1 /*
2  * Copyright (C) 2019 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 
18 #define LOG_TAG "MultinetworkApiTest"
19 
20 #include <arpa/inet.h>
21 #include <arpa/nameser.h>
22 #include <errno.h>
23 #include <inttypes.h>
24 #include <jni.h>
25 #include <netdb.h>
26 #include <poll.h> /* poll */
27 #include <resolv.h>
28 #include <stdio.h>
29 #include <stdlib.h>
30 #include <string.h>
31 #include <sys/socket.h>
32 #include <sys/time.h>
33 
34 #include <string>
35 
36 #include <android/log.h>
37 #include <android/multinetwork.h>
38 #include <nativehelper/JNIHelp.h>
39 
40 #define LOGD(fmt, ...) \
41         __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, fmt, ##__VA_ARGS__)
42 
43 // Since the tests in this file commonly pass expression statements as parameters to these macros,
44 // get the returned value of the statements to avoid statement double-called.
45 // By checking ExceptionCheck(), these macros don't throw another exception if an exception has
46 // been thrown, because ART's JNI disallows to throw another exception while an exception is
47 // pending (See CheckThread in check_jni.cc).
48 #define EXPECT_GE(env, actual_stmt, expected_stmt, msg)              \
49     do {                                                             \
50         const auto expected = (expected_stmt);                       \
51         const auto actual = (actual_stmt);                           \
52         if (actual < expected && !env->ExceptionCheck()) {           \
53             jniThrowExceptionFmt(env, "java/lang/AssertionError",    \
54                     "%s:%d: %s EXPECT_GE: expected %d, got %d",      \
55                     __FILE__, __LINE__, msg, expected, actual);      \
56         }                                                            \
57     } while (0)
58 
59 #define EXPECT_GT(env, actual_stmt, expected_stmt, msg)              \
60     do {                                                             \
61         const auto expected = (expected_stmt);                       \
62         const auto actual = (actual_stmt);                           \
63         if (actual <= expected && !env->ExceptionCheck()) {          \
64             jniThrowExceptionFmt(env, "java/lang/AssertionError",    \
65                     "%s:%d: %s EXPECT_GT: expected %d, got %d",      \
66                     __FILE__, __LINE__, msg, expected, actual);      \
67         }                                                            \
68     } while (0)
69 
70 #define EXPECT_EQ(env, expected_stmt, actual_stmt, msg)              \
71     do {                                                             \
72         const auto expected = (expected_stmt);                       \
73         const auto actual = (actual_stmt);                           \
74         if (actual != expected && !env->ExceptionCheck()) {          \
75             jniThrowExceptionFmt(env, "java/lang/AssertionError",    \
76                     "%s:%d: %s EXPECT_EQ: expected %d, got %d",      \
77                     __FILE__, __LINE__, msg, expected, actual);      \
78         }                                                            \
