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This improves the performance of parsing the file and reduces memory pressure.
Running 'fuzz-etc-hosts timeout-strv' with valgrind,
Before:
total heap usage: 321,020 allocs, 321,020 frees, 15,820,387,193 bytes allocated
real 0m23.531s
user 0m21.458s
sys 0m1.961s
After:
total heap usage: 112,408 allocs, 112,408 frees, 7,297,480 bytes allocated
real 0m8.664s
user 0m8.545s
sys 0m0.065s
Hopefully fixes oss-fuzz#47708 (https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=47708).
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https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=43942 is a simple case
where a repeated entry generates a timeout. I didn't import that case, but
generated a simpler one by hand.
$ time build/fuzz-etc-hosts test/fuzz/fuzz-etc-hosts/timeout-many-entries
test/fuzz/fuzz-etc-hosts/timeout-many-entries... ok
build/fuzz-etc-hosts test/fuzz/fuzz-etc-hosts/timeout-many-entries 3.17s (old)
↓
build/fuzz-etc-hosts test/fuzz/fuzz-etc-hosts/timeout-many-entries 0.11s (new)
I considered simply disallowing too many aliases. E.g. microsoft appearently
sometimes ignores entries after the ninth [1], and other systems set stringent
limits [2,3], but the recommended way to get around that is to simply use more
lines (as is done in the sample), so this wouldn't change anything.
Even if we cannot put all those names in a reply packet, the resolution from
the alias to the address should work. I think cases where people define lots
and lots of aliases through some programmatic interface is realistic, for
example for a blocklist, and such a file shouldn't bring resolved down to its
knees.
[1] https://superuser.com/questions/932112/is-there-a-maximum-number-of-hostname-aliases-per-line-in-a-windows-hosts-file
[2] https://library.netapp.com/ecmdocs/ECMP1516135/html/GUID-C6F3B6D1-232D-44BB-A76C-3304C19607A3.html
[3] https://www.ibm.com/docs/en/zos/2.1.0?topic=optional-creating-etchosts
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