made some fixes

src/main.rs

@@ -2,19 +2,16 @@ use rand::Rng;
 use rand::rngs::OsRng;
 use std::fs;
 
-// enum variant (i keep forgetting the terminology)
-// enum PasswordType {
-//     RandomChars(usize),
-//     Passphrase(usize, usize),
-// }
+// alphanumeric only
+const CHARSET: &[u8] =
+    b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
 
-// non-CTRL chars
-fn random_ascii() -> u8 {
-    // we definitely want to use the OS for randomness
-    // doesn't require seeding because it is backed by CSPRNG, backed by OS
-    // the OS maintains it's own entropy from mouse movement, hardware noise,etc
-    let mut rng = OsRng;
+// excludes backtick(`), quote('), dquote("), slash(/), bslash(\)
+const CHARSET_WITH_SYMBOLS: &[u8] = 
+    b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()[]{}|?<>,.-_=+~";
 
+
+fn random_ascii(rng: &mut OsRng, char_set: &[u8]) -> u8 {
     // NOT IDEAL FOR CRYPTO/password generation 
     // let range_max = 122; // 125 - 33
     // let n = rng.next_u32() % range_max; // slightly modulo biased
@@ -22,47 +19,56 @@ fn random_ascii() -> u8 {
 
     // this function under the hood creates a zone that divides evenly
     // into the range so we don't encounter modulo bias
-    rng.gen_range(33..125) as u8
+    let index = rng.gen_range(0..char_set.len()); 
+    char_set[index]
 }
 
-fn generate_random_chars(len: usize) -> String {
+fn generate_random_chars(len: usize, symbols: bool, rng: &mut OsRng) -> String {
     // 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
-    let mut res = String::new();
+    // However, with_capacity will perform only one allocation anyway
+    let mut res = String::with_capacity(len);
+    let char_set = if symbols { CHARSET_WITH_SYMBOLS } else { CHARSET };
     for _ in 0..len {
-        res.push(random_ascii() as char);
+        res.push(random_ascii(rng, char_set) as char);
     }
     res
 }
 
-fn generate_passphrase(phrases: usize, len: usize, words: &Vec<&str>) -> String {
-    let mut res = String::new();
-    let mut count = 0;
-    while count < phrases {
-        let word = random_word(words);
-        if word.is_ascii() { // only add ascii words
-            res.push_str(random_word(words));
-            count += 1;
+// we can take a slice of "words" because we don't care about:
+// capacity, mutation (push/pop), allocation strategy
+fn generate_passphrase(phrase_count: usize,
+        word_list: &[&str], rng: &mut OsRng) -> String {
+    let mut res = String::with_capacity(phrase_count*2); // save a couple allocations
+    for _ in 0..phrase_count {
+        res.push_str(random_word(word_list, rng));
     }
-    }
-    res.truncate(len); // only works on ascii
     res
 }
 
-fn random_word<'a>(words: &'a Vec<&'a str>) -> &'a str {
-    let mut rng = OsRng;
-    words[rng.gen_range(0..words.len())]
+fn random_word<'a>(word_list: &'a [&'a str], rng: &mut OsRng) -> &'a str {
+    word_list[rng.gen_range(0..word_list.len())]
 }
 
 
 fn main() {
     let content = fs::read_to_string("/usr/share/dict/words")
         .expect("could not read dictionary");
-    let words: Vec<&str> = content.lines().collect();
 
-    let chars = generate_random_chars(20);
+    // filter words here for only ascii
+    let word_list: Vec<&str> = content.lines().filter(|w|
+        w.is_ascii()).collect();
+
+    // we definitely want to use the OS for randomness
+    // doesn't require seeding because it is backed by CSPRNG, backed by OS
+    // the OS maintains it's own entropy from mouse movement, hardware noise,etc
+    // we pass it through the functions to avoid a potential syscall
+    let mut rng = OsRng;
+    let chars = generate_random_chars(20, true, &mut rng);
     println!("generated random chars: {}", chars.as_str());
 
-    let phrase = generate_passphrase(3, 20, &words);
+    let phrase = generate_passphrase(3, &word_list, &mut rng);
     println!("generated passphrase: {}", phrase.as_str());
+
+    println!("words in dictionary: {}", word_list.len());
 }