79     } while (0)
80 
81 static const int MAXPACKET = 8 * 1024;
82 static const int TIMEOUT_MS = 15000;
83 static const char kHostname[] = "connectivitycheck.android.com";
84 static const char kNxDomainName[] = "test1-nx.metric.gstatic.com";
85 static const char kGoogleName[] = "www.google.com";
86 
makeQuery(const char * name,int qtype,uint8_t * buf,size_t buflen)87 int makeQuery(const char* name, int qtype, uint8_t* buf, size_t buflen) {
88     return res_mkquery(ns_o_query, name, ns_c_in, qtype, NULL, 0, NULL, buf, buflen);
89 }
90 
getAsyncResponse(JNIEnv * env,int fd,int timeoutMs,int * rcode,uint8_t * buf,size_t bufLen)91 int getAsyncResponse(JNIEnv* env, int fd, int timeoutMs, int* rcode, uint8_t* buf, size_t bufLen) {
92     struct pollfd wait_fd = { .fd = fd, .events = POLLIN };
93 
94     poll(&wait_fd, 1, timeoutMs);
95     if (wait_fd.revents & POLLIN) {
96         int n = android_res_nresult(fd, rcode, buf, bufLen);
97         // Verify that android_res_nresult() closed the fd
98         char dummy;
99         EXPECT_EQ(env, -1, read(fd, &dummy, sizeof(dummy)), "res_nresult check for closing fd");
100         EXPECT_EQ(env, EBADF, errno, "res_nresult check for errno");
101         return n;
102     }
103 
104     return -ETIMEDOUT;
105 }
106 
extractIpAddressAnswers(uint8_t * buf,size_t bufLen,int family)107 int extractIpAddressAnswers(uint8_t* buf, size_t bufLen, int family) {
108     ns_msg handle;
109     if (ns_initparse((const uint8_t*) buf, bufLen, &handle) < 0) {
110         return -errno;
111     }
112     const int ancount = ns_msg_count(handle, ns_s_an);
113     // Answer count = 0 is valid(e.g. response of query with root)
114     if (!ancount) {
115         return 0;
116     }
117     ns_rr rr;
118     bool hasValidAns = false;
119     for (int i = 0; i < ancount; i++) {
120         if (ns_parserr(&handle, ns_s_an, i, &rr) < 0) {
121             // If there is no valid answer, test will fail.
122             continue;
123         }
124 
125         const int rtype = ns_rr_type(rr);
126         if (family == AF_INET) {
127             // If there is no expected address type, test will fail.
128             if (rtype != ns_t_a) continue;
129         } else if (family == AF_INET6) {
130             // If there is no expected address type, test will fail.
131             if (rtype != ns_t_aaaa) continue;
132         } else {
133             return -EAFNOSUPPORT;
134         }
135 
136         const uint8_t* rdata = ns_rr_rdata(rr);
137         char buffer[INET6_ADDRSTRLEN];
138         if (inet_ntop(family, (const char*) rdata, buffer, sizeof(buffer)) == NULL) {
139             return -errno;
140         }
141         hasValidAns = true;
142     }
143     return hasValidAns ? 0 : -EBADMSG;
144 }
145 
expectAnswersValid(JNIEnv * env,int fd,int family,int expectedRcode)146 int expectAnswersValid(JNIEnv* env, int fd, int family, int expectedRcode) {
147     int rcode = -1;
148     uint8_t buf[MAXPACKET] = {};
149     int res = getAsyncResponse(env, fd, TIMEOUT_MS, &rcode, buf, MAXPACKET);
150     if (res < 0) {
151         return res;
152     }
153 
154     EXPECT_EQ(env, expectedRcode, rcode, "rcode is not expected");
