lander/include/event_loop.h

#ifndef LANDER_EVENT_LOOP
#define LANDER_EVENT_LOOP

#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>

// Size of the read and write buffers for each connection, in bytes
#define EVENT_LOOP_BUFFER_SIZE 2048

/**
 * State of a connection
 */
typedef enum {
  event_loop_conn_state_req = 0,
  event_loop_conn_state_res = 1,
  event_loop_conn_state_end = 2,
} event_loop_conn_state;

/**
 * Represents an active connection managed by the event loop
 */
typedef struct event_loop_conn {
  int fd;
  event_loop_conn_state state;
  // Read buffer
  size_t rbuf_size;
  size_t rbuf_read;
  uint8_t rbuf[EVENT_LOOP_BUFFER_SIZE];
  // Write buffer
  size_t wbuf_size;
  size_t wbuf_sent;
  uint8_t wbuf[EVENT_LOOP_BUFFER_SIZE];

  // If true, the server will close the connection after the final write buffer
  // has been written
  bool close_after_write;
  // Context for a request
  void *ctx;
} event_loop_conn;

/*
 * Main struct object representing the event loop
 */
typedef struct event_loop {
  event_loop_conn **connections;
  size_t connection_count;
  // Global context passed to every connection
  void *gctx;
  /**
   * Function to initialize a connection context.
   *
   * @param gctx global context of the event loop
   * @return pointer to the allocated object.
   */
  void *(*ctx_init)(void *gctx);
  /**
   * Function to free a connection context object.
   *
   * @param ctx context to free
   */
  void (*ctx_free)(void *ctx);
  /**
   * Function to process incoming data while in the req state.
   *
   * @param conn connection to process
   * @return whether the function can be called again immediately in the same
   * event loop cycle. This allows quicly processing multiple requests without
   * waiting for I/O.
   */
  bool (*handle_data)(event_loop_conn *conn);
  /**
   * Function to process outgoing data while in the res state.
   *
   * @param conn connection to proces
   */
  void (*write_data)(event_loop_conn *conn);
} event_loop;

/*
 * Initialize a new connection struct
 *
 * @param el the event loop
 * @return pointer to the newly allocated connection struct
 */
event_loop_conn *event_loop_conn_init(event_loop *el);

/*
 * Free a connection struct
 *
 * @param el the event loop
 * @param conn connection struct to free
 */
void event_loop_conn_free(event_loop *el, event_loop_conn *conn);

/*
 * Handle I/O for a connection, be it reading input or writing output.
 *
 * @param el the event loop
 * @param conn the connection to process
 */
void event_loop_conn_io(event_loop *el, event_loop_conn *conn);

/*
 * Initialize a new event loop struct
 *
 * @return pointer to the newly allocated event loop struct
 */
event_loop *event_loop_init();

/*
 * Place a new connection into the event loop's internal array.
 *
 * @param el the event loop
 * @param conn connection to insert
 * @return 0 on success, -1 if the internal realloc failed.
 */
int event_loop_put(event_loop *el, event_loop_conn *conn);

/**
 * Accept a new connection for the given file descriptor.
 *
 * @param el the event loop
 * @param fd file descriptor for the connection
 * @return 0 if successful, negative value otherwise
 */
int event_loop_accept(event_loop *el, int fd);

/*
 * Run the event loop. This function never returns.
 *
 * @param el the event loop
 * @param port on what port to listen
 */
void event_loop_run(event_loop *el, int port);

#endif