added better error handling for weak passwords

src/main.rs

@@ -31,7 +31,6 @@ struct PasswordConfig {
 struct PasswordPolicy(PasswordConfig);
 
 // todo: support multiple password policies
-// todo: add support for Errors
 fn validate_password(password: &str, policy: &PasswordPolicy) -> bool {
     if policy.0.charset.contains(CharSet::UPPERCASE) {
         let mut found_upper = false;
@@ -72,14 +71,17 @@ fn random_ascii(rng: &mut OsRng, char_set: &[u8]) -> u8 {
     *char_set.choose(rng).expect("char_set should not be empty")
 }
 
-// todo: protect from small len
+// todo: does not guarantee that a password will contain the necessary chars
 //
 // How many bits of entropy?
 // max_chars_available -> 80
 // log2(possible_symbols^len) yields bits of entropy
 // so say len is 20 and we use all 80 chars:
 // that's log2(80^20) -> 126.4 bits of entropy per password
-fn generate_random_chars(config: PasswordConfig, rng: &mut OsRng) -> String {
+fn generate_random_chars(config: PasswordConfig, rng: &mut OsRng) -> Result<String,String> {
+    if config.len < 8 {
+        return Err(String::from("Password length not long enough"));
+    }
     // String is a thin wrapper around Vec<u8> so we can expect re-allocation
     // and copy only when we exceed the capacity of the vector
     // However, with_capacity will perform only one allocation anyway
@@ -106,11 +108,11 @@ fn generate_random_chars(config: PasswordConfig, rng: &mut OsRng) -> String {
     for _ in 0..config.len {
         res.push(random_ascii(rng, &chars) as char);
     }
-    res
+    Ok(res)
 }
 
-// todo: protect from small phrase_count 
-
+// todo: we should add symbols, numbers, and Capitalization
+//
 // we can take a slice of "words" because we don't care about:
 // capacity, mutation (push/pop), allocation strategy
 //
@@ -119,7 +121,10 @@ fn generate_random_chars(config: PasswordConfig, rng: &mut OsRng) -> String {
 // log2(18) -> 4.1 bits for separator assuming seporator is one of our SYMBOLs
 // total 70.5 bits of entropy
 fn generate_passphrase(phrase_count: usize,
-        word_list: &[&str], separator: char, rng: &mut OsRng) -> String {
+        word_list: &[&str], separator: char, rng: &mut OsRng) -> Result<String,String> {
+    if phrase_count < 2 {
+        return Err("Phrase count too low".to_string());
+    }
     let mut res = String::new(); // don't bother saving allocations with a bad guess 
     for i in 0..phrase_count {
         res.push_str(random_word(word_list, rng));
@@ -127,7 +132,7 @@ fn generate_passphrase(phrase_count: usize,
             res.push(separator);
         }
     }
-    res
+    Ok(res)
 }
 
 fn random_word<'a>(word_list: &[&'a str], rng: &mut OsRng) -> &'a str {
@@ -154,17 +159,24 @@ fn main() {
     let mut rng = OsRng;
 
     // todo: add actual tests
-    let chars = generate_random_chars(Default::default(), &mut rng);
-    println!("generated random chars (alphanumeric): {}", chars.as_str());
-    assert!(validate_password(&chars, &Default::default()));
+    // password with alphnumeric
+    let password_res = generate_random_chars(Default::default(), &mut rng);
+    if let Err(e) = password_res {
+        println!("Error during first password gen: {}", e);
+    } else {
+        let password = password_res.unwrap();
+        println!("generated random chars (alphanumeric): {}", password.as_str());
+        assert!(validate_password(&password, &Default::default()));
+    }
 
+    // password with alphanumeric + symbols
     let config = PasswordConfig {
         charset: CharSet::SYMBOLS,
         ..Default::default()
     };
-    let chars = generate_random_chars(config, &mut rng);
-    println!("generated random chars (with symbols): {}", chars.as_str());
+    let password_res2 = generate_random_chars(config, &mut rng);
+    println!("generated random chars (with symbols): {}", password_res2.unwrap().as_str());
 
-    let phrase = generate_passphrase(3, &word_list, '-', &mut rng);
-    println!("generated passphrase: {}", phrase.as_str());
+    let passphrase_res = generate_passphrase(3, &word_list, '-', &mut rng);
+    println!("generated passphrase: {}", passphrase_res.unwrap().as_str());
 }