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[TAR] Correctly handle gnu format when used for incremental backups

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Previously, in such cases the resulting entries were having incorrect file names instead of having ctime/atime.
This commit is contained in:
Timofey Solomko
2018-07-23 09:25:06 +03:00
parent 46f88e1d60
commit ef162c4b4f
1 changed files with 46 additions and 27 deletions
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Sources/TAR/TarEntryInfo.swift
+46 -27
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@@ -111,7 +111,7 @@ public struct TarEntryInfo: ContainerEntryInfo {
// the alternative, which was used in previous versions, is to throw an error.
if let posixAttributes = byteReader.tarInt(maxLength: 8, radix: 8) {
// Sometimes file mode also contains unix type, so we need to filter it out.
// Sometimes file mode field also contains unix type, so we need to filter it out.
self.permissions = Permissions(rawValue: UInt32(truncatingIfNeeded: posixAttributes) & 0xFFF)
} else {
self.permissions = nil
@@ -160,13 +160,17 @@ public struct TarEntryInfo: ContainerEntryInfo {
// Linked file name
let linkName = byteReader.tarCString(maxLength: 100)
// There are two POSIX-like formats: pre-POSIX used by GNU tools (aka "old-GNU") and POSIX (aka "ustar").
// They differ in `magic` field value and how other fields are padded (either SPACEs or NULLs).
// Padding is taken care of in Data extension functions in "ByteReader+Tar.swift" file.
// Here we deal with magic. First one is "old-GNU", second is "ustar", third is for compatiblity with strange
// implementations of "ustar", which use SPACEs instead of NULLs.
// There are two different formats utilizing this section of TAR header: GNU format and POSIX (aka "ustar";
// also PAX containers can also be considered POSIX). They differ in the value of magic field as well as what
// comes after deviceMinorNumber field. While "ustar" format may contain prefix for file name, GNU format
// uses this place for storing atime/ctime and fields related to sparse-files. In practice, these fields are
// rarely used by GNU tar and only present if "incremental backups" options were used. Thus, GNU format TAR
// container can often be incorrectly considered as having prefix field containing only NULLs.
let magic = byteReader.uint64()
var gnuAtime: Int?
var gnuCtime: Int?
if magic == 0x0020207261747375 || magic == 0x3030007261747375 || magic == 0x3030207261747375 {
self.hasRecognizedMagic = true
let uname = byteReader.tarCString(maxLength: 32)
@@ -175,22 +179,33 @@ public struct TarEntryInfo: ContainerEntryInfo {
let gname = byteReader.tarCString(maxLength: 32)
self.ownerGroupName = (local?.gname ?? global?.gname) ?? gname
deviceMajorNumber = byteReader.tarInt(maxLength: 8)
deviceMinorNumber = byteReader.tarInt(maxLength: 8)
let prefix = byteReader.tarCString(maxLength: 155)
if prefix != "" {
if prefix.last == "/" {
name = prefix + name
} else {
name = prefix + "/" + name
self.deviceMajorNumber = byteReader.tarInt(maxLength: 8)
self.deviceMinorNumber = byteReader.tarInt(maxLength: 8)
if magic == 0x00_20_20_72_61_74_73_75 { // GNU format.
// GNU format mostly is identical to POSIX format and in the common situations can be considered as
// having prefix containing only NULLs. However, in the case of incremental backups produced by GNU tar
// this part of the TAR header is used for storing a lot of different properties. For now, we are only
// reading atime and ctime.
gnuAtime = byteReader.tarInt(maxLength: 12, radix: 8)
gnuCtime = byteReader.tarInt(maxLength: 12, radix: 8)
} else {
let prefix = byteReader.tarCString(maxLength: 155)
if prefix != "" {
if prefix.last == "/" {
name = prefix + name
} else {
name = prefix + "/" + name
}
}
}
} else {
self.hasRecognizedMagic = false
ownerUserName = local?.uname ?? global?.uname
ownerGroupName = local?.gname ?? global?.gname
deviceMajorNumber = nil
deviceMinorNumber = nil
self.ownerUserName = local?.uname ?? global?.uname
self.ownerGroupName = local?.gname ?? global?.gname
self.deviceMajorNumber = nil
self.deviceMinorNumber = nil
}
// Set `name` and `linkName` to values from PAX or GNU format if possible.
@@ -199,27 +214,31 @@ public struct TarEntryInfo: ContainerEntryInfo {
// Set additional properties from PAX extended headers.
if let atime = local?.atime ?? global?.atime {
accessTime = Date(timeIntervalSince1970: atime)
self.accessTime = Date(timeIntervalSince1970: atime)
} else if let gnuAtime = gnuAtime {
self.accessTime = Date(timeIntervalSince1970: TimeInterval(gnuAtime))
} else {
accessTime = nil
self.accessTime = nil
}
if let ctime = local?.ctime ?? global?.ctime {
creationTime = Date(timeIntervalSince1970: ctime)
self.creationTime = Date(timeIntervalSince1970: ctime)
} else if let gnuCtime = gnuCtime {
self.creationTime = Date(timeIntervalSince1970: TimeInterval(gnuCtime))
} else {
creationTime = nil
self.creationTime = nil
}
charset = local?.charset ?? global?.charset
comment = local?.comment ?? global?.comment
self.charset = local?.charset ?? global?.charset
self.comment = local?.comment ?? global?.comment
if let localUnknownRecords = local?.unknownRecords {
if let globalUnknownRecords = global?.unknownRecords {
unknownExtendedHeaderRecords = globalUnknownRecords.merging(localUnknownRecords) { $1 }
self.unknownExtendedHeaderRecords = globalUnknownRecords.merging(localUnknownRecords) { $1 }
} else {
unknownExtendedHeaderRecords = localUnknownRecords
self.unknownExtendedHeaderRecords = localUnknownRecords
}
} else {
unknownExtendedHeaderRecords = global?.unknownRecords
self.unknownExtendedHeaderRecords = global?.unknownRecords
}
}