Okay, I think I’ve got it now. Not sure if this is the best option though.
I am assuming UInt32 headers here, for simplicity. As an example I used np.arange(1_000, dtype=np.float64) with blocks of size 1024 bytes, to keep the XML “small”.
import numpy as np
import zlib
from base64 import b64encode, b64decode
# the example array here is np.arange(1_000, dtype=np.float64) with same endianness
# of the system, i.e. dtype='=f8'
# Information (or "header") is:
# [ 8, 1024, 832, 210, 172, 188, 188, 204, 205, 204, 177]
# I used 1024 byte blocks to keep the XML example here "small"
Xml_file_extract = '_CAAAAAAEAABAAwAA0gAAAKwAAAC8AAAAvAAAAMwAAADNAAAAzAAAALEAAAA=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'
header_bin = b64decode(Xml_file_extract[1::])
header_arr = np.frombuffer(header_bin, dtype='=u4')
header_b64_len = len(b64encode(header_bin))
# compressed array
arr_comp = b64decode(Xml_file_extract[1+header_b64_len::])
float64_size = 8 # in bytes
nb = header_arr[0] # number of blocks
bs = header_arr[1] # block size in bytes
ls = header_arr[2] # size of last block in bytes
# pointer array for each block in arr_comp
ptr_arr = np.insert(header_arr[3::], 0, 0)
ptr_arr = np.cumsum(ptr_arr)
sl_s = bs//float64_size # slice size (in quantity, not bytes)
# retrieve array
complete_arr = np.empty(((nb-1)*bs+ls)//float64_size, dtype=np.float64)
for i in range(nb-1):
complete_arr[i*sl_s:(i+1)*sl_s] = np.frombuffer(zlib.decompress(arr_comp[ptr_arr[i]:ptr_arr[i+1]]), dtype='=f8')
complete_arr[(nb-1)*sl_s::] = np.frombuffer(zlib.decompress(arr_comp[ptr_arr[-2]:ptr_arr[-1]]), dtype='=f8')
# complete_arr should be the same as np.arange(1_000, dtype=np.float64)