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Writing a sqlite clone from scratch in C

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Open database file and read user input.
2017-08-31 10:58:19 -07:00
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct InputBuffer_t {
char* buffer;
size_t buffer_length;
ssize_t input_length;
};
typedef struct InputBuffer_t InputBuffer;
Implement insert and select on in-memory database.
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enum ExecuteResult_t { EXECUTE_SUCCESS, EXECUTE_TABLE_FULL };
typedef enum ExecuteResult_t ExecuteResult;
Parse 'select' and 'insert'.
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enum MetaCommandResult_t {
META_COMMAND_SUCCESS,
META_COMMAND_UNRECOGNIZED_COMMAND
};
typedef enum MetaCommandResult_t MetaCommandResult;
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enum PrepareResult_t {
PREPARE_SUCCESS,
PREPARE_SYNTAX_ERROR,
PREPARE_UNRECOGNIZED_STATEMENT
};
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typedef enum PrepareResult_t PrepareResult;
enum StatementType_t { STATEMENT_INSERT, STATEMENT_SELECT };
typedef enum StatementType_t StatementType;
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const uint32_t COLUMN_USERNAME_SIZE = 32;
const uint32_t COLUMN_EMAIL_SIZE = 255;
struct Row_t {
uint32_t id;
char username[COLUMN_USERNAME_SIZE];
char email[COLUMN_EMAIL_SIZE];
};
typedef struct Row_t Row;
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struct Statement_t {
StatementType type;
Implement insert and select on in-memory database.
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Row row_to_insert; // only used by insert statement
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};
typedef struct Statement_t Statement;
Implement insert and select on in-memory database.
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const uint32_t ID_SIZE = sizeof(((Row*)0)->id);
const uint32_t USERNAME_SIZE = sizeof(((Row*)0)->username);
const uint32_t EMAIL_SIZE = sizeof(((Row*)0)->email);
const uint32_t ID_OFFSET = 0;
const uint32_t USERNAME_OFFSET = ID_OFFSET + ID_SIZE;
const uint32_t EMAIL_OFFSET = USERNAME_OFFSET + USERNAME_SIZE;
const uint32_t ROW_SIZE = ID_SIZE + USERNAME_SIZE + EMAIL_SIZE;
const uint32_t PAGE_SIZE = 4096;
const uint32_t TABLE_MAX_PAGES = 100;
const uint32_t ROWS_PER_PAGE = PAGE_SIZE / ROW_SIZE;
const uint32_t TABLE_MAX_ROWS = ROWS_PER_PAGE * TABLE_MAX_PAGES;
struct Table_t {
void* pages[TABLE_MAX_PAGES];
uint32_t num_rows;
};
typedef struct Table_t Table;
void print_row(Row* row) {
printf("(%d, %s, %s)\n", row->id, row->username, row->email);
}
void serialize_row(Row* source, void* destination) {
memcpy(destination + ID_OFFSET, &(source->id), ID_SIZE);
memcpy(destination + USERNAME_OFFSET, &(source->username), USERNAME_SIZE);
memcpy(destination + EMAIL_OFFSET, &(source->email), EMAIL_SIZE);
}
void deserialize_row(void* source, Row* destination) {
memcpy(&(destination->id), source + ID_OFFSET, ID_SIZE);
memcpy(&(destination->username), source + USERNAME_OFFSET, USERNAME_SIZE);
memcpy(&(destination->email), source + EMAIL_OFFSET, EMAIL_SIZE);
}
void* row_slot(Table* table, uint32_t row_num) {
uint32_t page_num = row_num / ROWS_PER_PAGE;
void* page = table->pages[page_num];
if (!page) {
// Allocate memory only when we try to access page
page = table->pages[page_num] = malloc(PAGE_SIZE);
}
uint32_t row_offset = row_num % ROWS_PER_PAGE;
uint32_t byte_offset = row_offset * ROW_SIZE;
return page + byte_offset;
}
Table* new_table() {
Table* table = malloc(sizeof(Table));
table->num_rows = 0;
return table;
}
Open database file and read user input.
