Replace uuid dependency with tiny internal RNG (#679)

Cargo.toml

@@ -55,7 +55,6 @@ mime_guess = "2.0"
 percent-encoding = "2.1"
 tokio = { version = "=0.2.0-alpha.6", default-features = false, features = ["io", "tcp", "timer"] }
 tokio-executor = "=0.2.0-alpha.6"
-uuid = { version = "0.7", features = ["v4"] }
 time = "0.1.42"
 
 # TODO: candidates for optional features

src/async_impl/multipart.rs

@@ -7,7 +7,6 @@ use bytes::Bytes;
 use http::HeaderMap;
 use mime_guess::Mime;
 use percent_encoding::{self, AsciiSet, NON_ALPHANUMERIC};
-use uuid::Uuid;
 
 use futures_core::Stream;
 use futures_util::{future, stream, StreamExt};
@@ -265,7 +264,7 @@ impl PartProps for Part {
 impl<P: PartProps> FormParts<P> {
     pub(crate) fn new() -> Self {
         FormParts {
-            boundary: format!("{}", Uuid::new_v4().to_simple()),
+            boundary: gen_boundary(),
             computed_headers: Vec::new(),
             fields: Vec::new(),
             percent_encoding: PercentEncoding::PathSegment,
@@ -481,6 +480,51 @@ impl PercentEncoding {
     }
 }
 
+fn gen_boundary() -> String {
+    let a = random();
+    let b = random();
+    let c = random();
+    let d = random();
+
+    format!("{:016x}-{:016x}-{:016x}-{:016x}", a, b, c, d)
+}
+
+// xor-shift
+fn random() -> u64 {
+    use std::cell::Cell;
+    use std::collections::hash_map::RandomState;
+    use std::hash::{BuildHasher, Hasher};
+    use std::num::Wrapping;
+
+    thread_local! {
+        static RNG: Cell<Wrapping<u64>> = Cell::new(Wrapping(seed()));
+    }
+
+    fn seed() -> u64 {
+        let seed = RandomState::new();
+
+        let mut out = 0;
+        let mut cnt = 0;
+        while out == 0 {
+            cnt += 1;
+            let mut hasher = seed.build_hasher();
+            hasher.write_usize(cnt);
+            out = hasher.finish();
+        }
+        out
+    }
+
+    RNG.with(|rng| {
+        let mut n = rng.get();
+        debug_assert_ne!(n.0, 0);
+        n ^= n >> 12;
+        n ^= n << 25;
+        n ^= n >> 27;
+        rng.set(n);
+        n.0.wrapping_mul(0x2545_f491_4f6c_dd1d)
+    })
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

tests/multipart.rs

@@ -25,7 +25,10 @@ async fn text_part() {
         async move {
             assert_eq!(req.method(), "POST");
             assert_eq!(req.headers()["content-type"], ct);
-            assert_eq!(req.headers()["content-length"], "125");
+            assert_eq!(
+                req.headers()["content-length"],
+                expected_body.len().to_string()
+            );
 
             let mut full: Vec<u8> = Vec::new();
             while let Some(item) = req.body_mut().next().await {