github.com/minio/mc@v0.0.0-20240507152021-646712d5e5fb/pkg/hookreader/hookreader.go (about)

     1  // Copyright (c) 2015-2021 MinIO, Inc.
     2  //
     3  // This file is part of MinIO Object Storage stack
     4  //
     5  // This program is free software: you can redistribute it and/or modify
     6  // it under the terms of the GNU Affero General Public License as published by
     7  // the Free Software Foundation, either version 3 of the License, or
     8  // (at your option) any later version.
     9  //
    10  // This program is distributed in the hope that it will be useful
    11  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    12  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13  // GNU Affero General Public License for more details.
    14  //
    15  // You should have received a copy of the GNU Affero General Public License
    16  // along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17  
    18  // Package hookreader hooks additional reader in the source
    19  // stream. It is useful for making progress bars. Second reader is
    20  // appropriately notified about the exact number of bytes read from
    21  // the primary source on each Read operation.
    22  package hookreader
    23  
    24  import "io"
    25  
    26  // hookReader hooks additional reader in the source stream. It is
    27  // useful for making progress bars. Second reader is appropriately
    28  // notified about the exact number of bytes read from the primary
    29  // source on each Read operation.
    30  type hookReader struct {
    31  	source io.Reader
    32  	hook   io.Reader
    33  }
    34  
    35  // Seek implements io.Seeker. Seeks source first, and if necessary
    36  // seeks hook if Seek method is appropriately found.
    37  func (hr *hookReader) Seek(offset int64, whence int) (n int64, err error) {
    38  	// Verify for source has embedded Seeker, use it.
    39  	sourceSeeker, ok := hr.source.(io.Seeker)
    40  	if ok {
    41  		return sourceSeeker.Seek(offset, whence)
    42  	}
    43  	// Verify if hook has embedded Seeker, use it.
    44  	hookSeeker, ok := hr.hook.(io.Seeker)
    45  	if ok {
    46  		return hookSeeker.Seek(offset, whence)
    47  	}
    48  	return n, nil
    49  }
    50  
    51  // Read implements io.Reader. Always reads from the source, the return
    52  // value 'n' number of bytes are reported through the hook. Returns
    53  // error for all non io.EOF conditions.
    54  func (hr *hookReader) Read(b []byte) (n int, err error) {
    55  	n, err = hr.source.Read(b)
    56  	if err != nil && err != io.EOF {
    57  		return n, err
    58  	}
    59  	// Progress the hook with the total read bytes from the source.
    60  	if _, herr := hr.hook.Read(b[:n]); herr != nil {
    61  		if herr != io.EOF {
    62  			return n, herr
    63  		}
    64  	}
    65  	return n, err
    66  }
    67  
    68  // NewHook returns a io.Reader which implements hookReader that
    69  // reports the data read from the source to the hook.
    70  func NewHook(source, hook io.Reader) io.Reader {
    71  	if hook == nil {
    72  		return source
    73  	}
    74  	return &hookReader{source, hook}
    75  }