write(), print(), and println() now return number of bytes written.

The type is long, and negative values indicate errors.  Needs more testing.
http://code.google.com/p/arduino/issues/detail?id=551

hardware/arduino/cores/arduino/HardwareSerial.cpp

@@ -352,12 +352,13 @@ void HardwareSerial::flush()
     ;
 }
 
-void HardwareSerial::write(uint8_t c)
+long HardwareSerial::write(uint8_t c)
 {
   int i = (_tx_buffer->head + 1) % SERIAL_BUFFER_SIZE;
 	
   // If the output buffer is full, there's nothing for it other than to 
   // wait for the interrupt handler to empty it a bit
+  // ???: return 0 here instead?
   while (i == _tx_buffer->tail)
     ;
 	
@@ -365,6 +366,8 @@ void HardwareSerial::write(uint8_t c)
   _tx_buffer->head = i;
 	
   sbi(*_ucsrb, _udrie);
+  
+  return 1;
 }
 
 // Preinstantiate Objects //////////////////////////////////////////////////////

hardware/arduino/cores/arduino/HardwareSerial.h

@@ -55,7 +55,7 @@ class HardwareSerial : public Stream
     virtual int peek(void);
     virtual int read(void);
     virtual void flush(void);
-    virtual void write(uint8_t);
+    virtual long write(uint8_t);
     using Print::write; // pull in write(str) and write(buf, size) from Print
 };
 

hardware/arduino/cores/arduino/Print.cpp

@@ -30,167 +30,196 @@
 // Public Methods //////////////////////////////////////////////////////////////
 
 /* default implementation: may be overridden */
-void Print::write(const char *str)
+long Print::write(const char *str)
 {
-  while (*str)
-    write(*str++);
+  long n = 0;
+  while (*str) {
+    if (write(*str++) <= 0) break;
+    n++;
+  }
+  return n;
 }
 
 /* default implementation: may be overridden */
-void Print::write(const uint8_t *buffer, size_t size)
+long Print::write(const uint8_t *buffer, size_t size)
 {
-  while (size--)
-    write(*buffer++);
+  long n = 0;
+  while (size--) {
+    if (write(*buffer++) <= 0) break;
+    n++;
+  }
+  return n;
 }
 
-void Print::print(const __FlashStringHelper *ifsh)
+long Print::print(const __FlashStringHelper *ifsh)
 {
   const prog_char *p = (const prog_char *)ifsh;
+  long n = 0;
   while (1) {
     unsigned char c = pgm_read_byte(p++);
-    if (c == 0) return;
-    write(c);
+    if (c == 0) break;
+    if (write(c) <= 0) break;
+    n++;
   }
+  return n;
 }
 
-void Print::print(const String &s)
+long Print::print(const String &s)
 {
+  long n = 0;
   for (int i = 0; i < s.length(); i++) {
-    write(s[i]);
+    if (write(s[i]) < 0) break;
+    n++;
   }
+  return n;
 }
 
-void Print::print(const char str[])
+long Print::print(const char str[])
 {
-  write(str);
+  return write(str);
 }
 
-void Print::print(char c)
+long Print::print(char c)
 {
-  write(c);
+  return write(c);
 }
 
-void Print::print(unsigned char b, int base)
+long Print::print(unsigned char b, int base)
 {
-  print((unsigned long) b, base);
+  return print((unsigned long) b, base);
 }
 
-void Print::print(int n, int base)
+long Print::print(int n, int base)
 {
-  print((long) n, base);
+  return print((long) n, base);
 }
 
-void Print::print(unsigned int n, int base)
+long Print::print(unsigned int n, int base)
 {
-  print((unsigned long) n, base);
+  return print((unsigned long) n, base);
 }
 
-void Print::print(long n, int base)
+long Print::print(long n, int base)
 {
   if (base == 0) {
-    write(n);
+    return write(n);
   } else if (base == 10) {
     if (n < 0) {
-      print('-');
+      long t = print('-');
+      if (t <= 0) return t;
       n = -n;
+      return printNumber(n, 10) + 1;
     }
-    printNumber(n, 10);
+    return printNumber(n, 10);
   } else {
-    printNumber(n, base);
+    return printNumber(n, base);
   }
 }
 
-void Print::print(unsigned long n, int base)
+long Print::print(unsigned long n, int base)
 {
-  if (base == 0) write(n);
-  else printNumber(n, base);
+  if (base == 0) return write(n);
+  else return printNumber(n, base);
 }
 
