ohos/android: Redirect stdout/stderr to log sink (#32858)

* ohos: redirect stdout/stderr to logging sink

Based on the existing android `redirect_stdout_to_logcat` implementation,
but using the safe abstractions from `nix` and dumping to the `log` sink,
instead of directly writing the log.

Signed-off-by: Jonathan Schwender <jonathan.schwender@huawei.com>

* android: Use new shared implementation for logcat redirection.

Signed-off-by: Jonathan Schwender <jonathan.schwender@huawei.com>

* servoshell: Register cfg(production)

Signed-off-by: Jonathan Schwender <jonathan.schwender@huawei.com>

* Update ports/servoshell/egl/log.rs

Co-authored-by: Martin Robinson <mrobinson@igalia.com>
Signed-off-by: Jonathan Schwender <55576758+jschwe@users.noreply.github.com>

* Change info! to debug! to match original behavior on android

Signed-off-by: Jonathan Schwender <jonathan.schwender@huawei.com>

---------

Signed-off-by: Jonathan Schwender <jonathan.schwender@huawei.com>
Signed-off-by: Jonathan Schwender <55576758+jschwe@users.noreply.github.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

ports/servoshell/egl/log.rs

@@ -0,0 +1,96 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Helper Module to redirect stdout/stderr to the logging sink
+
+use std::os::fd::{AsRawFd, IntoRawFd, RawFd};
+use std::thread;
+
+use log::{debug, error, info, warn};
+
+#[derive(Debug)]
+#[allow(dead_code)]
+pub(crate) enum LogRedirectError {
+    CreatePipeFailed(nix::Error),
+    RedirectToPipeFailed(nix::Error),
+}
+
+/// Redirect stdout and stderr to the logging system
+pub(crate) fn redirect_stdout_and_stderr() -> Result<(), LogRedirectError> {
+    fn log_raw_msg(raw_msg: &[u8]) {
+        if let Ok(utf8_msg) = std::str::from_utf8(raw_msg) {
+            debug!("{utf8_msg}");
+        } else {
+            // Note: This could happen if the message is long, and we hit the length
+            // limitation in the middle of a utf-8 codepoint. We could try to handle this
+            // by using `error.valid_up_to()`, but lets see first if we hit this problem
+            // in practice.
+            warn!("Dropping 1 log message due to invalid encoding.");
+            debug!("Raw byte content: {raw_msg:?}")
+        }
+    }
+
+    // The first step is to redirect stdout and stderr to the logs.
+    // We redirect stdout and stderr to a custom descriptor.
+    let (readerfd, writerfd) =
+        nix::unistd::pipe().map_err(|e| LogRedirectError::CreatePipeFailed(e))?;
+    // Leaks the writer fd. We want to log for the whole program lifetime.
+    let raw_writerfd = writerfd.into_raw_fd();
+    let _fd = nix::unistd::dup2(raw_writerfd, RawFd::from(1))
+        .map_err(|e| LogRedirectError::RedirectToPipeFailed(e))?;
+    let _fd = nix::unistd::dup2(raw_writerfd, RawFd::from(2))
+        .map_err(|e| LogRedirectError::RedirectToPipeFailed(e))?;
+
+    // Then we spawn a thread whose only job is to read from the other side of the
+    // pipe and redirect to the logs.
+    let _detached = thread::spawn(move || {
+        const BUF_LENGTH: usize = 512;
+        let mut buf = vec![b'\0'; BUF_LENGTH];
+
+        let mut cursor = 0_usize;
+
+        loop {
+            let result = {
+                let read_into = &mut buf[cursor..];
+                nix::unistd::read(readerfd.as_raw_fd(), read_into)
+            };
+
+            let end = match result {
+                Ok(0) => {
+                    info!("Log pipe closed. Terminating log thread");
+                    return;
+                },
+                Ok(bytes) => bytes + cursor,
+                Err(nix::errno::Errno::EINTR) => continue,
+                Err(e) => {
+                    error!("Failed to read from redirected stdout/stderr pipe due to {e:?}. Closing log thread");
+                    return;
+                },
+            };
+
+            // Only modify the portion of the buffer that contains real data.
+            let buf = &mut buf[0..end];
+
+            if let Some(last_newline_pos) = buf.iter().rposition(|&c| c == b'\n') {
+                log_raw_msg(&buf[0..last_newline_pos]);
+
+                if last_newline_pos < buf.len() {
+                    let pos_after_newline = last_newline_pos + 1;
+                    let len_not_logged_yet = buf[pos_after_newline..].len();
+                    buf.copy_within(pos_after_newline..end, 0);
+                    cursor = len_not_logged_yet;
+                } else {
+                    cursor = 0;
+                }
+            } else if end == BUF_LENGTH {
+                // No newline found but the buffer is full, flush it anyway.
+                log_raw_msg(buf);
+                cursor = 0;
+            } else {
+                cursor = end;
+            }
+        }
+    });
+    Ok(())
+}