feat(tfstated): implement states locking

cmd/tfstated/lock.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"net/http"
+	"time"
+
+	"git.adyxax.org/adyxax/tfstated/pkg/database"
+)
+
+type lockRequest struct {
+	Created   time.Time `json:"Created"`
+	ID        string    `json:"ID"`
+	Info      string    `json:"Info"`
+	Operation string    `json:"Operation"`
+	Path      string    `json:"Path"`
+	Version   string    `json:"Version"`
+	Who       string    `json:"Who"`
+}
+
+func handleLock(db *database.DB) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/" {
+			_ = encode(w, http.StatusBadRequest,
+				fmt.Errorf("no state path provided, cannot LOCK /"))
+			return
+		}
+
+		var lock lockRequest
+		if err := decode(r, &lock); err != nil {
+			_ = encode(w, http.StatusBadRequest, err)
+			return
+		}
+		if success, err := db.SetLockOrGetExistingLock(r.URL.Path, &lock); err != nil {
+			if errors.Is(err, sql.ErrNoRows) {
+				_ = encode(w, http.StatusNotFound,
+					fmt.Errorf("state path not found: %s", r.URL.Path))
+			} else {
+				_ = errorResponse(w, http.StatusInternalServerError, err)
+			}
+		} else if success {
+			w.WriteHeader(http.StatusOK)
+		} else {
+			_ = encode(w, http.StatusConflict, lock)
+		}
+	})
+}

cmd/tfstated/post.go

@@ -16,13 +16,20 @@ func handlePost(db *database.DB) http.Handler {
 			)
 			return
 		}
+
+		id := r.URL.Query().Get("ID")
+
 		data, err := io.ReadAll(r.Body)
 		if err != nil {
 			_ = errorResponse(w, http.StatusBadRequest, err)
 			return
 		}
-		if err := db.SetState(r.URL.Path, data); err != nil {
+		if idMismatch, err := db.SetState(r.URL.Path, data, id); err != nil {
-			_ = errorResponse(w, http.StatusInternalServerError, err)
+			if idMismatch {
+				_ = errorResponse(w, http.StatusConflict, err)
+			} else {
+				_ = errorResponse(w, http.StatusInternalServerError, err)
+			}
 		} else {
 			w.WriteHeader(http.StatusOK)
 		}

cmd/tfstated/routes.go

@@ -14,5 +14,7 @@ func addRoutes(
 
 	mux.Handle("DELETE /", handleDelete(db))
 	mux.Handle("GET /", handleGet(db))
+	mux.Handle("LOCK /", handleLock(db))
 	mux.Handle("POST /", handlePost(db))
+	mux.Handle("UNLOCK /", handleUnlock(db))
 }

cmd/tfstated/unlock.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"net/http"
+
+	"git.adyxax.org/adyxax/tfstated/pkg/database"
+)
+
+func handleUnlock(db *database.DB) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/" {
+			_ = encode(w, http.StatusBadRequest,
+				fmt.Errorf("no state path provided, cannot LOCK /"))
+			return
+		}
+
+		var lock lockRequest
+		if err := decode(r, &lock); err != nil {
+			_ = encode(w, http.StatusBadRequest, err)
+			return
+		}
+		if success, err := db.Unlock(r.URL.Path, &lock); err != nil {
+			if errors.Is(err, sql.ErrNoRows) {
+				_ = encode(w, http.StatusNotFound,
+					fmt.Errorf("state path not found: %s", r.URL.Path))
+			} else {
+				_ = errorResponse(w, http.StatusInternalServerError, err)
+			}
+		} else if success {
+			w.WriteHeader(http.StatusOK)
+		} else {
+			_ = encode(w, http.StatusConflict, lock)
+		}
+	})
+}

pkg/database/locks.go

@@ -0,0 +1,50 @@
+package database
+
+import (
+	"encoding/json"
+)
+
+// Atomically check if there is an existing lock in place on the state. Returns
+// true if it can be set, otherwise returns false and lock is set to the value
+// of the existing lock
+func (db *DB) SetLockOrGetExistingLock(name string, lock any) (bool, error) {
+	tx, err := db.Begin()
+	if err != nil {
+		return false, err
+	}
+	defer func() {
+		if err != nil {
+			_ = tx.Rollback()
+		}
+	}()
+	var data []byte
+	if err = tx.QueryRowContext(db.ctx, `SELECT lock FROM states WHERE name = ?;`, name).Scan(&data); err != nil {
+		return false, err
+	}
+	if data != nil {
+		err = json.Unmarshal(data, lock)
+		return false, err
+	}
+	if data, err = json.Marshal(lock); err != nil {
+		return false, err
+	}
+	_, err = tx.Exec(`UPDATE states SET lock = json(?) WHERE name = ?;`, data, name)
+	if err != nil {
+		return false, err
+	}
+	err = tx.Commit()
+	return true, err
+}
+
+func (db *DB) Unlock(name, lock any) (bool, error) {
+	data, err := json.Marshal(lock)
+	if err != nil {
+		return false, err
+	}
+	result, err := db.Exec(`UPDATE states SET lock = NULL WHERE name = ? and lock = json(?);`, name, data)
+	if err != nil {
+		return false, err
+	}
+	n, err := result.RowsAffected()
+	return n == 1, err
+}

pkg/database/sql/000_init.sql

@@ -5,6 +5,7 @@ CREATE TABLE schema_version (
 CREATE TABLE states (
   id INTEGER PRIMARY KEY,
   name TEXT NOT NULL,
-  data BLOB NOT NULL
+  data BLOB NOT NULL,
+  lock TEXT
 ) STRICT;
 CREATE UNIQUE INDEX states_name on states(name);

pkg/database/states.go

@@ -2,6 +2,7 @@ package database
 
 import (
 	"database/sql"
+	"fmt"
 )
 
 func (db *DB) DeleteState(name string) error {
@@ -18,18 +19,31 @@ func (db *DB) GetState(name string) ([]byte, error) {
 	return db.dataEncryptionKey.DecryptAES256(encryptedData)
 }
 
-func (db *DB) SetState(name string, data []byte) error {
+// returns true in case of id mismatch
+func (db *DB) SetState(name string, data []byte, id string) (bool, error) {
 	encryptedData, err := db.dataEncryptionKey.EncryptAES256(data)
 	if err != nil {
-		return err
+		return false, err
 	}
-	_, err = db.Exec(
+	if id == "" {
-		`INSERT INTO states(name, data) VALUES (:name, :data) ON CONFLICT DO UPDATE SET data = :data WHERE name = :name;`,
+		_, err = db.Exec(
-		sql.Named("data", encryptedData),
+			`INSERT INTO states(name, data) VALUES (:name, :data) ON CONFLICT DO UPDATE SET data = :data WHERE name = :name;`,
-		sql.Named("name", name),
+			sql.Named("data", encryptedData),
-	)
+			sql.Named("name", name),
-	if err != nil {
+		)
-		return err
+		return false, err
+	} else {
+		result, err := db.Exec(`UPDATE states SET data = ? WHERE name = ? and lock->>'ID' = ?;`, encryptedData, name, id)
+		if err != nil {
+			return false, err
+		}
+		n, err := result.RowsAffected()
+		if err != nil {
+			return false, err
+		}
+		if n != 1 {
+			return true, fmt.Errorf("failed to update state, lock ID does not match")
+		}
+		return false, nil
 	}
-	return nil
 }