From 767f4980e54415c4680a4619c69b14f5b3ec24bb Mon Sep 17 00:00:00 2001
From: cbdev <cb@cbcdn.com>
Date: Sat, 20 Feb 2021 20:06:06 +0100
Subject: Implement dynamic32 framing function

---
 plugins/framing_dynamic32.c  | 74 ++++++++++++++++++++++++++++++++++++++++++++
 plugins/framing_dynamic32.md | 21 +++++++++++++
 plugins/makefile             |  2 +-
 3 files changed, 96 insertions(+), 1 deletion(-)
 create mode 100644 plugins/framing_dynamic32.c
 create mode 100644 plugins/framing_dynamic32.md

diff --git a/plugins/framing_dynamic32.c b/plugins/framing_dynamic32.c
new file mode 100644
index 0000000..3b66588
--- /dev/null
+++ b/plugins/framing_dynamic32.c
@@ -0,0 +1,74 @@
+#include <stdio.h>
+#include <string.h>
+#include <endian.h>
+
+#include "../websocksy.h"
+
+typedef struct /*_framing_config*/ {
+	uint32_t offset;
+	int32_t fixed;
+	uint8_t endian;
+} dynamic32_config_t;
+
+static int64_t framing_dynamic32(uint8_t* data, size_t length, size_t last_read, ws_operation* opcode, void** framing_data, const char* config){
+	size_t u;
+	uint32_t* size_p, size = 0;
+	//get the current config if set
+	dynamic32_config_t* conncfg = (*framing_data) ? ((dynamic32_config_t*) (*framing_data)) : NULL;
+
+	//configure framing for this connection
+	if(data && !conncfg){
+		conncfg = calloc(1, sizeof(dynamic32_config_t));
+		if(!conncfg){
+			fprintf(stderr, "Failed to allocate memory\n");
+			return -1;
+		}
+
+		//parse config string
+		for(u = 0; config[u];){
+			if(!strncmp(config + u, "offset=", 7)){
+				conncfg->offset = strtoul(config + u + 7, NULL, 0);
+			}
+			else if(!strncmp(config + u, "static=", 7)){
+				conncfg->fixed = strtoul(config + u + 7, NULL, 0);
+			}
+			else if(!strncmp(config + u, "endian=", 7)){
+				conncfg->endian = 0;
+				if(!strncmp(config + u + 7, "big", 3)){
+					conncfg->endian = 1;
+				}
+			}
+
+			//skip to next item
+			for(; config[u] && config[u] != ','; u++){
+			}
+		}
+
+		//store configuration
+		*framing_data = conncfg;
+	}
+	//clean up configuration
+	else if(!data && conncfg){
+		free(*framing_data);
+		*framing_data = NULL;
+	}
+
+	if(length > conncfg->offset + 4){
+		//read size field
+		size_p = (uint32_t*) (data + conncfg->offset);
+		size = le32toh(*size_p);
+		if(conncfg->endian){
+			size = be32toh(*size_p);
+		}
+
+		if(length >= conncfg->offset + 4 + conncfg->fixed + size){
+			return conncfg->offset + 4 + conncfg->fixed + size;
+		}
+	}
+
+	return 0;
+}
+
+static void __attribute__((constructor)) init(){
+	core_register_framing("dynamic32", framing_dynamic32);
+}
diff --git a/plugins/framing_dynamic32.md b/plugins/framing_dynamic32.md
new file mode 100644
index 0000000..51ca04c
--- /dev/null
+++ b/plugins/framing_dynamic32.md
@@ -0,0 +1,21 @@
+# The `dynamic32` framing function
+
+The `dynamic32` peer stream framing function segments the peer stream into binary frames
+at dynamic byte boundaries inferred from the stream data itself. The function will read
+a 32bit length value at a specified offset from the stream and treat it as the length
+of the next segment to be framed.
+
+## Configuration
+
+The framing configuration string may be a comma-separated list of options of the form
+`<key>=<value>`, containing one or more of the following keys:
+
+* `offset`: Set the offset (in bytes) of the 32-bit segment size in the stream, counted from the start of a segment/stream (Default: `0`)
+* `static`: Static amount to add to the segment length, e.g. to account for fixed headers (Default: `0`)
+* `endian`: Set the byte order of the transmitteed size to either `big` or `little` (Default: `little`)
+
+The total size of the segment sent to the Websocket peer can be calculated using the formula
+
+```
+offset + 4 /*32bit size field*/ + static + size field content
+```
diff --git a/plugins/makefile b/plugins/makefile
index b09466d..f0b38cb 100644
--- a/plugins/makefile
+++ b/plugins/makefile
@@ -1,5 +1,5 @@
 .PHONY: all clean
-PLUGINS = backend_file.so framing_fixedlength.so framing_json.so
+PLUGINS = backend_file.so framing_fixedlength.so framing_json.so framing_dynamic32.so
 
 CFLAGS += -fPIC -g -I../
 LDFLAGS += -shared
-- 
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