github.com/slspeek/camlistore_namedsearch@v0.0.0-20140519202248-ed6f70f7721a/pkg/readerutil/readersize.go (about)

     1  /*
     2  Copyright 2012 The Camlistore Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8       http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  // Package readerutil provides and operates on io.Readers.
    18  package readerutil
    19  
    20  import (
    21  	"bytes"
    22  	"io"
    23  	"os"
    24  )
    25  
    26  // ReaderSize tries to determine the length of r.
    27  func ReaderSize(r io.Reader) (size int64, ok bool) {
    28  	switch rt := r.(type) {
    29  	case io.Seeker:
    30  		pos, err := rt.Seek(0, os.SEEK_CUR)
    31  		if err != nil {
    32  			return
    33  		}
    34  		end, err := rt.Seek(0, os.SEEK_END)
    35  		if err != nil {
    36  			return
    37  		}
    38  		size = end - pos
    39  		pos1, err := rt.Seek(pos, os.SEEK_SET)
    40  		if err != nil || pos1 != pos {
    41  			msg := "failed to restore seek position"
    42  			if err != nil {
    43  				msg += ": " + err.Error()
    44  			}
    45  			panic(msg)
    46  		}
    47  		return size, true
    48  	case *bytes.Buffer:
    49  		return int64(rt.Len()), true
    50  	}
    51  	return
    52  }