Fix panic on android when run under termux (fixes #53)

src/android.rs

@@ -1,6 +1,6 @@
 use crate::{Browser, BrowserOptions, Error, ErrorKind, Result};
 use jni::objects::JValue;
-pub use std::os::unix::process::ExitStatusExt;
+use std::process::{Command, Stdio};
 
 /// Deal with opening of browsers on Android. Only [Browser::Default] is supported, and
 /// in options, only [BrowserOptions::dry_run] is honoured.
@@ -17,17 +17,27 @@ pub fn open_browser_internal(browser: Browser, url: &str, options: &BrowserOptio
 
 /// Open the default browser
 #[inline]
-pub fn open_browser_default(url: &str, options: &BrowserOptions) -> Result<()> {
+fn open_browser_default(url: &str, options: &BrowserOptions) -> Result<()> {
     // always return true for a dry run
     if options.dry_run {
         return Ok(());
     }
 
+    // first we try to see if we're in a termux env, because if we are, then
+    // the android context may not have been initialized, and it'll panic
+    if try_for_termux(url, options).is_ok() {
+        return Ok(());
+    }
+
     // Create a VM for executing Java calls
     let ctx = ndk_context::android_context();
-    let vm = unsafe {
-        jni::JavaVM::from_raw(ctx.vm() as _).expect("Expected to find JVM via ndk_context crate")
-    };
+    let vm = unsafe { jni::JavaVM::from_raw(ctx.vm() as _) }.map_err(|_| -> Error {
+        Error::new(
+            ErrorKind::NotFound,
+            "Expected to find JVM via ndk_context crate",
+        )
+    })?;
+
     let activity = unsafe { jni::objects::JObject::from_raw(ctx.context() as _) };
     let env = vm.attach_current_thread().map_err(|_| -> Error {
         Error::new(ErrorKind::Other, "Failed to attach current thread")
@@ -82,3 +92,36 @@ pub fn open_browser_default(url: &str, options: &BrowserOptions) -> Result<()> {
 
     Ok(())
 }
+
+/// Attemps to open a browser assuming a termux environment
+///
+/// See [issue #53](https://github.com/amodm/webbrowser-rs/issues/53)
+#[inline]
+fn try_for_termux(url: &str, options: &BrowserOptions) -> Result<()> {
+    use std::env;
+    if env::var("TERMUX_VERSION").is_ok() {
+        // return true on dry-run given that termux-open command is guaranteed to be present
+        if options.dry_run {
+            return Ok(());
+        }
+        let mut cmd = Command::new("termux-open");
+        cmd.arg(url);
+        if options.suppress_output {
+            cmd.stdin(Stdio::null())
+                .stdout(Stdio::null())
+                .stderr(Stdio::null());
+        }
+        cmd.status().and_then(|status| {
+            if status.success() {
+                Ok(())
+            } else {
+                Err(Error::new(
+                    ErrorKind::Other,
+                    "command present but exited unsuccessfully",
+                ))
+            }
+        })
+    } else {
+        Err(Error::new(ErrorKind::Other, "Not a termux environment"))
+    }
+}