-void Print::print(double n, int digits)
+long Print::print(double n, int digits)
 {
-  printFloat(n, digits);
+  return printFloat(n, digits);
 }
 
-void Print::println(const __FlashStringHelper *ifsh)
+long Print::println(const __FlashStringHelper *ifsh)
 {
-  print(ifsh);
-  println();
+  long n = print(ifsh);
+  if (n >= 0) n += println();
+  return n;
 }
 
-void Print::print(const Printable& x)
+long Print::print(const Printable& x)
 {
-  x.printTo(*this);
+  return x.printTo(*this);
 }
 
-void Print::println(void)
+long Print::println(void)
 {
-  print('\r');
-  print('\n');
+  long t = print('\r');
+  if (t <= 0) return t;
+  if (print('\n') <= 0) return 1;
+  return 2;
 }
 
-void Print::println(const String &s)
+long Print::println(const String &s)
 {
-  print(s);
-  println();
+  long n = print(s);
+  if (n >= 0) n += println();
+  return n;
 }
 
-void Print::println(const char c[])
+long Print::println(const char c[])
 {
-  print(c);
-  println();
+  long n = print(c);
+  if (n >= 0) n += println();
+  return n;
 }
 
-void Print::println(char c)
+long Print::println(char c)
 {
-  print(c);
-  println();
+  long n = print(c);
+  if (n > 0) n += println();
+  return n;
 }
 
-void Print::println(unsigned char b, int base)
+long Print::println(unsigned char b, int base)
 {
-  print(b, base);
-  println();
+  long n = print(b, base);
+  if (n >= 0) n += println();
+  return n;
 }
 
-void Print::println(int n, int base)
+long Print::println(int num, int base)
 {
-  print(n, base);
-  println();
+  long n = print(num, base);
+  if (n >= 0) n += println();
+  return n;
 }
 
-void Print::println(unsigned int n, int base)
+long Print::println(unsigned int num, int base)
 {
-  print(n, base);
-  println();
+  long n = print(num, base);
+  if (n >= 0) n += println();
+  return n;
 }
 
-void Print::println(long n, int base)
+long Print::println(long num, int base)
 {
-  print(n, base);
-  println();
+  long n = print(num, base);
+  if (n >= 0) n += println();
+  return n;
 }
 
-void Print::println(unsigned long n, int base)
+long Print::println(unsigned long num, int base)
 {
-  print(n, base);
-  println();
+  long n = print(num, base);
+  if (n >= 0) n += println();
+  return n;
 }
 
-void Print::println(double n, int digits)
+long Print::println(double num, int digits)
 {
-  print(n, digits);
-  println();
+  long n = print(num, digits);
+  if (n >= 0) n += println();
+  return n;
 }
 
-void Print::println(const Printable& x)
+long Print::println(const Printable& x)
 {
-  print(x);
-  println();
+  long n = print(x);
+  if (n >= 0) n += println();
+  return n;
 }
 
 // Private Methods /////////////////////////////////////////////////////////////
 
-void Print::printNumber(unsigned long n, uint8_t base) {
+long Print::printNumber(unsigned long n, uint8_t base) {
   char buf[8 * sizeof(long) + 1]; // Assumes 8-bit chars plus zero byte.
   char *str = &buf[sizeof(buf) - 1];
 
@@ -206,15 +235,17 @@ void Print::printNumber(unsigned long n, uint8_t base) {
     *--str = c < 10 ? c + '0' : c + 'A' - 10;
   } while(n);
 
-  write(str);
+  return write(str);
 }
 
-void Print::printFloat(double number, uint8_t digits) 
+long Print::printFloat(double number, uint8_t digits) 
 { 
+  long n = 0, t;
+  
   // Handle negative numbers
   if (number < 0.0)
   {
-     print('-');
+     if ((n = print('-')) <= 0) return n;
      number = -number;
   }
 
@@ -228,18 +259,27 @@ void Print::printFloat(double number, uint8_t digits)
   // Extract the integer part of the number and print it
   unsigned long int_part = (unsigned long)number;
   double remainder = number - (double)int_part;
-  print(int_part);
+  if ((t = print(int_part)) < 0) return n;
+  
+  n += t;
 
   // Print the decimal point, but only if there are digits beyond
-  if (digits > 0)
-    print("."); 
+  if (digits > 0) {
+    t = print("."); 
+    if (t <= 0) return n;
+    n += t;
+  }
 
