Merge pull request #471 from lunarmodules/fix/zero-read

fix(receive): a receive 0 should immediately return, not block

4 files changed, 36 insertions, 10 deletions

diff --git a/src/buffer.c b/src/buffer.c
index 3d48a09..b7e97f7 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -11,7 +11,7 @@
 static int recvraw(p_buffer buf, size_t wanted, luaL_Buffer *b);
 static int recvline(p_buffer buf, luaL_Buffer *b, size_t budget);
 static int recvall(p_buffer buf, luaL_Buffer *b, size_t budget);
-static int buffer_get(p_buffer buf, const char **data, size_t *count);
+static int buffer_get(p_buffer buf, const char **data, size_t *count, size_t wanted);
 static void buffer_skip(p_buffer buf, size_t count);
 static int sendraw(p_buffer buf, const char *data, size_t count, size_t *sent);
 
@@ -230,15 +230,14 @@ static int sendraw(p_buffer buf, const char *data, size_t count, size_t *sent) {
 static int recvraw(p_buffer buf, size_t wanted, luaL_Buffer *b) {
     int err = IO_DONE;
     size_t total = 0;
-    while (err == IO_DONE) {
+    do {
         size_t count; const char *data;
-        err = buffer_get(buf, &data, &count);
+        err = buffer_get(buf, &data, &count, wanted - total);
         count = MIN(count, wanted - total);
         luaL_addlstring(b, data, count);
         buffer_skip(buf, count);
         total += count;
-        if (total >= wanted) break;
-    }
+    } while (total < wanted && err == IO_DONE);
     return err;
 }
 
@@ -253,7 +252,7 @@ static int recvall(p_buffer buf, luaL_Buffer *b, size_t budget) {
     size_t total = 0;
     while (err == IO_DONE) {
         const char *data; size_t count;
-        err = buffer_get(buf, &data, &count);
+        err = buffer_get(buf, &data, &count, BUF_SIZE);
         if (budget && count > budget - total) {   /* strictly more than fits */
             count = budget - total;
             luaL_addlstring(b, data, count);
@@ -286,7 +285,7 @@ static int recvline(p_buffer buf, luaL_Buffer *b, size_t budget) {
     size_t total = 0;
     while (err == IO_DONE) {
         size_t count, pos; const char *data;
-        err = buffer_get(buf, &data, &count);
+        err = buffer_get(buf, &data, &count, BUF_SIZE);
         pos = 0;
         while (pos < count && data[pos] != '\n') {
             /* we ignore all \r's -- they are consumed but never counted */
@@ -325,15 +324,19 @@ static void buffer_skip(p_buffer buf, size_t count) {
 
 /*-------------------------------------------------------------------------*\
 * Return any data available in buffer, or get more data from transport layer
-* if buffer is empty
+* if buffer is empty. 'wanted' is how many more bytes the caller is still
+* after; when it is zero, the transport layer is still consulted (so an
+* already-closed connection is still reported), but no more than zero bytes
+* are requested from it, so a healthy connection with no data pending can
+* never block.
 \*-------------------------------------------------------------------------*/
-static int buffer_get(p_buffer buf, const char **data, size_t *count) {
+static int buffer_get(p_buffer buf, const char **data, size_t *count, size_t wanted) {
     int err = IO_DONE;
     p_io io = buf->io;
     p_timeout tm = buf->tm;
     if (buffer_isempty(buf)) {
         size_t got;
-        err = io->recv(io->ctx, buf->data, BUF_SIZE, &got, tm);
+        err = io->recv(io->ctx, buf->data, wanted == 0 ? 0 : BUF_SIZE, &got, tm);
         buf->first = 0;
         buf->last = got;
     }
diff --git a/src/udp.c b/src/udp.c
index 6c0d39e..6d017da 100644
--- a/src/udp.c
+++ b/src/udp.c
@@ -283,6 +283,7 @@ static int meth_receivefrom(lua_State *L) {
         lua_pushliteral(L, "out of memory");
         return 2;
     }
+    memset(&addr, 0, sizeof(addr));
     err = socket_recvfrom(&udp->sock, dgram, wanted, &got, (SA *) &addr,
             &addr_len, tm);
     /* Unlike TCP, recv() of zero is not closed, but a zero-length packet. */
@@ -292,6 +293,17 @@ static int meth_receivefrom(lua_State *L) {
         if (wanted > sizeof(buf)) free(dgram);
         return 2;
     }
+    /* a zero-length request may be satisfied by some kernels (notably
+     * Darwin/BSD) without ever touching the sender's address -- only
+     * resolve it when the OS actually reported one, instead of feeding
+     * getnameinfo() a garbage/zeroed sockaddr. */
+    if (addr.ss_family != AF_INET && addr.ss_family != AF_INET6) {
+        lua_pushlstring(L, dgram, got);
+        lua_pushnil(L);
+        lua_pushnil(L);
+        if (wanted > sizeof(buf)) free(dgram);
+        return 3;
+    }
     err = getnameinfo((struct sockaddr *)&addr, addr_len, addrstr,
         INET6_ADDRSTRLEN, portstr, 6, NI_NUMERICHOST | NI_NUMERICSERV);
         if (err) {
diff --git a/src/usocket.c b/src/usocket.c
index 7965db6..e00c43d 100644
--- a/src/usocket.c
+++ b/src/usocket.c
@@ -258,6 +258,7 @@ int socket_recv(p_socket ps, char *data, size_t count, size_t *got, p_timeout tm
     int err;
     *got = 0;
     if (*ps == SOCKET_INVALID) return IO_CLOSED;
+    if (count == 0) return IO_DONE;
     for ( ;; ) {
         long taken = (long) recv(*ps, data, count, 0);
         if (taken > 0) {
@@ -343,6 +344,7 @@ int socket_read(p_socket ps, char *data, size_t count, size_t *got, p_timeout tm
     int err;
     *got = 0;
     if (*ps == SOCKET_INVALID) return IO_CLOSED;
+    if (count == 0) return IO_DONE;
     for ( ;; ) {
         long taken = (long) read(*ps, data, count);
         if (taken > 0) {
diff --git a/src/wsocket.c b/src/wsocket.c
index d3af9d4..b2b668c 100644
--- a/src/wsocket.c
+++ b/src/wsocket.c
@@ -247,6 +247,7 @@ int socket_recv(p_socket ps, char *data, size_t count, size_t *got,
     int err, prev = IO_DONE;
     *got = 0;
     if (*ps == SOCKET_INVALID) return IO_CLOSED;
+    if (count == 0) return IO_DONE;
     for ( ;; ) {
         int taken = recv(*ps, data, (int) count, 0);
         if (taken > 0) {
@@ -285,6 +286,14 @@ int socket_recvfrom(p_socket ps, char *data, size_t count, size_t *got,
         }
         if (taken == 0) return IO_CLOSED;
         err = WSAGetLastError();
+        /* a zero-length request is trivially "too small" for any
+         * non-empty datagram; unlike POSIX, which truncates and succeeds
+         * silently, Windows reports this as WSAEMSGSIZE even though the
+         * datagram -- and its sender's address, already written to addr/
+         * len above -- was still consumed. Normalize it to match POSIX's
+         * silent-truncation instead of surfacing a platform-specific
+         * error for what is otherwise a successful, if empty, receive. */
+        if (count == 0 && err == WSAEMSGSIZE) return IO_DONE;
         /* On UDP, a connreset simply means the previous send failed.
          * So we try again.
          * On TCP, it means our socket is now useless, so the error passes.