df: treat env var with zero block size as invalid

src/uu/df/src/blocks.rs

@@ -9,7 +9,7 @@ use std::{env, fmt};
 
 use uucore::{
     display::Quotable,
-    parser::parse_size::{ParseSizeError, parse_size_u64},
+    parser::parse_size::{ParseSizeError, parse_size_non_zero_u64, parse_size_u64},
 };
 
 /// The first ten powers of 1024.
@@ -213,7 +213,7 @@ pub(crate) fn read_block_size(matches: &ArgMatches) -> Result<BlockSize, ParseSi
 fn block_size_from_env() -> Option<u64> {
     for env_var in ["DF_BLOCK_SIZE", "BLOCK_SIZE", "BLOCKSIZE"] {
         if let Ok(env_size) = env::var(env_var) {
-            return parse_size_u64(&env_size).ok();
+            return parse_size_non_zero_u64(&env_size).ok();
         }
     }
 

tests/by-util/test_df.rs

@@ -690,6 +690,24 @@ fn test_block_size_from_env() {
     assert_eq!(get_header("BLOCKSIZE", "333"), "333B-blocks");
 }
 
+#[test]
+fn test_block_size_from_env_zero() {
+    fn get_header(env_var: &str, env_value: &str) -> String {
+        let output = new_ucmd!()
+            .arg("--output=size")
+            .env(env_var, env_value)
+            .succeeds()
+            .stdout_str_lossy();
+        output.lines().next().unwrap().trim().to_string()
+    }
+
+    let default_block_size_header = "1K-blocks";
+
+    assert_eq!(get_header("DF_BLOCK_SIZE", "0"), default_block_size_header);
+    assert_eq!(get_header("BLOCK_SIZE", "0"), default_block_size_header);
+    assert_eq!(get_header("BLOCKSIZE", "0"), default_block_size_header);
+}
+
 #[test]
 fn test_block_size_from_env_precedences() {
     fn get_header(one: (&str, &str), two: (&str, &str)) -> String {
@@ -747,6 +765,16 @@ fn test_invalid_block_size_from_env() {
     let header = output.lines().next().unwrap().trim().to_string();
 
     assert_eq!(header, default_block_size_header);
+
+    let output = new_ucmd!()
+        .arg("--output=size")
+        .env("DF_BLOCK_SIZE", "0")
+        .env("BLOCK_SIZE", "222")
+        .succeeds()
+        .stdout_str_lossy();
+    let header = output.lines().next().unwrap().trim().to_string();
+
+    assert_eq!(header, default_block_size_header);
 }
 
 #[test]