OSSL_HTTP_TRANSFER(3ossl) OpenSSL OSSL_HTTP_TRANSFER(3ossl)
NAME
OSSL_HTTP_open, OSSL_HTTP_bio_cb_t, OSSL_HTTP_proxy_connect,
OSSL_HTTP_set1_request, OSSL_HTTP_exchange, OSSL_HTTP_get,
OSSL_HTTP_transfer, OSSL_HTTP_close - HTTP client high-level functions
SYNOPSIS
#include <openssl/http.h>
typedef BIO *(*OSSL_HTTP_bio_cb_t)(BIO *bio, void *arg,
int connect, int detail);
OSSL_HTTP_REQ_CTX *OSSL_HTTP_open(const char *server, const char *port,
const char *proxy, const char *no_proxy,
int use_ssl, BIO *bio, BIO *rbio,
OSSL_HTTP_bio_cb_t bio_update_fn, void *arg,
int buf_size, int overall_timeout);
int OSSL_HTTP_proxy_connect(BIO *bio, const char *server, const char *port,
const char *proxyuser, const char *proxypass,
int timeout, BIO *bio_err, const char *prog);
int OSSL_HTTP_set1_request(OSSL_HTTP_REQ_CTX *rctx, const char *path,
const STACK_OF(CONF_VALUE) *headers,
const char *content_type, BIO *req,
const char *expected_content_type, int expect_asn1,
size_t max_resp_len, int timeout, int keep_alive);
BIO *OSSL_HTTP_exchange(OSSL_HTTP_REQ_CTX *rctx, char **redirection_url);
BIO *OSSL_HTTP_get(const char *url, const char *proxy, const char *no_proxy,
BIO *bio, BIO *rbio,
OSSL_HTTP_bio_cb_t bio_update_fn, void *arg,
int buf_size, const STACK_OF(CONF_VALUE) *headers,
const char *expected_content_type, int expect_asn1,
size_t max_resp_len, int timeout);
BIO *OSSL_HTTP_transfer(OSSL_HTTP_REQ_CTX **prctx,
const char *server, const char *port,
const char *path, int use_ssl,
const char *proxy, const char *no_proxy,
BIO *bio, BIO *rbio,
OSSL_HTTP_bio_cb_t bio_update_fn, void *arg,
int buf_size, const STACK_OF(CONF_VALUE) *headers,
const char *content_type, BIO *req,
const char *expected_content_type, int expect_asn1,
size_t max_resp_len, int timeout, int keep_alive);
int OSSL_HTTP_close(OSSL_HTTP_REQ_CTX *rctx, int ok);
DESCRIPTION
OSSL_HTTP_open() initiates an HTTP session using the bio argument if not
NULL, else by connecting to a given server optionally via a proxy.
Typically the OpenSSL build supports sockets and the bio parameter is
NULL. In this case rbio must be NULL as well and the server must be non-
NULL. The function creates a network BIO internally using
BIO_new_connect(3) for connecting to the given server and the optionally
given port, defaulting to 80 for HTTP or 443 for HTTPS. Then this
internal BIO is used for setting up a connection and for exchanging one
or more request and response.
If bio is given and rbio is NULL then this bio is used instead. If both
bio and rbio are given (which may be memory BIOs for instance) then no
explicit connection is set up, but bio is used for writing requests and
rbio for reading responses. As soon as the client has flushed bio the
server must be ready to provide a response or indicate a waiting
condition via rbio.
If bio is given, it is an error to provide non-NULL proxy or no_proxy
arguments, while server and port arguments may be given to support
diagnostic output. If bio is NULL the optional proxy parameter can be
used to set an HTTP(S) proxy to use (unless overridden by "no_proxy"
settings). If TLS is not used this defaults to the environment variable
"http_proxy" if set, else "HTTP_PROXY". If use_ssl != 0 it defaults to
"https_proxy" if set, else "HTTPS_PROXY". An empty proxy string ""
forbids using a proxy. Otherwise, the format is
"[http[s]://][userinfo@]host[:port][/path][?query][#fragment]", where any
userinfo, path, query, and fragment given is ignored. If the host string
is an IPv6 address, it must be enclosed in "[" and "]". The default
proxy port number is 80, or 443 in case "https:" is given. The HTTP
client functions connect via the given proxy unless the server is found
in the optional list no_proxy of proxy hostnames or IP addresses
separated by "," and/or whitespace (if not NULL; default is the
environment variable "no_proxy" if set, else "NO_PROXY"). Proxying plain
HTTP is supported directly, while using a proxy for HTTPS connections
requires a suitable callback function such as OSSL_HTTP_proxy_connect(),
described below.
