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实现一个简单的Database1(译文）

实现一个简单的Database2(译文）

实现一个简单的Database3(译文）

译注：cstsck在github维护了一个简单的、类似SQLite的数据库实现，通过这个简单的项目，可以很好的理解数据库是如何运行的。本文是第四篇，主要是使用rspec对目前实现的功能进行测试并解决测试出现BUG

译注：cstsck在github维护了一个简单的、类似sqlite的数据库实现，通过这个简单的项目，可以很好的理解数据库是如何运行的。本文是第四篇，主要是使用rspec对目前实现的功能进行测试并解决测试出现BUG

Part 4 我们的第一个测试（和BUG）

我们已经获得插入数据到数据库并打印所有数据的能力。现在来测试一下目前microseconds已有的功能。

我要使用rspec来写我的测试，因为我对rspec很熟悉，它的语法也相当易读。

译注：rsepec 是一个基于Ruby的测试框架，语法非常简单，可以很方便的测试各种可执行程序，判断输出

我定义一个短小的help来发送一个帮助命令列表到数据库，然后对输出进行断言。

describe 'database' do  def run_script(commands)    raw_output = nil    IO.popen("./db", "r+") do |pipe|      commands.each do |command|        pipe.puts command      end      pipe.close_write      # Read entire output      raw_output = pipe.gets(nil)    end    raw_output.split("\n")  end  it 'inserts and retrieves a row' do    result = run_script([      "insert 1 user1 person1@example.com",      "select",      ".exit",    ])    expect(result).to match_array([      "db > Executed.",      "db > (1, user1, person1@example.com)",      "Executed.",      "db > ",    ])  endend

这个简单的测试是确认我们的输入能够获取返回结果。并确保能通过测试：

bundle exec rspec.Finished in 0.00871 seconds (files took 0.09506 seconds to load)1 example, 0 failures

现在测试插入更多行数据到数据库是可行的：

it 'prints error message when table is full' do  script = (1..1401).map do |i|    "insert #{i} user#{i} person#{i}@example.com"  end  script < Error: Table full.')end

再次运行测试：

bundle exec rspec..Finished in 0.01553 seconds (files took 0.08156 seconds to load)2 examples, 0 failures

妙啊，测试通过了！我们的数据库现在能够hold住1400行数据，这是因为我们设置pages最大数量是100页，每页可以存放14行数据。

查看我们目前写的的代码，我意识到我们可能没有正确处理存储文本字段。很容易用下面的例子测试出来（插入边界长度的字符串）：

it 'allows inserting strings that are the maximum length' do  long_username = "a"*32  long_email = "a"*255  script = [    "insert 1 #{long_username} #{long_email}",    "select",    ".exit",  ]  result = run_script(script)  expect(result).to match_array([    "db > Executed.",    "db > (1, #{long_username}, #{long_email})",    "Executed.",    "db > ",  ])end

测试失败了：

Failures:  1) database allows inserting strings that are the maximum length     Failure/Error: raw_output.split("\n")     ArgumentError:       invalid byte sequence in UTF-8     # ./spec/main_spec.rb:14:in `split'     # ./spec/main_spec.rb:14:in `run_script'     # ./spec/main_spec.rb:48:in `block (2 levels) in '

如果是我们自己人工来测试，当我们打印行数据时，会看到有一些奇怪的字符（例子中，我把很长的字符串进行了缩写）：

db > insert 1 aaaaa... aaaaa...Executed.db > select(1, aaaaa...aaa\�, aaaaa...aaa\�)Executed.db >

发生了什么？如果看一下代码中我们定义的Row结构，我们确实为username字段分配了32个字节长度，为email字段分配255个字节长度。但是C语言的strings是以一个null字符来作为结尾的，这个字符我们没有为它分配空间。解决方法就是多分配一个额外的字节(来存放这个null字符)：

const uint32_t COLUMN_EMAIL_SIZE = 255;typedef struct {  uint32_t id;-  char username[COLUMN_USERNAME_SIZE];-  char email[COLUMN_EMAIL_SIZE];+  char username[COLUMN_USERNAME_SIZE + 1];+  char email[COLUMN_EMAIL_SIZE + 1];} Row;

这样确实解决了上面的问题（重新运行上面插入边界长度字符串的测试）：

bundle exec rspec...Finished in 0.0188 seconds (files took 0.08516 seconds to load)3 examples, 0 failures

我们不允许插入的username或者email的长度超过固定的列的长度。这样的超出长度要求的spec测试看起来就像下面这样：

it 'prints error message if strings are too long' do  long_username = "a"*33  long_email = "a"*256  script = [    "insert 1 #{long_username} #{long_email}",    "select",    ".exit",  ]  result = run_script(script)  expect(result).to match_array([    "db > String is too long.",    "db > Executed.",    "db > ",  ])end

