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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,98 @@ | ||
| // Copyright 2021-2023 Martin Pool | ||
|
|
||
| //! Tail a log file: watch for new writes and return the last line. | ||
| use std::fs::File; | ||
| use std::io::Read; | ||
| use std::path::Path; | ||
|
|
||
| use anyhow::Context; | ||
|
|
||
| use crate::Result; | ||
|
|
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| #[derive(Debug)] | ||
| pub struct TailFile { | ||
| file: File, | ||
| last_line_seen: String, | ||
| read_buf: Vec<u8>, | ||
| } | ||
|
|
||
| impl TailFile { | ||
| /// Watch the given path. | ||
| pub fn new<P: AsRef<Path>>(path: P) -> Result<Self> { | ||
| let file = File::open(path.as_ref()).context("Open log file")?; | ||
| Ok(TailFile { | ||
| file, | ||
| last_line_seen: String::new(), | ||
| read_buf: Vec::new(), | ||
| }) | ||
| } | ||
|
|
||
| /// Return the last non-empty, non-whitespace line from this file, or an empty string | ||
| /// if none have been seen yet. | ||
| /// | ||
| /// Non-UTF8 content is lost. | ||
| pub fn last_line(&mut self) -> Result<&str> { | ||
| // This assumes that the file always sees writes of whole lines, which seems | ||
| // pretty likely: we don't attempt to stitch up writes of partial lines with | ||
| // later writes, although we could... | ||
| self.read_buf.clear(); | ||
| let n_read = self | ||
| .file | ||
| .read_to_end(&mut self.read_buf) | ||
| .context("Read from log file")?; | ||
| if n_read > 0 { | ||
| if let Some(new_last) = String::from_utf8_lossy(&self.read_buf) | ||
| .lines() | ||
| .filter(|l| !l.trim().is_empty()) | ||
| .last() | ||
| { | ||
| self.last_line_seen = new_last.to_owned(); | ||
| } | ||
| } | ||
| Ok(self.last_line_seen.as_str()) | ||
| } | ||
| } | ||
|
|
||
| #[cfg(test)] | ||
| mod test { | ||
| use camino::Utf8PathBuf; | ||
|
|
||
| use std::io::Write; | ||
|
|
||
| use super::*; | ||
|
|
||
| #[test] | ||
| fn last_line_of_file() { | ||
| let mut tempfile = tempfile::NamedTempFile::new().unwrap(); | ||
| let path: Utf8PathBuf = tempfile.path().to_owned().try_into().unwrap(); | ||
| let mut tailer = TailFile::new(path).unwrap(); | ||
|
|
||
| assert_eq!( | ||
| tailer.last_line().unwrap(), | ||
| "", | ||
| "empty file has an empty last line" | ||
| ); | ||
|
|
||
| tempfile.write_all(b"hello").unwrap(); | ||
| assert_eq!( | ||
| tailer.last_line().unwrap(), | ||
| "hello", | ||
| "single line file with no terminator has that line as last line" | ||
| ); | ||
|
|
||
| tempfile.write_all(b"\n\n\n").unwrap(); | ||
| assert_eq!( | ||
| tailer.last_line().unwrap(), | ||
| "hello", | ||
| "trailing blank lines are ignored" | ||
| ); | ||
|
|
||
| tempfile.write_all(b"that's all folks!\n").unwrap(); | ||
| assert_eq!( | ||
| tailer.last_line().unwrap(), | ||
| "that's all folks!", | ||
| "newline terminated last line is returned" | ||
| ); | ||
| } | ||
| } |
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