From 416dc7beae907cf99b51dfeef3800fcfb9a34973 Mon Sep 17 00:00:00 2001
From: "Sergio R. Caprile" <scaprile@cesanta.com>
Date: Fri, 5 Jun 2026 16:59:44 -0300
Subject: [PATCH] fix no room

---
 mongoose.c        | 13 ++++++++-----
 src/net_builtin.c |  9 ++++++---
 src/tls_mbed.c    |  2 +-
 src/tls_openssl.c |  2 +-
 4 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/mongoose.c b/mongoose.c
index c8b91d25..4ebfe2f8 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -8712,13 +8712,16 @@ long mg_io_send(struct mg_connection *c, const void *buf, size_t len) {
 }
 
 static void handle_tls_recv(struct mg_connection *c) {
-  size_t avail = mg_tls_pending(c);
+  size_t avail = mg_tls_pending(c); // will change after mg_tls_recv()
   size_t min = avail > MG_MAX_RECV_SIZE ? MG_MAX_RECV_SIZE : avail;
-  struct mg_iobuf *io = &c->recv;
+  struct mg_iobuf *io = &c->recv; // allocated on first avail > 0
   if (io->size - io->len < min && !mg_iobuf_resize(io, io->len + min)) {
     mg_error(c, "oom");
   } else {
-    // Decrypt data directly into c->recv
+    // Decrypt data directly into c->recv. If io->buf = NULL or
+    // io->len = io->size (no room), there can be outstanding data that can't be
+    // moved (mg_tls_pending() > 0 after mg_tls_recv() returns). So mg_tls_recv()
+    // takes care of returning 0 in this case (commented as "MIP")
     long n = mg_tls_recv(c, io->buf != NULL ? &io->buf[io->len] : io->buf,
                          io->size - io->len);
     if (n == MG_IO_ERR) {
@@ -19631,7 +19634,7 @@ size_t mg_tls_pending(struct mg_connection *c) {
 long mg_tls_recv(struct mg_connection *c, void *buf, size_t len) {
   struct mg_tls *tls = (struct mg_tls *) c->tls;
   long n = mbedtls_ssl_read(&tls->ssl, (unsigned char *) buf, len);
-  if (!c->is_tls_hs && buf == NULL && n == 0) return 0;  // TODO(): MIP
+  if (!c->is_tls_hs && (buf == NULL || len == 0) && n == 0) return 0;  // MIP
   if (n == MBEDTLS_ERR_SSL_WANT_READ || n == MBEDTLS_ERR_SSL_WANT_WRITE)
     return MG_IO_WAIT;
 #if defined(MBEDTLS_ERR_SSL_RECEIVED_NEW_SESSION_TICKET)
@@ -20027,7 +20030,7 @@ size_t mg_tls_pending(struct mg_connection *c) {
 long mg_tls_recv(struct mg_connection *c, void *buf, size_t len) {
   struct mg_tls *tls = (struct mg_tls *) c->tls;
   int n = SSL_read(tls->ssl, buf, (int) len);
-  if (!c->is_tls_hs && buf == NULL && n == 0) return 0;  // TODO(): MIP
+  if (!c->is_tls_hs && (buf == NULL || len == 0) && n == 0) return 0;  // MIP
   if (n < 0 && mg_tls_err(c, tls, n) == 0) return MG_IO_WAIT;
   if (n <= 0) return MG_IO_ERR;
   return n;
diff --git a/src/net_builtin.c b/src/net_builtin.c
index de8907a9..8ee87d26 100644
--- a/src/net_builtin.c
+++ b/src/net_builtin.c
@@ -1403,13 +1403,16 @@ long mg_io_send(struct mg_connection *c, const void *buf, size_t len) {
 }
 
 static void handle_tls_recv(struct mg_connection *c) {
-  size_t avail = mg_tls_pending(c);
+  size_t avail = mg_tls_pending(c); // will change after mg_tls_recv()
   size_t min = avail > MG_MAX_RECV_SIZE ? MG_MAX_RECV_SIZE : avail;
-  struct mg_iobuf *io = &c->recv;
+  struct mg_iobuf *io = &c->recv; // allocated on first avail > 0
   if (io->size - io->len < min && !mg_iobuf_resize(io, io->len + min)) {
     mg_error(c, "oom");
   } else {
-    // Decrypt data directly into c->recv
+    // Decrypt data directly into c->recv. If io->buf = NULL or
+    // io->len = io->size (no room), there can be outstanding data that can't be
+    // moved (mg_tls_pending() > 0 after mg_tls_recv() returns). So mg_tls_recv()
+    // takes care of returning 0 in this case (commented as "MIP")
     long n = mg_tls_recv(c, io->buf != NULL ? &io->buf[io->len] : io->buf,
                          io->size - io->len);
     if (n == MG_IO_ERR) {
diff --git a/src/tls_mbed.c b/src/tls_mbed.c
index 1bee87a0..19778d2b 100644
--- a/src/tls_mbed.c
+++ b/src/tls_mbed.c
@@ -201,7 +201,7 @@ size_t mg_tls_pending(struct mg_connection *c) {
 long mg_tls_recv(struct mg_connection *c, void *buf, size_t len) {
   struct mg_tls *tls = (struct mg_tls *) c->tls;
   long n = mbedtls_ssl_read(&tls->ssl, (unsigned char *) buf, len);
-  if (!c->is_tls_hs && buf == NULL && n == 0) return 0;  // TODO(): MIP
+  if (!c->is_tls_hs && (buf == NULL || len == 0) && n == 0) return 0;  // MIP
   if (n == MBEDTLS_ERR_SSL_WANT_READ || n == MBEDTLS_ERR_SSL_WANT_WRITE)
     return MG_IO_WAIT;
 #if defined(MBEDTLS_ERR_SSL_RECEIVED_NEW_SESSION_TICKET)
diff --git a/src/tls_openssl.c b/src/tls_openssl.c
index 6faaf0b6..c64f70b4 100644
--- a/src/tls_openssl.c
+++ b/src/tls_openssl.c
@@ -293,7 +293,7 @@ size_t mg_tls_pending(struct mg_connection *c) {
 long mg_tls_recv(struct mg_connection *c, void *buf, size_t len) {
   struct mg_tls *tls = (struct mg_tls *) c->tls;
   int n = SSL_read(tls->ssl, buf, (int) len);
-  if (!c->is_tls_hs && buf == NULL && n == 0) return 0;  // TODO(): MIP
+  if (!c->is_tls_hs && (buf == NULL || len == 0) && n == 0) return 0;  // MIP
   if (n < 0 && mg_tls_err(c, tls, n) == 0) return MG_IO_WAIT;
   if (n <= 0) return MG_IO_ERR;
   return n;