hashsum/b2sum: when the checksum file is untagged, detect the size

Should fix tests/cksum/b2sum.sh

src/uucore/src/lib/features/checksum.rs

@@ -502,7 +502,6 @@ where
                     get_expected_checksum(filename_to_check, &caps, &chosen_regex)?;
 
                 // If the algo_name is provided, we use it, otherwise we try to detect it
-
                 let (algo_name, length) = if is_algo_based_format {
                     identify_algo_name_and_length(
                         &caps,
@@ -513,7 +512,15 @@ where
                     .unwrap_or((String::new(), None))
                 } else if let Some(a) = algo_name_input {
                     // When a specific algorithm name is input, use it and use the provided bits
-                    (a.to_lowercase(), length_input)
+                    // except when dealing with blake2b, where we will detect the length
+                    if algo_name_input == Some(ALGORITHM_OPTIONS_BLAKE2B) {
+                        // division by 2 converts the length of the Blake2b checksum from hexadecimal
+                        // characters to bytes, as each byte is represented by two hexadecimal characters.
+                        let length = Some(expected_checksum.len() / 2);
+                        (ALGORITHM_OPTIONS_BLAKE2B.to_string(), length)
+                    } else {
+                        (a.to_lowercase(), length_input)
+                    }
                 } else {
                     // Default case if no algorithm is specified and non-algo based format is matched
                     (String::new(), None)

tests/by-util/test_hashsum.rs

@@ -890,3 +890,39 @@ fn test_star_to_start() {
         .succeeds()
         .stdout_only("f: OK\n");
 }
+
+#[test]
+fn test_check_b2sum_strict_check() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+    at.touch("f");
+
+    let checksums = [
+        "2e  f\n",
+        "e4a6a0577479b2b4  f\n",
+        "cae66941d9efbd404e4d88758ea67670  f\n",
+        "246c0442cd564aced8145b8b60f1370aa7  f\n",
+        "0e5751c026e543b2e8ab2eb06099daa1d1e5df47778f7787faab45cdf12fe3a8  f\n",
+        "4ded8c5fc8b12f3273f877ca585a44ad6503249a2b345d6d9c0e67d85bcb700db4178c0303e93b8f4ad758b8e2c9fd8b3d0c28e585f1928334bb77d36782e8  f\n",
+        "786a02f742015903c6c6fd852552d272912f4740e15847618a86e217f71f5419d25e1031afee585313896444934eb04b903a685b1448b755d56f701afe9be2ce  f\n",
+    ];
+
+    at.write("ck", &checksums.join(""));
+
+    let output = "f: OK\n".to_string().repeat(checksums.len());
+
+    scene
+        .ccmd("b2sum")
+        .arg("-c")
+        .arg(at.subdir.join("ck"))
+        .succeeds()
+        .stdout_only(&output);
+
+    scene
+        .ccmd("b2sum")
+        .arg("--strict")
+        .arg("-c")
+        .arg(at.subdir.join("ck"))
+        .succeeds()
+        .stdout_only(&output);
+}