If use_ssl is nonzero a TLS connection is requested and the bio_update_fn
parameter must be provided.
The parameter bio_update_fn, which is optional if use_ssl is 0, may be
used to modify the connection BIO used by the HTTP client, but cannot be
used when both bio and rbio are given. bio_update_fn is a BIO
connect/disconnect callback function with prototype
BIO *(*OSSL_HTTP_bio_cb_t)(BIO *bio, void *arg, int connect, int detail)
The callback function may modify the BIO provided in the bio argument,
whereby it may use an optional custom defined argument arg, which can for
instance point to an SSL_CTX structure. During connection establishment,
just after calling BIO_do_connect_retry(), the callback function is
invoked with the connect argument being 1 and detail being 1 if use_ssl
is nonzero (i.e., HTTPS is requested), else 0. On disconnect connect is
0 and detail is 1 if no error occurred, else 0. For instance, on connect
the callback may push an SSL BIO to implement HTTPS; after disconnect it
may do some diagnostic output and pop and free the SSL BIO.
The callback function must return either the potentially modified BIO bio
or NULL to indicate failure, in which case it should not modify the BIO.
Here is a simple example that supports TLS connections (but not via a
proxy):
BIO *http_tls_cb(BIO *bio, void *arg, int connect, int detail)
{
if (connect && detail) { /* connecting with TLS */
SSL_CTX *ctx = (SSL_CTX *)arg;
BIO *sbio = BIO_new_ssl(ctx, 1);
bio = sbio != NULL ? BIO_push(sbio, bio) : NULL;
} else if (!connect) { /* disconnecting */
BIO *hbio;
if (!detail) { /* an error has occurred */
/* optionally add diagnostics here */
}
BIO_ssl_shutdown(bio);
hbio = BIO_pop(bio);
BIO_free(bio); /* SSL BIO */
bio = hbio;
}
return bio;
}
After disconnect the modified BIO will be deallocated using
BIO_free_all(). The optional callback function argument arg is not
consumed, so must be freed by the caller when not needed any more.
The buf_size parameter specifies the response header maximum line length.
A value <= 0 means that the OSSL_HTTP_DEFAULT_MAX_LINE_LEN (4KiB) is
used. buf_size is also used as the number of content bytes that are read
at a time.
If the overall_timeout parameter is > 0 this indicates the maximum number
of seconds the overall HTTP transfer (i.e., connection setup if needed,
sending requests, and receiving responses) is allowed to take until
completion. A value <= 0 enables waiting indefinitely, i.e., no timeout.
OSSL_HTTP_proxy_connect() may be used by an above BIO connect callback
function to set up an SSL/TLS connection via an HTTPS proxy. It promotes
the given BIO bio representing a connection pre-established with a TLS
proxy using the HTTP CONNECT method, optionally using proxy client
credentials proxyuser and proxypass, to connect with TLS protection
ultimately to server and port. If the port argument is NULL or the empty
string it defaults to "443". The server and port arguments must not
contain CR or LF characters. If the timeout parameter is > 0 this
indicates the maximum number of seconds the connection setup is allowed
to take. A value <= 0 enables waiting indefinitely, i.e., no timeout.
Since this function is typically called by applications such as
openssl-s_client(1) it uses the bio_err and prog parameters (unless NULL)
to print additional diagnostic information in a user-oriented way.
OSSL_HTTP_set1_request() sets up in rctx the request header and content
data and expectations on the response using the following parameters. If
<rctx> indicates using a proxy for HTTP (but not HTTPS), the server host
(and optionally port) needs to be placed in the header; thus it must be
present in rctx. For backward compatibility, the server (and optional
port) may also be given in the path argument beginning with "http://"
(thus giving an absoluteURI). If path is NULL it defaults to "/". If
req is NULL the HTTP GET method will be used to send the request else
HTTP POST with the contents of req and optional content_type, where the
length of the data in req does not need to be determined in advance: the
BIO will be read on-the-fly while sending the request, which supports
streaming. The optional list headers may contain additional custom HTTP
header lines. The path, headers names and values, and content_type must
not contain CR or LF characters. The max_resp_len parameter specifies
the maximum allowed response content length, where the value 0 indicates
no limit. For the meaning of the expected_content_type, expect_asn1,
timeout, and keep_alive parameters, see
OSSL_HTTP_REQ_CTX_set_expected(3).
