1 files changed, 110 insertions, 0 deletions
diff --git a/communication.h b/communication.h
new file mode 100644
index 0000000..b40022b
--- /dev/null
+++ b/communication.h
@@ -0,0 +1,110 @@
+/* See LICENSE file for copyright and license details. */
+#ifndef COMMUNICATION_H
+#define COMMUNICATION_H
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#ifndef GCC_ONLY
+# if defined(__GNUC__) && !defined(__clang__)
+#  define GCC_ONLY(...) __VA_ARGS__
+# else
+#  define GCC_ONLY(...) /* nothing */
+# endif
+#endif
+
+/**
+ * Construct a message
+ * 
+ * @param  bufp:char**            Output parameter for the buffer, must not have side-effects
+ * @param  np:size_t*             Output parameter for the size of the buffer sans `extra`
+ * @param  extra:size_t           The extra number for bytes to allocate to the buffer
+ * @param  format:string-literal  Message format string
+ * @param  ...                    Message formatting arguments
+ */
+#define MAKE_MESSAGE(bufp, np, extra, format, ...)\
+	do {\
+		ssize_t m__;\
+		snprintf(NULL, 0, format "%zn", __VA_ARGS__, &m__);\
+		*(bufp) = malloc((size_t)(extra) + (size_t)m__ + (size_t)1);\
+		if (!*(bufp))\
+			return -1;\
+		sprintf(*(bufp), format, __VA_ARGS__);\
+		*(np) = (size_t)m__;\
+	} while (0)
+
+/**
+ * Send a custom error without an error number
+ * 
+ * @param   ...  The error description to send
+ * @return       1: Client disconnected
+ *               0: Success (possibily delayed)
+ *               -1: An error occurred
+ */
+#define send_error(...) ((send_error)(conn, message_id, __VA_ARGS__))
+
+/**
+ * Send a standard error
+ * 
+ * @param   ...  The value of `errno`, 0 to indicate success
+ * @return       1: Client disconnected
+ *               0: Success (possibily delayed)
+ *               -1: An error occurred
+ */
+#define send_errno(...) ((send_errno)(conn, message_id, __VA_ARGS__))
+
+/**
+ * Send a message
+ * 
+ * @param   conn  The index of the connection
+ * @param   buf   The data to send
+ * @param   n     The size of `buf`
+ * @return        Zero on success, -1 on error, 1 if disconncted
+ *                EINTR, EAGAIN, EWOULDBLOCK, and ECONNRESET count
+ *                as success (ECONNRESET cause 1 to be returned),
+ *                and are handled appropriately.
+ */
+int send_message(size_t conn, char *restrict buf, size_t n);
+
+/**
+ * Send a custom error without an error number
+ * 
+ * @param   conn        The index of the connection
+ * @param   message_id  The ID of the message to which this message is a response
+ * @param   desc        The error description to send
+ * @return              1: Client disconnected
+ *                      0: Success (possibily delayed)
+ *                      -1: An error occurred
+ */
+GCC_ONLY(__attribute__((__nonnull__)))
+int (send_error)(size_t conn, const char *restrict message_id, const char *restrict desc);
+
+/**
+ * Send a standard error
+ * 
+ * @param   conn        The index of the connection
+ * @param   message_id  The ID of the message to which this message is a response
+ * @param   number      The value of `errno`, 0 to indicate success
+ * @return              1: Client disconnected
+ *                      0: Success (possibily delayed)
+ *                      -1: An error occurred
+ */
+GCC_ONLY(__attribute__((__nonnull__)))
+int (send_errno)(size_t conn, const char *restrict message_id, int number);
+
+/**
+ * Continue sending the queued messages
+ * 
+ * @param   conn  The index of the connection
+ * @return        Zero on success, -1 on error, 1 if disconncted
+ *                EINTR, EAGAIN, EWOULDBLOCK, and ECONNRESET count
+ *                as success (ECONNRESET cause 1 to be returned),
+ *                and are handled appropriately.
+ */
+static inline int
+continue_send(size_t conn)
+{
+	return send_message(conn, NULL, 0);
+}
+
+#endif