Provided by: libssl-doc_3.0.13-0ubuntu3.5_all 
NAME
OSSL_HTTP_REQ_CTX, OSSL_HTTP_REQ_CTX_new, OSSL_HTTP_REQ_CTX_free, OSSL_HTTP_REQ_CTX_set_request_line,
OSSL_HTTP_REQ_CTX_add1_header, OSSL_HTTP_REQ_CTX_set_expected, OSSL_HTTP_REQ_CTX_set1_req,
OSSL_HTTP_REQ_CTX_nbio, OSSL_HTTP_REQ_CTX_nbio_d2i, OSSL_HTTP_REQ_CTX_exchange,
OSSL_HTTP_REQ_CTX_get0_mem_bio, OSSL_HTTP_REQ_CTX_get_resp_len,
OSSL_HTTP_REQ_CTX_set_max_response_length, OSSL_HTTP_is_alive - HTTP client low-level functions
SYNOPSIS
#include <openssl/http.h>
typedef struct ossl_http_req_ctx_st OSSL_HTTP_REQ_CTX;
OSSL_HTTP_REQ_CTX *OSSL_HTTP_REQ_CTX_new(BIO *wbio, BIO *rbio, int buf_size);
void OSSL_HTTP_REQ_CTX_free(OSSL_HTTP_REQ_CTX *rctx);
int OSSL_HTTP_REQ_CTX_set_request_line(OSSL_HTTP_REQ_CTX *rctx, int method_POST,
const char *server, const char *port,
const char *path);
int OSSL_HTTP_REQ_CTX_add1_header(OSSL_HTTP_REQ_CTX *rctx,
const char *name, const char *value);
int OSSL_HTTP_REQ_CTX_set_expected(OSSL_HTTP_REQ_CTX *rctx,
const char *content_type, int asn1,
int timeout, int keep_alive);
int OSSL_HTTP_REQ_CTX_set1_req(OSSL_HTTP_REQ_CTX *rctx, const char *content_type,
const ASN1_ITEM *it, const ASN1_VALUE *req);
int OSSL_HTTP_REQ_CTX_nbio(OSSL_HTTP_REQ_CTX *rctx);
int OSSL_HTTP_REQ_CTX_nbio_d2i(OSSL_HTTP_REQ_CTX *rctx,
ASN1_VALUE **pval, const ASN1_ITEM *it);
BIO *OSSL_HTTP_REQ_CTX_exchange(OSSL_HTTP_REQ_CTX *rctx);
BIO *OSSL_HTTP_REQ_CTX_get0_mem_bio(const OSSL_HTTP_REQ_CTX *rctx);
size_t OSSL_HTTP_REQ_CTX_get_resp_len(const OSSL_HTTP_REQ_CTX *rctx);
void OSSL_HTTP_REQ_CTX_set_max_response_length(OSSL_HTTP_REQ_CTX *rctx,
unsigned long len);
int OSSL_HTTP_is_alive(const OSSL_HTTP_REQ_CTX *rctx);
DESCRIPTION
OSSL_HTTP_REQ_CTX is a context structure for an HTTP request and response, used to collect all the
necessary data to perform that request.
This file documents low-level HTTP functions rarely used directly. High-level HTTP client functions like
OSSL_HTTP_get(3) and OSSL_HTTP_transfer(3) should be preferred.
OSSL_HTTP_REQ_CTX_new() allocates a new HTTP request context structure, which gets populated with the BIO
to write/send the request to (wbio), the BIO to read/receive the response from (rbio, which may be equal
to wbio), and the maximum expected response header line length buf_size. A value <= 0 indicates that the
OSSL_HTTP_DEFAULT_MAX_LINE_LEN of 4KiB should be used. buf_size is also used as the number of content
bytes that are read at a time. The allocated context structure includes an internal memory BIO, which
collects the HTTP request header lines.
OSSL_HTTP_REQ_CTX_free() frees up the HTTP request context rctx. The rbio is not free'd, wbio will be
free'd if free_wbio is set.
