converter{context}, nil
 }
 
-// destroy is called during garbage collection
-func (this *Converter) destroy() {
-	this.Close()
+// Close a Converter's iconv descriptor explicitly
+func (converter *Converter) Close() error {
+	_, err := C.iconv_close(converter.context)
+	return err
 }
 
-// Close a Converter's iconv description explicitly
-func (this *Converter) Close() (err error) {
-	if this.open {
-		_, err = C.iconv_close(this.context)
-	}
-
-	return
+// Reset state of iconv context
+func (converter *Converter) Reset() error {
+	_, _, err := converter.Convert(nil, nil)
+	return err
 }
 
 // Convert bytes from an input byte slice into a give output byte slice
@@ -74,50 +68,32 @@ func (this *Converter) Close() (err error) {
 // For shift based output encodings, any end shift byte sequences can be generated by
 // passing a 0 length byte slice as input. Also passing a 0 length byte slice for output
 // will simply reset the iconv descriptor shift state without writing any bytes.
-func (this *Converter) Convert(input []byte, output []byte) (bytesRead int, bytesWritten int, err error) {
-	// make sure we are still open
-	if this.open {
+func (converter *Converter) Convert(input []byte, output []byte) (bytesRead int, bytesWritten int, err error) {
 	inputLeft := C.size_t(len(input))
 	outputLeft := C.size_t(len(output))
 
-		if inputLeft > 0 && outputLeft > 0 {
-			// we have to give iconv a pointer to a pointer of the underlying
-			// storage of each byte slice - so far this is the simplest
-			// way i've found to do that in Go, but it seems ugly
-			inputPointer := (*C.char)(unsafe.Pointer(&input[0]))
-			outputPointer := (*C.char)(unsafe.Pointer(&output[0]))
+	var inputPointer, outputPointer *C.char
 
-			_, err = C.call_iconv(this.context, inputPointer, &inputLeft, outputPointer, &outputLeft)
+	if inputLeft > 0 {
+		inputPointer = (*C.char)(unsafe.Pointer(&input[0]))
+	}
+
+	if outputLeft > 0 {
+		outputPointer = (*C.char)(unsafe.Pointer(&output[0]))
+	}
+
+	_, err = C.call_iconv(converter.context, inputPointer, &inputLeft, outputPointer, &outputLeft)
 
-			// update byte counters
 	bytesRead = len(input) - int(inputLeft)
 	bytesWritten = len(output) - int(outputLeft)
-		} else if inputLeft == 0 && outputLeft > 0 {
-			// inputPointer will be nil, outputPointer is generated as above
-			outputPointer := (*C.char)(unsafe.Pointer(&output[0]))
-
-			_, err = C.call_iconv(this.context, nil, &inputLeft, outputPointer, &outputLeft)
-
-			// update write byte counter
-			bytesWritten = len(output) - int(outputLeft)
-		} else {
-			// both input and output are zero length, do a shift state reset
-			_, err = C.call_iconv(this.context, nil, &inputLeft, nil, &outputLeft)
-		}
-	} else {
-		err = syscall.EBADF
-	}
 
 	return bytesRead, bytesWritten, err
 }
 
 // Convert an input string
 //
-// EILSEQ error may be returned if input contains invalid bytes for the
-// Converter's fromEncoding.
-func (this *Converter) ConvertString(input string) (output string, err error) {
-	// make sure we are still open
-	if this.open {
+// EILSEQ error may be returned if input contains invalid bytes for the Converter's fromEncoding
+func (converter *Converter) ConvertString(input string) (output string, err error) {
 	// construct the buffers
 	inputBuffer := []byte(input)
 	outputBuffer := make([]byte, len(inputBuffer)*2) // we use a larger buffer to help avoid resizing later
@@ -127,14 +103,13 @@ func (this *Converter) ConvertString(input string) (output string, err error) {
 
 	for totalBytesRead < len(inputBuffer) && err == nil {
 		// use the totals to create buffer slices
-			bytesRead, bytesWritten, err = this.Convert(inputBuffer[totalBytesRead:], outputBuffer[totalBytesWritten:])
+		bytesRead, bytesWritten, err = converter.Convert(inputBuffer[totalBytesRead:], outputBuffer[totalBytesWritten:])
 
 		totalBytesRead += bytesRead
 		totalBytesWritten += bytesWritten
 
-			// check for the E2BIG error specifically, we can add to the output
-			// buffer to correct for it and then continue
-			if err == syscall.E2BIG {
+		switch err {
+		case syscall.E2BIG:
 			// increase the size of the output buffer by another input length
 			// first, create a new buffer
 			tempBuffer := make([]byte, len(outputBuffer)+len(inputBuffer))
@@ -147,12 +122,17 @@ func (this *Converter) ConvertString(input string) (output string, err error) {
 