OSSL_HTTP_exchange() exchanges any form of HTTP request and response as
specified by rctx, which must include both connection and request data,
typically set up using OSSL_HTTP_open() and OSSL_HTTP_set1_request(). It
implements the core of the functions described below. If the HTTP method
is GET and redirection_url is not NULL the latter pointer is used to
provide any new location that the server may return with HTTP code 301
(MOVED_PERMANENTLY) or 302 (FOUND). In this case the function returns
NULL and the caller is responsible for deallocating the URL with
OPENSSL_free(3). If the response header contains one or more
"Content-Length" lines and/or an ASN.1-encoded response is expected,
which should include a total length, the length indications received are
checked for consistency and for not exceeding any given maximum response
length. If an ASN.1-encoded response is expected, the function returns
on success the contents buffered in a memory BIO, which does not support
streaming. Otherwise it returns directly the read BIO that holds the
response contents, which allows a response of indefinite length and may
support streaming. The caller is responsible for freeing the BIO pointer
obtained.
OSSL_HTTP_get() uses HTTP GET to obtain data from bio if non-NULL, else
from the server contained in the url, and returns it as a BIO. It
supports redirection via HTTP status code 301 or 302. Redirection from
HTTPS to HTTP is not allowed. It is meant for transfers with a single
round trip, so does not support persistent connections. If bio is non-
NULL, any host and port components in the url are not used for connecting
but the hostname is used, as usual, for the "Host" header. Any userinfo
and fragment components in the url are ignored. Any query component is
handled as part of the path component. If the scheme component of the
url is "https" a TLS connection is requested and the bio_update_fn, as
described for OSSL_HTTP_open(), must be provided. Also the remaining
parameters are interpreted as described for OSSL_HTTP_open() and
OSSL_HTTP_set1_request(), respectively. The caller is responsible for
freeing the BIO pointer obtained.
OSSL_HTTP_transfer(3) exchanges an HTTP request and response over a
connection managed via prctx without supporting redirection. It combines
OSSL_HTTP_open(), OSSL_HTTP_set1_request(), OSSL_HTTP_exchange(), and
OSSL_HTTP_close(). If prctx is not NULL it reuses any open connection
represented by a non-NULL *prctx. It keeps the connection open if a
persistent connection is requested or required and this was granted by
the server, else it closes the connection and assigns NULL to *prctx.
The remaining parameters are interpreted as described for
OSSL_HTTP_open() and OSSL_HTTP_set1_request(), respectively. The caller
is responsible for freeing the BIO pointer obtained.
OSSL_HTTP_close() closes the connection and releases rctx. The ok
parameter is passed to any BIO update function given during setup as
described above for OSSL_HTTP_open(). It must be 1 if no error occurred
during the HTTP transfer and 0 otherwise.
NOTES
The names of the environment variables used by this implementation:
"http_proxy", "HTTP_PROXY", "https_proxy", "HTTPS_PROXY", "no_proxy", and
"NO_PROXY", have been chosen for maximal compatibility with other HTTP
client implementations such as wget, curl, and git.
When built with tracing enabled, OSSL_HTTP_transfer(3) and all functions
using it may be traced using OSSL_TRACE_CATEGORY_HTTP. See also
OSSL_trace_enabled(3) and openssl-env(7).
RETURN VALUES
OSSL_HTTP_open() returns on success a OSSL_HTTP_REQ_CTX, else NULL.
OSSL_HTTP_proxy_connect() and OSSL_HTTP_set1_request() return 1 on
success, 0 on error.
On success, OSSL_HTTP_exchange(), OSSL_HTTP_get(), and
OSSL_HTTP_transfer(3) return a memory BIO that buffers all the data
received if an ASN.1-encoded response is expected, otherwise a BIO that
may support streaming. The BIO must be freed by the caller. On failure,
they return NULL. Failure conditions include connection/transfer timeout,
parse errors, etc. The caller is responsible for freeing the BIO pointer
obtained.
OSSL_HTTP_close() returns 0 if anything went wrong while disconnecting,
else 1.
SEE ALSO
OSSL_HTTP_parse_url(3), BIO_new_connect(3), ASN1_item_i2d_mem_bio(3),
ASN1_item_d2i_bio(3), OSSL_HTTP_REQ_CTX_set_expected(3),
OSSL_HTTP_is_alive(3), OSSL_trace_enabled(3), and openssl-env(7).
HISTORY
All the functions described here were added in OpenSSL 3.0.
COPYRIGHT
Copyright 2019-2026 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.6.5 2026-09-29 OSSL_HTTP_TRANSFER(3ossl)
openssl 3.6.5 - Generated Sat Oct 3 08:30:21 CDT 2026