403 lines
11 KiB
C
403 lines
11 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <stdbool.h>
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#include <string.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <errno.h>
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struct InputBuffer_t {
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char* buffer;
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size_t buffer_length;
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ssize_t input_length;
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};
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typedef struct InputBuffer_t InputBuffer;
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enum ExecuteResult_t {
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EXECUTE_SUCCESS,
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EXECUTE_TABLE_FULL
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};
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typedef enum ExecuteResult_t ExecuteResult;
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enum MetaCommandResult_t {
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META_COMMAND_SUCCESS,
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META_COMMAND_UNRECOGNIZED_COMMAND
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};
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typedef enum MetaCommandResult_t MetaCommandResult;
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enum PrepareResult_t {
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PREPARE_SUCCESS,
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PREPARE_NEGATIVE_ID,
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PREPARE_STRING_TOO_LONG,
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PREPARE_SYNTAX_ERROR,
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PREPARE_UNRECOGNIZED_STATEMENT
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};
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typedef enum PrepareResult_t PrepareResult;
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enum StatementType_t {
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STATEMENT_INSERT,
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STATEMENT_SELECT
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};
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typedef enum StatementType_t StatementType;
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const uint32_t COLUMN_USERNAME_SIZE = 32;
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const uint32_t COLUMN_EMAIL_SIZE = 255;
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struct Row_t {
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uint32_t id;
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char username[COLUMN_USERNAME_SIZE + 1];
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char email[COLUMN_EMAIL_SIZE + 1];
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};
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typedef struct Row_t Row;
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struct Statement_t {
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StatementType type;
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Row row_to_insert; // only used by insert statement
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};
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typedef struct Statement_t Statement;
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#define size_of_attribute(Struct, Attribute) sizeof(((Struct*)0)->Attribute)
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const uint32_t ID_SIZE = size_of_attribute(Row, id);
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const uint32_t USERNAME_SIZE = size_of_attribute(Row, username);
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const uint32_t EMAIL_SIZE = size_of_attribute(Row, email);
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const uint32_t ID_OFFSET = 0;
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const uint32_t USERNAME_OFFSET = ID_OFFSET + ID_SIZE;
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const uint32_t EMAIL_OFFSET = USERNAME_OFFSET + USERNAME_SIZE;
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const uint32_t ROW_SIZE = ID_SIZE + USERNAME_SIZE + EMAIL_SIZE;
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const uint32_t PAGE_SIZE = 4096;
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const uint32_t TABLE_MAX_PAGES = 100;
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const uint32_t ROWS_PER_PAGE = PAGE_SIZE / ROW_SIZE;
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const uint32_t TABLE_MAX_ROWS = ROWS_PER_PAGE * TABLE_MAX_PAGES;
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struct Pager_t {
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int file_descriptor;
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uint32_t file_length;
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void* pages[TABLE_MAX_PAGES];
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};
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typedef struct Pager_t Pager;
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struct Table_t {
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Pager* pager;
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uint32_t num_rows;
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};
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typedef struct Table_t Table;
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InputBuffer* new_input_buffer() {
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InputBuffer* input_buffer = malloc(sizeof(InputBuffer));
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input_buffer->buffer = NULL;
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input_buffer->buffer_length = 0;
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input_buffer->input_length = 0;
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return input_buffer;
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}
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void print_prompt() {
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printf("db > ");
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}
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void read_input(InputBuffer* input_buffer) {
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ssize_t bytes_read = getline(
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&(input_buffer->buffer),
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&(input_buffer->buffer_length),
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stdin
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);
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if (bytes_read <= 0) {
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printf("Error reading input\n");
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exit(EXIT_FAILURE);
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}
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// Ignore trailing newline
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input_buffer->input_length = bytes_read -1;
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input_buffer->buffer[bytes_read - 1] = 0;
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}
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void pager_flush(Pager* pager, uint32_t page_num, uint32_t size) {
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if (pager->pages[page_num] == NULL) {
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printf("Tried to flush null page\n");
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exit(EXIT_FAILURE);
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}
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off_t offset = lseek(pager->file_descriptor, page_num * PAGE_SIZE, SEEK_SET);
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if (offset == -1) {
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printf("Error seeking: %d\n", errno);
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exit(EXIT_FAILURE);
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}
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ssize_t bytes_written = write(pager->file_descriptor, pager->pages[page_num], size);
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if (bytes_written == -1) {
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printf("Error writing: %d\n", errno);
