Extract libusb context to a longer living lifetime

This is due to a limitation where we can't hold a struct that has both
the context and a device handle (that internally references back to it).
The libusb context has to outlive the device handle.

Github issue:

https://github.com/dcuddeback/libusb-rs/issues/3

Example solution via IRC:

https://play.rust-lang.org/?gist=c68bda27266249c781e6335c4127f301&version=stable&mode=debug&edition=2015

2 files changed, 13 insertions, 17 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 9468997..b13d7be 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,32 +5,26 @@ const KNOWN_DEVICES: [(u16, u16, &str); 2] = [
     (0x0bda, 0x2838, "Generic RTL2832U OEM")
 ];
 
-struct Usb<'a> {
-    ctx: libusb::Context,
-    dev: Option<libusb::DeviceHandle<'a>>
-}
-
 pub struct RtlSdr<'a> {
-    usb: Usb<'a>
+    ctx: &'a libusb::Context,
+    dev: Option<libusb::DeviceHandle<'a>>
 }
 
 impl<'a> RtlSdr<'a> {
     
-    pub fn new() -> RtlSdr<'a> {
+    pub fn new(ctx: &'a libusb::Context) -> RtlSdr<'a> {
         RtlSdr {
-            usb: Usb {
-                ctx: libusb::Context::new().unwrap(),
-                dev: None
-            }
+            ctx,
+            dev: None
         }
     }
 
     pub fn init(&mut self) {
-        self.usb.dev = self.find_device();
+        self.dev = self.find_device();
     }
 
     pub fn find_device(&self) -> Option<libusb::DeviceHandle<'a>> {
-        for mut dev in self.usb.ctx.devices().unwrap().iter() {
+        for mut dev in self.ctx.devices().unwrap().iter() {
             let desc = dev.device_descriptor().unwrap();
             let vid = desc.vendor_id();
             let pid = desc.product_id();
@@ -51,9 +45,10 @@ mod tests {
 
     #[test]
     fn test_init() {
-        let mut rtlsdr = RtlSdr::new();
-        assert!(rtlsdr.usb.dev.is_none());
+        let ctx = libusb::Context::new().unwrap();
+        let mut rtlsdr = RtlSdr::new(&ctx);
+        assert!(rtlsdr.dev.is_none());
         rtlsdr.init();
-        assert!(rtlsdr.usb.dev.is_some());
+        assert!(rtlsdr.dev.is_some());
     }
 }
diff --git a/src/main.rs b/src/main.rs
index e1dfc5d..1bdade5 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -6,6 +6,7 @@ use lib::RtlSdr;
 
 fn main() {
     println!("Running");
-    let mut rtlsdr = RtlSdr::new();
+    let ctx = libusb::Context::new().unwrap();
+    let mut rtlsdr = RtlSdr::new(&ctx);
     rtlsdr.init();
 }