Fix BLEUUID toString

[tanakamasayuki]

uuid16 is Missing first 4 characters.
uuid is Missing last 2 characters.

UUID string format:
AABBCCDD-EEFF-GGHH-IIJJ-KKLLMMNNOOPP
123456789012345678901234567890123456 < 36 characters + null

Test code

#include "BLEDevice.h"

void setup() {
  Serial.begin(115200);
  delay(1000);

  BLEUUID uuid("00001812-0000-1000-8000-00805F9B34FB");
  Serial.printf("uuid     : %s\n", uuid.toString().c_str());

  BLEUUID uuid16("1812");
  Serial.printf("uuid16   : %s\n", uuid16.toString().c_str());

  BLEUUID uuid16_2(uuid16.toString().c_str());
  Serial.printf("uuid16_2 : %s\n", uuid16_2.toString().c_str());

  BLEUUID uuid32("00001812");
  Serial.printf("uuid32   : %s\n", uuid32.toString().c_str());
}

void loop() {
}

1.0.3 Run

uuid     : 00001812-0000-1000-8000-00805f9b34
uuid16   : 1812-0000-1000-8000-00805f9b34fb
uuid16_2 : <NULL>
uuid32   : 00001812-0000-1000-8000-00805f9b34fb

uuid -> Missing last 2 characters
uuid16 -> Missing first 4 characters
uuid32 -> Good

This patch

uuid     : 00001812-0000-1000-8000-00805f9b34fb
uuid16   : 00001812-0000-1000-8000-00805f9b34fb
uuid16_2 : 00001812-0000-1000-8000-00805f9b34fb
uuid32   : 00001812-0000-1000-8000-00805f9b34fb

[me-no-dev]

what is the purpose of those 4 leading zeroes? I have never seen them printed or discussed before.

[tanakamasayuki]

The UUID format is specified.

https://en.wikipedia.org/wiki/Universally_unique_identifier

123e4567-e89b-12d3-a456-426655440000
xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

in the form 8-4-4-4-12 for a total of 36 characters (32 alphanumeric characters and 4 hyphens).

https://www.bluetooth.com/specifications/assigned-numbers/service-discovery/

BASE_UUID | 00000000-0000-1000-8000-00805F9B34FB

/libraries/BLE/src/BLEUUID.cpp

/**
 * @brief Create a UUID from a string.
 *
 * Create a UUID from a string.  There will be two possible stories here.  Either the string represents
 * a binary data field or the string represents a hex encoding of a UUID.
 * For the hex encoding, here is an example:
 *
 * ```
 * "beb5483e-36e1-4688-b7f5-ea07361b26a8"
 *  0 1 2 3  4 5  6 7  8 9  0 1 2 3 4 5
 *  12345678-90ab-cdef-1234-567890abcdef
 * ```
 *
 * This has a length of 36 characters.  We need to parse this into 16 bytes.
 *
 * @param [in] value The string to build a UUID from.
 */
BLEUUID::BLEUUID(std::string value) {
	m_valueSet = true;
	if (value.length() == 4) {
		m_uuid.len         = ESP_UUID_LEN_16;
		m_uuid.uuid.uuid16 = 0;
		for(int i=0;i<value.length();){
			uint8_t MSB = value.c_str()[i];
			uint8_t LSB = value.c_str()[i+1];
			
			if(MSB > '9') MSB -= 7;
			if(LSB > '9') LSB -= 7;
			m_uuid.uuid.uuid16 += (((MSB&0x0F) <<4) | (LSB & 0x0F))<<(2-i)*4;
			i+=2;	
		}
	}
	else if (value.length() == 8) {
		m_uuid.len         = ESP_UUID_LEN_32;
		m_uuid.uuid.uuid32 = 0;
		for(int i=0;i<value.length();){
			uint8_t MSB = value.c_str()[i];
			uint8_t LSB = value.c_str()[i+1];
			
			if(MSB > '9') MSB -= 7; 
			if(LSB > '9') LSB -= 7;
			m_uuid.uuid.uuid32 += (((MSB&0x0F) <<4) | (LSB & 0x0F))<<(6-i)*4;
			i+=2;
		}		
	}
	else if (value.length() == 16) {  // how we can have 16 byte length string reprezenting 128 bit uuid??? needs to be investigated (lack of time)
		m_uuid.len = ESP_UUID_LEN_128;
		memrcpy(m_uuid.uuid.uuid128, (uint8_t*)value.data(), 16);
	}
	else if (value.length() == 36) {
		// If the length of the string is 36 bytes then we will assume it is a long hex string in
		// UUID format.
		m_uuid.len = ESP_UUID_LEN_128;
		int n = 0;
		for(int i=0;i<value.length();){
			if(value.c_str()[i] == '-')
				i++;
			uint8_t MSB = value.c_str()[i];
			uint8_t LSB = value.c_str()[i+1];
			
			if(MSB > '9') MSB -= 7; 
			if(LSB > '9') LSB -= 7;
			m_uuid.uuid.uuid128[15-n++] = ((MSB&0x0F) <<4) | (LSB & 0x0F);
			i+=2;	
		}
	}
	else {
		log_e("ERROR: UUID value not 2, 4, 16 or 36 bytes");
		m_valueSet = false;
	}
} //BLEUUID(std::string)

 * This has a length of 36 characters.  We need to parse this into 16 bytes.

	else if (value.length() == 36) {

If it is 32 characters, an input error occurs.