我了能够支持上面这种效果，我们需要升级我们的解析器（parser）。提醒一下，我们现在使用的是scanf()：

if (strncmp(input_buffer->buffer, "insert", 6) == 0) {  statement->type = STATEMENT_INSERT;  int args_assigned = sscanf(      input_buffer->buffer, "insert %d %s %s", &(statement->row_to_insert.id),      statement->row_to_insert.username, statement->row_to_insert.email);  if (args_assigned < 3) {    return PREPARE_SYNTAX_ERROR;  }  return PREPARE_SUCCESS;}

但是scanf()有一些缺点。如果读取的string大于正在读取它的缓存（buffer），就会引起缓存溢出（buffer overflow）并写入到意想不到的地方。所以我们需要在拷贝string到Row结构前检查每一个string的长度。为了检查string长度，我们需要用空格分割输入。

我使用 strtok() 来做这些。如果你看到过程就会觉得它很容易理解：

译注: strtok: 字符串处理函数，char * strtok ( char * str, const char * delimiters ); 分解字符串为一组字符串。str为要分解的字符，delimiters为分隔符字符（如果传入字符串，则传入的字符串中每个字符均为分割符）

+PrepareResult prepare_insert(InputBuffer* input_buffer, Statement* statement) {+  statement->type = STATEMENT_INSERT;++  char* keyword = strtok(input_buffer->buffer, " ");+  char* id_string = strtok(NULL, " ");+  char* username = strtok(NULL, " ");+  char* email = strtok(NULL, " ");++  if (id_string == NULL || username == NULL || email == NULL) {+    return PREPARE_SYNTAX_ERROR;+  }++  int id = atoi(id_string);+  if (strlen(username) > COLUMN_USERNAME_SIZE) {+    return PREPARE_STRING_TOO_LONG;+  }+  if (strlen(email) > COLUMN_EMAIL_SIZE) {+    return PREPARE_STRING_TOO_LONG;+  }++  statement->row_to_insert.id = id;+  strcpy(statement->row_to_insert.username, username);+  strcpy(statement->row_to_insert.email, email);++  return PREPARE_SUCCESS;+}+ PrepareResult prepare_statement(InputBuffer* input_buffer,                                 Statement* statement) {   if (strncmp(input_buffer->buffer, "insert", 6) == 0) {+    return prepare_insert(input_buffer, statement);-    statement->type = STATEMENT_INSERT;-    int args_assigned = sscanf(-        input_buffer->buffer, "insert %d %s %s", &(statement->row_to_insert.id),-        statement->row_to_insert.username, statement->row_to_insert.email);-    if (args_assigned < 3) {-      return PREPARE_SYNTAX_ERROR;-    }-    return PREPARE_SUCCESS;   }

每当输入到一个分隔符时（在我们的例子中就是空格），就在输入缓冲（input buffer）上连续调用strtok()，把它分解成子字符串。它返回一个指向子字符串开始位置的指针。

我们可以在每个文本值上调用strlen()，看看它是否太长（strlen()函数，获取字符串的长度）。

我们可以像处理其他错误码一样处理错误：

enum PrepareResult_t {  PREPARE_SUCCESS,+  PREPARE_STRING_TOO_LONG,  PREPARE_SYNTAX_ERROR,  PREPARE_UNRECOGNIZED_STATEMENT};
switch (prepare_statement(input_buffer, &statement)) {  case (PREPARE_SUCCESS):    break;+  case (PREPARE_STRING_TOO_LONG):+    printf("String is too long.\n");+    continue;  case (PREPARE_SYNTAX_ERROR):    printf("Syntax error. Could not parse statement.\n");    continue;

这样就能通过测试了。

bundle exec rspec....Finished in 0.02284 seconds (files took 0.116 seconds to load)4 examples, 0 failures

到了这里，我们不妨再多处理一个错误情况（id值插入一个负值）：

it 'prints an error message if id is negative' do  script = [    "insert -1 cstack foo@bar.com",    "select",    ".exit",  ]  result = run_script(script)  expect(result).to match_array([    "db > ID must be positive.",    "db > Executed.",    "db > ",  ])end
enum PrepareResult_t {  PREPARE_SUCCESS,+  PREPARE_NEGATIVE_ID,  PREPARE_STRING_TOO_LONG,  PREPARE_SYNTAX_ERROR,  PREPARE_UNRECOGNIZED_STATEMENT@@ -148,9 +147,6 @@ PrepareResult prepare_insert(InputBuffer* input_buffer, Statement* statement) {  }  int id = atoi(id_string);+  if (id  COLUMN_USERNAME_SIZE) {    return PREPARE_STRING_TOO_LONG;  }@@ -230,9 +226,6 @@ int main(int argc, char* argv[]) {    switch (prepare_statement(input_buffer, &statement)) {      case (PREPARE_SUCCESS):        break;+      case (PREPARE_NEGATIVE_ID):+        printf("ID must be positive.\n");+        continue;      case (PREPARE_STRING_TOO_LONG):        printf("String is too long.\n");        continue;

