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

     1  /*
     2  Copyright 2011 Google Inc.
     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 blob
    18  
    19  // TODO: use Generics if/when available
    20  type ChanPeeker struct {
    21  	Ch <-chan SizedRef
    22  
    23  	// A channel should either have a peek value or be closed:
    24  	peek   *SizedRef
    25  	closed bool
    26  }
    27  
    28  func (cp *ChanPeeker) MustPeek() SizedRef {
    29  	sr, ok := cp.Peek()
    30  	if !ok {
    31  		panic("No Peek value available")
    32  	}
    33  	return sr
    34  }
    35  
    36  func (cp *ChanPeeker) Peek() (sr SizedRef, ok bool) {
    37  	if cp.closed {
    38  		return
    39  	}
    40  	if cp.peek != nil {
    41  		return *cp.peek, true
    42  	}
    43  	v, ok := <-cp.Ch
    44  	if !ok {
    45  		cp.closed = true
    46  		return
    47  	}
    48  	cp.peek = &v
    49  	return *cp.peek, true
    50  }
    51  
    52  func (cp *ChanPeeker) Closed() bool {
    53  	cp.Peek()
    54  	return cp.closed
    55  }
    56  
    57  func (cp *ChanPeeker) MustTake() SizedRef {
    58  	sr, ok := cp.Take()
    59  	if !ok {
    60  		panic("MustTake called on empty channel")
    61  	}
    62  	return sr
    63  }
    64  
    65  func (cp *ChanPeeker) Take() (sr SizedRef, ok bool) {
    66  	v, ok := cp.Peek()
    67  	if !ok {
    68  		return
    69  	}
    70  	cp.peek = nil
    71  	return v, true
    72  }
    73  
    74  func (cp *ChanPeeker) ConsumeAll() {
    75  	for !cp.Closed() {
    76  		cp.Take()
    77  	}
    78  }