1 files changed, 94 insertions, 0 deletions
diff --git a/lib9p/9p.c b/lib9p/9p.c
new file mode 100644
index 0000000..64b09a6
--- /dev/null
+++ b/lib9p/9p.c
@@ -0,0 +1,94 @@
+/* lib9p/9p.c - Base 9P protocol utilities for both clients and servers
+ *
+ * Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-Licence-Identifier: AGPL-3.0-or-later
+ */
+
+#include <inttypes.h> /* for PRIu{n} */
+#include <stdarg.h>   /* for va_* */
+#include <stdio.h>    /* for vsnprintf() */
+#include <string.h>   /* for strncpy() */
+
+#include <lib9p/9p.h>
+
+#include "internal.h"
+
+enum lib9p_version lib9p_ctx_version(lib9p_ctx *ctx) {
+	assert(ctx);
+	return ctx->version;
+}
+
+uint32_t lib9p_ctx_max_msg_size(lib9p_ctx *ctx) {
+	assert(ctx);
+	return ctx->max_msg_size;
+}
+
+int lib9p_error(struct lib9p_ctx *ctx, uint32_t linux_errno, char const *msg) {
+	strncpy(ctx->err_msg, msg, sizeof(ctx->err_msg));
+	ctx->err_msg[sizeof(ctx->err_msg)-1] = '\0';
+	ctx->err_num = linux_errno;
+	return -1;
+}
+
+int lib9p_errorf(struct lib9p_ctx *ctx, uint32_t linux_errno, char const *fmt, ...) {
+	int n;
+	va_list args;
+
+	va_start(args, fmt);
+	n = vsnprintf(ctx->err_msg, sizeof(ctx->err_msg), fmt, args);
+	va_end(args);
+	if ((size_t)(n+1) < sizeof(ctx->err_msg))
+		memset(&ctx->err_msg[n+1], 0, sizeof(ctx->err_msg)-(n+1));
+
+	ctx->err_num = linux_errno;
+
+	return -1;
+}
+
+size_t lib9p_unmarshal_size(struct lib9p_ctx *ctx, uint8_t *net_bytes) {
+	/* Header */
+	uint32_t net_len = decode_u32le(net_bytes);
+	if (net_len < 7)
+		return lib9p_error(ctx, LINUX_EBADMSG, "message is too short");
+	uint8_t typ = net_bytes[4];
+	uint32_t net_offset = 7;
+
+	/* Body */
+	if (!versions[ctx->version]->msgs[typ].unmarshal_extrasize)
+		return lib9p_errorf(ctx, LINUX_EOPNOTSUPP, "unknown message type %"PRIu8, typ);
+	size_t host_size = versions[ctx->version]->msgs[typ].unmarshal_basesize;
+	if (versions[ctx->version]->msgs[typ].unmarshal_extrasize(net_len, net_bytes, &net_offset, &host_size))
+		return lib9p_error(ctx, LINUX_EBADMSG, "message is too short for content");
+
+	return host_size;
+}
+
+uint8_t lib9p_unmarshal(struct lib9p_ctx *ctx, uint8_t *net_bytes, uint16_t *out_tag, void *out_body) {
+	/* Header */
+	uint8_t typ = net_bytes[4];
+	*out_tag = decode_u16le(&net_bytes[5]);
+	uint32_t net_offset = 7;
+
+	/* Body */
+	void *host_extra = out_body + versions[ctx->version]->msgs[typ].unmarshal_basesize;
+	if (versions[ctx->version]->msgs[typ].unmarshal(net_bytes, &net_offset, &host_extra, out_body))
+		return lib9p_error(ctx, LINUX_EBADMSG, "message contains invalid UTF-8");
+
+	return typ;
+}
+
+uint32_t lib9p_marshal(struct lib9p_ctx *ctx, uint8_t typ, uint16_t msgid, void *body, uint8_t *out_bytes) {
+	/* Header */
+	out_bytes[4] = typ;
+	encode_u16le(msgid, &out_bytes[5]);
+	uint32_t net_offset = 7;
+	
+	/* Body */
+	if (versions[ctx->version]->msgs[typ].marshal(ctx, body, out_bytes, &net_offset))
+		return 0;
+
+	/* Header, again */
+	encode_u32le(net_offset, out_bytes);
+
+	return net_offset;
+}