ts_control_serde: handle unicode escapes in Resolver - #418
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September 17, 2026 16:45
Updates ResolverAddr to use alloc::string::String instead of &'a str in its variants, allowing DoH/DoT/WireGuard DNS resolver addresses to contain Unicode escapes without panicking. Adds a fake NextDNS address with escaped ampersands to map_response.json so test_map_response_parse can confirm the fix. The control plane escapes ampersands in JSON that it sends as "\u0026", which affects NextDNS users with per-device configuration profiles on their tailnet, as their DoH URLs contain ampersands. serde_json can't deserialize this in-place, leading to "expected a borrowed string" panics that kill the control runner. Moving to alloc::string::String allows the field to be mutated during deserialization. I originally went for Cow<'a, str> to avoid the unconditional allocation, but apparently a Cow becomes an unconditional allocation on deserialization, so we gain nothing over an alloc::string::String. Signed-off-by: Dylan Bargatze <dylan@tailscale.com>
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Updates
ResolverAddrto usealloc::string::Stringinstead of&'a strin its variants, allowing DoH/DoT/WireGuard DNS resolver addresses to contain Unicode escapes without panicking. Adds a fake NextDNS address with escaped ampersands tomap_response.jsonso test_map_response_parse to confirm the fix.The control plane escapes ampersands in JSON that it sends as
\u0026, which affects NextDNS users with per-device configuration profiles on their tailnet, as their DoH URLs contain ampersands.serde_jsoncan't deserialize this without mutating it, leading to "expected a borrowed string" panics that kill the control runner. Moving toalloc::string::Stringletsserde_jsonmutate aResolverAddr's JSON representation if necessary to deserialize it.This originally used
Cow<'a, &str>, but @npry reminded me thatCow<'a, &str>unconditionally allocates on deserialization anyway, so we might as well go withalloc::string::String. To avoid unnecessary allocation, we'll need to come up with an approach/custom types to allocate only when necessary to decode, since we'll need this in way more fields than just DNS-related ones. Putting this PR up to fix the issue while we cook up a different solution; opened #420 to track developing a better approach.Closes #400.