Add SQLite schema metadata for DB resources

crates/geth-db/Cargo.toml

@@ -6,6 +6,11 @@ rust-version.workspace = true
 license.workspace = true
 
 [dependencies]
+blake3.workspace = true
+rusqlite.workspace = true
 serde.workspace = true
 thiserror.workspace = true
 geth-types = { path = "../geth-types" }
+
+[dev-dependencies]
+tempfile.workspace = true

crates/geth-db/src/lib.rs

@@ -1,5 +1,7 @@
 use geth_types::{DbId, ResourceId};
+use rusqlite::{Connection, OpenFlags};
 use serde::{Deserialize, Serialize};
+use std::path::Path;
 
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub struct DbResource {
@@ -17,6 +19,8 @@ pub struct DbResource {
 pub enum DbError {
     #[error("invalid db resource name: {0}")]
     InvalidName(String),
+    #[error("sqlite error: {0}")]
+    Sqlite(#[from] rusqlite::Error),
 }
 
 pub fn validate_db_name(name: &str) -> Result<(), DbError> {
@@ -30,6 +34,50 @@ pub fn validate_db_name(name: &str) -> Result<(), DbError> {
     Ok(())
 }
 
+pub fn schema_metadata(path: &Path) -> Result<String, DbError> {
+    let conn = Connection::open_with_flags(path, OpenFlags::SQLITE_OPEN_READ_ONLY)?;
+    let mut stmt = conn.prepare(
+        r#"SELECT type, name, COALESCE(sql, '')
+           FROM sqlite_master
+           WHERE name NOT LIKE 'sqlite_%'
+           ORDER BY type, name"#,
+    )?;
+    let rows = stmt.query_map([], |row| {
+        Ok((
+            row.get::<_, String>(0)?,
+            row.get::<_, String>(1)?,
+            row.get::<_, String>(2)?,
+        ))
+    })?;
+
+    let mut canonical = String::new();
+    let mut table_count = 0_usize;
+    let mut index_count = 0_usize;
+    let mut view_count = 0_usize;
+    let mut trigger_count = 0_usize;
+    for row in rows {
+        let (kind, name, sql) = row?;
+        match kind.as_str() {
+            "table" => table_count += 1,
+            "index" => index_count += 1,
+            "view" => view_count += 1,
+            "trigger" => trigger_count += 1,
+            _ => {}
+        }
+        canonical.push_str(&kind);
+        canonical.push('\0');
+        canonical.push_str(&name);
+        canonical.push('\0');
+        canonical.push_str(&sql);
+        canonical.push('\n');
+    }
+
+    Ok(format!(
+        "tables={table_count} indexes={index_count} views={view_count} triggers={trigger_count} schema_hash={}",
+        blake3::hash(canonical.as_bytes())
+    ))
+}
+
 #[must_use]
 pub fn crsqlite_sync_roadmap() -> &'static str {
     "future db sync reads crsql_changes, exchanges changes over Iroh, and applies through crsql_changes"
@@ -48,4 +96,27 @@ mod tests {
         assert!(validate_db_name("notes/main").is_err());
         assert!(validate_db_name("notes main").is_err());
     }
+
+    #[test]
+    fn schema_metadata_reports_counts_and_stable_hash() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let path = dir.path().join("notes.sqlite");
+        let conn = Connection::open(&path).expect("open sqlite");
+        conn.execute(
+            "CREATE TABLE notes(id INTEGER PRIMARY KEY, body TEXT NOT NULL)",
+            [],
+        )
+        .expect("create table");
+        conn.execute("CREATE INDEX notes_body ON notes(body)", [])
+            .expect("create index");
+        drop(conn);
+
+        let first = schema_metadata(&path).expect("schema metadata");
+        let second = schema_metadata(&path).expect("schema metadata again");
+
+        assert_eq!(first, second);
+        assert!(first.contains("tables=1"));
+        assert!(first.contains("indexes=1"));
+        assert!(first.contains("schema_hash="));
+    }
 }