1TLS_READ(3) BSD Library Functions Manual TLS_READ(3)
2
4 tls_read, tls_write, tls_handshake, tls_error, tls_close, tls_reset — use
5 a TLS connection
6
8 #include <tls.h>
9 ssize_t
11 tls_read(struct tls *ctx, void *buf, size_t buflen);
12 ssize_t
14 tls_write(struct tls *ctx, const void *buf, size_t buflen);
15 int
17 tls_handshake(struct tls *ctx);
18 const char *
20 tls_error(struct tls *ctx);
21 int
23 tls_close(struct tls *ctx);
24 void
26 tls_reset(struct tls *ctx);
27
29 tls_read() reads buflen bytes of data from the socket into buf. It
30 returns the amount of data read.
31 tls_write() writes buflen bytes of data from buf to the socket. It
33 returns the amount of data written.
34 tls_handshake() explicitly performs the TLS handshake. It is only neces‐
36 sary to call this function if you need to guarantee that the handshake
37 has completed, as both tls_read() and tls_write() automatically perform
38 the TLS handshake when necessary.
39 The tls_error() function may be used to retrieve a string containing more
41 information about the most recent error relating to a context.
42 tls_close() closes a connection after use. Only the TLS layer will be
44 shut down and the caller is responsible for closing the file descriptors,
45 unless the connection was established using tls_connect(3) or
46 tls_connect_servername(3). After closing the connection, ctx can be
47 passed to tls_free(3).
48
50 tls_read() and tls_write() return a size on success or -1 on error.
51 tls_handshake() and tls_close() return 0 on success or -1 on error.
53 The tls_read(), tls_write(), tls_handshake(), and tls_close() functions
55 also have two special return values:
56 TLS_WANT_POLLIN The underlying read file descriptor needs to be
58 readable in order to continue.
59 TLS_WANT_POLLOUT The underlying write file descriptor needs to be
60 writeable in order to continue.
61 In the case of blocking file descriptors, the same function call should
63 be repeated immediately. In the case of non-blocking file descriptors,
64 the same function call should be repeated when the required condition has
65 been met.
66 Callers of these functions cannot rely on the value of the global errno.
68 To prevent mishandling of error conditions, tls_read(), tls_write(),
69 tls_handshake(), and tls_close() all explicitly clear errno.
70 tls_error() returns NULL if no error occurred with ctx during or since
72 the last call to tls_handshake(), tls_read(), tls_write(), tls_close(),
73 or tls_reset() involving ctx, or if memory allocation failed while trying
74 to assemble the string describing the most recent error related to ctx.
75
77 The following example demonstrates how to handle TLS writes on a blocking
78 file descriptor:
79 ...
81 while (len > 0) {
82 ssize_t ret;
83 ret = tls_write(ctx, buf, len);
85 if (ret == TLS_WANT_POLLIN || ret == TLS_WANT_POLLOUT)
86 continue;
87 if (ret == -1)
88 errx(1, "tls_write: %s", tls_error(ctx));
89 buf += ret;
90 len -= ret;
91 }
92 ...
93 The following example demonstrates how to handle TLS writes on a non-
95 blocking file descriptor using poll(2):
96 ...
98 pfd[0].fd = fd;
99 pfd[0].events = POLLIN|POLLOUT;
100 while (len > 0) {
101 nready = poll(pfd, 1, 0);
102 if (nready == -1)
103 err(1, "poll");
104 if ((pfd[0].revents & (POLLERR|POLLNVAL)))
105 errx(1, "bad fd %d", pfd[0].fd);
106 if ((pfd[0].revents & (pfd[0].events|POLLHUP))) {
107 ssize_t ret;
108 ret = tls_write(ctx, buf, len);
110 if (ret == TLS_WANT_POLLIN)
111 pfd[0].events = POLLIN;
112 else if (ret == TLS_WANT_POLLOUT)
113 pfd[0].events = POLLOUT;
114 else if (ret == -1)
115 errx(1, "tls_write: %s", tls_error(ctx));
116 else {
117 buf += ret;
118 len -= ret;
119 }
120 }
121 }
122 ...
123
125 tls_accept_socket(3), tls_configure(3), tls_conn_version(3),
126 tls_connect(3), tls_init(3), tls_ocsp_process_response(3)
127
129 tls_read(), tls_write(), tls_error(), tls_close(), and tls_reset()
130 appeared in OpenBSD 5.6 and got their final names in OpenBSD 5.7.
131 tls_handshake() appeared in OpenBSD 5.9.
133
135 Joel Sing <jsing@openbsd.org> with contributions from
136 Bob Beck <beck@openbsd.org>
137
139 The function tls_error() returns an internal pointer. It must not be
140 freed by the application, or a double free error will occur. The pointer
141 will become invalid when the next error occurs with ctx. Consequently,
142 if the application may need the message at a later time, it has to copy
143 the string before calling the next libtls function involving ctx, or a
144 segmentation fault or read access to unintended data is the likely
145 result.
146BSD July 9, 2019 BSD