From: zooko Date: Thu, 25 Jan 2007 21:25:19 +0000 (+0530) Subject: add utility method file_fec X-Git-Url: https://git.rkrishnan.org/pf/content/en/CLI.txt?a=commitdiff_plain;h=2594d395923dd945cd62c836f34c0688ba6adfd7;p=tahoe-lafs%2Fzfec.git add utility method file_fec darcs-hash:96fa282d9bf90f4817029dc6d3f4de3f4ee5a6fb --- diff --git a/pyfec/fec/filefec.py b/pyfec/fec/filefec.py new file mode 100644 index 0000000..a2c036e --- /dev/null +++ b/pyfec/fec/filefec.py @@ -0,0 +1,107 @@ +import fec + +import array + +def encode_file(inf, cb, k, m, chunksize=4096): + """ + Read in the contents of inf, encode, and call cb with the results. + + First, k "input shares" will be read from inf, each input share being of + size chunksize. Then these k shares will be encoded into m "result + shares". Then cb will be invoked, passing a list of the m result shares + as its first argument, and the length of the encoded data as its second + argument. (The length of the encoded data is always equal to k*chunksize, + until the last iteration, when the end of the file has been reached and + less than k*chunksize bytes could be read from the file.) This procedure + is iterated until the end of the file is reached, in which case the space + of the input shares that is unused is filled with zeroes before encoding. + + Note that the sequence passed in calls to cb() contains mutable array + objects in its first k elements whose contents will be overwritten when + the next segment is read from the input file. Therefore the + implementation of cb() has to either be finished with those first k arrays + before returning, or if it wants to keep the contents of those arrays for + subsequent use after it has returned then it must make a copy of them to + keep. + + @param inf the file object from which to read the data + @param cb the callback to be invoked with the results + @param k the number of shares required to reconstruct the file + @param m the total number of shares created + @param chunksize how much data to read from inf for each of the k input + shares + """ + enc = fec.Encoder(k, m) + l = tuple([ array.array('c') for i in range(k) ]) + indatasize = k*chunksize # will be reset to shorter upon EOF + ZEROES=array.array('c', ['\x00'])*chunksize + while indatasize == k*chunksize: + # This loop body executes once per segment. + i = 0 + while (i