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archive/tar: beginning effort to prune the vendored archive/tar

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NOTE: I'm not sure this is really the route I want to go here, but it
would need benchmarking to show if it's actually beneficial.
It would still be nicer to get something like this upstreamed instead.

trim down anything not used directly by tar-split.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>
This commit is contained in:
Vincent Batts 2023-04-27 14:01:09 -04:00
parent 58175ba396
commit d97b8009bb
Signed by: vbatts
GPG key ID: E30EFAA812C6E5ED
6 changed files with 58 additions and 2053 deletions
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30
archive/tar/common.go
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@ -221,9 +221,11 @@ func (s sparseEntry) endOffset() int64 { return s.Offset + s.Length }
// that the file has no data in it, which is rather odd.
//
// As an example, if the underlying raw file contains the 10-byte data:
//
// var compactFile = "abcdefgh"
//
// And the sparse map has the following entries:
//
// var spd sparseDatas = []sparseEntry{
// {Offset: 2, Length: 5}, // Data fragment for 2..6
// {Offset: 18, Length: 3}, // Data fragment for 18..20
@ -235,6 +237,7 @@ func (s sparseEntry) endOffset() int64 { return s.Offset + s.Length }
// }
//
// Then the content of the resulting sparse file with a Header.Size of 25 is:
//
// var sparseFile = "\x00"*2 + "abcde" + "\x00"*11 + "fgh" + "\x00"*4
type (
sparseDatas []sparseEntry
@ -293,9 +296,9 @@ func alignSparseEntries(src []sparseEntry, size int64) []sparseEntry {
// The input must have been already validated.
//
// This function mutates src and returns a normalized map where:
// * adjacent fragments are coalesced together
// * only the last fragment may be empty
// * the endOffset of the last fragment is the total size
// - adjacent fragments are coalesced together
// - only the last fragment may be empty
// - the endOffset of the last fragment is the total size
func invertSparseEntries(src []sparseEntry, size int64) []sparseEntry {
dst := src[:0]
var pre sparseEntry
@ -721,3 +724,24 @@ func min(a, b int64) int64 {
}
return b
}
// splitUSTARPath splits a path according to USTAR prefix and suffix rules.
// If the path is not splittable, then it will return ("", "", false).
func splitUSTARPath(name string) (prefix, suffix string, ok bool) {
length := len(name)
if length <= nameSize || !isASCII(name) {
return "", "", false
} else if length > prefixSize+1 {
length = prefixSize + 1
} else if name[length-1] == '/' {
length--
}
i := strings.LastIndex(name[:length], "/")
nlen := len(name) - i - 1 // nlen is length of suffix
plen := i // plen is length of prefix
if i <= 0 || nlen > nameSize || nlen == 0 || plen > prefixSize {
return "", "", false
}
return name[:i], name[i+1:], true
}