 			// forget the error
 			err = nil
+		case syscall.EILSEQ, syscall.EINVAL:
+			// iconv can still return these in cases where it still can proceed such as //IGNORE
+			if bytesRead > 0 || bytesWritten > 0 {
+				err = nil
+			}
 		}
 	}
 
 	if err == nil {
 		// perform a final shift state reset
-			_, bytesWritten, err = this.Convert([]byte{}, outputBuffer[totalBytesWritten:])
+		_, bytesWritten, err = converter.Convert(nil, outputBuffer[totalBytesWritten:])
 
 		// update total count
 		totalBytesWritten += bytesWritten
@@ -160,9 +140,10 @@ func (this *Converter) ConvertString(input string) (output string, err error) {
 
 	// construct the final output string
 	output = string(outputBuffer[:totalBytesWritten])
-	} else {
-		err = syscall.EBADF
-	}
 
 	return output, err
 }
+
+func finalizeConverter(converter *Converter) {
+	converter.Close()
+}

iconv_test.go

@@ -1,6 +1,9 @@
 package iconv
 
 import (
+	"bytes"
+	"io"
+	"strings"
 	"syscall"
 	"testing"
 )
@@ -13,105 +16,486 @@ type iconvTest struct {
 	outputEncoding string
 	bytesRead      int
 	bytesWritten   int
-	err            error
+	convertErr     error // err from Convert (raw iconv)
+	err            error // err from CovertString, Reader, Writer
 }
 
-var iconvTests = []iconvTest{
+var (
+	iconvTests = []iconvTest{
 		iconvTest{
 			"simple utf-8 to latin1 conversion success",
 			"Hello World!", "utf-8",
 			"Hello World!", "latin1",
-		12, 12, nil,
+			12, 12, nil, nil,
 		},
 		iconvTest{
 			"invalid source encoding causes EINVAL",
 			"", "doesnotexist",
 			"", "utf-8",
-		0, 0, syscall.EINVAL,
+			0, 0, syscall.EINVAL, syscall.EINVAL,
 		},
 		iconvTest{
 			"invalid destination encoding causes EINVAL",
 			"", "utf-8",
 			"", "doesnotexist",
-		0, 0, syscall.EINVAL,
+			0, 0, syscall.EINVAL, syscall.EINVAL,
+		},
+		iconvTest{
+			"utf-8 to utf-8 passthrough",
+			"Hello world!", "utf-8",
+			"Hello world!", "utf-8",
+			12, 12, nil, nil,
+		},
+		iconvTest{
+			"utf-8 to utf-8 partial",
+			"Hello\xFFWorld!", "utf-8",
+			"Hello", "utf-8",
+			5, 5, syscall.EILSEQ, syscall.EILSEQ,
+		},
+		iconvTest{
+			"utf-8 to utf-8 ignored",
+			"Hello \xFFWorld!", "utf-8",
+			"Hello World!", "utf-8//IGNORE",
+			13, 12, syscall.EILSEQ, nil,
 		},
 		iconvTest{
 			"invalid input sequence causes EILSEQ",
 			"\xFF", "utf-8",
 			"", "latin1",
-		0, 0, syscall.EILSEQ,
+			0, 0, syscall.EILSEQ, syscall.EILSEQ,
+		},
+		iconvTest{
+			"incomplete input sequence causes EINVAL",
+			"\xC2", "utf-8",
+			"", "latin1",
+			0, 0, syscall.EINVAL, syscall.EINVAL,
 		},
 		iconvTest{
 			"invalid input causes partial output and EILSEQ",
 			"Hello\xFF", "utf-8",
 			"Hello", "latin1",
-		5, 5, syscall.EILSEQ,
+			5, 5, syscall.EILSEQ, syscall.EILSEQ,
+		},
+		iconvTest{
+			"incomplete input causes partial output and EILSEQ",
+			"Hello\xC2", "utf-8",
+			"Hello", "latin1",
+			5, 5, syscall.EINVAL, syscall.EINVAL,
+		},
+		/* this is only true for glibc / iconv
+		iconvTest{
+			"valid input but no conversion causes EILSEQ",
+			"你好世界 Hello World", "utf-8",
+			"", "latin1",
+			0, 0, syscall.EILSEQ, syscall.EILSEQ,
+		},*/
+		iconvTest{
+			"invalid input with ignore",
+			"Hello\xFF World!", "utf-8",
+			"Hello World!", "latin1//IGNORE",
+			13, 12, syscall.EILSEQ, nil,
+		},
+		iconvTest{
+			"valid input but no conversion with IGNORE",
+			"你好世界 Hello World", "utf-8",
+			" Hello World", "latin1//IGNORE",
+			24, 12, syscall.EILSEQ, nil,
+		},
+		iconvTest{
+			"valid input but no conversion with TRANSLIT",
+			"你好世界 Hello World", "utf-8",
+			"???? Hello World", "latin1//TRANSLIT",
+			24, 16, nil, nil,
 		},
 	}
 