155 
156     if (expectedRcode == ns_r_noerror && res > 0) {
157         return extractIpAddressAnswers(buf, res, family);
158     }
159     return 0;
160 }
161 
expectAnswersNotValid(JNIEnv * env,int fd,int expectedErrno)162 int expectAnswersNotValid(JNIEnv* env, int fd, int expectedErrno) {
163     int rcode = -1;
164     uint8_t buf[MAXPACKET] = {};
165     int res = getAsyncResponse(env, fd, TIMEOUT_MS, &rcode, buf, MAXPACKET);
166     if (res != expectedErrno) {
167         LOGD("res:%d, expectedErrno = %d", res, expectedErrno);
168         return (res > 0) ? -EREMOTEIO : res;
169     }
170     return 0;
171 }
172 
173 extern "C"
Java_android_net_cts_MultinetworkApiTest_runResNqueryCheck(JNIEnv * env,jclass,jlong nethandle)174 JNIEXPORT void Java_android_net_cts_MultinetworkApiTest_runResNqueryCheck(
175         JNIEnv* env, jclass, jlong nethandle) {
176     net_handle_t handle = (net_handle_t) nethandle;
177 
178     // V4
179     int fd = android_res_nquery(handle, kHostname, ns_c_in, ns_t_a, 0);
180     EXPECT_GE(env, fd, 0, "v4 res_nquery");
181     EXPECT_EQ(env, 0, expectAnswersValid(env, fd, AF_INET, ns_r_noerror),
182             "v4 res_nquery check answers");
183 
184     // V6
185     fd = android_res_nquery(handle, kHostname, ns_c_in, ns_t_aaaa, 0);
186     EXPECT_GE(env, fd, 0, "v6 res_nquery");
187     EXPECT_EQ(env, 0, expectAnswersValid(env, fd, AF_INET6, ns_r_noerror),
188             "v6 res_nquery check answers");
189 }
190 
191 extern "C"
Java_android_net_cts_MultinetworkApiTest_runResNsendCheck(JNIEnv * env,jclass,jlong nethandle)192 JNIEXPORT void Java_android_net_cts_MultinetworkApiTest_runResNsendCheck(
193         JNIEnv* env, jclass, jlong nethandle) {
194     net_handle_t handle = (net_handle_t) nethandle;
195     // V4
196     uint8_t buf1[MAXPACKET] = {};
197 
198     int len1 = makeQuery(kGoogleName, ns_t_a, buf1, sizeof(buf1));
199     EXPECT_GT(env, len1, 0, "v4 res_mkquery 1st");
200 
201     uint8_t buf2[MAXPACKET] = {};
202     int len2 = makeQuery(kHostname, ns_t_a, buf2, sizeof(buf2));
203     EXPECT_GT(env, len2, 0, "v4 res_mkquery 2nd");
204 
205     int fd1 = android_res_nsend(handle, buf1, len1, 0);
206     EXPECT_GE(env, fd1, 0, "v4 res_nsend 1st");
207     int fd2 = android_res_nsend(handle, buf2, len2, 0);
208     EXPECT_GE(env, fd2, 0, "v4 res_nsend 2nd");
209 
210     EXPECT_EQ(env, 0, expectAnswersValid(env, fd2, AF_INET, ns_r_noerror),
211             "v4 res_nsend 2nd check answers");
212     EXPECT_EQ(env, 0, expectAnswersValid(env, fd1, AF_INET, ns_r_noerror),
213             "v4 res_nsend 1st check answers");
214 
215     // V6
216     memset(buf1, 0, sizeof(buf1));
217     memset(buf2, 0, sizeof(buf2));
218     len1 = makeQuery(kGoogleName, ns_t_aaaa, buf1, sizeof(buf1));
219     EXPECT_GT(env, len1, 0, "v6 res_mkquery 1st");
220     len2 = makeQuery(kHostname, ns_t_aaaa, buf2, sizeof(buf2));
221     EXPECT_GT(env, len2, 0, "v6 res_mkquery 2nd");
222 
223     fd1 = android_res_nsend(handle, buf1, len1, 0);
224     EXPECT_GE(env, fd1, 0, "v6 res_nsend 1st");
225     fd2 = android_res_nsend(handle, buf2, len2, 0);
226     EXPECT_GE(env, fd2, 0, "v6 res_nsend 2nd");