OSSL_HTTP_REQ_CTX_set_request_line() adds the 1st HTTP request line to rctx. The HTTP method is
determined by method_POST, which should be 1 to indicate "POST" or 0 to indicate "GET". server and port
may be set to give the server and the optional port that an HTTP proxy shall forward the request to,
otherwise they must be left NULL. path provides the HTTP request path; if left NULL, "/" is used. For
backward compatibility, path may begin with "http://" and thus convey an absoluteURI. In this case it
indicates HTTP proxy use and provides also the server (and optionally the port) that the proxy shall
forward the request to. In this case the server and port arguments must be NULL.
OSSL_HTTP_REQ_CTX_add1_header() adds header name with value value to the context rctx. It can be called
more than once to add multiple header lines. For example, to add a "Host" header for "example.com" you
would call:
OSSL_HTTP_REQ_CTX_add1_header(ctx, "Host", "example.com");
OSSL_HTTP_REQ_CTX_set_expected() optionally sets in rctx some expectations of the HTTP client on the
response. Due to the structure of an HTTP request, if the keep_alive argument is nonzero the function
must be used before calling OSSL_HTTP_REQ_CTX_set1_req(). If the content_type parameter is not NULL then
the client will check that the given content type string is included in the HTTP header of the response
and return an error if not. If the asn1 parameter is nonzero a structure in ASN.1 encoding will be
expected as the response content and input streaming is disabled. This means that an ASN.1 sequence
header is required, its length field is checked, and OSSL_HTTP_REQ_CTX_get0_mem_bio() should be used to
get the buffered response. Otherwise (by default) any input format is allowed without length checks. In
this case the BIO given as rbio argument to OSSL_HTTP_REQ_CTX_new() should be used directly to read the
response contents, which may support streaming. If the timeout parameter is > 0 this indicates the
maximum number of seconds the subsequent HTTP transfer (sending the request and receiving a response) is
allowed to take. timeout == 0 enables waiting indefinitely, i.e., no timeout can occur. This is the
default. timeout < 0 takes over any value set via the overall_timeout argument of OSSL_HTTP_open(3) with
the default being 0, which means no timeout. If the keep_alive parameter is 0, which is the default, the
connection is not kept open after receiving a response. This is the default behavior for HTTP 1.0. If
the value is 1 or 2 then a persistent connection is requested. If the value is 2 then a persistent
connection is required, i.e., an error occurs in case the server does not grant it.
OSSL_HTTP_REQ_CTX_set1_req() finalizes the HTTP request context. It is needed if the method_POST
parameter in the OSSL_HTTP_REQ_CTX_set_request_line() call was 1 and an ASN.1-encoded request should be
sent. It must also be used when requesting "keep-alive", even if a GET request is going to be sent, in
which case req must be NULL. Unless req is NULL, the function adds the DER encoding of req using the
ASN.1 template it to do the encoding (which does not support streaming). The HTTP header
"Content-Length" is filled out with the length of the request. content_type must be NULL if req is NULL.
If content_type isn't NULL, the HTTP header "Content-Type" is also added with the given string value.
The header lines are added to the internal memory BIO for the request header.
OSSL_HTTP_REQ_CTX_nbio() attempts to send the request prepared in rctx and to gather the response via
HTTP, using the wbio and rbio that were given when calling OSSL_HTTP_REQ_CTX_new(). The function may
need to be called again if its result is -1, which indicates BIO_should_retry(3). In such a case it is
advisable to sleep a little in between, using BIO_wait(3) on the read BIO to prevent a busy loop.
OSSL_HTTP_REQ_CTX_nbio_d2i() is like OSSL_HTTP_REQ_CTX_nbio() but on success in addition parses the
response, which must be a DER-encoded ASN.1 structure, using the ASN.1 template it and places the result
in *pval.
OSSL_HTTP_REQ_CTX_exchange() calls OSSL_HTTP_REQ_CTX_nbio() as often as needed in order to exchange a
request and response or until a timeout is reached. On success it returns a pointer to the BIO that can
be used to read the result. If an ASN.1-encoded response was expected, this is the BIO returned by
OSSL_HTTP_REQ_CTX_get0_mem_bio() when called after the exchange. This memory BIO does not support
streaming. Otherwise the returned BIO is the rbio given to OSSL_HTTP_REQ_CTX_new(), which may support
streaming. When this BIO is returned, it has been read past the end of the response header, such that
the actual response body can be read from it. The returned BIO pointer MUST NOT be freed by the caller.