-func TestConvertString(t *testing.T) {
-	for _, test := range iconvTests {
-		// perform the conversion
-		output, err := ConvertString(test.input, test.inputEncoding, test.outputEncoding)
+	ignoreDetected, translitDetected bool
+)
 
-		// check that output and err match
+func init() {
+	// detect if IGNORE / TRANSLIT is supported (glic / libiconv)
+	conv, err := NewConverter("utf-8", "ascii//IGNORE")
+
+	if err == nil {
+		ignoreDetected = true
+		conv.Close()
+	}
+
+	conv, err = NewConverter("utf-8", "ascii//TRANSLIT")
+
+	if err == nil {
+		translitDetected = true
+		conv.Close()
+	}
+}
+
+func runTests(t *testing.T, f func(iconvTest, *testing.T) (int, int, string, error)) {
+	for _, test := range iconvTests {
+		t.Run(test.description, func(t *testing.T) {
+			if !ignoreDetected && strings.HasSuffix(test.outputEncoding, "//IGNORE") {
+				t.Skip("//IGNORE not supported")
+			}
+
+			if !translitDetected && strings.HasSuffix(test.outputEncoding, "//TRANSLIT") {
+				t.Skip("//TRANSLIT not supported")
+			}
+
+			bytesRead, bytesWritten, output, err := f(test, t)
+
+			// check that bytesRead is same as expected
+			if bytesRead != test.bytesRead {
+				t.Errorf("bytesRead: %d expected: %d", bytesRead, test.bytesRead)
+			}
+
+			// check that bytesWritten is same as expected
+			if bytesWritten != test.bytesWritten {
+				t.Errorf("bytesWritten: %d expected: %d", bytesWritten, test.bytesWritten)
+			}
+
+			// check output bytes against expected
 			if output != test.output {
-			t.Errorf("test \"%s\" failed, output did not match expected", test.description)
+				t.Errorf("output: %x expected: %x", output, test.output)
 			}
 
 			// check that err is same as expected
 			if err != test.err {
 				if test.err != nil {
 					if err != nil {
-					t.Errorf("test \"%s\" failed, got %s when expecting %s", test.description, err, test.err)
+						t.Errorf("err: %q expected: %q", err, test.err)
 					} else {
-					t.Errorf("test \"%s\" failed, got nil when expecting %s", test.description, test.err)
+						t.Errorf("err: nil expected %q", test.err)
 					}
 				} else {
-				t.Errorf("test \"%s\" failed, got unexpected error: %s", test.description, err)
+					t.Errorf("unexpected error: %q", err)
 				}
 			}
+		})
 	}
 }
 
 func TestConvert(t *testing.T) {
-	for _, test := range iconvTests {
-		// setup input buffer
+	runTests(t, func(test iconvTest, t *testing.T) (int, int, string, error) {
 		input := []byte(test.input)
-
-		// setup a buffer as large as the expected bytesWritten
 		output := make([]byte, 50)
 
 		// peform the conversion
 		bytesRead, bytesWritten, err := Convert(input, output, test.inputEncoding, test.outputEncoding)
 