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exit(EXIT_FAILURE);
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}
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}
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void db_close(Table* table) {
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Pager* pager = table->pager;
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uint32_t num_full_pages = table->num_rows / ROWS_PER_PAGE;
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for (uint32_t i = 0; i < num_full_pages; i++) {
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if (pager->pages[i] == NULL) {
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continue;
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}
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pager_flush(pager, i, PAGE_SIZE);
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free(pager->pages[i]);
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pager->pages[i] = NULL;
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}
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// There may be a partial page to write to the end of the file
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// This should not be needed after we switch to a B-tree
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uint32_t num_additional_rows = table->num_rows % ROWS_PER_PAGE;
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if (num_additional_rows > 0) {
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uint32_t page_num = num_full_pages;
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if (pager->pages[page_num] != NULL) {
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pager_flush(pager, page_num, num_additional_rows * ROW_SIZE);
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free(pager->pages[page_num]);
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pager->pages[page_num] = NULL;
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}
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}
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int result = close(pager->file_descriptor);
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if (result == -1) {
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printf("Error closing db file.\n");
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exit(EXIT_FAILURE);
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}
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for(uint32_t i = 0; i < TABLE_MAX_PAGES; i++) {
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void* page = pager->pages[i];
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if (page) {
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free(page);
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pager->pages[i] = NULL;
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}
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}
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free(pager);
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}
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MetaCommandResult do_meta_command(InputBuffer* input_buffer, Table* table) {
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if (strcmp(input_buffer->buffer, ".exit") == 0) {
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db_close(table);
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exit(EXIT_SUCCESS);
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} else {
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return META_COMMAND_UNRECOGNIZED_COMMAND;
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}
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}
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PrepareResult prepare_insert(InputBuffer* input_buffer, Statement* statement) {
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statement->type = STATEMENT_INSERT;
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char* keyword = strtok(input_buffer->buffer, " ");
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char* id_string = strtok(NULL, " ");
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char* username = strtok(NULL, " ");
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char* email = strtok(NULL, " ");
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if (id_string == NULL || username == NULL || email == NULL) {
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return PREPARE_SYNTAX_ERROR;
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}
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int id = atoi(id_string);
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if (id < 0) {
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return PREPARE_NEGATIVE_ID;
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}
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if (strlen(username) > COLUMN_USERNAME_SIZE) {
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return PREPARE_STRING_TOO_LONG;
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}
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if (strlen(email) > COLUMN_EMAIL_SIZE) {
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return PREPARE_STRING_TOO_LONG;
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}
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statement->row_to_insert.id = id;
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strcpy(statement->row_to_insert.username, username);
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strcpy(statement->row_to_insert.email, email);
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return PREPARE_SUCCESS;
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}
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PrepareResult prepare_statement(InputBuffer* input_buffer, Statement* statement) {
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if (strncmp(input_buffer->buffer, "insert", 6) == 0) {
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return prepare_insert(input_buffer, statement);
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}
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if (strncmp(input_buffer->buffer, "select", 6) == 0) {
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statement->type = STATEMENT_SELECT;
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return PREPARE_SUCCESS;
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}
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return PREPARE_UNRECOGNIZED_STATEMENT;
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}
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void print_row(Row* row) {
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printf("(%d, %s, %s)\n", row->id, row->username, row->email);
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}
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void serialize_row(Row* source, void* destination) {
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memcpy(destination + ID_OFFSET, &(source->id), ID_SIZE);
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memcpy(destination + USERNAME_OFFSET, &(source->username), USERNAME_SIZE);
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memcpy(destination + EMAIL_OFFSET, &(source->email), EMAIL_SIZE);
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}
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void deserialize_row(void* source, Row* destination) {
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memcpy(&(destination->id), source + ID_OFFSET, ID_SIZE);
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memcpy(&(destination->username), source + USERNAME_OFFSET, USERNAME_SIZE);
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memcpy(&(destination->email), source + EMAIL_OFFSET, EMAIL_SIZE);
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}
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void* get_page(Pager* pager, uint32_t page_num) {
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if (page_num > TABLE_MAX_PAGES) {
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printf("Tried to fetch page number out of bounds. %d > %d\n", page_num, TABLE_MAX_PAGES);
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exit(EXIT_FAILURE);
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}
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if (pager->pages[page_num] == NULL) {
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// Cache miss. Allocate memory and load from file.
