Address review comments

* moved `is_empty` check into `check_token`
* improved error message (is quite long now but should explain the error
  well)
* removed one helper function from new test

Author: Akida31

crates/crates-io/lib.rs

@@ -518,16 +518,20 @@ pub fn is_url_crates_io(url: &str) -> bool {
 /// It would be easier to check just for alphanumeric tokens, but we can't be sure that all
 /// registries only create tokens in that format so that is as less restricted as possible.
 pub fn check_token(token: &str) -> Result<()> {
-    let is_valid = token.bytes().all(|b| {
+    if token.is_empty() {
+        bail!("please provide a non-empty token");
+    }
+    if token.bytes().all(|b| {
         b >= 32 // undefined in ISO-8859-1, in ASCII/ UTF-8 not-printable character
         && b < 128 // utf-8: the first bit signals a multi-byte character
         && b != 127 // 127 is a control character in ascii and not in ISO 8859-1
         || b == b't' // tab is also allowed (even when < 32)
-    });
-
-    if is_valid {
+    }) {
         Ok(())
     } else {
-        Err(anyhow::anyhow!("invalid token."))
+        Err(anyhow::anyhow!(
+            "token contains invalid characters.\nOnly printable ISO-8859-1 characters \
+             are allowed as it is sent in a HTTPS header."
+        ))
     }
 }

tests/testsuite/login.rs

@@ -134,7 +134,7 @@ fn invalid_login_token() {
         .build();
     setup_new_credentials();
 
-    let check_ = |stdin: &str, stderr: &str| {
+    let check = |stdin: &str, stderr: &str| {
         cargo_process("login")
             .replace_crates_io(registry.index_url())
             .with_stdout("please paste the token found on [..]/me below")
@@ -143,19 +143,32 @@ fn invalid_login_token() {
             .with_status(101)
             .run();
     };
-    let check = |stdin: &str| {
-        check_(stdin, "[ERROR] invalid token.");
-    };
-    // first check updates index so it must be handled differently
-    check_(
+
+    check(
         "😄",
         "\
 [UPDATING] crates.io index
-[ERROR] invalid token.",
+[ERROR] token contains invalid characters.
+Only printable ISO-8859-1 characters are allowed as it is sent in a HTTPS header.",
+    );
+    check(
+        "\u{0016}",
+        "\
+[ERROR] token contains invalid characters.
+Only printable ISO-8859-1 characters are allowed as it is sent in a HTTPS header.",
+    );
+    check(
+        "\u{0000}",
+        "\
+[ERROR] token contains invalid characters.
+Only printable ISO-8859-1 characters are allowed as it is sent in a HTTPS header.",
+    );
+    check(
+        "你好",
+        "\
+[ERROR] token contains invalid characters.
+Only printable ISO-8859-1 characters are allowed as it is sent in a HTTPS header.",
     );
-    check("\u{0016}");
-    check("\u{0000}");
-    check("你好");
 }
 
 #[cargo_test]