-		// check that bytesRead is same as expected
-		if bytesRead != test.bytesRead {
-			t.Errorf("test \"%s\" failed, bytesRead did not match expected", test.description)
-		}
-
-		// check that bytesWritten is same as expected
-		if bytesWritten != test.bytesWritten {
-			t.Errorf("test \"%s\" failed, bytesWritten did not match expected", test.description)
-		}
-
-		// check output bytes against expected - simplest to convert output to
-		// string and then do an equality check which is actually a byte wise operation
-		if string(output[:bytesWritten]) != test.output {
-			t.Errorf("test \"%s\" failed, output did not match expected", test.description)
-		}
-
-		// check that err is same as expected
-		if err != test.err {
-			if test.err != nil {
+		// HACK Convert has different erorrs, so check ourselves, and then fake out later check
+		if err != test.convertErr {
+			if test.convertErr != nil {
 				if err != nil {
-					t.Errorf("test \"%s\" failed, got %s when expecting %s", test.description, err, test.err)
+					t.Errorf("err: %q expected: %q", err, test.convertErr)
 				} else {
-					t.Errorf("test \"%s\" failed, got nil when expecting %s", test.description, test.err)
+					t.Errorf("err: nil expected %q", test.convertErr)
 				}
 			} else {
-				t.Errorf("test \"%s\" failed, got unexpected error: %s", test.description, err)
+				t.Errorf("unexpected error: %q", err)
+			}
+		}
+		err = test.err
+
+		return bytesRead, bytesWritten, string(output[:bytesWritten]), err
+	})
+}
+
+func TestConvertString(t *testing.T) {
+	runTests(t, func(test iconvTest, t *testing.T) (int, int, string, error) {
+		// perform the conversion
+		output, err := ConvertString(test.input, test.inputEncoding, test.outputEncoding)
+
+		// bytesRead and bytesWritten are spoofed a little
+		return test.bytesRead, len(output), output, err
+	})
+}
+
+func TestReader(t *testing.T) {
+	runTests(t, func(test iconvTest, t *testing.T) (int, int, string, error) {
+		var bytesRead, bytesWritten, finalBytesWritten int
+		var err error
+
+		input := bytes.NewBufferString(test.input)
+		output := make([]byte, 50)
+
+		reader, err := NewReader(input, test.inputEncoding, test.outputEncoding)
+
+		if err == nil {
+			bytesWritten, err = reader.Read(output)
+
+			// we can compute how many bytes iconv read by inspecting the reader state
+			bytesRead = len([]byte(test.input)) - input.Len() - (reader.writePos - reader.readPos)
+
+			// with current tests and buffer sizes, we'd expect all input to be buffered if we called read
+			if input.Len() != 0 {
+				t.Error("not all bytes from input were buffered")
+			}
+
+			// do final read test if we can - either get EOF or same test error
+			if err == nil {
+				finalBytesWritten, err = reader.Read(output[bytesWritten:])
+
+				if finalBytesWritten != 0 {
+					t.Errorf("finalBytesWritten: %d expected: 0", finalBytesWritten)
+				}
+
+				if err == io.EOF {
+					err = nil
 				}
 			}
 		}
+
+		return bytesRead, bytesWritten, string(output[:bytesWritten]), err
+	})
+}
+
+func TestWriter(t *testing.T) {
+	runTests(t, func(test iconvTest, t *testing.T) (int, int, string, error) {
+		var bytesRead, bytesWritten int
+		var err error
+
+		input := []byte(test.input)
+		output := new(bytes.Buffer)
+
+		writer, err := NewWriter(output, test.inputEncoding, test.outputEncoding)
+
+		if err == nil {
+			bytesRead, err = writer.Write(input)
+			bytesRead -= writer.readPos
+			writer.Close()
+
+			bytesWritten = output.Len()
+		}
+
+		return bytesRead, bytesWritten, output.String(), err
+	})
+}
+
+func TestReaderWithCopy(t *testing.T) {
+	runTests(t, func(test iconvTest, t *testing.T) (int, int, string, error) {
+		input := bytes.NewBufferString(test.input)
+		output := new(bytes.Buffer)
+
+		reader, err := NewReader(input, test.inputEncoding, test.outputEncoding)
+
+		if err == nil {
+			_, err := io.Copy(output, reader)
+
+			bytesRead := len(test.input) - input.Len() - reader.writePos
+			bytesWritten := output.Len()
+
+			return bytesRead, bytesWritten, output.String(), err
+		}
+
+		return 0, 0, output.String(), err
+	})
+}
+
+func TestWriterWithCopy(t *testing.T) {
+	runTests(t, func(test iconvTest, t *testing.T) (int, int, string, error) {
+		input := bytes.NewBufferString(test.input)
+		output := new(bytes.Buffer)
+
+		writer, err := NewWriter(output, test.inputEncoding, test.outputEncoding)
+
+		if err == nil {
+			bytesCopied, err := io.Copy(writer, input)
+			bytesRead := int(bytesCopied) - writer.readPos
+			writer.Close()
+
+			bytesWritten := output.Len()
+
+			return bytesRead, bytesWritten, output.String(), err
+		}
+
+		return 0, 0, output.String(), err
+	})
+}
+
+func TestReaderMultipleReads(t *testing.T) {
+	// setup a source reader and our expected output string
+	source := bytes.NewBufferString("\x80\x8A\x99\x95\x8B\x86\x87")
+	expected := "€Š™•‹†‡"
+
+	// setup reader - use our minimum buffer size so we can force it to shuffle the buffer around
+	reader, err := NewReaderSized(source, "cp1252", "utf-8", minReadBufferSize)
+
+	if err != nil {
+		if err == syscall.EINVAL {
+			t.Skip("Either cp1252 or utf-8 isn't supported by iconv on your system")
