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+/*! Filter duplicate shows of credentials and open invitations by id
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+ * (which will typically be a Scalar). This implementation just keeps
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+ * the table of seen ids in memory, but a production one would of course
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+ * use a disk-backed database. */
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+
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+use std::collections::HashMap;
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+use std::hash::Hash;
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+use std::cmp::Eq;
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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)]
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+pub struct DupFilter<IdType> {
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+ seen_table: HashMap<IdType, ()>,
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+}
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+
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+impl<IdType: Hash + Eq + Copy> 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 true if it is already in the table,
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+ /// false if not.
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+ pub fn check(&self, id: &IdType) -> bool {
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+ self.seen_table.contains_key(id)
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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 Ok(()) if it was not already
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+ /// in the table, and Err(()) if it was.
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+ pub fn filter(&mut self, id: &IdType) -> Result<(),()> {
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+ match self.seen_table.insert(*id, ()) {
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+ None => Ok(()),
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+ Some(()) => Err(()),
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+ }
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+ }
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+}
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