   // Extract digits from the remainder one at a time
   while (digits-- > 0)
   {
     remainder *= 10.0;
     int toPrint = int(remainder);
-    print(toPrint);
+    t = print(toPrint);
+    if (t <= 0) return n;
+    n += t;
     remainder -= toPrint; 
   } 
+  
+  return n;
 }

hardware/arduino/cores/arduino/Print.h

@@ -34,37 +34,37 @@
 class Print
 {
   private:
-    void printNumber(unsigned long, uint8_t);
-    void printFloat(double, uint8_t);
+    long printNumber(unsigned long, uint8_t);
+    long printFloat(double, uint8_t);
   public:
-    virtual void write(uint8_t) = 0;
-    virtual void write(const char *str);
-    virtual void write(const uint8_t *buffer, size_t size);
+    virtual long write(uint8_t) = 0;
+    virtual long write(const char *str);
+    virtual long write(const uint8_t *buffer, size_t size);
     
-    void print(const __FlashStringHelper *);
-    void print(const String &);
-    void print(const char[]);
-    void print(char);
-    void print(unsigned char, int = DEC);
-    void print(int, int = DEC);
-    void print(unsigned int, int = DEC);
-    void print(long, int = DEC);
-    void print(unsigned long, int = DEC);
-    void print(double, int = 2);
-    void print(const Printable&);
+    long print(const __FlashStringHelper *);
+    long print(const String &);
+    long print(const char[]);
+    long print(char);
+    long print(unsigned char, int = DEC);
+    long print(int, int = DEC);
+    long print(unsigned int, int = DEC);
+    long print(long, int = DEC);
+    long print(unsigned long, int = DEC);
+    long print(double, int = 2);
+    long print(const Printable&);
 
-    void println(const __FlashStringHelper *);
-    void println(const String &s);
-    void println(const char[]);
-    void println(char);
-    void println(unsigned char, int = DEC);
-    void println(int, int = DEC);
-    void println(unsigned int, int = DEC);
-    void println(long, int = DEC);
-    void println(unsigned long, int = DEC);
-    void println(double, int = 2);
-    void println(const Printable&);
-    void println(void);
+    long println(const __FlashStringHelper *);
+    long println(const String &s);
+    long println(const char[]);
+    long println(char);
+    long println(unsigned char, int = DEC);
+    long println(int, int = DEC);
+    long println(unsigned int, int = DEC);
+    long println(long, int = DEC);
+    long println(unsigned long, int = DEC);
+    long println(double, int = 2);
+    long println(const Printable&);
+    long println(void);
 };
 
 #endif

hardware/arduino/cores/arduino/Printable.h

@@ -30,7 +30,7 @@ class Print;
 class Printable
 {
   public:
-    virtual void printTo(Print& p) const = 0;
+    virtual long printTo(Print& p) const = 0;
 };
 
 #endif

libraries/ArduinoTestSuite/examples/ATS_Write_Print/ATS_Write_Print.ino

@@ -0,0 +1,61 @@
+#include <ArduinoTestSuite.h>
+
+void Test_Equal(long actual, long expected)
+{
+  char buf[100];
+  boolean b = expected == actual;
+  ATS_PrintTestStatus("", b);
+  if (!b) {
+    Serial.print("expected '");
+    Serial.print(expected);
+    Serial.print("', actual '");
+    Serial.print(actual);
+    Serial.println("'");
+  }
+}
+
+void setup()
+{
+  byte buf[5] = { 65, 66, 67, 0, 69 };
+  ATS_begin("Arduino", "Write & Print Return Values Test");
+
+  Test_Equal(Serial.write('a'), 1);
+  Test_Equal(Serial.write(byte(0)), 1);
+  Test_Equal(Serial.write("abc"), 3);
+  Test_Equal(Serial.write(""), 0);
+  Test_Equal(Serial.write(buf, 5), 5);
+  Test_Equal(Serial.print(0), 1);
+  Test_Equal(Serial.print(""), 0);
+  Test_Equal(Serial.print("abc"), 3);
+  Test_Equal(Serial.print(0), 1);
+  Test_Equal(Serial.print(1), 1);
+  Test_Equal(Serial.print(11), 2);
+  Test_Equal(Serial.print(12345), 5);
+  Test_Equal(Serial.print(-1), 2);
+  Test_Equal(Serial.print(-123), 4);
+  Test_Equal(Serial.println(), 2);
+  Test_Equal(Serial.println(""), 2);
+  Test_Equal(Serial.println("abc"), 5);
+  Test_Equal(Serial.println(0), 3);
+  Test_Equal(Serial.println(1), 3);
+  Test_Equal(Serial.println(11), 4);
+  Test_Equal(Serial.println(12345), 7);
+  Test_Equal(Serial.println(-1), 4);
+  Test_Equal(Serial.println(-123), 6);
+  
+  ATS_end();
+}
+
+void loop() {}
+
+
+
+
+
+
+
+
+
+
+
+

libraries/Ethernet/Client.cpp

@@ -70,19 +70,18 @@ int Client::connect(IPAddress ip, uint16_t port) {
   return 1;
 }
 