+		} else {
+			t.Fatalf("Unexpected error when creating reader: %s", err)
+		}
+	}
+
+	// setup a read buffer - we'll slice it to different sizes in our tests
+	buffer := make([]byte, 64)
+
+	// first read should fill internal buffer, but we'll only read part of it
+	bytesRead, err := reader.Read(buffer[:5])
+
+	if bytesRead != 5 || err != nil {
+		t.Fatalf("first read did not give expected 5, nil: %d, %s", bytesRead, err)
+	}
+
+	// because of how small teh source is and our minimum buffer size, source shoudl be fully read
+	if source.Len() != 0 {
+		t.Fatalf("first read did not buffer all of source like expected: %d bytes remain", source.Len())
+	}
+
+	// Buffer doesn't return EOF with last bytes, reader shouldn't know its EOF yet
+	if reader.eof {
+		t.Fatalf("first read was not expected to receive EOF")
+	}
+
+	// second read should shift internal buffer, and fill again - make buffer too small for last utf-8 character
+	// E2BIG from iconv should be ignored because we wrote at least 1 byte
+	bytesRead, err = reader.Read(buffer[5:18])
+
+	if bytesRead != 12 || err != nil {
+		t.Fatalf("second read did not give expected 15, nil: %d, %s", bytesRead, err)
+	}
+
+	if !reader.eof {
+		t.Fatalf("second read did not put reader into eof state")
+	}
+
+	// try to read the last 3 byte character with only a buffer of 2 bytes - this time we should see the E2BIG
+	bytesRead, err = reader.Read(buffer[17:19])
+
+	if bytesRead != 0 || err != syscall.E2BIG {
+		t.Fatalf("third read did not give expected 0, E2BIG: %d, %s", bytesRead, err)
+	}
+
+	// fourth read should finish last character
+	bytesRead, err = reader.Read(buffer[17:])
+
+	if bytesRead != 3 || err != nil {
+		t.Fatalf("fourth read did not give expected 3, nil: %d, %s", bytesRead, err)
+	}
+
+	// last read should be EOF
+	bytesRead, err = reader.Read(buffer[20:])
+
+	if bytesRead != 0 || err != io.EOF {
+		t.Fatalf("final read did not give expected 0, EOF: %d, %s", bytesRead, err)
+	}
+
+	// check full utf-8 output
+	if string(buffer[:20]) != expected {
+		t.Fatalf("output did not match expected %q: %q", expected, string(buffer[:20]))
+	}
+}
+
+func TestWriteWithIncompleteSequence(t *testing.T) {
+	expected := "\x80\x8A\x99\x95\x8B\x86\x87"
+	input := []byte("€Š™•‹†‡")
+	output := new(bytes.Buffer)
+
+	writer, err := NewWriter(output, "utf-8", "cp1252")
+
+	if err != nil {
+		t.Fatalf("unexpected error while creating writer %q", err)
+	}
+
+	// the input string is made of 3 byte characters, for the test we want to only write part of the last character
+	bytesFromBuffer := len(input) - 2
+
+	bytesRead, err := writer.Write(input[:bytesFromBuffer])
+
+	if bytesRead != bytesFromBuffer {
+		t.Fatalf("did a short write on first write: %d, %s", bytesRead, err)
+	}
+
+	// finish the rest
+	bytesRead, err = writer.Write(input[bytesFromBuffer:])
+
+	if bytesRead != 2 {
+		t.Fatalf("did a short write on second write: %d, %s", bytesRead, err)
+	}
+
+	err = writer.Close()
+	actual := output.String()
+
+	if err != nil {
+		t.Errorf("got an error on close: %s", err)
+	}
+
+	if actual != expected {
+		t.Errorf("output %x did not match expected %x", actual, expected)
+	}
+}
+
+func TestWriteWithIncompleteSequenceAndIgnore(t *testing.T) {
+	if !ignoreDetected {
+		t.Skip("//IGNORE not supported")
+	}
+
+	expected := "\x80\x8A\x99\x95\x8B\x86\x87"
+	input := []byte("€Š™•‹†‡")
+	output := new(bytes.Buffer)
+
+	writer, err := NewWriter(output, "utf-8", "cp1252//IGNORE")
+
+	if err != nil {
+		t.Fatalf("unexpected error while creating writer %q", err)
+	}
+
+	// the input string is made of 3 byte characters, for the test we want to only write part of the last character
+	bytesFromBuffer := len(input) - 2
+
+	bytesRead, err := writer.Write(input[:bytesFromBuffer])
+
+	if bytesRead != bytesFromBuffer {
+		t.Fatalf("did a short write on first write: %d, %s", bytesRead, err)
+	}
+
+	// finish the rest
+	bytesRead, err = writer.Write(input[bytesFromBuffer:])
+
+	if bytesRead != 2 {
+		t.Fatalf("did a short write on second write: %d, %s", bytesRead, err)
+	}
+
+	err = writer.Close()
+	actual := output.String()
+
+	if err != nil {
+		t.Errorf("got an error on close: %s", err)
+	}
+
+	if actual != expected {
+		t.Errorf("output %x did not match expected %x", actual, expected)
+	}
+}
+
+func TestWriteWithIncompleteSequenceAtEOF(t *testing.T) {
+	expected := "\x80\x8A\x99\x95\x8B\x86"
+	input := []byte("€Š™•‹†‡")
+	output := new(bytes.Buffer)
+
+	writer, err := NewWriter(output, "utf-8", "cp1252")
+
+	if err != nil {
+		t.Fatalf("unexpected error while creating writer %q", err)
+	}
+
+	// the input string is made of 3 byte characters, for the test we want to only write part of the last character
+	bytesFromBuffer := len(input) - 2
+
+	bytesRead, err := writer.Write(input[:bytesFromBuffer])
+
+	if bytesRead != bytesFromBuffer {
+		t.Fatalf("did a short write on first write: %d, %s", bytesRead, err)
+	}
+
+	err = writer.Close()
+	actual := output.String()
+
+	if err != nil {
+		t.Errorf("got an error on close: %s", err)
+	}
+
+	if actual != expected {
+		t.Errorf("output %x did not match expected %x", actual, expected)
+	}
 }

