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@@ -0,0 +1,48 @@
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+/*! Filter duplicate shows of credentials and open invitations by id
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+(which will typically be a Scalar).
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+
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+This implementation just keeps the table of seen ids in memory, but a
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+production one would of course use a disk-backed database. */
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+
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+use std::collections::HashSet;
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+use std::hash::Hash;
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+
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+use serde::{Deserialize, Serialize};
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+
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+/// Each instance of DupFilter maintains its own independent table of
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+/// seen ids. IdType will typically be Scalar.
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+#[derive(Default, Debug, Clone, Serialize, Deserialize)]
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+pub struct DupFilter<IdType: Hash + Eq + Copy + Serialize> {
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+ seen_table: HashSet<IdType>,
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+}
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+
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+/// A return type indicating whether the item was fresh (not previously
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+/// seen) or previously seen
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+#[derive(PartialEq, Eq, Debug)]
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+pub enum SeenType {
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+ Fresh,
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+ Seen,
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+}
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+
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+impl<IdType: Hash + Eq + Copy + Serialize> DupFilter<IdType> {
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+ /// Check to see if the id is in the seen table, but do not add it
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+ /// to the seen table. Return Seen if it is already in the table,
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+ /// Fresh if not.
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+ pub fn check(&self, id: &IdType) -> SeenType {
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+ if self.seen_table.contains(id) {
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+ SeenType::Seen
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+ } else {
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+ SeenType::Fresh
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+ }
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+ }
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+
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+ /// As atomically as possible, check to see if the id is in the seen
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+ /// table, and add it if not. Return Fresh if it was not already
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+ /// in the table, and Seen if it was.
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+ pub fn filter(&mut self, id: &IdType) -> SeenType {
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+ match self.seen_table.insert(*id) {
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+ true => SeenType::Fresh,
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+ false => SeenType::Seen,
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+ }
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+ }
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+}
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