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crypto/tls: maxHandshake is not documented #35153

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zhangyoufu opened this issue Oct 25, 2019 · 2 comments
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crypto/tls: maxHandshake is not documented #35153

zhangyoufu opened this issue Oct 25, 2019 · 2 comments
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Documentation FrozenDueToAge NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made.

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@zhangyoufu
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crypto/tls has a hard-coded limitation const maxHandshake = 65536 for handshake message length.

While a ClientHello message could has a maximum length of 131396 under extreme conditions, according to OpenSSL source code.

The 64KiB limitation is good at security perspective, to reduce server resource consumption. But I think it should be documented, as a Go specific behavior.
@dmitshur dmitshur added the NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. label Oct 25, 2019
@dmitshur
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/cc @FiloSottile

@FiloSottile
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Documenting something makes it a backwards compatibility promise, while this should be just an internal detail. What we do have is a clear error for when the limit is exceeded, so if it starts happening users can open an issue about it.

go/src/crypto/tls/conn.go

Line 982 in 0fb95e7

return nil, c.in.setErrorLocked(fmt.Errorf("tls: handshake message of length %d bytes exceeds maximum of %d bytes", n, maxHandshake))

(If you opened this issue because you hit the limit and you think we should increase it, feel free to open an issue for that.)

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@FiloSottile @zhangyoufu @dmitshur @gopherbot