-void Client::write(uint8_t b) {
-  if (_sock != MAX_SOCK_NUM)
-    send(_sock, &b, 1);
+long Client::write(uint8_t b) {
+  return write(&b, 1);
 }
 
-void Client::write(const char *str) {
-  if (_sock != MAX_SOCK_NUM)
-    send(_sock, (const uint8_t *)str, strlen(str));
+long Client::write(const char *str) {
+  return write((const uint8_t *) str, strlen(str));
 }
 
-void Client::write(const uint8_t *buf, size_t size) {
-  if (_sock != MAX_SOCK_NUM)
-    send(_sock, buf, size);
+long Client::write(const uint8_t *buf, size_t size) {
+  if (_sock == MAX_SOCK_NUM) return -1;
+  if (!send(_sock, buf, size)) return -2;
+  return size;
 }
 
 int Client::available() {

libraries/Ethernet/Client.h

@@ -12,9 +12,9 @@ public:
   uint8_t status();
   int connect(IPAddress ip, uint16_t port);
   int connect(const char *host, uint16_t port);
-  virtual void write(uint8_t);
-  virtual void write(const char *str);
-  virtual void write(const uint8_t *buf, size_t size);
+  virtual long write(uint8_t);
+  virtual long write(const char *str);
+  virtual long write(const uint8_t *buf, size_t size);
   virtual int available();
   virtual int read();
   virtual int read(uint8_t *buf, size_t size);

libraries/Ethernet/IPAddress.cpp

@@ -42,13 +42,15 @@ bool IPAddress::operator==(const uint8_t* addr)
     return memcmp(addr, _address, sizeof(_address)) == 0;
 }
 
-void IPAddress::printTo(Print& p) const
+long IPAddress::printTo(Print& p) const
 {
+    long n = 0, t;
     for (int i =0; i < 3; i++)
     {
-        p.print(_address[i], DEC);
-        p.print('.');
+        if ((t = p.print(_address[i], DEC)) > 0) n += t;
+        if ((t = p.print('.')) > 0) n+= t;
     }
-    p.print(_address[3], DEC);
+    if ((t = p.print(_address[3], DEC)) > 0) n += t;
+    return n;
 }
 

libraries/Ethernet/IPAddress.h

@@ -60,7 +60,7 @@ public:
     IPAddress& operator=(const uint8_t *address);
     IPAddress& operator=(uint32_t address);
 
-    virtual void printTo(Print& p) const;
+    virtual long printTo(Print& p) const;
 
     friend class EthernetClass;
     friend class UDP;

libraries/Ethernet/Server.cpp

@@ -67,18 +67,20 @@ Client Server::available()
   return Client(MAX_SOCK_NUM);
 }
 
-void Server::write(uint8_t b) 
+long Server::write(uint8_t b) 
 {
   write(&b, 1);
 }
 
-void Server::write(const char *str) 
+long Server::write(const char *str) 
 {
   write((const uint8_t *)str, strlen(str));
 }
 
-void Server::write(const uint8_t *buffer, size_t size) 
+long Server::write(const uint8_t *buffer, size_t size) 
 {
+  long n = 0;
+  
   accept();
 
   for (int sock = 0; sock < MAX_SOCK_NUM; sock++) {
@@ -86,7 +88,9 @@ void Server::write(const uint8_t *buffer, size_t size)
 
     if (EthernetClass::_server_port[sock] == _port &&
       client.status() == SnSR::ESTABLISHED) {
-      client.write(buffer, size);
+      n += client.write(buffer, size);
     }
   }
+  
+  return n;
 }

libraries/Ethernet/Server.h

@@ -14,9 +14,9 @@ public:
   Server(uint16_t);
   Client available();
   void begin();
-  virtual void write(uint8_t);
-  virtual void write(const char *str);
-  virtual void write(const uint8_t *buf, size_t size);
+  virtual long write(uint8_t);
+  virtual long write(const char *str);
+  virtual long write(const uint8_t *buf, size_t size);
 };
 
