A Reader is an io.Reader that can be read to retrieve uncompressed data from a gzip-format compressed file.

In general, a gzip file can be a concatenation of gzip files, each with its own header. Reads from the Reader return the concatenation of the uncompressed data of each. Only the first header is recorded in the Reader fields.

Gzip files store a length and checksum of the uncompressed data. The Reader will return a ErrChecksum when Read reaches the end of the uncompressed data if it does not have the expected length or checksum. Clients should treat data returned by Read as tentative until they receive the io.EOF marking the end of the data.