Reset errno to 0 before checking it

errno is never set to zero by any system call or library function,
and it's programmer's resposibility to reset it before doing checks.
Otherwise the error might be misleading.

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

src/local.c

@@ -222,7 +222,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
     }
 
     ssize_t r;
-
+    errno = 0;
     r = recv(server->fd, buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -312,6 +312,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
                         s = send(remote->fd, remote->buf->array, remote->buf->len, 0);
                     }
 #else
+                    errno = 0;
                     int s = sendto(remote->fd, remote->buf->array, remote->buf->len, MSG_FASTOPEN,
                                    (struct sockaddr *)&(remote->addr), remote->addr_len);
 #endif
@@ -349,6 +350,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
 #endif
                 }
             } else {
+                errno = 0;
                 int s = send(remote->fd, remote->buf->array, remote->buf->len, 0);
                 if (s == -1) {
                     if (errno == EAGAIN || errno == EWOULDBLOCK) {
@@ -581,6 +583,7 @@ static void server_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(server->fd, server->buf->array + server->buf->idx,
                          server->buf->len, 0);
         if (s < 0) {
@@ -644,7 +647,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
 #ifdef ANDROID
     stat_update_cb(loop);
 #endif
-
+    errno = 0;
     ssize_t r = recv(remote->fd, server->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -679,7 +682,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
             return;
         }
     }
-
+    errno = 0;
     int s = send(server->fd, server->buf->array, server->buf->len, 0);
 
     if (s == -1) {
@@ -742,6 +745,7 @@ static void remote_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(remote->fd, remote->buf->array + remote->buf->idx,
                          remote->buf->len, 0);
         if (s < 0) {

src/manager.c

@@ -758,6 +758,7 @@ int main(int argc, char **argv)
     const char *homedir = pw->pw_dir;
     snprintf(working_dir, PATH_MAX, "%s/.shadowsocks", homedir);
 
+    errno = 0;
     int err = mkdir(working_dir, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
     if (err != 0 && errno != EEXIST) {
         ERROR("mkdir");
@@ -788,6 +789,7 @@ int main(int argc, char **argv)
 
         setnonblocking(sfd);
 
+        errno = 0;
         if (remove(manager_address) == -1 && errno != ENOENT) {
             ERROR("bind");
             exit(EXIT_FAILURE);

src/redir.c

@@ -171,6 +171,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
     server_t *server              = server_recv_ctx->server;
     remote_t *remote              = server->remote;
 
+    errno = 0;
     ssize_t r = recv(server->fd, remote->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -212,6 +213,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    errno = 0;
     int s = send(remote->fd, remote->buf->array, remote->buf->len, 0);
 
     if (s == -1) {
@@ -248,6 +250,7 @@ static void server_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(server->fd, server->buf->array + server->buf->idx,
                          server->buf->len, 0);
         if (s < 0) {
@@ -291,6 +294,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
     remote_t *remote              = remote_recv_ctx->remote;
     server_t *server              = remote->server;
 
+    errno = 0;
     ssize_t r = recv(remote->fd, server->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -320,6 +324,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
         close_and_free_server(EV_A_ server);
         return;
     }
+    errno = 0;
     int s = send(server->fd, server->buf->array, server->buf->len, 0);
 
     if (s == -1) {
@@ -424,6 +429,7 @@ static void remote_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(remote->fd, remote->buf->array + remote->buf->idx,
                          remote->buf->len, 0);
         if (s < 0) {

src/server.c

@@ -273,6 +273,7 @@ int setfastopen(int fd)
 #else
         int opt = 5;
 #endif
+        errno = 0;
         s = setsockopt(fd, IPPROTO_TCP, TCP_FASTOPEN, &opt, sizeof(opt));
         if (s == -1) {
             if (errno == EPROTONOSUPPORT || errno == ENOPROTOOPT) {
@@ -452,6 +453,7 @@ static remote_t *connect_to_remote(struct addrinfo *res,
             s = len;
         }
 #else
+        errno = 0;
         ssize_t s = sendto(sockfd, server->buf->array + server->buf->idx,
                            server->buf->len, MSG_FASTOPEN, res->ai_addr,
                            res->ai_addrlen);
@@ -501,6 +503,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
         len    = 0;
     }
 