 #endif

libraries/Ethernet/Udp.cpp

@@ -102,21 +102,22 @@ int UDP::endPacket()
   return sendUDP(_sock);
 }
 
-void UDP::write(uint8_t byte)
+long UDP::write(uint8_t byte)
 {
-  write(&byte, 1);
+  return write(&byte, 1);
 }
 
-void UDP::write(const char *str)
+long UDP::write(const char *str)
 {
   size_t len = strlen(str);
-  write((const uint8_t *)str, len);
+  return write((const uint8_t *)str, len);
 }
 
-void UDP::write(const uint8_t *buffer, size_t size)
+long UDP::write(const uint8_t *buffer, size_t size)
 {
   uint16_t bytes_written = bufferData(_sock, _offset, buffer, size);
   _offset += bytes_written;
+  return bytes_written;
 }
 
 int UDP::parsePacket()

libraries/Ethernet/Udp.h

@@ -67,11 +67,11 @@ public:
   // Returns 1 if the packet was sent successfully, 0 if there was an error
   int endPacket();
   // Write a single byte into the packet
-  virtual void write(uint8_t);
+  virtual long write(uint8_t);
   // Write a string of characters into the packet
-  virtual void write(const char *str);
+  virtual long write(const char *str);
   // Write size bytes from buffer into the packet
-  virtual void write(const uint8_t *buffer, size_t size);
+  virtual long write(const uint8_t *buffer, size_t size);
 
   // Start processing the next available incoming packet
   // Returns the size of the packet in bytes, or 0 if no packets are available

libraries/LiquidCrystal/LiquidCrystal.cpp

@@ -258,8 +258,9 @@ inline void LiquidCrystal::command(uint8_t value) {
   send(value, LOW);
 }
 
-inline void LiquidCrystal::write(uint8_t value) {
+inline long LiquidCrystal::write(uint8_t value) {
   send(value, HIGH);
+  return 1; // assume sucess
 }
 
 /************ low level data pushing commands **********/

libraries/LiquidCrystal/LiquidCrystal.h

@@ -79,7 +79,7 @@ public:
 
   void createChar(uint8_t, uint8_t[]);
   void setCursor(uint8_t, uint8_t); 
-  virtual void write(uint8_t);
+  virtual long write(uint8_t);
   void command(uint8_t);
 private:
   void send(uint8_t, uint8_t);

libraries/SD/File.cpp

@@ -58,19 +58,20 @@ boolean File::isDirectory(void) {
 }
 
 
-void File::write(uint8_t val) {
-  if (_file)
-    _file->write(val);
+long File::write(uint8_t val) {
+  return write(&val, 1);
 }
 
-void File::write(const char *str) {
-  if (_file) 
-    _file->write(str);
+long File::write(const char *str) {
+  return write((const uint8_t *) str, strlen(str));
 }
 
-void File::write(const uint8_t *buf, size_t size) {
-  if (_file)
-    _file->write(buf, size);
+long File::write(const uint8_t *buf, size_t size) {
+  long t;
+  if (!_file) return -1;
+  t = _file->write(buf, size);
+  if (t < 0) return t - 1;
+  return t;
 }
 
 int File::peek() {

libraries/SD/SD.h

@@ -32,9 +32,9 @@ public:
   File(SdFile f, char *name);     // wraps an underlying SdFile
   File(void);      // 'empty' constructor
   ~File(void);     // destructor
-  virtual void write(uint8_t);
-  virtual void write(const char *str);
-  virtual void write(const uint8_t *buf, size_t size);
+  virtual long write(uint8_t);
+  virtual long write(const char *str);
+  virtual long write(const uint8_t *buf, size_t size);
   virtual int read();
   virtual int peek();
   virtual int available();

libraries/SD/utility/SdFat.h

@@ -283,9 +283,9 @@ class SdFile : public Print {
   }
   /** \return SdVolume that contains this file. */
   SdVolume* volume(void) const {return vol_;}
-  void write(uint8_t b);
-  int16_t write(const void* buf, uint16_t nbyte);
-  void write(const char* str);
+  long write(uint8_t b);
+  long write(const void* buf, uint16_t nbyte);
+  long write(const char* str);
   void write_P(PGM_P str);
   void writeln_P(PGM_P str);
 //------------------------------------------------------------------------------

libraries/SD/utility/SdFile.cpp

@@ -1121,7 +1121,7 @@ uint8_t SdFile::truncate(uint32_t length) {
  * for a read-only file, device is full, a corrupt file system or an I/O error.
  *
  */
-int16_t SdFile::write(const void* buf, uint16_t nbyte) {
+long SdFile::write(const void* buf, uint16_t nbyte) {
   // convert void* to uint8_t*  -  must be before goto statements
   const uint8_t* src = reinterpret_cast<const uint8_t*>(buf);
 
