erasure-readfile: write to given Writer than returning buffer. (#1910)

Fixes #1889

erasure-utils.go

@@ -88,21 +88,14 @@ func getDataBlocks(enBlocks [][]byte, dataBlocks int, curBlockSize int) (data []
 	return data, nil
 }
 
-// checkBlockSize return the size of a single block.
-// The first non-zero size is returned,
-// or 0 if all blocks are size 0.
-func checkBlockSize(blocks [][]byte) int {
-	for _, block := range blocks {
-		if len(block) != 0 {
-			return len(block)
-		}
-	}
-	return 0
-}
+// getBlockInfo - find start/end block and bytes to skip for given offset, length and block size.
+func getBlockInfo(offset, length, blockSize int64) (startBlock, bytesToSkip, endBlock int64) {
+	// Calculate start block for given offset and how many bytes to skip to get the offset.
+	startBlock = offset / blockSize
+	bytesToSkip = offset % blockSize
 
-// calculate the blockSize based on input length and total number of
-// data blocks.
-func getEncodedBlockLen(inputLen int64, dataBlocks int) (curEncBlockSize int64) {
-	curEncBlockSize = (inputLen + int64(dataBlocks) - 1) / int64(dataBlocks)
-	return curEncBlockSize
+	// Calculate end block for given size to read
+	endBlock = (offset + length) / blockSize
+
+	return
 }