github.com/dolthub/dolt/go@v0.40.5-0.20240520175717-68db7794bea6/store/blobstore/range.go (about)

     1  // Copyright 2019 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package blobstore
    16  
    17  import (
    18  	"fmt"
    19  )
    20  
    21  // BlobRange represents a segment of a blob of data.  Offset is the beginning of
    22  // the range and Length is the size.  If Length is 0 that means all data beyond
    23  // offset will be read. Lengths cannot be negative.  Negative offsets indicate
    24  // distance from the end of the end of the blob.
    25  type BlobRange struct {
    26  	offset int64
    27  	length int64
    28  }
    29  
    30  // NewBlobRange creates a BlobRange with a given offset and length
    31  func NewBlobRange(offset, length int64) BlobRange {
    32  	if length < 0 {
    33  		panic("BlobRanges cannot have 0 length")
    34  	}
    35  
    36  	return BlobRange{offset, length}
    37  }
    38  
    39  // IsAllRange is true if it represents the entire blob from index 0 to the end
    40  // and false if it is any subset of the data
    41  func (br BlobRange) isAllRange() bool {
    42  	return br.offset == 0 && br.length == 0
    43  }
    44  
    45  // PositiveRange returns a BlobRange which represents the same range but with
    46  // negative offsets replaced with actual values
    47  func (br BlobRange) positiveRange(size int64) BlobRange {
    48  	offset := br.offset
    49  	length := br.length
    50  
    51  	if offset < 0 {
    52  		offset = size + offset
    53  	}
    54  
    55  	if offset+length > size || length == 0 {
    56  		length = size - offset
    57  	}
    58  
    59  	return BlobRange{offset, length}
    60  }
    61  
    62  func (br BlobRange) asHttpRangeHeader() string {
    63  	if br.isAllRange() {
    64  		return ""
    65  	}
    66  	if br.length == 0 || br.offset < 0 {
    67  		return fmt.Sprintf("bytes=%d", br.offset)
    68  	}
    69  	return fmt.Sprintf("bytes=%d-%d", br.offset, br.offset+br.length-1)
    70  }
    71  
    72  // AllRange is a BlobRange instance covering all values
    73  var AllRange = NewBlobRange(0, 0)