Small refactor of librespot-core

* Remove default impl for `SessionConfig`
* Move util mod to single file
* Restore privacy of mods
* Move `fn get_credentials` to application
* Remove `extern crate` statements

core/src/util.rs

@@ -0,0 +1,75 @@
+use num_bigint::BigUint;
+use num_integer::Integer;
+use num_traits::{One, Zero};
+use rand::Rng;
+use std::mem;
+use std::ops::{Mul, Rem, Shr};
+
+pub fn rand_vec<G: Rng>(rng: &mut G, size: usize) -> Vec<u8> {
+    ::std::iter::repeat(())
+        .map(|()| rng.gen())
+        .take(size)
+        .collect()
+}
+
+pub fn url_encode(inp: &str) -> String {
+    let mut encoded = String::new();
+
+    for c in inp.as_bytes().iter() {
+        match *c as char {
+            'A'..='Z' | 'a'..='z' | '0'..='9' | '-' | '_' | '.' | '~' | ':' | '/' => {
+                encoded.push(*c as char)
+            }
+            c => encoded.push_str(format!("%{:02X}", c as u32).as_str()),
+        };
+    }
+
+    encoded
+}
+
+pub fn powm(base: &BigUint, exp: &BigUint, modulus: &BigUint) -> BigUint {
+    let mut base = base.clone();
+    let mut exp = exp.clone();
+    let mut result: BigUint = One::one();
+
+    while !exp.is_zero() {
+        if exp.is_odd() {
+            result = result.mul(&base).rem(modulus);
+        }
+        exp = exp.shr(1);
+        base = (&base).mul(&base).rem(modulus);
+    }
+
+    result
+}
+
+pub trait ReadSeek: ::std::io::Read + ::std::io::Seek {}
+impl<T: ::std::io::Read + ::std::io::Seek> ReadSeek for T {}
+
+pub trait Seq {
+    fn next(&self) -> Self;
+}
+
+macro_rules! impl_seq {
+    ($($ty:ty)*) => { $(
+        impl Seq for $ty {
+            fn next(&self) -> Self { (*self).wrapping_add(1) }
+        }
+    )* }
+}
+
+impl_seq!(u8 u16 u32 u64 usize);
+
+#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord, Default)]
+pub struct SeqGenerator<T: Seq>(T);
+
+impl<T: Seq> SeqGenerator<T> {
+    pub fn new(value: T) -> Self {
+        SeqGenerator(value)
+    }
+
+    pub fn get(&mut self) -> T {
+        let value = self.0.next();
+        mem::replace(&mut self.0, value)
+    }
+}