Add a "fork" of musl as //fusl.

fusl/src/network/res_msend.c

+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netdb.h>
+#include <arpa/inet.h>
+#include <stdint.h>
+#include <string.h>
+#include <poll.h>
+#include <time.h>
+#include <ctype.h>
+#include <unistd.h>
+#include <errno.h>
+#include <pthread.h>
+#include "stdio_impl.h"
+#include "syscall.h"
+#include "lookup.h"
+
+static void cleanup(void *p)
+{
+        __syscall(SYS_close, (intptr_t)p);
+}
+
+static unsigned long mtime()
+{
+        struct timespec ts;
+        clock_gettime(CLOCK_REALTIME, &ts);
+        return (unsigned long)ts.tv_sec * 1000
+                + ts.tv_nsec / 1000000;
+}
+
+int __res_msend(int nqueries, const unsigned char *const *queries,
+        const int *qlens, unsigned char *const *answers, int *alens, int asize)
+{
+        int fd;
+        FILE *f, _f;
+        unsigned char _buf[256];
+        char line[64], *s, *z;
+        int timeout = 5000, attempts = 2, retry_interval, servfail_retry;
+        union {
+                struct sockaddr_in sin;
+                struct sockaddr_in6 sin6;
+        } sa = {0}, ns[3] = {{0}};
+        socklen_t sl = sizeof sa.sin;
+        int nns = 0;
+        int family = AF_INET;
+        int rlen;
+        int next;
+        int i, j;
+        int cs;
+        struct pollfd pfd;
+        unsigned long t0, t1, t2;
+        struct address iplit;
+
+        pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
+
+        /* Get nameservers from resolv.conf, fallback to localhost */
+        f = __fopen_rb_ca("/etc/resolv.conf", &_f, _buf, sizeof _buf);
+        if (!f) switch (errno) {
+        case ENOENT:
+        case ENOTDIR:
+        case EACCES:
+                goto no_resolv_conf;
+        default:
+                return -1;
+        }
+        for (nns=0; nns<3 && fgets(line, sizeof line, f); ) {
+                if (!strncmp(line, "options", 7) && isspace(line[7])) {
+                        unsigned long x;
+                        char *p, *z;
+                        p = strstr(line, "timeout:");
+                        if (p && isdigit(p[8])) {
+                                p += 8;
+                                x = strtoul(p, &z, 10);
+                                if (z != p) timeout = x < 30 ? x*1000 : 30000;
+                        }
+                        p = strstr(line, "attempts:");
+                        if (p && isdigit(p[9])) {
+                                p += 9;
+                                x = strtoul(p, &z, 10);
+                                if (z != p) attempts = x < 10 ? x : 10;
+                                if (!attempts) attempts = 1;
+                        }
+                }
+                if (strncmp(line, "nameserver", 10) || !isspace(line[10]))
+                        continue;
+                for (s=line+11; isspace(*s); s++);
+                for (z=s; *z && !isspace(*z); z++);
+                *z=0;
+
+                if (__lookup_ipliteral(&iplit, s, AF_UNSPEC)>0) {
+                        if (iplit.family == AF_INET) {
+                                memcpy(&ns[nns].sin.sin_addr, iplit.addr, 4);
+                                ns[nns].sin.sin_port = htons(53);
+                                ns[nns++].sin.sin_family = AF_INET;
+                        } else {
+                                sl = sizeof sa.sin6;
+                                memcpy(&ns[nns].sin6.sin6_addr, iplit.addr, 16);
+                                ns[nns].sin6.sin6_port = htons(53);
+                                ns[nns].sin6.sin6_scope_id = iplit.scopeid;
+                                ns[nns++].sin6.sin6_family = family = AF_INET6;
+                        }
+                }
+        }
+        __fclose_ca(f);
+no_resolv_conf:
+        if (!nns) {
+                ns[0].sin.sin_family = AF_INET;
+                ns[0].sin.sin_port = htons(53);
+                ns[0].sin.sin_addr.s_addr = htonl(0x7f000001);
+                nns=1;
+        }
+
+        /* Get local address and open/bind a socket */
+        sa.sin.sin_family = family;
+        fd = socket(family, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+
+        /* Handle case where system lacks IPv6 support */
+        if (fd < 0 && family == AF_INET6 && errno == EAFNOSUPPORT) {
+                fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+                family = AF_INET;
