unzip 使用什麼方法在存檔中查找單個文件？

假設我創建了 100 個文件，每個文件的隨機文本數據大小為 30MB。現在我創建一個壓縮率為 0 的 zip 存檔，即zip dataset.zip -r -0 *.txt. 現在我想從這個檔案中只提取一個文件。

如此處所述，有兩種方法可以從檔案中解壓/提取文件：

1. 查找文件末尾並查找中央目錄。然後使用它來快速隨機訪問要提取的文件。（攤銷O(1)複雜度）
2. 查看每個本地標頭並提取匹配的標頭。（O(n)複雜性）

unzip 使用哪種方法？從我的實驗來看，它似乎使用了方法 2？

在大型存檔中搜尋單個文件時，它使用方法 1，您可以使用以下方法查看strace：

open("dataset.zip", O_RDONLY)           = 3
ioctl(1, TIOCGWINSZ, 0x7fff9a895920)    = -1 ENOTTY (Inappropriate ioctl for device)
write(1, "Archive:  dataset.zip\n", 22Archive:  dataset.zip
) = 22
lseek(3, 943718400, SEEK_SET)           = 943718400
read(3, "\340P\356(s\342\306\205\201\27\360U[\250/2\207\346<\252+u\234\225\1[<\2310E\342\274"..., 4522) = 4522
lseek(3, 943722880, SEEK_SET)           = 943722880
read(3, "\3\f\225P\\ux\v\0\1\4\350\3\0\0\4\350\3\0\0", 20) = 20
lseek(3, 943718400, SEEK_SET)           = 943718400
read(3, "\340P\356(s\342\306\205\201\27\360U[\250/2\207\346<\252+u\234\225\1[<\2310E\342\274"..., 8192) = 4522
lseek(3, 849346560, SEEK_SET)           = 849346560
read(3, "D\262nv\210\343\240C\24\227\344\367q\300\223\231\306\330\275\266\213\276M\7I'&35\2\234J"..., 8192) = 8192
stat("rand-28.txt", 0x559f43e0a550)     = -1 ENOENT (No such file or directory)
lstat("rand-28.txt", 0x559f43e0a550)    = -1 ENOENT (No such file or directory)
stat("rand-28.txt", 0x559f43e0a550)     = -1 ENOENT (No such file or directory)
lstat("rand-28.txt", 0x559f43e0a550)    = -1 ENOENT (No such file or directory)
open("rand-28.txt", O_RDWR|O_CREAT|O_TRUNC, 0666) = 4
ioctl(1, TIOCGWINSZ, 0x7fff9a895790)    = -1 ENOTTY (Inappropriate ioctl for device)
write(1, " extracting: rand-28.txt        "..., 37 extracting: rand-28.txt             ) = 37
read(3, "\275\3279Y\206\223\217}\355W%:\220YNT\0\257\260z^\361T\242\2\370\21\336\372+\306\310"..., 8192) = 8192

unzipopens dataset.zip，尋找到結尾，然後尋找存檔中請求文件的開頭（rand-28.txt，在偏移量 849346560 處）並從那裡讀取。

通過掃描檔案的最後 65557 個字節找到中心目錄；查看從這裡開始的程式碼：

/*---------------------------------------------------------------------------
   Find and process the end-of-central-directory header.  UnZip need only
   check last 65557 bytes of zipfile:  comment may be up to 65535, end-of-
   central-directory record is 18 bytes, and signature itself is 4 bytes;
   add some to allow for appended garbage.  Since ZipInfo is often used as
   a debugging tool, search the whole zipfile if zipinfo_mode is true.
 ---------------------------------------------------------------------------*/

引用自：https://unix.stackexchange.com/questions/497509