private pastes

Fixes #66.

Needs:

```bash
varnishadm ban 'req.http.host == ptpb.pw && req.url == /f'
varnishadm ban 'req.http.host == ptpb.pw && req.url == /'
```

```sql
DELIMITER ;
ALTER TABLE paste CHANGE uuid secret BINARY(20) NOT NULL;

DROP TABLE IF EXISTS private;
CREATE TABLE private (
  digest BINARY(20) NOT NULL,
  secret BINARY(16) NOT NULL,
  content BLOB NOT NULL,
  PRIMARY KEY (digest),
  UNIQUE KEY (secret)
)
ENGINE = InnoDB;

DELIMITER @@

DROP PROCEDURE IF EXISTS paste_insert@@
CREATE PROCEDURE paste_insert (
  p_secret BINARY(16),
  p_content MEDIUMBLOB,
  OUT p_id MEDIUMINT
)
BEGIN
  START TRANSACTION;
  INSERT paste (secret, digest, content)
  VALUES (p_secret, UNHEX(SHA1(p_content)), p_content);
  SELECT last_insert_id() INTO p_id;
  COMMIT;
END;
@@

DROP PROCEDURE IF EXISTS paste_insert_private@@
CREATE PROCEDURE paste_insert_private (
  p_secret BINARY(16),
  p_content MEDIUMBLOB,
  OUT p_digest BINARY(20)
)
BEGIN
  START TRANSACTION;
  INSERT private (secret, digest, content)
  VALUES (p_secret, @d:=UNHEX(SHA1(p_content)), p_content);
  SELECT @d INTO p_digest;
  COMMIT;
END;
@@

DROP PROCEDURE IF EXISTS paste_put@@
CREATE PROCEDURE paste_put (
  p_secret BINARY(16),
  p_content MEDIUMBLOB,
  OUT p_id MEDIUMINT,
  OUT p_digest BINARY(20)
)
BEGIN
  START TRANSACTION;
  UPDATE paste
  SET digest = UNHEX(SHA1(p_content)), content = p_content
  WHERE secret = p_secret;
  UPDATE private
  SET digest = UNHEX(SHA1(p_content)), content = p_content
  WHERE secret = p_secret;
  /* .. */
  SELECT id INTO p_id
  FROM paste
  WHERE secret = p_secret;
  SELECT digest INTO p_digest
  FROM private
  WHERE secret = p_secret;
  COMMIT;
END;
@@

DROP PROCEDURE IF EXISTS paste_delete@@
CREATE PROCEDURE paste_delete (
  p_secret BINARY(16),
  OUT p_id MEDIUMINT,
  OUT p_digest BINARY(20)
)
BEGIN
  START TRANSACTION;
  SELECT id INTO p_id
  FROM paste
  WHERE secret = p_secret;
  SELECT digest INTO p_digest
  FROM private
  WHERE secret = p_secret;
  /* .. */
  DELETE
  FROM paste
  WHERE secret = p_secret;
  DELETE
  FROM private
  WHERE secret = p_secret;
  COMMIT;
END;
@@

DROP PROCEDURE IF EXISTS paste_get_stats@@
CREATE PROCEDURE paste_get_stats (
  OUT p_count INT,
  OUT p_length INT
)
BEGIN
  SELECT COUNT(*), SUM(LENGTH(content)) INTO p_count, p_length
  FROM (
    SELECT content FROM paste
    UNION
    SELECT content FROM private
  ) AS p;
END;
@@

DROP PROCEDURE IF EXISTS paste_get_digest@@
CREATE PROCEDURE paste_get_digest (
  p_digest BINARY(20),
  OUT p_id MEDIUMINT,
  OUT p_exists BIT(1)
)
BEGIN
  SELECT id INTO p_id
  FROM paste
  WHERE digest = p_digest;
  SELECT 1 INTO p_exists
  FROM private
  WHERE digest = p_digest;
END;
@@

DROP PROCEDURE IF EXISTS paste_get_content_digest@@
CREATE PROCEDURE paste_get_content_digest (
  p_digest BINARY(20),
  OUT p_content MEDIUMBLOB
)
BEGIN
  SELECT p.content INTO p_content
  FROM (
    SELECT content
    FROM paste
    WHERE digest = p_digest
    UNION
    SELECT content
    FROM private
    WHERE digest = p_digest
  ) AS p;
END;
@@
```