reader.go

@@ -2,7 +2,12 @@ package iconv
 
 import (
 	"io"
-	"syscall"
+	"runtime"
+)
+
+const (
+	defaultReadBufferSize = 8 * 1024
+	minReadBufferSize     = 16
 )
 
 type Reader struct {
@@ -10,91 +15,100 @@ type Reader struct {
 	converter         *Converter
 	buffer            []byte
 	readPos, writePos int
-	err               error
+	eof               bool
 }
 
-func NewReader(source io.Reader, fromEncoding string, toEncoding string) (*Reader, error) {
-	// create a converter
+func NewReader(source io.Reader, fromEncoding, toEncoding string) (*Reader, error) {
+	return NewReaderSized(source, fromEncoding, toEncoding, defaultReadBufferSize)
+}
+
+func NewReaderFromConverter(source io.Reader, converter *Converter) *Reader {
+	return NewReaderFromConverterSized(source, converter, defaultReadBufferSize)
+}
+
+func NewReaderSized(source io.Reader, fromEncoding, toEncoding string, size int) (*Reader, error) {
 	converter, err := NewConverter(fromEncoding, toEncoding)
 
-	if err == nil {
-		return NewReaderFromConverter(source, converter), err
-	}
-
-	// return the error
+	if err != nil {
 		return nil, err
 	}
 
-func NewReaderFromConverter(source io.Reader, converter *Converter) (reader *Reader) {
-	reader = new(Reader)
+	// add a finalizer for the converter we created
+	runtime.SetFinalizer(converter, finalizeConverter)
 
-	// copy elements
-	reader.source = source
-	reader.converter = converter
-
-	// create 8K buffers
-	reader.buffer = make([]byte, 8*1024)
-
-	return reader
+	return NewReaderFromConverterSized(source, converter, size), nil
 }
 
-func (this *Reader) fillBuffer() {
-	// slide existing data to beginning
-	if this.readPos > 0 {
-		// copy current bytes - is this guaranteed safe?
-		copy(this.buffer, this.buffer[this.readPos:this.writePos])
-
-		// adjust positions
-		this.writePos -= this.readPos
-		this.readPos = 0
+func NewReaderFromConverterSized(source io.Reader, converter *Converter, size int) *Reader {
+	if size < minReadBufferSize {
+		size = minReadBufferSize
 	}
 
-	// read new data into buffer at write position
-	bytesRead, err := this.source.Read(this.buffer[this.writePos:])
-
-	// adjust write position
-	this.writePos += bytesRead
-
-	// track any reader error / EOF
-	if err != nil {
-		this.err = err
+	return &Reader{
+		source:    source,
+		converter: converter,
+		buffer:    make([]byte, size),
 	}
 }
 
-// implement the io.Reader interface
-func (this *Reader) Read(p []byte) (n int, err error) {
-	// checks for when we have no data
-	for this.writePos == 0 || this.readPos == this.writePos {
-		// if we have an error / EOF, just return it
-		if this.err != nil {
-			return n, this.err
+func (r *Reader) Read(p []byte) (int, error) {
+	if len(p) == 0 {
+		return 0, nil
 	}
 
-		// else, fill our buffer
-		this.fillBuffer()
+	var bytesRead, bytesWritten int
+	var err error
+
+	// setup for a single read into buffer if possible
+	if !r.eof {
+		if r.readPos > 0 {
+			// slide data to front of buffer
+			r.readPos, r.writePos = 0, copy(r.buffer, r.buffer[r.readPos:r.writePos])
 		}
 
-	// TODO: checks for when we have less data than len(p)
+		if r.writePos < len(r.buffer) {
+			// do the single read
+			bytesRead, err = r.source.Read(r.buffer[r.writePos:])
 
