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Explicitly specify binary encoding for string truncation #2017

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merged 8 commits into from
May 27, 2024
Merged

Explicitly specify binary encoding for string truncation #2017

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3361ef4
Explicitly specify binary encoding for string truncation
emlun Jan 19, 2024
bdb2dab
Apply suggestions from review
emlun Jan 22, 2024
0127902
Unify language on truncation between name/displayName, and simplify both
emlun Jan 22, 2024
527629c
Add missing "to" in "equal to or greater than"
emlun Jan 22, 2024
f337fce
Address review comments
emlun Feb 28, 2024
8f89a8e
Rewrite "UTF-8 sequence(s)" to "UTF-8 code point(s)"
emlun Feb 28, 2024
0102d01
Rewrite string truncation to clarify difference in client/authnr resp…
emlun Mar 20, 2024
ccf4e32
Don't mention only authenticators in reference to string truncation s…
emlun Mar 20, 2024
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11 changes: 7 additions & 4 deletions index.bs
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Expand Up @@ -3194,7 +3194,9 @@ associated with or [=scoped=] to, respectively.

When [=clients=], [=client platforms=], or [=authenticators=] display a {{PublicKeyCredentialEntity/name}}'s value, they should always use UI elements to provide a clear boundary around the displayed value, and not allow overflow into other elements [[css-overflow-3]].

Authenticators MAY truncate a {{PublicKeyCredentialEntity/name}} member's value so that it fits within 64 bytes, if the authenticator stores the value. See [[#sctn-strings-truncation]] about truncation and other considerations.
When storing a {{PublicKeyCredentialEntity/name}} member's value,
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Very minor nit: this comma (and in the next diff hunk) read oddly to me, but I'm happy either way.

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Hm, I see. If you don't mind I'll keep it as is, if only for consistency with the first sentence in the paragraph immediately preceding this (and also the next hunk).

[=authenticators=] MUST support any value whose length in the UTF-8 character encoding is 64 bytes or less.
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Authenticators MAY truncate the value as described in [[#sctn-strings-truncation]].
</div>


Expand Down Expand Up @@ -3265,8 +3267,9 @@ credential.

When [=clients=], [=client platforms=], or [=authenticators=] display a {{PublicKeyCredentialUserEntity/displayName}}'s value, they should always use UI elements to provide a clear boundary around the displayed value, and not allow overflow into other elements [[css-overflow-3]].

[=Authenticators=] MUST accept and store a 64-byte minimum length for a {{PublicKeyCredentialUserEntity/displayName}}
member's value. Authenticators MAY truncate a {{PublicKeyCredentialUserEntity/displayName}} member's value so that it fits within 64 bytes. See [[#sctn-strings-truncation]] about truncation and other considerations.
When storing a {{PublicKeyCredentialUserEntity/displayName}} member's value,
[=authenticators=] MUST support any value whose length in the UTF-8 character encoding is 64 bytes or less.
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Authenticators MAY truncate the value as described in [[#sctn-strings-truncation]].
</div>


Expand Down Expand Up @@ -4919,7 +4922,7 @@ Authenticators may be required to store arbitrary strings chosen by a [=[RP]=],

### String Truncation ### {#sctn-strings-truncation}

Each arbitrary string in the API will have some accommodation for the potentially limited resources available to an [=authenticator=]. If string value truncation is the chosen accommodation then authenticators MAY truncate in order to make the string fit within a length equal or greater than the specified minimum supported length. Such truncation SHOULD also respect UTF-8 sequence boundaries or [=grapheme cluster=] boundaries [[UAX29]]. This defines the maximum truncation permitted and authenticators MUST NOT truncate further.
Each arbitrary string in the API will have some accommodation for the potentially limited resources available to an [=authenticator=]. If string value truncation is the chosen accommodation then authenticators MAY truncate in order to make the string fit within a length equal to or greater than the specified minimum supported length. Such truncation SHOULD also respect UTF-8 sequence boundaries or [=grapheme cluster=] boundaries [[UAX29]]. This defines the maximum truncation permitted and authenticators MUST NOT truncate further.
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For example, in <a href="#fig-stringTruncation">figure <span class="figure-num-following"></span></a> the string is 65 bytes long. If truncating to 64 bytes then the final 0x88 byte must be removed purely because of space reasons. Since that leaves a partial UTF-8 sequence the remainder of that sequence may also be removed. Since that leaves a partial [=grapheme cluster=] an authenticator may remove the remainder of that cluster.

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