227 
228     EXPECT_EQ(env, 0, expectAnswersValid(env, fd2, AF_INET6, ns_r_noerror),
229             "v6 res_nsend 2nd check answers");
230     EXPECT_EQ(env, 0, expectAnswersValid(env, fd1, AF_INET6, ns_r_noerror),
231             "v6 res_nsend 1st check answers");
232 }
233 
234 extern "C"
Java_android_net_cts_MultinetworkApiTest_runResNnxDomainCheck(JNIEnv * env,jclass,jlong nethandle)235 JNIEXPORT void Java_android_net_cts_MultinetworkApiTest_runResNnxDomainCheck(
236         JNIEnv* env, jclass, jlong nethandle) {
237     net_handle_t handle = (net_handle_t) nethandle;
238 
239     // res_nquery V4 NXDOMAIN
240     int fd = android_res_nquery(handle, kNxDomainName, ns_c_in, ns_t_a, 0);
241     EXPECT_GE(env, fd, 0, "v4 res_nquery NXDOMAIN");
242     EXPECT_EQ(env, 0, expectAnswersValid(env, fd, AF_INET, ns_r_nxdomain),
243             "v4 res_nquery NXDOMAIN check answers");
244 
245     // res_nquery V6 NXDOMAIN
246     fd = android_res_nquery(handle, kNxDomainName, ns_c_in, ns_t_aaaa, 0);
247     EXPECT_GE(env, fd, 0, "v6 res_nquery NXDOMAIN");
248     EXPECT_EQ(env, 0, expectAnswersValid(env, fd, AF_INET6, ns_r_nxdomain),
249             "v6 res_nquery NXDOMAIN check answers");
250 
251     uint8_t buf[MAXPACKET] = {};
252     // res_nsend V4 NXDOMAIN
253     int len = makeQuery(kNxDomainName, ns_t_a, buf, sizeof(buf));
254     EXPECT_GT(env, len, 0, "v4 res_mkquery NXDOMAIN");
255     fd = android_res_nsend(handle, buf, len, 0);
256     EXPECT_GE(env, fd, 0, "v4 res_nsend NXDOMAIN");
257     EXPECT_EQ(env, 0, expectAnswersValid(env, fd, AF_INET, ns_r_nxdomain),
258             "v4 res_nsend NXDOMAIN check answers");
259 
260     // res_nsend V6 NXDOMAIN
261     memset(buf, 0, sizeof(buf));
262     len = makeQuery(kNxDomainName, ns_t_aaaa, buf, sizeof(buf));
263     EXPECT_GT(env, len, 0, "v6 res_mkquery NXDOMAIN");
264     fd = android_res_nsend(handle, buf, len, 0);
265     EXPECT_GE(env, fd, 0, "v6 res_nsend NXDOMAIN");
266     EXPECT_EQ(env, 0, expectAnswersValid(env, fd, AF_INET6, ns_r_nxdomain),
267             "v6 res_nsend NXDOMAIN check answers");
268 }
269 
270 
271 extern "C"
Java_android_net_cts_MultinetworkApiTest_runResNcancelCheck(JNIEnv * env,jclass,jlong nethandle)272 JNIEXPORT void Java_android_net_cts_MultinetworkApiTest_runResNcancelCheck(
273         JNIEnv* env, jclass, jlong nethandle) {
274     net_handle_t handle = (net_handle_t) nethandle;
275 
276     int fd = android_res_nquery(handle, kGoogleName, ns_c_in, ns_t_a, 0);
277     errno = 0;
278     android_res_cancel(fd);
279     int err = errno;
280     EXPECT_EQ(env, 0, err, "res_cancel");
281     // DO NOT call cancel or result with the same fd more than once,
282     // otherwise it will hit fdsan double-close fd.
283 }
284 
285 extern "C"
Java_android_net_cts_MultinetworkApiTest_runResNapiMalformedCheck(JNIEnv * env,jclass,jlong nethandle)286 JNIEXPORT void Java_android_net_cts_MultinetworkApiTest_runResNapiMalformedCheck(
287         JNIEnv* env, jclass, jlong nethandle) {
288     net_handle_t handle = (net_handle_t) nethandle;
289 
290     // It is the equivalent of "dig . a", Query with an empty name.