-	// we should have an appropriate amount of data, convert it into the given buffer
-	bytesRead, bytesWritten, err := this.converter.Convert(this.buffer[this.readPos:this.writePos], p)
+			if bytesRead < 0 {
+				panic("iconv: source reader returned negative count from Read")
+			}
 
-	// adjust byte counters
-	this.readPos += bytesRead
-	n += bytesWritten
-
-	// if we experienced an iconv error, check it
-	if err != nil {
-		// E2BIG errors can be ignored (we'll get them often) as long
-		// as at least 1 byte was written. If we experienced an E2BIG
-		// and no bytes were written then the buffer is too small for
-		// even the next character
-		if err != syscall.E2BIG || bytesWritten == 0 {
-			// track anything else
-			this.err = err
+			r.writePos += bytesRead
+			r.eof = err == io.EOF
 		}
 	}
 
-	// return our results
-	return n, this.err
+	if r.readPos < r.writePos || r.eof {
+		// convert any buffered data we have, or do a final reset (for shift based conversions)
+		bytesRead, bytesWritten, err = r.converter.Convert(r.buffer[r.readPos:r.writePos], p)
+		r.readPos += bytesRead
+
+		// if we experienced an iconv error and didn't make progress, report it.
+		// if we did make progress, it may be informational only (i.e. reporting
+		// an EILSEQ even when using //ignore to skip them)
+		if err != nil && bytesWritten == 0 {
+			return bytesWritten, err
+		}
+
+		// signal an EOF only if we didn't write anything - accomodates premature
+		// errror checking in user code
+		if bytesWritten == 0 && r.eof {
+			return 0, io.EOF
+		}
+
+		return bytesWritten, nil
+	}
+
+	return 0, err
+}
+
+func (r *Reader) Reset(source io.Reader) {
+	r.converter.Reset()
+
+	*r = Reader{
+		source:    source,
+		converter: r.converter,
+		buffer:    r.buffer,
+	}
 }

writer.go

@@ -1,82 +1,181 @@
 package iconv
 
-import "io"
+import (
+	"io"
+	"runtime"
+	"syscall"
+)
+
+const (
+	defaultWriteBufferSize = 8 * 1024
+	minWriteBufferSize     = 16
+)
 
 type Writer struct {
 	destination             io.Writer
 	converter               *Converter
-	buffer            []byte
+	readBuffer, writeBuffer []byte
 	readPos, writePos       int
-	err               error
 }
 
 func NewWriter(destination io.Writer, fromEncoding string, toEncoding string) (*Writer, error) {
-	// create a converter
-	converter, err := NewConverter(fromEncoding, toEncoding)
-
-	if err == nil {
-		return NewWriterFromConverter(destination, converter), err
-	}
-
-	// return the error
-	return nil, err
+	return NewWriterSized(destination, fromEncoding, toEncoding, defaultWriteBufferSize)
 }
 
 func NewWriterFromConverter(destination io.Writer, converter *Converter) (writer *Writer) {
-	writer = new(Writer)
-
-	// copy elements
-	writer.destination = destination
-	writer.converter = converter
-
-	// create 8K buffers
-	writer.buffer = make([]byte, 8*1024)
-
-	return writer
+	return NewWriterFromConverterSized(destination, converter, defaultWriteBufferSize)
 }
 
-func (this *Writer) emptyBuffer() {
-	// write new data out of buffer
-	bytesWritten, err := this.destination.Write(this.buffer[this.readPos:this.writePos])
+func NewWriterSized(destination io.Writer, fromEncoding, toEncoding string, size int) (*Writer, error) {
+	converter, err := NewConverter(fromEncoding, toEncoding)
 
-	// update read position
-	this.readPos += bytesWritten
-
-	// slide existing data to beginning
-	if this.readPos > 0 {
-		// copy current bytes - is this guaranteed safe?
-		copy(this.buffer, this.buffer[this.readPos:this.writePos])
-
-		// adjust positions
-		this.writePos -= this.readPos
-		this.readPos = 0
-	}
-
-	// track any reader error / EOF
 	if err != nil {
-		this.err = err
+		return nil, err
+	}
+
+	// add a finalizer for the converter we created
+	runtime.SetFinalizer(converter, finalizeConverter)
+
+	return NewWriterFromConverterSized(destination, converter, size), nil
+}
+
+func NewWriterFromConverterSized(destination io.Writer, converter *Converter, size int) *Writer {
+	if size < minWriteBufferSize {
+		size = minWriteBufferSize
+	}
+
+	return &Writer{
+		destination: destination,
+		converter:   converter,
+		readBuffer:  make([]byte, size),
+		writeBuffer: make([]byte, size),
 	}
 }
 
