Slither.io stores its global server list using strange scrambled format.
This data can be found here: http://slither.io/i49526.txt
After some time reverse-engineering the javascript code I found the algorithm.
Lets take this string as an example:
abcdefg
For some reason the first character is never used.
This could be a version indicator (at the time of writing this the character is an a).
result: bcdefg
These can be calculated by subtracting 97 from each characters ascii value.
a = 0, b = 1, c = 2, .. z = 25
result: [1, 2, 3, 4, 5, 6]
v[i] = v[i] - 7*i
example: [1 - 7*0, 2 - 7*1, 3 - 7*2, 4 - 7*3, 5 - 7*4]
result: [1, -5, -11, -17, -23, -29]
v[i] = (v[i] % 26 + 26) % 26
result: [1, 21, 15, 9, 3, 23]
v[i] = v[i*2] * 16 + v[i*2 + 1]
example: [16*1 + 21, 16*15 + 9, 16*3 + 23]
result: [37, 249, 71]
Our example did not have enough bytes to extract any meaningful data.
Because of this, we are going to use the string: alhoegrwgelsarzubipydkt.
This string should contain exactly one server.
Lets converted the string to smaller numbers (step 1 to 4):
[11,0,0,9,4,8,6,9,0,0,0,1,11,12,0,0,0,0,2,0,0,2]
These get converted to bytes (step 5):
[176,9,72,105,0,1,188,0,0,32,2]
The first 4 bytes are IPv4 numbers.
Our example ip address is: 176.9.72.105
The next 3 bytes get combined into a 24bit port number:
In our example the port is: 0*256^2 + 1*256 + 188 = 444
The next 3 bytes get combined into a 24 bit ac value (I don't know what this value is used for):
In our example the ac value is: 0*256^2 + 0*256 + 32 = 32
The next number is the clu value (this could stands for cluster, I don't know what it is used for):
In our example the clu value is: 2
Repeat this until all values are consumed.
Each server will need need 4+3+3+1=11 bytes, which are 11*2 = 22 characters.