291     int fd = android_res_nquery(handle, "", ns_c_in, ns_t_a, 0);
292     EXPECT_GE(env, fd, 0, "res_nquery root");
293     EXPECT_EQ(env, 0, expectAnswersValid(env, fd, AF_INET, ns_r_noerror),
294             "res_nquery root check answers");
295 
296     // Label limit 63
297     std::string exceedingLabelQuery = "www." + std::string(70, 'g') + ".com";
298     // Name limit 255
299     std::string exceedingDomainQuery = "www." + std::string(255, 'g') + ".com";
300 
301     fd = android_res_nquery(handle, exceedingLabelQuery.c_str(), ns_c_in, ns_t_a, 0);
302     EXPECT_EQ(env, -EMSGSIZE, fd, "res_nquery exceedingLabelQuery");
303     fd = android_res_nquery(handle, exceedingDomainQuery.c_str(), ns_c_in, ns_t_aaaa, 0);
304     EXPECT_EQ(env, -EMSGSIZE, fd, "res_nquery exceedingDomainQuery");
305 
306     uint8_t buf[10] = {};
307     // empty BLOB
308     fd = android_res_nsend(handle, buf, 10, 0);
309     EXPECT_GE(env, fd, 0, "res_nsend empty BLOB");
310     EXPECT_EQ(env, 0, expectAnswersNotValid(env, fd, -EINVAL),
311             "res_nsend empty BLOB check answers");
312 
313     uint8_t largeBuf[2 * MAXPACKET] = {};
314     // A buffer larger than 8KB
315     fd = android_res_nsend(handle, largeBuf, sizeof(largeBuf), 0);
316     EXPECT_EQ(env, -EMSGSIZE, fd, "res_nsend buffer larger than 8KB");
317 
318     // 5000 bytes filled with 0. This returns EMSGSIZE because FrameworkListener limits the size of
319     // commands to 4096 bytes.
320     fd = android_res_nsend(handle, largeBuf, 5000, 0);
321     EXPECT_EQ(env, -EMSGSIZE, fd, "res_nsend 5000 bytes filled with 0");
322 
323     // 500 bytes filled with 0
324     fd = android_res_nsend(handle, largeBuf, 500, 0);
325     EXPECT_GE(env, fd, 0, "res_nsend 500 bytes filled with 0");
326     EXPECT_EQ(env, 0, expectAnswersNotValid(env, fd, -EINVAL),
327             "res_nsend 500 bytes filled with 0 check answers");
328 
329     // 5000 bytes filled with 0xFF
330     uint8_t ffBuf[5001] = {};
331     memset(ffBuf, 0xFF, sizeof(ffBuf));
332     ffBuf[5000] = '\0';
333     fd = android_res_nsend(handle, ffBuf, sizeof(ffBuf), 0);
334     EXPECT_EQ(env, -EMSGSIZE, fd, "res_nsend 5000 bytes filled with 0xFF");
335 
336     // 500 bytes filled with 0xFF
337     ffBuf[500] = '\0';
338     fd = android_res_nsend(handle, ffBuf, 501, 0);
339     EXPECT_GE(env, fd, 0, "res_nsend 500 bytes filled with 0xFF");
340     EXPECT_EQ(env, 0, expectAnswersNotValid(env, fd, -EINVAL),
341             "res_nsend 500 bytes filled with 0xFF check answers");
342 }
343 
344 extern "C"
Java_android_net_cts_MultinetworkApiTest_runGetaddrinfoCheck(JNIEnv *,jclass,jlong nethandle)345 JNIEXPORT jint Java_android_net_cts_MultinetworkApiTest_runGetaddrinfoCheck(
346         JNIEnv*, jclass, jlong nethandle) {
347     net_handle_t handle = (net_handle_t) nethandle;
348     struct addrinfo *res = NULL;
349 
350     errno = 0;
351     int rval = android_getaddrinfofornetwork(handle, kHostname, NULL, NULL, &res);
352     const int saved_errno = errno;
353     freeaddrinfo(res);
354 
355     LOGD("android_getaddrinfofornetwork(%" PRIu64 ", %s) returned rval=%d errno=%d",
356           handle, kHostname, rval, saved_errno);
357     return rval == 0 ? 0 : -saved_errno;
358 }
359 
360 extern "C"
