434 lines
16 KiB
Plaintext
434 lines
16 KiB
Plaintext
.\" Automatically generated by Pod::Man 2.28 (Pod::Simple 3.29)
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.\" ========================================================================
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.\"
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.IX Title "OSSL-GUIDE-QUIC-SERVER-BLOCK 7ossl"
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.TH OSSL-GUIDE-QUIC-SERVER-BLOCK 7ossl "2025-04-23" "3.5.1-dev" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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ossl\-guide\-quic\-server\-block
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\&\- OpenSSL Guide: Writing a simple blocking QUIC server
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.SH "SIMPLE BLOCKING QUIC SERVER EXAMPLE"
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.IX Header "SIMPLE BLOCKING QUIC SERVER EXAMPLE"
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This page will present various source code samples demonstrating how to write a
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simple, non-concurrent, \s-1QUIC \s0\*(L"echo\*(R" server application which accepts one client
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connection at a time, echoing input from the client back to the same client.
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Once the current client disconnects, the next client connection is accepted.
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.PP
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The server only accepts \s-1HTTP/1.0\s0 requests, which is non-standard and will not
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be supported by real world servers. This is for demonstration purposes only.
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.PP
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Both the accepting socket and client connections are \*(L"blocking\*(R". A more typical
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server might use nonblocking sockets with an event loop and callbacks for I/O
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events.
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.PP
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The complete source code for this example blocking \s-1QUIC\s0 server is available in
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the \fBdemos/guide\fR directory of the OpenSSL source distribution in the file
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\&\fBquic\-server\-block.c\fR. It is also available online at
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<https://github.com/openssl/openssl/blob/master/demos/guide/quic\-server\-block.c>.
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.PP
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We assume that you already have OpenSSL installed on your system; that you
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already have some fundamental understanding of OpenSSL concepts and \s-1QUIC \s0(see
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\&\fIossl\-guide\-libraries\-introduction\fR\|(7) and \fIossl\-guide\-quic\-introduction\fR\|(7));
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and that you know how to write and build C code and link it against the
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libcrypto and libssl libraries that are provided by OpenSSL. It also assumes
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that you have a basic understanding of \s-1UDP/IP\s0 and sockets.
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.SS "Creating the \s-1SSL_CTX\s0 and \s-1SSL\s0 objects"
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.IX Subsection "Creating the SSL_CTX and SSL objects"
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The first step is to create an \fB\s-1SSL_CTX\s0\fR object for our server. We use the
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\&\fISSL_CTX_new\fR\|(3) function for this purpose. We pass as an argument the return
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value of the function \fIOSSL_QUIC_server_method\fR\|(3). You should use this method
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whenever you are writing a \s-1QUIC\s0 server.
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.PP
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.Vb 8
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\& /*
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\& * An SSL_CTX holds shared configuration information for multiple
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\& * subsequent per\-client SSL connections. We specifically load a QUIC
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\& * server method here.
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\& */
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\& ctx = SSL_CTX_new(OSSL_QUIC_server_method());
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\& if (ctx == NULL)
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\& goto err;
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.Ve
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.PP
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Servers need a private key and certificate. Intermediate issuer \s-1CA\s0
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certificates are often required, and both the server (end-entity or \s-1EE\s0)
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certificate and the issuer (\*(L"chain\*(R") certificates are most easily configured in
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a single \*(L"chain file\*(R". Below we load such a chain file (the \s-1EE\s0 certificate
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must appear first), and then load the corresponding private key, checking that
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it matches the server certificate. No checks are performed to check the
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integrity of the chain (\s-1CA\s0 signatures or certificate expiration dates, for
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example), but we do verify the consistency of the private key with the
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corresponding certificate.
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.PP
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.Vb 10
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\& /*
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\& * Load the server\*(Aqs certificate *chain* file (PEM format), which includes
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\& * not only the leaf (end\-entity) server certificate, but also any
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\& * intermediate issuer\-CA certificates. The leaf certificate must be the
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\& * first certificate in the file.
