Initial support/tests for SQLite flags and db dump

This commit adds a pass through for specifying SQLite3 flags. This is
an absolute requirement for being able to create in-memory DB
representations.

spec/database_spec.cr

@@ -8,6 +8,12 @@ ensure
   File.delete(DB_FILENAME)
 end
 
+private def with_db(name)
+  yield Database.new name
+ensure
+  File.delete(name)
+end
+
 describe Database do
   it "opens a database" do
     with_db do |db|
@@ -15,6 +21,41 @@ describe Database do
     end
   end
 
+  it "opens a database and then backs it up to another db" do
+    with_db do |db|
+      db.execute "create table person (name string, age integer)"
+      db.execute "insert into person values (\"foo\", 10)"
+      with_db("./test2.db") do |backup_database|
+        db.dump(backup_database)
+
+        backup_rows = backup_database.execute "select * from person"
+        source_rows = db.execute "select * from person"
+        backup_rows.should eq(source_rows)
+      end
+    end
+  end
+
+  it "opens a database, inserts records, dumps to an in-memory db, insers some more, then dumps to the source" do
+    with_db do |db|
+      db.execute "create table person (name string, age integer)"
+      db.execute "insert into person values (\"foo\", 10)"
+      in_memory_db = Database.new("file:memdb1?mode=memory&cache=shared",
+        LibSQLite3::Flag::URI | LibSQLite3::Flag::CREATE | LibSQLite3::Flag::READWRITE |
+          LibSQLite3::Flag::FULLMUTEX)
+      source_rows = db.execute "select * from person"
+
+      db.dump(in_memory_db)
+      in_memory_db_rows = in_memory_db.execute "select * from person"
+      in_memory_db_rows.should eq(source_rows)
+      in_memory_db.execute "insert into person values (\"bar\", 22)"
+      in_memory_db.dump(db)
+
+      in_memory_db_rows = in_memory_db.execute "select * from person"
+      source_rows = db.execute "select * from person"
+      in_memory_db_rows.should eq(source_rows)
+    end
+  end
+
   [nil, 1, 1_i64, "hello", 1.5, 1.5_f32].each do |value|
     it "executes and select #{value}" do
       with_db(&.execute("select #{value ? value.inspect : "null"}")).should eq([[value]])

src/sqlite3/database.cr

@@ -3,7 +3,7 @@
 # ```
 # require "sqlite3"
 #
-# db = SQLite3::Database.new( "data.db" )
+# db = SQLite3::Database.new("data.db")
 # db.execute("select * from table") do |row|
 #   p row
 # end
@@ -21,6 +21,16 @@ class SQLite3::Database
     @closed = false
   end
 
+  # Allows for initialization with specific flags. Primary use case is to allow
+  # for sqlite3 URI opening and in memory DB operations.
+  def initialize(filename, flags : LibSQLite3::Flag)
+    code = LibSQLite3.open_v2(filename, out @db, flags, nil)
+    if code != 0
+      raise Exception.new(@db)
+    end
+    @closed = false
+  end
+
   # Creates a new Database object that opens the given file, yields it, and closes it at the end.
   def self.new(filename)
     db = new filename
@@ -31,6 +41,37 @@ class SQLite3::Database
     end
   end
 
+  # Dump the database to another SQLite3 instance. This can be used for backing up a SQLite3::Database
+  # to disk or the opposite
+  # Example:
+  #    ```
+  #     source_database = SQLite3::Database.new("mydatabase.db")
+  #     in_memory_db = SQLite3::Database.new(
+  #        "file:memdb1?mode=memory&cache=shared",
+  #        LibSQLite3::Flag::URI | LibSQLite3::Flag::CREATE | LibSQLite3::Flag::READWRITE |
+  #        LibSQLite3::Flag::FULLMUTEX)
+  #     source_database.dump(in_memory_db)
+  #     source_database.close()
+  #     in_memory_db.exectute { |row|
+  #      ...
+  #     }
+  #    ```
+  def dump(to : SQLite3::Database)
+    backup_item = LibSQLite3.backup_init(to.@db, "main", @db, "main")
+    if backup_item.nil?
+      raise Exception.new(to.@db)
+    end
+    code = LibSQLite3.backup_step(backup_item, -1)
+
+    if code != LibSQLite3::Code::DONE
+      raise Exception.new(to.@db)
+    end
+    code = LibSQLite3.backup_finish(backup_item)
+    if code != LibSQLite3::Code::OKAY
+      raise Exception.new(to.@db)
+    end
+  end
+
   # Executes the given SQL statement. If additional parameters are given, they are treated as bind variables,
   # and are bound to the placeholders in the query.
   #

src/sqlite3/lib_sqlite3.cr

@@ -4,6 +4,7 @@ require "./type"
 lib LibSQLite3
   type SQLite3 = Void*
   type Statement = Void*
+  type SQLite3Backup = Void*
 
   enum Flag
     READONLY         = 0x00000001  # Ok for sqlite3_open_v2()
@@ -29,6 +30,7 @@ lib LibSQLite3
   end
 
   enum Code
+    OKAY = 0
     ROW = 100
     DONE = 101
   end
@@ -41,6 +43,10 @@ lib LibSQLite3
   fun errcode = sqlite3_errcode(SQLite3) : Int32
   fun errmsg = sqlite3_errmsg(SQLite3) : UInt8*
 
+  fun backup_init = sqlite3_backup_init(SQLite3, UInt8*, SQLite3, UInt8*) : SQLite3Backup
+  fun backup_step = sqlite3_backup_step(SQLite3Backup, Int8): Code
+  fun backup_finish = sqlite3_backup_finish(SQLite3Backup): Code
+
   fun prepare_v2 = sqlite3_prepare_v2(db : SQLite3, zSql : UInt8*, nByte : Int32, ppStmt : Statement*, pzTail : UInt8**) : Int32
   fun step = sqlite3_step(stmt : Statement) : Int32
   fun column_count = sqlite3_column_count(stmt : Statement) : Int32