journal: take mutable references for C interior mutability

This commit changes some methods signature to take mutable references
wherever the FFI implies some internal status mutation by the C API.
While this is not stricly needed by Rust rules, it helps in explicitly
conveying the semantic across the layers.

Author: lucab

src/journal.rs

@@ -153,7 +153,7 @@ impl Journal {
 
     /// Read the next record from the journal. Returns `Ok(None)` if there
     /// are no more records to read.
-    pub fn next_record(&self) -> Result<Option<JournalRecord>> {
+    pub fn next_record(&mut self) -> Result<Option<JournalRecord>> {
         if sd_try!(ffi::sd_journal_next(self.j)) == 0 {
             return Ok(None);
         }
@@ -179,7 +179,7 @@ impl Journal {
 
     /// Seek to a specific position in journal. On success, returns a cursor
     /// to the current entry.
-    pub fn seek(&self, seek: JournalSeek) -> Result<String> {
+    pub fn seek(&mut self, seek: JournalSeek) -> Result<String> {
         match seek {
             JournalSeek::Head => sd_try!(ffi::sd_journal_seek_head(self.j)),
             JournalSeek::Current => 0,

tests/journal.rs

@@ -35,7 +35,7 @@ fn cursor() {
         return;
     }
 
-    let j = journal::Journal::open(journal::JournalFiles::All, false, false).unwrap();
+    let mut j = journal::Journal::open(journal::JournalFiles::All, false, false).unwrap();
     log!(log::LogLevel::Info, "rust-systemd test_seek entry");
     assert!(j.seek(journal::JournalSeek::Head).is_ok());
     let _s = j.cursor().unwrap();
@@ -47,7 +47,7 @@ fn ts() {
         return;
     }
 
-    let j = journal::Journal::open(journal::JournalFiles::All, false, false).unwrap();
+    let mut j = journal::Journal::open(journal::JournalFiles::All, false, false).unwrap();
     log!(log::LogLevel::Info, "rust-systemd test_seek entry");
     assert!(j.seek(journal::JournalSeek::Head).is_ok());
     let _s = j.timestamp().unwrap();
@@ -56,7 +56,7 @@ fn ts() {
 
 #[test]
 fn test_seek() {
-    let j = journal::Journal::open(journal::JournalFiles::All, false, false).unwrap();
+    let mut j = journal::Journal::open(journal::JournalFiles::All, false, false).unwrap();
     if ! have_journal() {
         return;
     }