Java_android_net_cts_MultinetworkApiTest_runSetprocnetwork(JNIEnv *,jclass,jlong nethandle)361 JNIEXPORT jint Java_android_net_cts_MultinetworkApiTest_runSetprocnetwork(
362         JNIEnv*, jclass, jlong nethandle) {
363     net_handle_t handle = (net_handle_t) nethandle;
364 
365     errno = 0;
366     int rval = android_setprocnetwork(handle);
367     const int saved_errno = errno;
368     LOGD("android_setprocnetwork(%" PRIu64 ") returned rval=%d errno=%d",
369           handle, rval, saved_errno);
370     return rval == 0 ? 0 : -saved_errno;
371 }
372 
373 extern "C"
Java_android_net_cts_MultinetworkApiTest_runSetsocknetwork(JNIEnv *,jclass,jlong nethandle)374 JNIEXPORT jint Java_android_net_cts_MultinetworkApiTest_runSetsocknetwork(
375         JNIEnv*, jclass, jlong nethandle) {
376     net_handle_t handle = (net_handle_t) nethandle;
377 
378     errno = 0;
379     int fd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
380     if (fd < 0) {
381         LOGD("socket() failed, errno=%d", errno);
382         return -errno;
383     }
384 
385     errno = 0;
386     int rval = android_setsocknetwork(handle, fd);
387     const int saved_errno = errno;
388     LOGD("android_setprocnetwork(%" PRIu64 ", %d) returned rval=%d errno=%d",
389           handle, fd, rval, saved_errno);
390     close(fd);
391     return rval == 0 ? 0 : -saved_errno;
392 }
393 
394 // Use sizeof("x") - 1 because we need a compile-time constant, and strlen("x")
395 // isn't guaranteed to fold to a constant.
396 static const int kSockaddrStrLen = INET6_ADDRSTRLEN + sizeof("[]:65535") - 1;
397 
sockaddr_ntop(const struct sockaddr * sa,socklen_t salen,char * dst,const size_t size)398 void sockaddr_ntop(const struct sockaddr *sa, socklen_t salen, char *dst, const size_t size) {
399     char addrstr[INET6_ADDRSTRLEN];
400     char portstr[sizeof("65535")];
401     char buf[kSockaddrStrLen+1];
402 
403     int ret = getnameinfo(sa, salen,
404                           addrstr, sizeof(addrstr),
405                           portstr, sizeof(portstr),
406                           NI_NUMERICHOST | NI_NUMERICSERV);
407     if (ret == 0) {
408         snprintf(buf, sizeof(buf),
409                  (sa->sa_family == AF_INET6) ? "[%s]:%s" : "%s:%s",
410                  addrstr, portstr);
411     } else {
412         sprintf(buf, "???");
413     }
414 
415     strlcpy(dst, buf, size);
416 }
417 
418 extern "C"
Java_android_net_cts_MultinetworkApiTest_runDatagramCheck(JNIEnv *,jclass,jlong nethandle)419 JNIEXPORT jint Java_android_net_cts_MultinetworkApiTest_runDatagramCheck(
420         JNIEnv*, jclass, jlong nethandle) {
421     const struct addrinfo kHints = {
422         .ai_flags = AI_ADDRCONFIG,
423         .ai_family = AF_UNSPEC,
424         .ai_socktype = SOCK_DGRAM,
425         .ai_protocol = IPPROTO_UDP,
426     };
427     struct addrinfo *res = NULL;
428     net_handle_t handle = (net_handle_t) nethandle;
429 
430     static const char kPort[] = "443";
431     int rval = android_getaddrinfofornetwork(handle, kHostname, kPort, &kHints, &res);
432     if (rval != 0) {
433         LOGD("android_getaddrinfofornetwork(%llu, %s) returned rval=%d errno=%d",
434               handle, kHostname, rval, errno);
435         freeaddrinfo(res);
436         return -errno;
437     }
438 
439     // Rely upon getaddrinfo sorting the best destination to the front.
