tor-netdoc: b64 tests: add exhaustive roundtrip test

Cargo.lock

@@ -3830,6 +3830,7 @@ dependencies = [
  "educe",
  "hex",
  "hex-literal",
+ "itertools",
  "once_cell",
  "phf",
  "rand 0.8.5",

crates/tor-netdoc/Cargo.toml

@@ -72,4 +72,5 @@ weak-table = "0.3.0"
 
 [dev-dependencies]
 hex-literal = "0.3"
+itertools = "0.10.1"
 serde_json = "1.0.50"

crates/tor-netdoc/src/types/misc.rs

@@ -460,6 +460,9 @@ mod nickname {
 #[cfg(test)]
 mod test {
     #![allow(clippy::unwrap_used)]
+    use itertools::Itertools;
+    use std::iter;
+
     use base64ct::Encoding;
 
     use super::*;
@@ -533,6 +536,45 @@ mod test {
         Ok(())
     }
 
+    #[test]
+    fn base64_rev() {
+        use base64ct::{Base64, Base64Unpadded};
+
+        // Check that strings that we accept are precisely ones which
+        // can be generated by either Base64 or Base64Unpadded
+        for n in 0..=5 {
+            for c_vec in iter::repeat("ACEQg/=".chars())
+                .take(n)
+                .multi_cartesian_product()
+            {
+                let s: String = c_vec.into_iter().collect();
+                let b = match s.parse::<B64>() {
+                    Ok(b) => {
+                        eprintln!("{:10} {:?}", &s, b.as_bytes());
+                        b
+                    }
+                    Err(_) => {
+                        eprintln!("{:10} Err", &s);
+                        continue;
+                    }
+                };
+                let b = b.as_bytes();
+
+                let ep = Base64::encode_string(&b);
+                let eu = Base64Unpadded::encode_string(&b);
+
+                assert!(
+                    &s == &ep || &s == &eu,
+                    "{:?} decoded to {:?} giving neither {:?} nor {:?}",
+                    s,
+                    b,
+                    ep,
+                    eu
+                );
+            }
+        }
+    }
+
     #[test]
     fn base16() -> Result<()> {
         assert_eq!("332e313432".parse::<B16>()?.as_bytes(), &b"3.142"[..]);