对于https，在tcp三次握手后就会进行ssl的握手，ssl握手的详细过程网上介绍的不少。下面跟踪下okhttp3对于ssl握手的实现过程。java

在okhttp3.internal.io.RealConnection#connectSocket中git

private void connectSocket(int connectTimeout, int readTimeout, int writeTimeout,

ConnectionSpecSelector connectionSpecSelector) throws IOException {

rawSocket.setSoTimeout(readTimeout);

try {

Platform.get().connectSocket(rawSocket, route.socketAddress(), connectTimeout);

} catch (ConnectException e) {

throw new ConnectException("Failed to connect to " + route.socketAddress());

}

source = Okio.buffer(Okio.source(rawSocket));

sink = Okio.buffer(Okio.sink(rawSocket));

if (route.address().sslSocketFactory() != null) {

connectTls(readTimeout, writeTimeout, connectionSpecSelector);

} else {

protocol = Protocol.HTTP_1_1;

socket = rawSocket;

}

。。。

}

首先tcp三次握手：Platform.get().connectSocket

其次得到I/O流：source = Okio.buffer(Okio.source(rawSocket));sink = Okio.buffer(Okio.sink(rawSocket));

而后判断是否须要ssl，若是须要则进行ssl：connectTls(readTimeout, writeTimeout, connectionSpecSelector);github

在connectTls中，忽略其余的，ssl握手发生在web

sslSocket.startHandshake();

startHandshake的实如今org.conscrypt.OpenSSLSocketImpl#startHandshake中，

(/libcore/crypto/src/main/java/org/conscrypt/OpenSSLSocketImpl.java)app

@Override public synchronized void startHandshake() throws IOException {

。。。

int sslSessionNativePointer;

try {

sslSessionNativePointer = NativeCrypto.SSL_do_handshake(sslNativePointer,

socket.getFileDescriptor$(), this, getSoTimeout(), client, npnProtocols,client ? null : alpnProtocols);

} catch (CertificateException e) {

SSLHandshakeException wrapper = new SSLHandshakeException(e.getMessage());

wrapper.initCause(e);

throw wrapper;

}

。。。

}

调用的是native函数NativeCrypto.SSL_do_handshake()，实如今/libcore/crypto/src/main/native/org_conscrypt_NativeCrypto.cpp中，取出关键部分进行分析socket

static jlong NativeCrypto_SSL_do_handshake(JNIEnv* env, jclass, jlong ssl_address, jobject fdObject,jobject shc, jint timeout_millis, jboolean client_mode, jbyteArray npnProtocols,

jbyteArray alpnProtocols) {

。。。

/*

* Make socket non-blocking, so SSL_connect SSL_read() and SSL_write() don't hang

* forever and we can use select() to find out if the socket is ready.

*/

if (!setBlocking(fd.get(), false)) {

throwSSLExceptionStr(env, "Unable to make socket non blocking");

SSL_clear(ssl);

JNI_TRACE("ssl=%p NativeCrypto_SSL_do_handshake setBlocking => 0", ssl);

return 0;

}

。。。

ret = 0;

while (appData->aliveAndKicking) {

errno = 0;

if (!appData->setCallbackState(env, shc, fdObject, npnProtocols, alpnProtocols)) {

// SocketException thrown by NetFd.isClosed

SSL_clear(ssl);

JNI_TRACE("ssl=%p NativeCrypto_SSL_do_handshake setCallbackState => 0", ssl);

return 0;

}

ret = SSL_do_handshake(ssl);

appData->clearCallbackState();

// cert_verify_callback threw exception

if (env->ExceptionCheck()) {

SSL_clear(ssl);

JNI_TRACE("ssl=%p NativeCrypto_SSL_do_handshake exception => 0", ssl);

return 0;

}

// success case

if (ret == 1) {

break;

}

// retry case

if (errno == EINTR) {

continue;

}

// error case

int sslError = SSL_get_error(ssl, ret);

JNI_TRACE("ssl=%p NativeCrypto_SSL_do_handshake ret=%d errno=%d sslError=%d timeout_millis=%d",

ssl, ret, errno, sslError, timeout_millis);

/*

* If SSL_do_handshake doesn't succeed due to the socket being

* either unreadable or unwritable, we use sslSelect to

* wait for it to become ready. If that doesn't happen

* before the specified timeout or an error occurs, we

* cancel the handshake. Otherwise we try the SSL_connect

* again.

*/

if (sslError == SSL_ERROR_WANT_READ || sslError == SSL_ERROR_WANT_WRITE) {

appData->waitingThreads++;

int selectResult = sslSelect(env, sslError, fdObject, appData, timeout_millis);

if (selectResult == THROWN_EXCEPTION) {

// SocketException thrown by NetFd.isClosed

SSL_clear(ssl);

JNI_TRACE("ssl=%p NativeCrypto_SSL_do_handshake sslSelect => 0", ssl);

return 0;

}

if (selectResult == -1) {

throwSSLExceptionWithSslErrors(env, ssl, SSL_ERROR_SYSCALL, "handshake error");

SSL_clear(ssl);

JNI_TRACE("ssl=%p NativeCrypto_SSL_do_handshake selectResult == -1 => 0", ssl);

return 0;

}

if (selectResult == 0) {

throwSocketTimeoutException(env, "SSL handshake timed out");

SSL_clear(ssl);

freeOpenSslErrorState();

JNI_TRACE("ssl=%p NativeCrypto_SSL_do_handshake selectResult == 0 => 0", ssl);

return 0;

}

} else {

// ALOGE("Unknown error %d during handshake", error);

break;

}

}

// clean error. See SSL_do_handshake(3SSL) man page.

if (ret == 0) {

/*

* The other side closed the socket before the handshake could be

* completed, but everything is within the bounds of the TLS protocol.

* We still might want to find out the real reason of the failure.

*/

int sslError = SSL_get_error(ssl, ret);

if (sslError == SSL_ERROR_NONE || (sslError == SSL_ERROR_SYSCALL && errno == 0)) {

throwSSLExceptionStr(env, "Connection closed by peer");

} else {

throwSSLExceptionWithSslErrors(env, ssl, sslError, "SSL handshake terminated");

}

SSL_clear(ssl);

JNI_TRACE("ssl=%p NativeCrypto_SSL_do_handshake clean error => 0", ssl);

return 0;

}

// unclean error. See SSL_do_handshake(3SSL) man page.

if (ret < 0) {

/*

* Translate the error and throw exception. We are sure it is an error

* at this point.

*/

int sslError = SSL_get_error(ssl, ret);

throwSSLExceptionWithSslErrors(env, ssl, sslError, "SSL handshake aborted");

SSL_clear(ssl);

JNI_TRACE("ssl=%p NativeCrypto_SSL_do_handshake unclean error => 0", ssl);

return 0;

}

。。。

}

(1)设置SSL为非阻塞模式

(2)在while里调用openssl的SSL_do_handshake进行握手，返回后检查是否握手成功了，成功则直接跳出while

(3)若是不成功，则检查是不是由于socket不能读写形成的

(4)若是是由于socket此时不能读写，则调用sellect进行等待，这次握手成功则返回，这次失败则继续while，即回到(2)

(5)若是不是由于socket读写的缘由，则握手失败，跳出while，进行失败缘由判断tcp