WString: change strcpy() to memcpy()

It is worth to use memcpy() to avoid extra checks. Furthermore,
it fixes possible issues when copied WString has zero byte stored
intentionally.

copy() methods are protected and always used to copy zero-terminated
strings, so it is safe to copy termination zero byte from source buffer.

cores/arduino/WString.cpp

@@ -174,7 +174,7 @@ String & String::copy(const char *cstr, unsigned int length)
  return *this;
  }
  len = length;
- strcpy(buffer, cstr);
+ memcpy(buffer, cstr, length + 1);
  return *this;
 }
 
@@ -185,7 +185,7 @@ String & String::copy(const __FlashStringHelper *pstr, unsigned int length)
  return *this;
  }
  len = length;
- strcpy_P(buffer, (PGM_P)pstr);
+ memcpy_P(buffer, (PGM_P)pstr, length + 1);
  return *this;
 }
 
@@ -194,7 +194,7 @@ void String::move(String &rhs)
 {
  if (buffer) {
  if (rhs && capacity >= rhs.len) {
- strcpy(buffer, rhs.buffer);
+ memcpy(buffer, rhs.buffer, rhs.len + 1);
  len = rhs.len;
  rhs.len = 0;
  return;
@@ -266,8 +266,9 @@ unsigned char String::concat(const char *cstr, unsigned int length)
  if (!cstr) return 0;
  if (length == 0) return 1;
  if (!reserve(newlen)) return 0;
- strcpy(buffer + len, cstr);
+ memcpy(buffer + len, cstr, length);
  len = newlen;
+ buffer[len] = 0;
  return 1;
 }
 
@@ -341,7 +342,7 @@ unsigned char String::concat(const __FlashStringHelper * str)
  if (length == 0) return 1;
  unsigned int newlen = len + length;
  if (!reserve(newlen)) return 0;
- strcpy_P(buffer + len, (const char *) str);
+ memcpy_P(buffer + len, (const char *) str, length + 1);
  len = newlen;
  return 1;
 }
@@ -653,6 +654,7 @@ void String::replace(const String& find, const String& replace)
  }
  } else if (diff < 0) {
  char *writeTo = buffer;
+ char *end = buffer + len;
  while ((foundAt = strstr(readFrom, find.buffer)) != NULL) {
  unsigned int n = foundAt - readFrom;
  memcpy(writeTo, readFrom, n);
@@ -662,7 +664,7 @@ void String::replace(const String& find, const String& replace)
  readFrom = foundAt + find.len;
  len += diff;
  }
- strcpy(writeTo, readFrom);
+ memcpy(writeTo, readFrom, end - readFrom + 1);
  } else {
  unsigned int size = len; // compute size needed for result
  while ((foundAt = strstr(readFrom, find.buffer)) != NULL) {