Fix read_generic blocking on non-blocking files when a length is not …

…specified (#117)

* Fix read_generic blocking on non-blocking files when a length is not specified

* Cargo fmt

crates/bh_agent_server/src/util/mod.rs

@@ -8,6 +8,6 @@ mod unix_functions;
 pub use read_chars::*;
 pub use read_lines::read_lines;
 #[cfg(target_family = "unix")]
-pub use set_blocking::set_blocking;
+pub use set_blocking::{is_blocking, set_blocking};
 #[cfg(target_family = "unix")]
 pub use unix_functions::{chmod, chown, stat};

crates/bh_agent_server/src/util/read_chars.rs

@@ -7,17 +7,47 @@ use unicode_reader::Graphemes;
 
 use bh_agent_common::FileOpenType;
 
-pub fn read_generic(file: &mut File, n: Option<u32>, file_type: FileOpenType) -> Result<Vec<u8>> {
+#[cfg(target_family = "unix")]
+use crate::util::is_blocking;
+
+// This is uhhh... a bit messy. The error handling is the main issue that is
+//necessitating this inner function.
+pub fn read_generic(
+    file: &mut File,
+    mut n: Option<u32>,
+    file_type: FileOpenType,
+) -> Result<Vec<u8>> {
     trace!("Entering read_generic");
-    if let Some(num_bytes) = n {
-        match file_type {
-            FileOpenType::Binary => Ok(read_bytes(file, num_bytes as usize)?),
-            FileOpenType::Text => Ok(read_graphemes(file, num_bytes as usize)?),
-        }
-    } else {
-        // if n is None, we just read the whole file, text parsing happens on the client
-        Ok(file.bytes().collect::<Result<Vec<u8>, std::io::Error>>()?)
+
+    #[cfg(target_family = "unix")]
+    if n.is_none() && !is_blocking(file)? {
+        n = Some(1024_u32.pow(2));
     }
+
+    let inner: Result<Vec<u8>> = (|| {
+        trace!("read_generic: entering inner closure...");
+        if let Some(num_bytes) = n {
+            match file_type {
+                FileOpenType::Binary => Ok(read_bytes(file, num_bytes as usize)?),
+                FileOpenType::Text => Ok(read_graphemes(file, num_bytes as usize)?),
+            }
+        } else {
+            // if n is None, we just read the whole file, text parsing happens on the client
+            Ok(file.bytes().collect::<Result<Vec<u8>, std::io::Error>>()?)
+        }
+    })();
+    trace!("read_generic: processing inner result...");
+    inner.or_else(|e| {
+        if let Some(std::io::ErrorKind::WouldBlock) =
+            e.downcast_ref::<std::io::Error>().map(|e| e.kind())
+        {
+            trace!("read_generic: WouldBlock error, returning empty vec");
+            Ok(Vec::new())
+        } else {
+            trace!("read_generic: returning error");
+            Err(e)
+        }
+    })
 }
 
 fn read_bytes(file: &mut File, n: usize) -> Result<Vec<u8>> {

crates/bh_agent_server/src/util/set_blocking.rs

@@ -3,7 +3,7 @@ use std::io;
 use std::os::unix::io::AsRawFd;
 
 // TODO: This is using libc directly, but nix has a wrapper for this. We should use that instead.
-pub fn set_blocking<T: AsRawFd>(fd: &T, blocking: bool) -> io::Result<()> {
+pub fn set_blocking(fd: &impl AsRawFd, blocking: bool) -> io::Result<()> {
     let raw_fd = fd.as_raw_fd();
     let flags = unsafe { fcntl(raw_fd, F_GETFL, 0) };
     if flags < 0 {
@@ -22,3 +22,13 @@ pub fn set_blocking<T: AsRawFd>(fd: &T, blocking: bool) -> io::Result<()> {
 
     Ok(())
 }
+
+pub fn is_blocking(fd: &impl AsRawFd) -> io::Result<bool> {
+    let raw_fd = fd.as_raw_fd();
+    let flags = unsafe { fcntl(raw_fd, F_GETFL, 0) };
+    if flags < 0 {
+        return Err(io::Error::last_os_error());
+    }
+
+    Ok(flags & O_NONBLOCK == 0)
+}