Fix panic when listen backlog is one

regression/apps/network/listen_backlog.c

@@ -0,0 +1,140 @@
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <stdio.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+static int new_bound_socket(struct sockaddr_in *addr)
+{
+    int sockfd;
+
+    sockfd = socket(PF_INET, SOCK_STREAM, 0);
+    if (sockfd < 0) {
+        perror("new_bound_socket: socket");
+        return -1;
+    }
+
+    if (bind(sockfd, (struct sockaddr *)addr, sizeof(*addr)) < 0) {
+        perror("new_bound_socket: bind");
+        close(sockfd);
+        return -1;
+    }
+
+    return sockfd;
+}
+
+static int new_connected_socket(struct sockaddr_in *addr)
+{
+    int sockfd;
+
+    sockfd = socket(AF_INET, SOCK_STREAM, 0);
+    if (sockfd < 0) {
+        perror("new_connected_socket: socket");
+        return -1;
+    }
+
+    if (connect(sockfd, (struct sockaddr *)addr, sizeof(*addr)) < 0) {
+        perror("new_connected_socket: connect");
+        close(sockfd);
+        return -1;
+    }
+
+    return sockfd;
+}
+
+#define MAX_TEST_BACKLOG 5
+
+int test_listen_backlog(struct sockaddr_in *addr, int backlog)
+{
+    int listenfd;
+    int connectfd[MAX_TEST_BACKLOG], acceptfd[MAX_TEST_BACKLOG];
+    int num_connectfd = 0, num_acceptfd = 0;
+    int ret = -1;
+    struct sockaddr caddr;
+    socklen_t caddrlen = sizeof(caddr);
+
+    listenfd = new_bound_socket(addr);
+    if (listenfd < 0) {
+        fprintf(stderr,
+            "Test failed: Error occurs in new_bound_socket\n");
+        return -1;
+    }
+
+    if (listen(listenfd, backlog) < 0) {
+        perror("listen");
+        fprintf(stderr, "Test failed: Error occurs in listen\n");
+        goto out;
+    }
+
+    for (; num_connectfd < backlog; ++num_connectfd) {
+        connectfd[num_connectfd] = new_connected_socket(addr);
+        if (connectfd[num_connectfd] < 0)
+            break;
+    }
+
+    if (num_connectfd != backlog) {
+        fprintf(stderr,
+            "Test failed: listen(backlog=%d) allows only %d pending connections\n",
+            backlog, num_connectfd);
+        goto out;
+    }
+    fprintf(stderr,
+        "Test passed: listen(backlog=%d) allows >=%d pending connections\n",
+        backlog, num_connectfd);
+
+    for (; num_acceptfd < num_connectfd; ++num_acceptfd) {
+        acceptfd[num_acceptfd] = accept(listenfd, &caddr, &caddrlen);
+        if (acceptfd[num_acceptfd] < 0) {
+            perror("accept");
+            break;
+        }
+    }
+
+    if (num_acceptfd != num_connectfd) {
+        fprintf(stderr,
+            "Test failed: Only %d pending connections can be accept()'ed out "
+            "of %d\n",
+            num_acceptfd, num_connectfd);
+        goto out;
+    }
+    fprintf(stderr,
+        "Test passed: All of %d pending connections can be accept()'ed\n",
+        num_acceptfd);
+
+    ret = 0;
+
+out:
+    while (--num_acceptfd >= 0)
+        close(acceptfd[num_acceptfd]);
+
+    while (--num_connectfd >= 0)
+        close(connectfd[num_connectfd]);
+
+    close(listenfd);
+
+    return ret;
+}
+
+int main(void)
+{
+    struct sockaddr_in addr;
+    int backlog;
+    int err = 0;
+
+    addr.sin_family = AF_INET;
+    if (inet_aton("127.0.0.1", &addr.sin_addr) < 0) {
+        fprintf(stderr, "inet_aton cannot parse 127.0.0.1\n");
+        return -1;
+    }
+
+    for (backlog = 0; backlog <= MAX_TEST_BACKLOG; ++backlog) {
+        // Avoid "bind: Address already in use"
+        addr.sin_port = htons(8080 + backlog);
+
+        err = test_listen_backlog(&addr, backlog);
+        if (err != 0)
+            break;
+    }
+
+    return err ? -1 : 0;
+}