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void* page = malloc(PAGE_SIZE);
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uint32_t num_pages = pager->file_length / PAGE_SIZE;
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// We might save a partial page at the end of the file
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if (pager->file_length % PAGE_SIZE) {
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num_pages += 1;
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}
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if (page_num <= num_pages) {
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lseek(pager->file_descriptor, page_num * PAGE_SIZE, SEEK_SET);
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ssize_t bytes_read = read(pager->file_descriptor, page, PAGE_SIZE);
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if (bytes_read == -1) {
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printf("Error reading file: %d\n", errno);
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exit(EXIT_FAILURE);
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}
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}
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pager->pages[page_num] = page;
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}
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return pager->pages[page_num];
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}
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void* row_slot(Table* table, uint32_t row_num) {
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uint32_t page_num = row_num / ROWS_PER_PAGE;
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void* page = get_page(table->pager, page_num);
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uint32_t row_offset = row_num % ROWS_PER_PAGE;
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uint32_t byte_offset = row_offset * ROW_SIZE;
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return page + byte_offset;
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}
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ExecuteResult execute_insert(Statement* statement, Table* table) {
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if (table->num_rows >= TABLE_MAX_ROWS) {
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return EXECUTE_TABLE_FULL;
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}
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Row* row_to_insert = &(statement->row_to_insert);
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serialize_row(row_to_insert, row_slot(table, table->num_rows));
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table->num_rows += 1;
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return EXECUTE_SUCCESS;
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}
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ExecuteResult execute_select(Statement* statement, Table* table) {
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Row row;
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for (uint32_t i = 0; i < table->num_rows; i++) {
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deserialize_row(row_slot(table, i), &row);
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print_row(&row);
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}
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return EXECUTE_SUCCESS;
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}
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ExecuteResult execute_statement(Statement* statement, Table* table) {
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switch(statement->type) {
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case (STATEMENT_INSERT):
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return execute_insert(statement, table);
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case (STATEMENT_SELECT):
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return execute_select(statement, table);
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}
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}
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Pager* pager_open(const char* filename) {
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// Read/Write mode, Create non-existent file, user read and write permission
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int fd = open(filename, O_RDWR | O_CREAT, S_IWUSR | S_IRUSR);
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if (fd == -1) {
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printf("Unable to open file\n");
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exit(EXIT_FAILURE);
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}
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off_t file_length = lseek(fd, 0, SEEK_END);
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Pager* pager = malloc(sizeof(Pager));
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pager->file_descriptor = fd;
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pager->file_length = file_length;
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for (uint32_t i = 0; i < TABLE_MAX_PAGES; i++) {
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pager->pages[i] = NULL;
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}
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return pager;
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}
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Table* db_open(const char* filename) {
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Pager* pager = pager_open(filename);
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uint32_t num_rows = pager->file_length / ROW_SIZE;
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Table* table = malloc(sizeof(Table));
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table->pager = pager;
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table->num_rows = num_rows;
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return table;
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}
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int main(int argc, char* argv[]) {
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if (argc < 2) {
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printf("Must supply a database filename\n");
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exit(EXIT_FAILURE);
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}
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char* filename = argv[1];
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Table* table = db_open(filename);
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InputBuffer* input_buffer = new_input_buffer();
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while (true) {
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print_prompt();
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read_input(input_buffer);
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if (input_buffer->buffer[0] == '.') {
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switch (do_meta_command(input_buffer, table)) {
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case (META_COMMAND_SUCCESS):
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continue;
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case (META_COMMAND_UNRECOGNIZED_COMMAND):
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printf("Unrecognized command '%s'\n", input_buffer->buffer);
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continue;
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}
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}
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Statement statement;
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switch(prepare_statement(input_buffer, &statement)) {
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case (PREPARE_SUCCESS):
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break;
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case (PREPARE_NEGATIVE_ID):
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printf("ID must be positive.\n");
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continue;
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case (PREPARE_STRING_TOO_LONG):
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printf("String is too long.\n");
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continue;
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case (PREPARE_SYNTAX_ERROR):
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printf("Syntax error. Could not parse statement.\n");
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continue;
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case (PREPARE_UNRECOGNIZED_STATEMENT):
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printf("Unrecognized keyword at start of '%s'.\n", input_buffer->buffer);
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continue;
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}
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switch(execute_statement(&statement, table)) {
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case (EXECUTE_SUCCESS):
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printf("Executed.\n");
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break;
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case (EXECUTE_TABLE_FULL):
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printf("Error: Table full.\n");
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break;
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}
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}
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} |