OSSL_HTTP_REQ_CTX_get0_mem_bio() returns the internal memory BIO. Before the HTTP request is sent, this
could be used to adapt its header lines. Use with caution! After receiving a response via HTTP, the BIO
represents the current state of reading the response header. If the response was expected to be ASN.1
encoded, its contents can be read via this BIO, which does not support streaming. The returned BIO
pointer must not be freed by the caller.
OSSL_HTTP_REQ_CTX_get_resp_len() returns the size of the response contents in rctx if provided by the
server as <Content-Length> header field, else 0.
OSSL_HTTP_REQ_CTX_set_max_response_length() sets the maximum allowed response content length for rctx to
len. If not set or len is 0 then the OSSL_HTTP_DEFAULT_MAX_RESP_LEN is used, which currently is 100 KiB.
If the "Content-Length" header is present and exceeds this value or the content is an ASN.1 encoded
structure with a length exceeding this value or both length indications are present but disagree then an
error occurs.
OSSL_HTTP_is_alive() can be used to query if the HTTP connection given by rctx is still alive, i.e., has
not been closed. It returns 0 if rctx is NULL.
If the client application requested or required a persistent connection and this was granted by the
server, it can keep rctx as long as it wants to send further requests and OSSL_HTTP_is_alive() returns
nonzero, else it should call OSSL_HTTP_REQ_CTX_free(rctx) or OSSL_HTTP_close(3). In case the client
application keeps rctx but the connection then dies for any reason at the server side, it will notice
this obtaining an I/O error when trying to send the next request via rctx.
WARNINGS
The server's response may be unexpected if the hostname that was used to create the wbio, any "Host"
header, and the host specified in the request URL do not match.
Many of these functions must be called in a certain order.
First, the HTTP request context must be allocated: OSSL_HTTP_REQ_CTX_new().
Then, the HTTP request must be prepared with request data:
1. Calling OSSL_HTTP_REQ_CTX_set_request_line().
2. Adding extra header lines with OSSL_HTTP_REQ_CTX_add1_header(). This is optional and may be done
multiple times with different names.
3. Finalize the request using OSSL_HTTP_REQ_CTX_set1_req(). This may be omitted if the GET method is
used and "keep-alive" is not requested.
When the request context is fully prepared, the HTTP exchange may be performed with
OSSL_HTTP_REQ_CTX_nbio() or OSSL_HTTP_REQ_CTX_exchange().
RETURN VALUES
OSSL_HTTP_REQ_CTX_new() returns a pointer to a OSSL_HTTP_REQ_CTX, or NULL on error.
OSSL_HTTP_REQ_CTX_free() and OSSL_HTTP_REQ_CTX_set_max_response_length() do not return values.
OSSL_HTTP_REQ_CTX_set_request_line(), OSSL_HTTP_REQ_CTX_add1_header(), OSSL_HTTP_REQ_CTX_set1_req(), and
OSSL_HTTP_REQ_CTX_set_expected() return 1 for success and 0 for failure.
OSSL_HTTP_REQ_CTX_nbio() and OSSL_HTTP_REQ_CTX_nbio_d2i() return 1 for success, 0 on error or
redirection, -1 if retry is needed.
OSSL_HTTP_REQ_CTX_exchange() and OSSL_HTTP_REQ_CTX_get0_mem_bio() return a pointer to a BIO on success as
described above or NULL on failure. The returned BIO must not be freed by the caller.
OSSL_HTTP_REQ_CTX_get_resp_len() returns the size of the response contents or 0 if not available or an
error occurred.
OSSL_HTTP_is_alive() returns 1 if its argument is non-NULL and the client requested a persistent
connection and the server did not disagree on keeping the connection open, else 0.
SEE ALSO
BIO_should_retry(3), BIO_wait(3), ASN1_item_d2i_bio(3), ASN1_item_i2d_mem_bio(3), OSSL_HTTP_open(3),
OSSL_HTTP_get(3), OSSL_HTTP_transfer(3), OSSL_HTTP_close(3)
HISTORY
The functions described here were added in OpenSSL 3.0.
COPYRIGHT
Copyright 2015-2023 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>.