好了，测试做的差不多了。接下来是非常重要的功能：持久化！我们要实现保存我们的数据库到一个文件，再把它从文件中读取出来。（目前它还在内存当中）

现在它越来越牛了。

下面是和上一部分代码，修改位置的对比：

@@ -22,6 +22,8 @@ enum PrepareResult_t {   PREPARE_SUCCESS,+  PREPARE_NEGATIVE_ID,+  PREPARE_STRING_TOO_LONG,   PREPARE_SYNTAX_ERROR,   PREPARE_UNRECOGNIZED_STATEMENT  };@@ -34,8 +36,8 @@ #define COLUMN_EMAIL_SIZE 255 typedef struct {   uint32_t id;-  char username[COLUMN_USERNAME_SIZE];-  char email[COLUMN_EMAIL_SIZE];+  char username[COLUMN_USERNAME_SIZE + 1];+  char email[COLUMN_EMAIL_SIZE + 1]; } Row;@@ -150,18 +152,40 @@ MetaCommandResult do_meta_command(InputBuffer* input_buffer, Table *table) {   } }-PrepareResult prepare_statement(InputBuffer* input_buffer,-                                Statement* statement) {-  if (strncmp(input_buffer->buffer, "insert", 6) == 0) {+PrepareResult prepare_insert(InputBuffer* input_buffer, Statement* statement) {   statement->type = STATEMENT_INSERT;-  int args_assigned = sscanf(-     input_buffer->buffer, "insert %d %s %s", &(statement->row_to_insert.id),-     statement->row_to_insert.username, statement->row_to_insert.email-     );-  if (args_assigned buffer, " ");+  char* id_string = strtok(NULL, " ");+  char* username = strtok(NULL, " ");+  char* email = strtok(NULL, " ");++  if (id_string == NULL || username == NULL || email == NULL) {      return PREPARE_SYNTAX_ERROR;   }++  int id = atoi(id_string);+  if (id  COLUMN_USERNAME_SIZE) {+     return PREPARE_STRING_TOO_LONG;+  }+  if (strlen(email) > COLUMN_EMAIL_SIZE) {+     return PREPARE_STRING_TOO_LONG;+  }++  statement->row_to_insert.id = id;+  strcpy(statement->row_to_insert.username, username);+  strcpy(statement->row_to_insert.email, email);+   return PREPARE_SUCCESS;++}+PrepareResult prepare_statement(InputBuffer* input_buffer,+                                Statement* statement) {+  if (strncmp(input_buffer->buffer, "insert", 6) == 0) {+      return prepare_insert(input_buffer, statement);   }   if (strcmp(input_buffer->buffer, "select") == 0) {     statement->type = STATEMENT_SELECT;@@ -223,6 +247,12 @@ int main(int argc, char* argv[]) {     switch (prepare_statement(input_buffer, &statement)) {       case (PREPARE_SUCCESS):         break;+      case (PREPARE_NEGATIVE_ID):+printf("ID must be positive.\n");+continue;+      case (PREPARE_STRING_TOO_LONG):+printf("String is too long.\n");+continue;       case (PREPARE_SYNTAX_ERROR): printf("Syntax error. Could not parse statement.\n"); continue;

并且我们添加了一些测试：

+describe 'database' do+  def run_script(commands)+    raw_output = nil+    IO.popen("./db", "r+") do |pipe|+      commands.each do |command|+        pipe.puts command+      end++      pipe.close_write++      # Read entire output+      raw_output = pipe.gets(nil)+    end+    raw_output.split("\n")+  end++  it 'inserts and retrieves a row' do+    result = run_script([+      "insert 1 user1 person1@example.com",+      "select",+      ".exit",+    ])+    expect(result).to match_array([+      "db > Executed.",+      "db > (1, user1, person1@example.com)",+      "Executed.",+      "db > ",+    ])+  end++  it 'prints error message when table is full' do+    script = (1..1401).map do |i|+      "insert #{i} user#{i} person#{i}@example.com"+    end+    script < Error: Table full.')+  end++  it 'allows inserting strings that are the maximum length' do+    long_username = "a"*32+    long_email = "a"*255+    script = [+      "insert 1 #{long_username} #{long_email}",+      "select",+      ".exit",+    ]+    result = run_script(script)+    expect(result).to match_array([+      "db > Executed.",+      "db > (1, #{long_username}, #{long_email})",+      "Executed.",+      "db > ",+    ])+  end++  it 'prints error message if strings are too long' do+    long_username = "a"*33+    long_email = "a"*256+    script = [+      "insert 1 #{long_username} #{long_email}",+      "select",+      ".exit",+    ]+    result = run_script(script)+    expect(result).to match_array([+      "db > String is too long.",+      "db > Executed.",+      "db > ",+    ])+  end++  it 'prints an error message if id is negative' do+    script = [+      "insert -1 cstack foo@bar.com",+      "select",+      ".exit",+    ]+    result = run_script(script)+    expect(result).to match_array([+      "db > ID must be positive.",+      "db > Executed.",+      "db > ",+    ])+  end+end

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