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\& *
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\& * In advanced use\-cases this can be called multiple times, once per public
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\& * key algorithm for which the server has a corresponding certificate.
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\& * However, the corresponding private key (see below) must be loaded first,
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\& * *before* moving on to the next chain file.
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\& */
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\& if (SSL_CTX_use_certificate_chain_file(ctx, cert_path) <= 0) {
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\& fprintf(stderr, "couldn\*(Aqt load certificate file: %s\en", cert_path);
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\& goto err;
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\& }
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\&
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\& /*
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\& * Load the corresponding private key, this also checks that the private
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\& * key matches the just loaded end\-entity certificate. It does not check
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\& * whether the certificate chain is valid, the certificates could be
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\& * expired, or may otherwise fail to form a chain that a client can
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\& * validate.
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\& */
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\& if (SSL_CTX_use_PrivateKey_file(ctx, key_path, SSL_FILETYPE_PEM) <= 0) {
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\& fprintf(stderr, "couldn\*(Aqt load key file: %s\en", key_path);
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\& goto err;
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\& }
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.Ve
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.PP
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Most servers, including this one, do not solicit client certificates. We
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therefore do not need a \*(L"trust store\*(R" and allow the handshake to complete even
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when the client does not present a certificate. Note: Even if a client did
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present a trusted certificate, for it to be useful, the server application
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would still need custom code to use the verified identity to grant nondefault
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access to that particular client. Some servers grant access to all clients
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with certificates from a private \s-1CA,\s0 this then requires processing of
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certificate revocation lists to deauthorise a client. It is often simpler and
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more secure to instead keep a list of authorised public keys.
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.PP
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Though this is the default setting, we explicitly call the
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\&\fISSL_CTX_set_verify\fR\|(3) function and pass the \fB\s-1SSL_VERIFY_NONE\s0\fR value to it.
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The final argument to this function is a callback that you can optionally
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supply to override the default handling for certificate verification. Most
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|
applications do not need to do this so this can safely be set to \s-1NULL\s0 to get
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the default handling.
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.PP
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|
.Vb 12
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|
\& /*
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|
\& * Clients rarely employ certificate\-based authentication, and so we don\*(Aqt
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|
\& * require "mutual" TLS authentication (indeed there\*(Aqs no way to know
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|
\& * whether or how the client authenticated the server, so the term "mutual"
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|
\& * is potentially misleading).
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\& *
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|
\& * Since we\*(Aqre not soliciting or processing client certificates, we don\*(Aqt
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\& * need to configure a trusted\-certificate store, so no call to
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\& * SSL_CTX_set_default_verify_paths() is needed. The server\*(Aqs own
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\& * certificate chain is assumed valid.
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\& */
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\& SSL_CTX_set_verify(ctx, SSL_VERIFY_NONE, NULL);
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.Ve
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.PP
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\&\s-1QUIC\s0 also dictates using Application-Layer Protocol Negotiation (\s-1ALPN\s0) to select
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an application protocol. We use \fISSL_CTX_set_alpn_select_cb\fR\|(3) for this
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|
purpose. We can pass a callback which will be called for each connection to
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select an \s-1ALPN\s0 the server considers acceptable.
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.PP
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|
.Vb 2
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|
\& /* Setup ALPN negotiation callback to decide which ALPN is accepted. */
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|
\& SSL_CTX_set_alpn_select_cb(ctx, select_alpn, NULL);
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.Ve
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.PP
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In this case, we only accept \*(L"http/1.0\*(R" and \*(L"hq-interop\*(R".
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.PP
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.Vb 8
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|
\& /*
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|
\& * ALPN strings for TLS handshake. Only \*(Aqhttp/1.0\*(Aq and \*(Aqhq\-interop\*(Aq
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|
\& * are accepted.
