Tried things.

include/libg1m.h

@@ -135,6 +135,12 @@ extern int g1m_decode_mcsfile(g1m_mcsfile_t **handle,
 extern int g1m_decode_mcsfile_data(g1m_mcsfile_t **handle,
 	const g1m_mcshead_t *head, const unsigned char *data, size_t size);
 
+/* encode an MCS file */
+extern int g1m_encode_mcsfile(g1m_mcsfile_t *handle, g1m_buffer_t *buffer);
+# define g1m_announce_mcsfile(handle, size) \
+	(g1m_encode_mcsfile(handle, (g1m_buffer_t[]){{ \
+		.cookie = (size_t*)size, .announce = g1m_announce_callback }}))
+
 /* open CAS head for decoding, correct it for encoding */
 extern int g1m_decode_casfile_head(g1m_mcshead_t *head, g1m_buffer_t *buffer);
 extern int g1m_decode_casfiles_part(g1m_mcshead_t *head, g1m_mcshead_t *heads,
@@ -178,6 +184,9 @@ extern int g1m_check_date(const char *raw);
 extern int g1m_decode_date(const char *raw, time_t *date);
 extern int g1m_encode_date(const time_t *date, char *raw);
 
+/* Announce callback that just contributes to a size_t. */
+extern int g1m_announce_callback(void *cookie, size_t size);
+
 # ifdef __cplusplus
 }
 # endif

src/encode/main.c

@@ -67,8 +67,7 @@ int g1m_encode(g1m_handle_t *handle, g1m_buffer_t *buffer)
 		if (c->platforms && !(c->platforms & handle->platform))
 			continue;
 		break;
-	}
-	if (!c->encode) return (g1m_error_op);
+	} if (!c->encode) return (g1m_error_op);
 
 	/* announce, if necessary */
 	if (buffer->announce) {
@@ -81,7 +80,7 @@ int g1m_encode(g1m_handle_t *handle, g1m_buffer_t *buffer)
 	/* encode */
 	if (buffer->write) {
 		err = (*c->encode)(handle, buffer);
-		if (err) {
+		if (err && buffer->unannounce) {
 			(*buffer->unannounce)(buffer->cookie);
 			return (err);
 		}

src/encode/mcs.c

@@ -0,0 +1,127 @@
+/* *****************************************************************************
+ * encode/mcs.c -- encode an MCS file.
+ * Copyright (C) 2017 Thomas "Cakeisalie5" Touhey <thomas@touhey.fr>
+ *
+ * This file is part of libg1m.
+ * libg1m is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 3.0 of the License,
+ * or (at your option) any later version.
+ *
+ * libg1m is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with libg1m; if not, see <http://www.gnu.org/licenses/>.
+ * ************************************************************************** */
+#include <libg1m/internals.h>
+#define FUNCS(name) g1m_announce_mcs_##name, g1m_encode_mcs_##name
+
+/* ************************************************************************** */
+/*  Correspondances                                                           */
+/* ************************************************************************** */
+/* Types */
+typedef int (*announce_t)(const g1m_mcsfile_t*, size_t*);
+typedef int (*encode_t)(const g1m_mcsfile_t*, g1m_buffer_t *buffer);
+struct corresp {
+	/* 'identification' */
+	g1m_mcstype_t types;
+
+	/* functions */
+	announce_t announce;
+	encode_t encode;
+};
+
+/* All correspondances */
+static const struct corresp encodings[] = {
+	{g1m_mcstype_list | g1m_mcstype_matrix, FUNCS(cells)},
+	{g1m_mcstype_program,                   FUNCS(program)},
+	{g1m_mcstype_alpha,                     FUNCS(var)},
+
+	/* sentinel */
+	{0, NULL, NULL}
+};
+/* ************************************************************************** */
+/*  Default functions                                                         */
+/* ************************************************************************** */
+/**
+ *	default_announce:
+ *	Announce a file with no type.
+ *
+ *	@arg	handle		the file handle.
+ *	@arg	sz			the size to contribute to.
+ *	@return				the error code (0 if ok).
+ */
+
+static int default_announce(const g1m_mcsfile_t *handle, size_t *sz)
+{
+	*sz += handle->head.size;
+	return (0);
+}
+
+/**
+ *	default_encode:
+ *	'Encode' a file with no type.
+ *
+ *	@arg	handle		the file handle.
+ *	@arg	buffer		the buffer to write to.
+ *	@return				the error code (0 if ok).
+ */
+
+static int default_encode(const g1m_mcsfile_t *handle, g1m_buffer_t *buffer)
+{
+	WRITE(handle->content, handle->head.size)
+	return (0);
+}
+
+/* default correspondance */
+static struct corresp default_corresp = { 0, default_announce, default_encode};
+/* ************************************************************************** */
+/*  Main function                                                             */
+/* ************************************************************************** */
+/**
+ *	g1m_encode_mcsfile:
+ *	Encode an MCS file.
+ *
+ *	@arg	handle		the file handle.
+ *	@arg	buffer		the buffer to which to encode it.
+ *	@return				the error that occured (0 if ok).
+ */
+
+int g1m_encode_mcsfile(g1m_mcsfile_t *handle, g1m_buffer_t *buffer)
+{
+	int err;
+
+	/* find the announcement and encoding function */
+	const struct corresp *c = encodings - 1;
+	if (!c->types) c = &default_corresp;
+	else {
+		while ((++c)->encode) {
+			if (c->types && !(c->types & handle->head.type))
+				continue;
+			break;
+		} if (!c->encode) return (g1m_error_op);
+	}
+
+	/* announce if necessary */
+	if (buffer->announce) {
+		size_t size = 0;
+		if ((err = (*c->announce)(handle, &size))
+		 || (err = (*buffer->announce)(buffer->cookie, size)))
+			return (err);
+	}
+
+	/* encode */
+	if (buffer->write) {
+		err = (*c->encode)(handle, buffer);
+		if (err && buffer->unannounce) {
+			(*buffer->unannounce)(buffer->cookie);
+			return (err);
+		}
+	}
+
+	/* everything went well! */
+	return (0);
+}

src/utils/buffer.c

@@ -152,3 +152,21 @@ int g1m_empty_limbuffer(g1m_buffer_t *limbuffer)
 	SKIP(lim->left)
 	return (0);
 }
+/* ************************************************************************** */
+/*  The announce callback                                                     */
+/* ************************************************************************** */
+/**
+ *	g1m_announce_callback:
+ *	Main announce callback, that just contributes to a size.
+ *
+ *	@arg	vpsize		the size_t pointer.
+ *	@arg	size		the size to add.
+ *	@return				0 because OK.
+ */
+
+int g1m_announce_callback(void *vpsize, size_t size)
+{
+	size_t *psize = (void*)vpsize;
+	*psize += size;
+	return (0);
+}