XL/erasure-read: refactor erasure read and add tests (#2232)

erasure-utils.go

@@ -73,9 +73,9 @@ func getDataBlockLen(enBlocks [][]byte, dataBlocks int) int {
 
 // Writes all the data blocks from encoded blocks until requested
 // outSize length. Provides a way to skip bytes until the offset.
-func writeDataBlocks(dst io.Writer, enBlocks [][]byte, dataBlocks int, outOffset int64, outSize int64) (int64, error) {
+func writeDataBlocks(dst io.Writer, enBlocks [][]byte, dataBlocks int, offset int64, length int64) (int64, error) {
 	// Offset and out size cannot be negative.
-	if outOffset < 0 || outSize < 0 {
+	if offset < 0 || length < 0 {
 		return 0, errUnexpected
 	}
 
@@ -85,12 +85,12 @@ func writeDataBlocks(dst io.Writer, enBlocks [][]byte, dataBlocks int, outOffset
 	}
 
 	// Do we have enough data?
-	if int64(getDataBlockLen(enBlocks, dataBlocks)) < outSize {
+	if int64(getDataBlockLen(enBlocks, dataBlocks)) < length {
 		return 0, reedsolomon.ErrShortData
 	}
 
 	// Counter to decrement total left to write.
-	write := outSize
+	write := length
 
 	// Counter to increment total written.
 	totalWritten := int64(0)
@@ -98,17 +98,17 @@ func writeDataBlocks(dst io.Writer, enBlocks [][]byte, dataBlocks int, outOffset
 	// Write all data blocks to dst.
 	for _, block := range enBlocks[:dataBlocks] {
 		// Skip blocks until we have reached our offset.
-		if outOffset >= int64(len(block)) {
+		if offset >= int64(len(block)) {
 			// Decrement offset.
-			outOffset -= int64(len(block))
+			offset -= int64(len(block))
 			continue
 		} else {
 			// Skip until offset.
-			block = block[outOffset:]
+			block = block[offset:]
 
 			// Reset the offset for next iteration to read everything
 			// from subsequent blocks.
-			outOffset = 0
+			offset = 0
 		}
 		// We have written all the blocks, write the last remaining block.
 		if write < int64(len(block)) {
@@ -136,20 +136,12 @@ func writeDataBlocks(dst io.Writer, enBlocks [][]byte, dataBlocks int, outOffset
 	return totalWritten, nil
 }
 
-// getBlockInfo - find start/end block and bytes to skip for given offset, length and block size.
-func getBlockInfo(offset, length, blockSize int64) (startBlock, endBlock, bytesToSkip int64) {
-	// Calculate start block for given offset and how many bytes to skip to get the offset.
-	startBlock = offset / blockSize
-	bytesToSkip = offset % blockSize
-	endBlock = length / blockSize
-	return
-}
-
-// 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
+// chunkSize is roughly BlockSize/DataBlocks.
+// chunkSize is calculated such that chunkSize*DataBlocks accommodates BlockSize bytes.
+// So chunkSize*DataBlocks can be slightly larger than BlockSize if BlockSize is not divisible by
+// DataBlocks. The extra space will have 0-padding.
+func getChunkSize(blockSize int64, dataBlocks int) int64 {
+	return (blockSize + int64(dataBlocks) - 1) / int64(dataBlocks)
 }
 
 // copyN - copies from disk, volume, path to input writer until length