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|
\& */
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\& static const unsigned char alpn_ossltest[] = {
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\& 8, \*(Aqh\*(Aq, \*(Aqt\*(Aq, \*(Aqt\*(Aq, \*(Aqp\*(Aq, \*(Aq/\*(Aq, \*(Aq1\*(Aq, \*(Aq.\*(Aq, \*(Aq0\*(Aq,
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|
\& 10, \*(Aqh\*(Aq, \*(Aqq\*(Aq, \*(Aq\-\*(Aq, \*(Aqi\*(Aq, \*(Aqn\*(Aq, \*(Aqt\*(Aq, \*(Aqe\*(Aq, \*(Aqr\*(Aq, \*(Aqo\*(Aq, \*(Aqp\*(Aq,
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|
\& };
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\&
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\& static int select_alpn(SSL *ssl, const unsigned char **out,
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\& unsigned char *out_len, const unsigned char *in,
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\& unsigned int in_len, void *arg)
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|
\& {
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|
\& if (SSL_select_next_proto((unsigned char **)out, out_len, alpn_ossltest,
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|
\& sizeof(alpn_ossltest), in,
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|
\& in_len) == OPENSSL_NPN_NEGOTIATED)
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|
\& return SSL_TLSEXT_ERR_OK;
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\& return SSL_TLSEXT_ERR_ALERT_FATAL;
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|
\& }
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.Ve
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.PP
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|
That is all the setup that we need to do for the \fB\s-1SSL_CTX\s0\fR. Next, we create a
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\&\s-1UDP\s0 socket and bind to it on localhost.
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|
.PP
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|
.Vb 5
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|
\& /* Retrieve the file descriptor for a new UDP socket */
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|
\& if ((fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
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|
\& fprintf(stderr, "cannot create socket");
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|
\& goto err;
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|
\& }
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\&
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\& sa.sin_family = AF_INET;
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|
\& sa.sin_port = htons(port);
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|
\&
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|
\& /* Bind to the new UDP socket on localhost */
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|
\& if (bind(fd, (const struct sockaddr *)&sa, sizeof(sa)) < 0) {
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|
\& fprintf(stderr, "cannot bind to %u\en", port);
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|
\& BIO_closesocket(fd);
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|
\& goto err;
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|
\& }
|
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.Ve
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|
.PP
|
|
To run the \s-1QUIC\s0 server, we create an \fB\s-1SSL_LISTENER\s0\fR to listen for incoming
|
|
connections. We provide it with the bound \s-1UDP\s0 port to then explicitly begin
|
|
listening for new connections.
|
|
.PP
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|
.Vb 8
|
|
\& /*
|
|
\& * Create a new QUIC listener. Listeners, and other QUIC objects, default
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|
\& * to operating in blocking mode. The configured behaviour is inherited by
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|
\& * child objects.
|
|
\& */
|
|
\& if ((listener = SSL_new_listener(ctx, 0)) == NULL) {
|
|
\& goto err;
|
|
\& }
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|
\&
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|
\& /* Provide the listener with our UDP socket. */
|
|
\& if (!SSL_set_fd(listener, fd))
|
|
\& goto err;
|
|
\&
|
|
\& /* Begin listening. */
|
|
\& if (!SSL_listen(listener))
|
|
\& goto err;
|
|
.Ve
|
|
.SS "Server loop"
|
|
.IX Subsection "Server loop"
|
|
The server now enters a \*(L"forever\*(R" loop, handling one client connection at a
|
|
time. Before each connection, we clear the OpenSSL error stack so that any
|
|
error reports are related to just the new connection.
|
|
.PP
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|
.Vb 2
|
|
\& /* Pristine error stack for each new connection */
|
|
\& ERR_clear_error();
|
|
.Ve
|
|
.PP
|
|
At this point, the server blocks to accept the next client.
|
|
\&\fISSL_accept_connection\fR\|(3) will return an accepted connection within a fresh
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|
\&\s-1SSL,\s0 in which the handshake will have already occurred.
