Refactor in preparation to larger changes

1 files changed, 124 insertions, 0 deletions

diff --git a/log_db/src/log_reader_forward.rs b/log_db/src/log_reader_forward.rs
new file mode 100644
index 0000000..03726d0
--- /dev/null
+++ b/log_db/src/log_reader_forward.rs
@@ -0,0 +1,124 @@
+use super::common::*;
+use std::fs::{self};
+use std::io::{self, BufRead, Read};
+
+pub struct ForwardLogReader<'a> {
+    reader: io::BufReader<&'a mut fs::File>,
+}
+
+impl<'a> ForwardLogReader<'a> {
+    pub fn new(file: &mut fs::File) -> ForwardLogReader {
+        let reader = io::BufReader::new(file);
+        ForwardLogReader { reader }
+    }
+
+    fn read_record(&mut self) -> Result<Option<Record>, io::Error> {
+        // The buffer that stores the bytes read from the file.
+        let mut read_buf: Vec<u8> = Vec::new();
+        // The buffer that stores all the bytes of the record read so far in reverse order.
+        let mut result_buf: Vec<u8> = Vec::new();
+
+        // Try reading a byte from the file.
+        // If we've reached the end of the file, return None.
+        let mut peek_buf = vec![0];
+        match self.reader.read_exact(&mut peek_buf) {
+            Ok(_) => {
+                // Go back one byte
+                self.reader.seek_relative(-1)?;
+            }
+            Err(ref e) if e.kind() == io::ErrorKind::UnexpectedEof => {
+                return Ok(None);
+            }
+            Err(e) => {
+                return Err(e);
+            }
+        }
+
+        loop {
+            read_buf.clear();
+            self.reader.read_until(ESCAPE_CHARACTER, &mut read_buf)?;
+            self.reader.seek_relative(-1)?;
+            result_buf.extend(&read_buf[..read_buf.len() - 1]);
+
+            // Otherwise, we must have encountered an escape character.
+            match self.read_special_sequence()? {
+                SpecialSequence::RecordSeparator => {
+                    // The record is complete, so we can break out of the loop.
+                    break;
+                }
+                SpecialSequence::LiteralFieldSeparator => {
+                    // The field separator is escaped, so we need to add it to the result buffer.
+                    result_buf.push(FIELD_SEPARATOR);
+                }
+                SpecialSequence::LiteralEscape => {
+                    // The escape character is escaped, so we need to add it to the result buffer.
+                    result_buf.push(ESCAPE_CHARACTER);
+                }
+            }
+        }
+
+        let record = Record::deserialize(&result_buf);
+        Ok(Some(record))
+    }
+
+    fn read_special_sequence(&mut self) -> Result<SpecialSequence, io::Error> {
+        let mut special_buf: Vec<u8> = vec![0; SEQ_RECORD_SEP.len()];
+        self.reader.read_exact(&mut special_buf)?;
+
+        match validate_special(&special_buf.as_slice()) {
+            Some(special) => Ok(special),
+            None => Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                "Not a special sequence",
+            )),
+        }
+    }
+}
+
+impl Iterator for ForwardLogReader<'_> {
+    type Item = Record;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.read_record() {
+            Ok(Some(record)) => Some(record),
+            Ok(None) => None,
+            Err(err) => panic!("Error reading record: {:?}", err),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::path::Path;
+
+    #[test]
+    fn test_forward_log_reader_fixture_db1() {
+        let db_path = Path::new(TEST_RESOURCES_DIR).join("test_db1");
+        let mut file = fs::OpenOptions::new()
+            .read(true)
+            .open(&db_path)
+            .expect("Failed to open file");
+        let mut forward_log_reader = ForwardLogReader::new(&mut file);
+
+        // There are two records in the log with "schema": Int, Null
+
+        let first_record = forward_log_reader
+            .next()
+            .expect("Failed to read the first record");
+        assert!(match first_record.values.as_slice() {
+            [RecordValue::Int(0x1D), RecordValue::Null] => true,
+            _ => false,
+        });
+
+        let last_record = forward_log_reader
+            .next()
+            .expect("Failed to read the last record");
+        assert!(match last_record.values.as_slice() {
+            [RecordValue::Int(10), RecordValue::Null] => true,
+            _ => false,
+        });
+
+        assert!(forward_log_reader.next().is_none());
+    }
+}