@@ -1219,8 +1219,8 @@ int16_t SdFile::write(const void* buf, uint16_t nbyte) {
  *
  * Use SdFile::writeError to check for errors.
  */
-void SdFile::write(uint8_t b) {
-  write(&b, 1);
+long SdFile::write(uint8_t b) {
+  return write(&b, 1);
 }
 //------------------------------------------------------------------------------
 /**
@@ -1228,8 +1228,8 @@ void SdFile::write(uint8_t b) {
  *
  * Use SdFile::writeError to check for errors.
  */
-void SdFile::write(const char* str) {
-  write(str, strlen(str));
+long SdFile::write(const char* str) {
+  return write(str, strlen(str));
 }
 //------------------------------------------------------------------------------
 /**

libraries/SoftwareSerial/SoftwareSerial.cpp

@@ -440,10 +440,10 @@ int SoftwareSerial::available()
   return (_receive_buffer_tail + _SS_MAX_RX_BUFF - _receive_buffer_head) % _SS_MAX_RX_BUFF;
 }
 
-void SoftwareSerial::write(uint8_t b)
+long SoftwareSerial::write(uint8_t b)
 {
   if (_tx_delay == 0)
-    return;
+    return -1;
 
   uint8_t oldSREG = SREG;
   cli();  // turn off interrupts for a clean txmit
@@ -484,6 +484,8 @@ void SoftwareSerial::write(uint8_t b)
 
   SREG = oldSREG; // turn interrupts back on
   tunedDelay(_tx_delay);
+  
+  return 1;
 }
 
 void SoftwareSerial::flush()

libraries/SoftwareSerial/SoftwareSerial.h

@@ -89,7 +89,7 @@ public:
   bool overflow() { bool ret = _buffer_overflow; _buffer_overflow = false; return ret; }
   int peek();
 
-  virtual void write(uint8_t byte);
+  virtual long write(uint8_t byte);
   virtual int read();
   virtual int available();
   virtual void flush();

libraries/Wire/Wire.cpp

@@ -124,13 +124,13 @@ uint8_t TwoWire::endTransmission(void)
 // must be called in:
 // slave tx event callback
 // or after beginTransmission(address)
-void TwoWire::write(uint8_t data)
+long TwoWire::write(uint8_t data)
 {
   if(transmitting){
   // in master transmitter mode
     // don't bother if buffer is full
     if(txBufferLength >= BUFFER_LENGTH){
-      return;
+      return -1;
     }
     // put byte in tx buffer
     txBuffer[txBufferIndex] = data;
@@ -142,31 +142,33 @@ void TwoWire::write(uint8_t data)
     // reply to master
     twi_transmit(&data, 1);
   }
+  return 1;
 }
 
 // must be called in:
 // slave tx event callback
 // or after beginTransmission(address)
-void TwoWire::write(const uint8_t *data, size_t quantity)
+long TwoWire::write(const uint8_t *data, size_t quantity)
 {
   if(transmitting){
   // in master transmitter mode
     for(size_t i = 0; i < quantity; ++i){
-      write(data[i]);
+      if (write(data[i]) < 0) return i;
     }
   }else{
   // in slave send mode
     // reply to master
     twi_transmit(data, quantity);
   }
+  return quantity;
 }
 
 // must be called in:
 // slave tx event callback
 // or after beginTransmission(address)
-void TwoWire::write(const char *data)
+long TwoWire::write(const char *data)
 {
-  write((uint8_t*)data, strlen(data));
+  return write((uint8_t*)data, strlen(data));
 }
 
 // must be called in:

libraries/Wire/Wire.h

@@ -52,9 +52,9 @@ class TwoWire : public Stream
     uint8_t endTransmission(void);
     uint8_t requestFrom(uint8_t, uint8_t);
     uint8_t requestFrom(int, int);
-    virtual void write(uint8_t);
-    virtual void write(const char *);
-    virtual void write(const uint8_t *, size_t);
+    virtual long write(uint8_t);
+    virtual long write(const char *);
+    virtual long write(const uint8_t *, size_t);
     virtual int available(void);
     virtual int read(void);
     virtual int peek(void);