+    errno = 0;
     ssize_t r = recv(server->fd, buf->array + len, BUF_SIZE - len, 0);
 
     if (r == 0) {
@@ -563,6 +566,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
             close_and_free_remote(EV_A_ remote);
             return;
         }
+        errno = 0;
         int s = send(remote->fd, remote->buf->array, remote->buf->len, 0);
         if (s == -1) {
             if (errno == EAGAIN || errno == EWOULDBLOCK) {
@@ -833,6 +837,7 @@ static void server_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(server->fd, server->buf->array + server->buf->idx,
                          server->buf->len, 0);
         if (s < 0) {
@@ -948,6 +953,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
 
     ev_timer_again(EV_A_ & server->recv_ctx->watcher);
 
+    errno = 0;
     ssize_t r = recv(remote->fd, server->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -983,6 +989,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    errno = 0;
     int s = send(server->fd, server->buf->array, server->buf->len, 0);
 
     if (s == -1) {
@@ -1055,6 +1062,7 @@ static void remote_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(remote->fd, remote->buf->array + remote->buf->idx,
                          remote->buf->len, 0);
         if (s == -1) {

src/tunnel.c

@@ -186,6 +186,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    errno = 0;
     ssize_t r = recv(server->fd, remote->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -221,6 +222,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    errno = 0;
     int s = send(remote->fd, remote->buf->array, remote->buf->len, 0);
 
     if (s == -1) {
@@ -257,6 +259,7 @@ static void server_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(server->fd, server->buf->array + server->buf->idx,
                          server->buf->len, 0);
         if (s < 0) {
@@ -310,6 +313,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
     remote_t *remote              = remote_recv_ctx->remote;
     server_t *server              = remote->server;
 
+    errno = 0;
     ssize_t r = recv(remote->fd, server->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -341,6 +345,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    errno = 0;
     int s = send(server->fd, server->buf->array, server->buf->len, 0);
 
     if (s == -1) {
@@ -471,6 +476,7 @@ static void remote_send_cb(EV_P_ ev_io *w, int revents)
             return;
         } else {
             // has data to send
+            errno = 0;
             ssize_t s = send(remote->fd, remote->buf->array + remote->buf->idx,
                              remote->buf->len, 0);
             if (s < 0) {

src/utils.c

@@ -102,16 +102,19 @@ int run_as(const char *user)
             /* Note that we use getpwnam_r() instead of getpwnam(),
              * which returns its result in a statically allocated buffer and
              * cannot be considered thread safe. */
+            errno = 0;
             err = getpwnam_r(user, &pwdbuf, buf, buflen, &pwd);
 
             if (err == 0 && pwd) {
                 /* setgid first, because we may not be allowed to do it anymore after setuid */
+                errno = 0;
                 if (setgid(pwd->pw_gid) != 0) {
                     LOGE(
                         "Could not change group id to that of run_as user '%s': %s",
                         user, strerror(errno));
                     return 0;
                 }
+                errno = 0;
 
                 if (setuid(pwd->pw_uid) != 0) {
                     LOGE(
@@ -147,11 +150,13 @@ int run_as(const char *user)
             return 0;
         }
         /* setgid first, because we may not allowed to do it anymore after setuid */
+        errno = 0;
         if (setgid(pwd->pw_gid) != 0) {
             LOGE("Could not change group id to that of run_as user '%s': %s",
                  user, strerror(errno));
             return 0;
         }
+        errno = 0;
         if (setuid(pwd->pw_uid) != 0) {
             LOGE("Could not change user id to that of run_as user '%s': %s",
                  user, strerror(errno));
@@ -351,6 +356,7 @@ int set_nofile(int nofile)
     if (nofile <= 0) {
         FATAL("nofile must be greater than 0\n");
     }
+    errno = 0;
 
     if (setrlimit(RLIMIT_NOFILE, &limit) < 0) {
         if (errno == EPERM) {