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InputBuffer* new_input_buffer() {
InputBuffer* input_buffer = malloc(sizeof(InputBuffer));
input_buffer->buffer = NULL;
input_buffer->buffer_length = 0;
input_buffer->input_length = 0;
return input_buffer;
}
void print_prompt() { printf("db > "); }
void read_input(InputBuffer* input_buffer) {
ssize_t bytes_read =
getline(&(input_buffer->buffer), &(input_buffer->buffer_length), stdin);
if (bytes_read <= 0) {
printf("Error reading input\n");
exit(EXIT_FAILURE);
}
// Ignore trailing newline
input_buffer->input_length = bytes_read - 1;
input_buffer->buffer[bytes_read - 1] = 0;
}
Parse 'select' and 'insert'.
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MetaCommandResult do_meta_command(InputBuffer* input_buffer) {
if (strcmp(input_buffer->buffer, ".exit") == 0) {
exit(EXIT_SUCCESS);
} else {
return META_COMMAND_UNRECOGNIZED_COMMAND;
}
}
PrepareResult prepare_statement(InputBuffer* input_buffer,
Statement* statement) {
if (strncmp(input_buffer->buffer, "insert", 6) == 0) {
statement->type = STATEMENT_INSERT;
Implement insert and select on in-memory database.
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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;
}
Parse 'select' and 'insert'.
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return PREPARE_SUCCESS;
}
if (strcmp(input_buffer->buffer, "select") == 0) {
statement->type = STATEMENT_SELECT;
return PREPARE_SUCCESS;
}
return PREPARE_UNRECOGNIZED_STATEMENT;
}
Implement insert and select on in-memory database.
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ExecuteResult execute_insert(Statement* statement, Table* table) {
if (table->num_rows >= TABLE_MAX_ROWS) {
return EXECUTE_TABLE_FULL;
}
Row* row_to_insert = &(statement->row_to_insert);
serialize_row(row_to_insert, row_slot(table, table->num_rows));
table->num_rows += 1;
return EXECUTE_SUCCESS;
}
ExecuteResult execute_select(Statement* statement, Table* table) {
Row row;
for (uint32_t i = 0; i < table->num_rows; i++) {
deserialize_row(row_slot(table, i), &row);
print_row(&row);
}
return EXECUTE_SUCCESS;
}
ExecuteResult execute_statement(Statement* statement, Table* table) {
Parse 'select' and 'insert'.
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switch (statement->type) {
case (STATEMENT_INSERT):
Implement insert and select on in-memory database.
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return execute_insert(statement, table);
Parse 'select' and 'insert'.
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case (STATEMENT_SELECT):
Implement insert and select on in-memory database.
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return execute_select(statement, table);
Parse 'select' and 'insert'.
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}
}
Open database file and read user input.
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int main(int argc, char* argv[]) {
Implement insert and select on in-memory database.
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Table* table = new_table();
Open database file and read user input.
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InputBuffer* input_buffer = new_input_buffer();
while (true) {
print_prompt();
read_input(input_buffer);
Parse 'select' and 'insert'.
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if (input_buffer->buffer[0] == '.') {
switch (do_meta_command(input_buffer)) {
case (META_COMMAND_SUCCESS):
continue;
case (META_COMMAND_UNRECOGNIZED_COMMAND):
printf("Unrecognized command '%s'\n", input_buffer->buffer);
continue;
}
Open database file and read user input.
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}
Parse 'select' and 'insert'.
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Statement statement;
switch (prepare_statement(input_buffer, &statement)) {
case (PREPARE_SUCCESS):
break;
Implement insert and select on in-memory database.
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case (PREPARE_SYNTAX_ERROR):
printf("Syntax error. Could not parse statement.\n");
continue;
Parse 'select' and 'insert'.
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case (PREPARE_UNRECOGNIZED_STATEMENT):
printf("Unrecognized keyword at start of '%s'.\n",
input_buffer->buffer);
continue;
}
Implement insert and select on in-memory database.
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switch (execute_statement(&statement, table)) {
case (PREPARE_SUCCESS):
printf("Executed.\n");
break;
case (EXECUTE_TABLE_FULL):
printf("Error: Table full.\n");
break;
}
Open database file and read user input.
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}
}
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