Emit one JSON record per line

src/commands/backup.rs

@@ -467,7 +467,8 @@ impl BackupCmd {
             write_json_progress_summary(&snap)?;
         } else if self.json {
             let mut stdout = std::io::stdout();
-            serde_json::to_writer_pretty(&mut stdout, &snap)?;
+            serde_json::to_writer(&mut stdout, &snap)?;
+            println!();
         } else if self.long {
             let mut table = table();
 

src/commands/forget.rs

@@ -134,7 +134,8 @@ impl ForgetCmd {
 
         if self.json {
             let mut stdout = std::io::stdout();
-            serde_json::to_writer_pretty(&mut stdout, &groups)?;
+            serde_json::to_writer(&mut stdout, &groups)?;
+            println!();
         } else {
             print_groups(&groups);
         }

src/commands/merge.rs

@@ -65,7 +65,8 @@ impl MergeCmd {
 
         if self.json {
             let mut stdout = std::io::stdout();
-            serde_json::to_writer_pretty(&mut stdout, &snap)?;
+            serde_json::to_writer(&mut stdout, &snap)?;
+            println!();
         }
         info!("saved new snapshot as {}.", snap.id);
 

src/commands/repoinfo.rs

@@ -70,7 +70,8 @@ impl RepoInfoCmd {
 
         if self.json {
             let mut stdout = std::io::stdout();
-            serde_json::to_writer_pretty(&mut stdout, &infos)?;
+            serde_json::to_writer(&mut stdout, &infos)?;
+            println!();
             return Ok(());
         }
 

src/commands/snapshots.rs

@@ -94,7 +94,7 @@ impl SnapshotCmd {
             let mut stdout = std::io::stdout();
             if groups.len() == 1 && groups[0].group_key.is_empty() {
                 // we don't use grouping, only output snapshots list
-                serde_json::to_writer_pretty(&mut stdout, &groups[0].items)?;
+                serde_json::to_writer(&mut stdout, &groups[0].items)?;
             } else {
                 #[derive(Serialize, From)]
                 struct SnapshotsGroup {
@@ -105,8 +105,9 @@ impl SnapshotCmd {
                     .into_iter()
                     .map(|g| (g.group_key, g.items).into())
                     .collect();
-                serde_json::to_writer_pretty(&mut stdout, &groups)?;
+                serde_json::to_writer(&mut stdout, &groups)?;
             }
+            println!();
             return Ok(());
         }
 

tests/json_lines.rs

@@ -0,0 +1,58 @@
+use assert_cmd::Command;
+use rustic_testing::TestResult;
+use tempfile::{TempDir, tempdir};
+
+fn rustic_runner(temp_dir: &TempDir) -> TestResult<Command> {
+    let mut runner = Command::new(env!("CARGO_BIN_EXE_rustic"));
+    runner.arg("-r").arg(temp_dir.path().join("repo")).args([
+        "--password",
+        "test",
+        "--no-progress",
+    ]);
+    Ok(runner)
+}
+
+#[test]
+fn backup_json_writes_one_snapshot_per_line() -> TestResult<()> {
+    let temp_dir = tempdir()?;
+    let first_source = temp_dir.path().join("first-source");
+    let second_source = temp_dir.path().join("second-source");
+    std::fs::create_dir(&first_source)?;
+    std::fs::create_dir(&second_source)?;
+    std::fs::write(first_source.join("first.txt"), "first")?;
+    std::fs::write(second_source.join("second.txt"), "second")?;
+
+    rustic_runner(&temp_dir)?.arg("init").assert().success();
+
+    let profile = temp_dir.path().join("two-sources.toml");
+    let first_source = serde_json::to_string(&first_source.to_string_lossy())?;
+    let second_source = serde_json::to_string(&second_source.to_string_lossy())?;
+    std::fs::write(
+        &profile,
+        format!(
+            "[[backup.snapshots]]\nsources = [{first_source}]\n\n[[backup.snapshots]]\nsources = [{second_source}]\n"
+        ),
+    )?;
+
+    let output = rustic_runner(&temp_dir)?
+        .arg("-P")
+        .arg(profile)
+        .args(["backup", "--json"])
+        .output()?;
+    assert!(output.status.success());
+
+    let stdout = String::from_utf8(output.stdout)?;
+    assert!(
+        stdout.ends_with('\n'),
+        "JSON output is not line-terminated: {stdout}"
+    );
+    let lines: Vec<_> = stdout.lines().collect();
+    assert_eq!(lines.len(), 2, "unexpected JSON output: {stdout}");
+    let snapshots: Vec<serde_json::Value> = lines
+        .iter()
+        .map(|line| serde_json::from_str(line))
+        .collect::<Result<_, _>>()?;
+    assert_eq!(snapshots.len(), 2);
+
+    Ok(())
+}