前文回顾
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 > ", ])endenum 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+endEnjoy GreatSQL ?
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