440     int fd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
441     if (fd < 0) {
442         LOGD("socket(%d, %d, %d) failed, errno=%d",
443               res->ai_family, res->ai_socktype, res->ai_protocol, errno);
444         freeaddrinfo(res);
445         return -errno;
446     }
447 
448     rval = android_setsocknetwork(handle, fd);
449     LOGD("android_setprocnetwork(%llu, %d) returned rval=%d errno=%d",
450           handle, fd, rval, errno);
451     if (rval != 0) {
452         close(fd);
453         freeaddrinfo(res);
454         return -errno;
455     }
456 
457     char addrstr[kSockaddrStrLen+1];
458     sockaddr_ntop(res->ai_addr, res->ai_addrlen, addrstr, sizeof(addrstr));
459     LOGD("Attempting connect() to %s ...", addrstr);
460 
461     rval = connect(fd, res->ai_addr, res->ai_addrlen);
462     if (rval != 0) {
463         close(fd);
464         freeaddrinfo(res);
465         return -errno;
466     }
467     freeaddrinfo(res);
468 
469     struct sockaddr_storage src_addr;
470     socklen_t src_addrlen = sizeof(src_addr);
471     if (getsockname(fd, (struct sockaddr *)&src_addr, &src_addrlen) != 0) {
472         close(fd);
473         return -errno;
474     }
475     sockaddr_ntop((const struct sockaddr *)&src_addr, sizeof(src_addr), addrstr, sizeof(addrstr));
476     LOGD("... from %s", addrstr);
477 
478     // Don't let reads or writes block indefinitely.
479     const struct timeval timeo = { 2, 0 };  // 2 seconds
480     setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &timeo, sizeof(timeo));
481     setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &timeo, sizeof(timeo));
482 
483     // For reference see:
484     //     https://datatracker.ietf.org/doc/html/draft-ietf-quic-invariants
485     uint8_t quic_packet[1200] = {
486         0xc0,                    // long header
487         0xaa, 0xda, 0xca, 0xca,  // reserved-space version number
488         0x08,                    // destination connection ID length
489         0, 0, 0, 0, 0, 0, 0, 0,  // 64bit connection ID
490         0x00,                    // source connection ID length
491     };
492 
493     arc4random_buf(quic_packet + 6, 8);  // random connection ID
494 
495     uint8_t response[1500];
496     ssize_t sent, rcvd;
497     static const int MAX_RETRIES = 5;
498     int i, errnum = 0;
499 
500     for (i = 0; i < MAX_RETRIES; i++) {
501         sent = send(fd, quic_packet, sizeof(quic_packet), 0);
502         if (sent < (ssize_t)sizeof(quic_packet)) {
503             errnum = errno;
504             LOGD("send(QUIC packet) returned sent=%zd, errno=%d", sent, errnum);
505             close(fd);
506             return -errnum;
507         }
508 
509         rcvd = recv(fd, response, sizeof(response), 0);
510         if (rcvd > 0) {
511             break;
512         } else {
513             errnum = errno;
514             LOGD("[%d/%d] recv(QUIC response) returned rcvd=%zd, errno=%d",
515                   i + 1, MAX_RETRIES, rcvd, errnum);
516         }
517     }
518     if (rcvd < 15) {
519         LOGD("QUIC UDP %s: sent=%zd but rcvd=%zd, errno=%d", kPort, sent, rcvd, errnum);
520         if (rcvd <= 0) {
521             LOGD("Does this network block UDP port %s?", kPort);
522         }
523         close(fd);
524         return -EPROTO;
525     }
526 
527     int conn_id_cmp = memcmp(quic_packet + 6, response + 7, 8);
528     if (conn_id_cmp != 0) {
529         LOGD("sent and received connection IDs do not match");
530         close(fd);
531         return -EPROTO;
532     }
533 
534     // TODO: Replace this quick 'n' dirty test with proper QUIC-capable code.
535 
536     close(fd);
537     return 0;
538 }
539