Add support for DTLS fragmentation (#49)

Author: mickel8

bundlex.exs

@@ -10,7 +10,7 @@ defmodule ExDTLS.BundlexProject do
   defp natives() do
     [
       native: [
-        sources: ["native.c", "dtls.c", "dyn_buff.c"],
+        sources: ["native.c", "dtls.c", "dyn_buff.c", "bio_frag.c"],
         deps: [unifex: :unifex],
         os_deps: [openssl: :pkg_config],
         libs: ["pthread"],

c_src/ex_dtls/bio_frag.c

@@ -0,0 +1,142 @@
+
+#include "bio_frag.h"
+#include <openssl/bio.h>
+
+static int bwrite(BIO *bio, const char *buf, int len);
+static int bread(BIO *bio, char *buf, int len);
+static long ctrl(BIO *bio, int cmd, long arg1, void *arg2);
+static int create(BIO *bio);
+static int destroy(BIO *bio);
+static long callback_ctrl(BIO *bio, int cmd, BIO_info_cb *fp);
+
+static BIO_METHOD *bio_methods = NULL;
+
+#define MAX_FRAGS 100
+#define MTU 1200
+
+struct Ctx {
+  int frag_sizes[MAX_FRAGS];
+  int witer;
+  int riter;
+};
+
+const BIO_METHOD *BIO_f_frag(void) {
+  bio_methods = BIO_meth_new(BIO_TYPE_FILTER, "DTLS fragmentation for mem BIO");
+
+  BIO_meth_set_read(bio_methods, bread);
+  BIO_meth_set_write(bio_methods, bwrite);
+  BIO_meth_set_ctrl(bio_methods, ctrl);
+  BIO_meth_set_create(bio_methods, create);
+  BIO_meth_set_destroy(bio_methods, destroy);
+  BIO_meth_set_callback_ctrl(bio_methods, callback_ctrl);
+
+  return bio_methods;
+}
+
+static int create(BIO *bio) {
+  struct Ctx *ctx = calloc(1, sizeof(struct Ctx));
+  for (int i = 0; i < MAX_FRAGS; i++) {
+    ctx->frag_sizes[i] = 0;
+  }
+  ctx->witer = 0;
+  ctx->riter = 0;
+
+  BIO_set_data(bio, ctx);
+  BIO_set_init(bio, 1);
+  return 1;
+}
+
+static int destroy(BIO *bio) {
+  if (bio == NULL) {
+    return 0;
+  }
+
+  struct Ctx *ctx = BIO_get_data(bio);
+  free(ctx);
+  BIO_set_data(bio, NULL);
+  BIO_set_init(bio, 0);
+  return 1;
+}
+
+static int bread(BIO *bio, char *buf, int len) {
+  BIO *next = BIO_next(bio);
+  if (next == NULL) {
+    return 0;
+  }
+
+  struct Ctx *ctx = BIO_get_data(bio);
+
+  if (len != ctx->frag_sizes[ctx->riter]) {
+    return 0;
+  }
+
+  int ret = BIO_read(next, buf, len);
+
+  if (ret > 0) {
+    if (ret == ctx->frag_sizes[ctx->riter]) {
+      ctx->frag_sizes[ctx->riter] = 0;
+      ctx->riter++;
+
+      if (ctx->riter == ctx->witer && ctx->frag_sizes[ctx->riter] == 0) {
+        // reset iterators
+        ctx->riter = 0;
+        ctx->witer = 0;
+      }
+
+    } else if (ret < ctx->frag_sizes[ctx->riter]) {
+      ctx->frag_sizes[ctx->riter] -= ret;
+    } else {
+      // This should never happen
+      return 0;
+    }
+  };
+
+  return ret;
+}
+
+static int bwrite(BIO *bio, const char *buf, int len) {
+  BIO *next = BIO_next(bio);
+  if (next == NULL) {
+    return 0;
+  }
+
+  struct Ctx *ctx = BIO_get_data(bio);
+
+  if (ctx->witer >= MAX_FRAGS) {
+    return 0;
+  }
+
+  int ret = BIO_write(next, buf, len);
+  if (ret > 0) {
+    ctx->frag_sizes[ctx->witer] = ret;
+    ctx->witer++;
+  }
+
+  return ret;
+}
+
+static long ctrl(BIO *bio, int cmd, long num, void *ptr) {
+  BIO *next = BIO_next(bio);
+  if (next == NULL) {
+    return 0;
+  }
+
+  struct Ctx *ctx = BIO_get_data(bio);
+
+  if (cmd == BIO_CTRL_PENDING) {
+    return ctx->frag_sizes[ctx->riter];
+  } else if (cmd == BIO_CTRL_DGRAM_QUERY_MTU) {
+    return MTU;
+  }
+
+  return BIO_ctrl(next, cmd, num, ptr);
+}
+
+static long callback_ctrl(BIO *bio, int cmd, BIO_info_cb *fp) {
+  BIO *next = BIO_next(bio);
+  if (next == NULL) {
+    return 0;
+  }
+
+  return BIO_callback_ctrl(next, cmd, fp);
+}

c_src/ex_dtls/bio_frag.h

@@ -0,0 +1,7 @@
+#include <openssl/opensslv.h>
+#include <openssl/err.h>
+#include <openssl/ssl.h>
+
+#include "log.h"
+
+const BIO_METHOD *BIO_f_frag(void);

c_src/ex_dtls/dtls.c

@@ -1,5 +1,7 @@
 #include "dtls.h"
 
+#include "bio_frag.h"
+
 SSL_CTX *create_ctx(int dtls_srtp) {
   SSL_CTX *ssl_ctx = SSL_CTX_new(DTLS_method());
   if (ssl_ctx == NULL) {
@@ -33,19 +35,41 @@ SSL *create_ssl(SSL_CTX *ssl_ctx, int mode) {
     return NULL;
   }
 
-  BIO *rbio = BIO_new(BIO_s_mem());
-  if (rbio == NULL) {
-    DEBUG("Cannot create rbio");
+  BIO *frag_bio = BIO_new(BIO_f_frag());
+  if (frag_bio == NULL) {
+    DEBUG("Cannot create frag bio");
     return NULL;
   }
 
-  BIO *wbio = BIO_new(BIO_s_mem());
-  if (wbio == NULL) {
-    DEBUG("Cannot create wbio");
+  BIO *wmem_bio = BIO_new(BIO_s_mem());
+  if (wmem_bio == NULL) {
+    DEBUG("Cannot create write mem bio");
     return NULL;
   }
 
-  SSL_set_bio(ssl, rbio, wbio);
+  BIO *wchain = BIO_push(frag_bio, wmem_bio);
+
+  BIO *rmem_bio = BIO_new(BIO_s_mem());
+  if (rmem_bio == NULL) {
+    DEBUG("Cannot create read mem bio");
+    return NULL;
+  }
+
+  // #TODO Move to the BIO_s_dgram_mem once we require OpenSSL 3
+  // BIO *rbio = BIO_new(BIO_s_dgram_mem());
+  // if (rbio == NULL) {
+  //   DEBUG("Cannot create read dgram mem bio");
+  //   return NULL;
+  // }
+
+  // BIO *wbio = BIO_new(BIO_s_dgram_mem());
+  // if (wbio == NULL) {
+  //   DEBUG("Cannot create write dgram mem bio");
+  //   return NULL;
+  // }
+
+  SSL_set_bio(ssl, rmem_bio, wchain);
+  // SSL_set_bio(ssl, rbio, wbio);
 
   return ssl;
 }