diff --git a/api/String.cpp b/api/String.cpp
index 6f14ae13..1b6d4b28 100644
--- a/api/String.cpp
+++ b/api/String.cpp
@@ -45,6 +45,12 @@ String::String(const char *cstr)
 	if (cstr) copy(cstr, strlen(cstr));
 }
 
+String::String(const char *cstr, unsigned int length)
+{
+	init();
+	if (cstr) copy(cstr, length);
+}
+
 String::String(const String &value)
 {
 	init();
@@ -192,7 +198,8 @@ String & String::copy(const char *cstr, unsigned int length)
 		return *this;
 	}
 	len = length;
-	strcpy(buffer, cstr);
+	memcpy(buffer, cstr, length);
+	buffer[len] = '\0';
 	return *this;
 }
 
@@ -212,8 +219,9 @@ void String::move(String &rhs)
 {
 	if (buffer) {
 		if (rhs && capacity >= rhs.len) {
-			strcpy(buffer, rhs.buffer);
+			memcpy(buffer, rhs.buffer, rhs.len);
 			len = rhs.len;
+			buffer[len] = '\0';
 			rhs.len = 0;
 			return;
 		} else {
@@ -284,8 +292,9 @@ 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;
 }
 
@@ -297,59 +306,56 @@ unsigned char String::concat(const char *cstr)
 
 unsigned char String::concat(char c)
 {
-	char buf[2];
-	buf[0] = c;
-	buf[1] = 0;
-	return concat(buf, 1);
+	return concat(&c, 1);
 }
 
 unsigned char String::concat(unsigned char num)
 {
 	char buf[1 + 3 * sizeof(unsigned char)];
 	itoa(num, buf, 10);
-	return concat(buf, strlen(buf));
+	return concat(buf);
 }
 
 unsigned char String::concat(int num)
 {
 	char buf[2 + 3 * sizeof(int)];
 	itoa(num, buf, 10);
-	return concat(buf, strlen(buf));
+	return concat(buf);
 }
 
 unsigned char String::concat(unsigned int num)
 {
 	char buf[1 + 3 * sizeof(unsigned int)];
 	utoa(num, buf, 10);
-	return concat(buf, strlen(buf));
+	return concat(buf);
 }
 
 unsigned char String::concat(long num)
 {
 	char buf[2 + 3 * sizeof(long)];
 	ltoa(num, buf, 10);
-	return concat(buf, strlen(buf));
+	return concat(buf);
 }
 
 unsigned char String::concat(unsigned long num)
 {
 	char buf[1 + 3 * sizeof(unsigned long)];
 	ultoa(num, buf, 10);
-	return concat(buf, strlen(buf));
+	return concat(buf);
 }
 
 unsigned char String::concat(float num)
 {
 	char buf[20];
 	char* string = dtostrf(num, 4, 2, buf);
-	return concat(string, strlen(string));
+	return concat(string);
 }
 
 unsigned char String::concat(double num)
 {
 	char buf[20];
 	char* string = dtostrf(num, 4, 2, buf);
-	return concat(string, strlen(string));
+	return concat(string);
 }
 
 unsigned char String::concat(const __FlashStringHelper * str)
@@ -378,7 +384,7 @@ StringSumHelper & operator + (const StringSumHelper &lhs, const String &rhs)
 StringSumHelper & operator + (const StringSumHelper &lhs, const char *cstr)
 {
 	StringSumHelper &a = const_cast<StringSumHelper&>(lhs);
-	if (!cstr || !a.concat(cstr, strlen(cstr))) a.invalidate();
+	if (!cstr || !a.concat(cstr)) a.invalidate();
 	return a;
 }
 
@@ -629,10 +635,7 @@ String String::substring(unsigned int left, unsigned int right) const
 	String out;
 	if (left >= len) return out;
 	if (right > len) right = len;
-	char temp = buffer[right];  // save the replaced character
-	buffer[right] = '\0';	
-	out = buffer + left;  // pointer arithmetic
-	buffer[right] = temp;  //restore character
+	out.copy(buffer + left, right - left);
 	return out;
 }
 
diff --git a/api/String.h b/api/String.h
index d8f943eb..a3d0d9e8 100644
--- a/api/String.h
+++ b/api/String.h
@@ -68,6 +68,8 @@ class String
 	// fails, the string will be marked as invalid (i.e. "if (s)" will
 	// be false).
 	String(const char *cstr = "");
+	String(const char *cstr, unsigned int length);
+	String(const uint8_t *cstr, unsigned int length) : String((const char*)cstr, length) {}
 	String(const String &str);
 	String(const __FlashStringHelper *str);
 	#if __cplusplus >= 201103L || defined(__GXX_EXPERIMENTAL_CXX0X__)
@@ -109,6 +111,8 @@ class String
 	// concatenation is considered unsucessful.
 	unsigned char concat(const String &str);
 	unsigned char concat(const char *cstr);
+	unsigned char concat(const char *cstr, unsigned int length);
+	unsigned char concat(const uint8_t *cstr, unsigned int length) {return concat((const char*)cstr, length);}
 	unsigned char concat(char c);
 	unsigned char concat(unsigned char num);
 	unsigned char concat(int num);
@@ -225,7 +229,6 @@ class String
 	void init(void);
 	void invalidate(void);
 	unsigned char changeBuffer(unsigned int maxStrLen);
-	unsigned char concat(const char *cstr, unsigned int length);
 
 	// copy and move
 	String & copy(const char *cstr, unsigned int length);