+        }
+        if (fd < 0 || bind(fd, (void *)&sa, sl) < 0) return -1;
+
+        /* Past this point, there are no errors. Each individual query will
+         * yield either no reply (indicated by zero length) or an answer
+         * packet which is up to the caller to interpret. */
+
+        pthread_cleanup_push(cleanup, (void *)(intptr_t)fd);
+        pthread_setcancelstate(cs, 0);
+
+        /* Convert any IPv4 addresses in a mixed environment to v4-mapped */
+        if (family == AF_INET6) {
+                setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof 0);
+                for (i=0; i<nns; i++) {
+                        if (ns[i].sin.sin_family != AF_INET) continue;
+                        memcpy(ns[i].sin6.sin6_addr.s6_addr+12,
+                                &ns[i].sin.sin_addr, 4);
+                        memcpy(ns[i].sin6.sin6_addr.s6_addr,
+                                "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
+                        ns[i].sin6.sin6_family = AF_INET6;
+                        ns[i].sin6.sin6_flowinfo = 0;
+                        ns[i].sin6.sin6_scope_id = 0;
+                }
+        }
+
+        memset(alens, 0, sizeof *alens * nqueries);
+
+        pfd.fd = fd;
+        pfd.events = POLLIN;
+        retry_interval = timeout / attempts;
+        next = 0;
+        t0 = t2 = mtime();
+        t1 = t2 - retry_interval;
+
+        for (; t2-t0 < timeout; t2=mtime()) {
+                if (t2-t1 >= retry_interval) {
+                        /* Query all configured namservers in parallel */
+                        for (i=0; i<nqueries; i++)
+                                if (!alens[i])
+                                        for (j=0; j<nns; j++)
+                                                sendto(fd, queries[i],
+                                                        qlens[i], MSG_NOSIGNAL,
+                                                        (void *)&ns[j], sl);
+                        t1 = t2;
+                        servfail_retry = 2 * nqueries;
+                }
+
+                /* Wait for a response, or until time to retry */
+                if (poll(&pfd, 1, t1+retry_interval-t2) <= 0) continue;
+
+                while ((rlen = recvfrom(fd, answers[next], asize, 0,
+                  (void *)&sa, (socklen_t[1]){sl})) >= 0) {
+
+                        /* Ignore non-identifiable packets */
+                        if (rlen < 4) continue;
+
+                        /* Ignore replies from addresses we didn't send to */
+                        for (j=0; j<nns && memcmp(ns+j, &sa, sl); j++);
+                        if (j==nns) continue;
+
+                        /* Find which query this answer goes with, if any */
+                        for (i=next; i<nqueries && (
+                                answers[next][0] != queries[i][0] ||
+                                answers[next][1] != queries[i][1] ); i++);
+                        if (i==nqueries) continue;
+                        if (alens[i]) continue;
+
+                        /* Only accept positive or negative responses;
+                         * retry immediately on server failure, and ignore
+                         * all other codes such as refusal. */
+                        switch (answers[next][3] & 15) {
+                        case 0:
+                        case 3:
+                                break;
+                        case 2:
+                                if (servfail_retry && servfail_retry--)
+                                        sendto(fd, queries[i],
+                                                qlens[i], MSG_NOSIGNAL,
+                                                (void *)&ns[j], sl);
+                        default:
+                                continue;
+                        }
+
+                        /* Store answer in the right slot, or update next
+                         * available temp slot if it's already in place. */
+                        alens[i] = rlen;
+                        if (i == next)
+                                for (; next<nqueries && alens[next]; next++);
+                        else
+                                memcpy(answers[i], answers[next], rlen);
+
+                        if (next == nqueries) goto out;
+                }
+        }
+out:
+        pthread_cleanup_pop(1);
+
+        return 0;
+}