-// implement the io.Writer interface
-func (this *Writer) Write(p []byte) (n int, err error) {
-	// write data into our internal buffer
-	bytesRead, bytesWritten, err := this.converter.Convert(p, this.buffer[this.writePos:])
+// Implements io.Writer
+//
+// Will attempt to convert all of p into buffer. If there's not enough room in
+// the buffer to hold all converted bytes, the buffer will be flushed and p will
+// continue to be processed. Close should be called on a writer when finished
+// with all writes, to ensure final shift sequences are written and buffer is
+// flushed to underlying io.Writer.
+//
+// Can return all errors that Convert can, as well as any errors from Flush. Note
+// that some errors from Convert are suppressed if we continue making progress
+// on p.
+func (w *Writer) Write(p []byte) (int, error) {
+	var totalBytesRead, bytesRead, bytesWritten int
+	var err error
 
-	// update bytes written for return
-	n += bytesRead
-	this.writePos += bytesWritten
+	if w.readPos == 0 || len(p) == 0 {
+		bytesRead, bytesWritten, err = w.converter.Convert(p, w.writeBuffer[w.writePos:])
+		totalBytesRead += bytesRead
+		w.writePos += bytesWritten
+		w.readPos = 0
+	} else {
+		// we have left over bytes from previous write that weren't complete and there's at least
+		// one byte being written, fill read buffer with p and try to convert, if we make progress
+		// we can continue conversion from p itself
+		bytesCopied := copy(w.readBuffer[w.readPos:], p)
 
-	// checks for when we have a full buffer
-	for this.writePos > 0 {
-		// if we have an error, just return it
-		if this.err != nil {
-			return
+		bytesRead, bytesWritten, err = w.converter.Convert(w.readBuffer[:w.readPos+bytesCopied], w.writeBuffer[w.writePos:])
+
+		// if we made no progress, give up
+		if bytesRead <= w.readPos {
+			return 0, err
 		}
 
-		// else empty the buffer
-		this.emptyBuffer()
+		bytesRead -= w.readPos
+		totalBytesRead += bytesRead
+
+		w.readPos = 0
+		w.writePos += bytesWritten
 	}
 
-	return n, err
+	// try to process all of p - lots of io functions don't like short writes.
+	//
+	// There are a few error cases we need to treat specially, as long as we've
+	// made progress on p, E2BIG and EILSEQ should not be fatal. EINVAL isn't
+	// fatal as long as the rest of p fits in our buffers.
+	for err != nil && bytesRead > 0 {
+		switch err {
+		case syscall.E2BIG:
+			err = w.Flush()
+
+		case syscall.EILSEQ:
+			// IGNORE suffix still reports the error on convert
+			err = nil
+
+			// if no more bytes, don't do an empty convert (resets state)
+			if totalBytesRead == len(p) {
+				break
+			}
+
+		case syscall.EINVAL:
+			// if the rest of p fits in read buffer copy it there
+			if len(p[totalBytesRead:]) <= len(w.readBuffer) {
+				w.readPos = copy(w.readBuffer, p[totalBytesRead:])
+				totalBytesRead += w.readPos
+				break
+			}
+		}
+
+		// if not an ignoreable err or Flush err
+		if err != nil {
+			break
+		}
+
+		bytesRead, bytesWritten, err = w.converter.Convert(p[totalBytesRead:], w.writeBuffer[w.writePos:])
+		totalBytesRead += bytesRead
+		w.writePos += bytesWritten
+	}
+
+	return totalBytesRead, err
+}
+
+// Attempt to write any buffered data to destination writer. Returns error from
+// Write call or io.ErrShortWrite if Write didn't report an error but also didn't
+// accept all bytes given.
+func (w *Writer) Flush() error {
+	if w.readPos < w.writePos {
+		bytesWritten, err := w.destination.Write(w.writeBuffer[:w.writePos])
+
+		if bytesWritten < 0 {
+			panic("iconv: writer returned negative count from Write")
+		}
+
+		if bytesWritten > 0 {
+			w.writePos = copy(w.writeBuffer, w.writeBuffer[bytesWritten:w.writePos])
+		}
+
+		if err == nil && w.writePos > 0 {
+			err = io.ErrShortWrite
+		}
+
+		return err
+	}
+
+	return nil
+}
+
+// Perform a final write with empty buffer, which allows iconv to close any shift
+// sequences. A Flush is performed if needed.
+func (w *Writer) Close() error {
+	_, err := w.Write(nil)
+	if err != nil {
+		return err
+	}
+	return w.Flush()
+}
+
+// Reset state and direct writes to a new destination writer
+func (w *Writer) Reset(destination io.Writer) {
+	w.converter.Reset()
+
+	*w = Writer{
+		destination: destination,
+		converter:   w.converter,
+		readBuffer:  w.readBuffer,
+		writeBuffer: w.writeBuffer,
+	}
 }