RLP decoding question

I am trying to understand what this means from the RLP white paper wiki "The only purpose of RLP is to encode structure; encoding specific data types (eg. strings, floats) is left up to higher-order protocols;"

My understanding from this is that RLP encodes just the structure and does not deal with the data, and the interpretation of the data type is left to a custom function? can somebody give me an example of this input is the structure below using RLP encoding:

e:g: ["cat",[[]],"pig",[""],"sheep"]

Thanks in advance, also If there is any video reference just for RLP would be greatly helpful.

Taken from the documentation, you have the following axioms:

if a string is 0-55 bytes long, the RLP encoding consists of a single byte with value 0x80 plus the length of the string followed by the string. The range of the first byte is thus [0x80, 0xb7].

And

If the total payload of a list (i.e. the combined length of all its items being RLP encoded) is 0-55 bytes long, the RLP encoding consists of a single byte with value 0xc0 plus the length of the list followed by the concatenation of the RLP encodings of the items. The range of the first byte is thus [0xc0, 0xf7].

Hence, ["cat",[[]],"pig",[""],"sheep"] would be encoded with the following logic:

You would encore cat like 0x83, 'c', 'a', 't' "cat" is a string, hence you start from 0x80 and add the length of the string (3) so it gives us 0x83, then the characters of the string.

[[]] would be 0xc1, 0xc0 This array contains ONE empty array.

As 0xc1 is the length of the array (the array contain one element, here [] ), and 0xc0 is the length of the second array (empty element)

"pig" is same as "cat", a string of 3 characters so: 0x83, 'p', 'i', 'g'

[""] is an array of ONE element being an empty string (0 characters) so it would encode as 0xc1, 0x80 (0xc0 + 1 , 0x80 + 0)

"sheep" is a 5 characters string, so it would encode as: 0x85, 's', 'h', 'e', 'e', 'p' (0x80 + 5, and each letter of the string)

The whole array contains 18 bytes of value, so it would encode as:

[ 0xd2, 0x83, 'c', 'a', 't', 0xc1, 0xc0, 0x83, 'p', 'i', 'g', 0xc1, 0x80, 0x85, 's', 'h', 'e', 'e', 'p'] (0xd2 is 0xc0 + 0x12, 0x12 being 18 in decimal)

For clarity purpose, characters have not been encoded in hexadecimal, but the real encoding will look like this:

[0xd2, 0x83, 0x63, 0x61, 0x74, 0xc1, 0xc0, 0x83, 0x70, 0x69, 0x67, 0xc1, 0x80, 0x85, 0x73, 0x68, 0x65, 0x65, 0x70]

• Thank you so much for answering I will go through the answer again and ensure I understand. one more e:g to decode to clear up please, e:g : [ 978,12, ["cat"], {"dog"} ]
– drao
Mar 8 '18 at 14:35
• 978 is 0x3D2 so would encode as [0x82, 0x03, 0xd2] , 12 is just one byte so [0x0c], cat and dog are 3 letter words in a single-element array, so it encode as above, so the final encoding is [0xce, 0x82, 0x03, 0xD2, 0x0c, 0xc4, 0x83, "c", "a", "t", 0xc4, 0x83, "d", "o", "g"] (0xce is 0xc0+ #NUMBER_OF_ELEMENT, which is 15 in decimal, which is E in hexa) Mar 9 '18 at 8:48
• In the above example, does have RLP have encoding rule for {}, looks like it converted the {} as a list. for e.g how will RLP encode [ {"dog"} ]. I think RLP will only understand, Lists, Strings, Numbers.
– drao
Apr 3 '18 at 2:31