Bump maximum header size to 4KiB, alternative version #155
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This was referenced Feb 5, 2026
pires
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I am conceding on increasing the max V2 header size to 4KB as it seems to fix the issues observed by @clementnuss and others.
Up until now we were using Peek to ensure (1) the client sent at least the number of bytes announced in the length field and (2) the client doesn't exceed a 256 byte limit. This wasn't very explicit, and forces each connection to pay an up-front memory cost of the largest header size we want to accept. Instead, add an explicit check for the max header size (to avoid DoS), and check that all bytes have been read from the io.LimitedReader.
PP2_SUBTYPE_SSL_CLIENT_CERT is typically around 1 or 2KiB.
Add a test with a 2KiB TLV, which is typical for PP2_SUBTYPE_SSL_CLIENT_CERT.
This is important to check for security purposes: all TLVs are buffered in memory, and we don't want clients to be able to cause a DoS due to ENOMEM.
pires
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Alternative to #144 and #150. Based on #154.
See individual commits.