|
|
.PP
|
|
.Vb 6
|
|
\& /* Block while waiting for a client connection */
|
|
\& conn = SSL_accept_connection(listener, 0);
|
|
\& if (conn == NULL) {
|
|
\& fprintf(stderr, "error while accepting connection\en");
|
|
\& goto err;
|
|
\& }
|
|
.Ve
|
|
.PP
|
|
With the handshake complete, the server echoes client input back to the client
|
|
in a loop.
|
|
.PP
|
|
.Vb 8
|
|
\& while (SSL_read_ex(conn, buf, sizeof(buf), &nread) > 0) {
|
|
\& if (SSL_write_ex(conn, buf, nread, &nwritten) > 0 &&
|
|
\& nwritten == nread) {
|
|
\& continue;
|
|
\& }
|
|
\& fprintf(stderr, "Error echoing client input");
|
|
\& break;
|
|
\& }
|
|
.Ve
|
|
.PP
|
|
Once the client closes its connection, we signal the end of the stream by using
|
|
\&\fISSL_stream_conclude\fR\|(3). This will send a final Finished packet to the
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|
client.
|
|
.PP
|
|
.Vb 6
|
|
\& /* Signal the end of the stream. */
|
|
\& if (SSL_stream_conclude(conn, 0) != 1) {
|
|
\& fprintf(stderr, "Unable to conclude stream\en");
|
|
\& SSL_free(conn);
|
|
\& goto err;
|
|
\& }
|
|
.Ve
|
|
.PP
|
|
We then shut down the connection with \fISSL_shutdown_ex\fR\|(3), which may need
|
|
to be called multiple times to ensure the connection is shutdown completely.
|
|
.PP
|
|
.Vb 4
|
|
\& while (SSL_shutdown_ex(conn, 0, &shutdown_args,
|
|
\& sizeof(SSL_SHUTDOWN_EX_ARGS)) != 1) {
|
|
\& fprintf(stderr, "Re\-attempting SSL shutdown\en");
|
|
\& }
|
|
.Ve
|
|
.PP
|
|
Finally, we free the \s-1SSL\s0 connection, and the server is now ready to accept the
|
|
next client connection.
|
|
.PP
|
|
.Vb 1
|
|
\& SSL_free(conn);
|
|
.Ve
|
|
.SS "Final clean up"
|
|
.IX Subsection "Final clean up"
|
|
If the server somehow manages to break out of the infinite loop and
|
|
be ready to exit, it would deallocate the constructed \fB\s-1SSL\s0\fR.
|
|
.PP
|
|
.Vb 1
|
|
\& SSL_free(listener);
|
|
.Ve
|
|
.PP
|
|
And in the main function, it would deallocate the constructed \fB\s-1SSL_CTX\s0\fR.
|
|
.PP
|
|
.Vb 4
|
|
\& SSL_CTX_free(ctx);
|
|
\& BIO_closesocket(fd);
|
|
\& res = EXIT_SUCCESS;
|
|
\& return res;
|
|
.Ve
|
|
.SH "SEE ALSO"
|
|
.IX Header "SEE ALSO"
|
|
\&\fIossl\-guide\-introduction\fR\|(7), \fIossl\-guide\-libraries\-introduction\fR\|(7),
|
|
\&\fIossl\-guide\-libssl\-introduction\fR\|(7), \fIossl\-guide\-quic\-introduction\fR\|(7),
|
|
\&\fIossl\-guide\-quic\-client\-non\-block\fR\|(7), \fIossl\-guide\-quic\-client\-block\fR\|(7),
|
|
\&\fIossl\-guide\-tls\-server\-block\fR\|(7), \fIossl\-guide\-quic\-server\-non\-block\fR\|(7)
|
|
.SH "COPYRIGHT"
|
|
.IX Header "COPYRIGHT"
|
|
Copyright 2024\-2025 The OpenSSL Project Authors. All Rights Reserved.
|
|
.PP
|
|
Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
|
|
this file except in compliance with the License. You can obtain a copy
|
|
in the file \s-1LICENSE\s0 in the source distribution or at
|
|
<https://www.openssl.org/source/license.html>.
|