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_i2d, OSSL_HTTP_REQ_CTX_nbio, OSSL_HTTP_REQ_CTX_sendreq_d2i, OSSL_HTTP_REQ_CTX_get0_mem_bio, OSSL_HTTP_REQ_CTX_set_max_response_length - 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 method_POST, int maxline,
                                          unsigned long max_resp_len,
                                          int timeout,
                                          const char *expected_content_type,
                                          int expect_asn1);
 void OSSL_HTTP_REQ_CTX_free(OSSL_HTTP_REQ_CTX *rctx);

 int OSSL_HTTP_REQ_CTX_set_request_line(OSSL_HTTP_REQ_CTX *rctx,
                                        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_i2d(OSSL_HTTP_REQ_CTX *rctx, const char *content_type,
                           const ASN1_ITEM *it, ASN1_VALUE *req);
 int OSSL_HTTP_REQ_CTX_nbio(OSSL_HTTP_REQ_CTX *rctx);
 ASN1_VALUE *OSSL_HTTP_REQ_CTX_sendreq_d2i(OSSL_HTTP_REQ_CTX *rctx,
                                           const ASN1_ITEM *it);

 BIO *OSSL_HTTP_REQ_CTX_get0_mem_bio(const OSSL_HTTP_REQ_CTX *rctx);
 void OSSL_HTTP_REQ_CTX_set_max_response_length(OSSL_HTTP_REQ_CTX *rctx,
                                                unsigned long len);

DESCRIPTION

OSSL_HTTP_REQ_CTX is a context structure for an HTTP request, 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 send the request to (wbio), the BIO to read the response from (rbio, which may be equal to wbio), the maximum expected response header line length (maxline, where a value <= 0 indicates that the HTTP_DEFAULT_MAX_LINE_LENGTH of 4KiB should be used; this length is also used as the number of content bytes read at a time), the request method (method_POST, which may be 1 to indicate that the POST method is to be used, or 0 to indicate that the GET method is to be used), the maximum allowed response content length (max_resp_len, where 0 means that the HTTP_DEFAULT_MAX_RESP_LEN is used, which currently is 100 KiB), a response timeout measure in seconds (timeout, where 0 indicates no timeout, i.e., waiting indefinitely), the expected MIME content type of the response (expected_content_type, which may be NULL for no expectation), and a flag indicating that the response is expected to be a DER encoded ASN.1 structure (expect_asn1). The allocated context structure is also populated with an internal allocated memory BIO, which collects the HTTP request and additional headers as text. The returned context should only be used for a single HTTP request/response.

OSSL_HTTP_REQ_CTX_free() frees up the HTTP request context rctx. The wbio and rbio are not free'd and it is up to the application to do so.

OSSL_HTTP_REQ_CTX_set_request_line() adds the HTTP request line to the context. The request method itself becomes GET or POST depending on the value of method_POST in the OSSL_HTTP_REQ_CTX_new() call. server and port may be set to indicate a proxy server and port that the request should go through, otherwise they should be left NULL. path is the HTTP request path; if left NULL, / is used.

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 headers. 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_i2d() finalizes the HTTP request context by adding the DER encoding of req, using the ASN.1 template it to do the encoding. The HTTP header Content-Length is automatically filled out, and if content_type isn't NULL, the HTTP header Content-Type is also added with its content as value. All of this ends up in the internal memory BIO. This requires that method_POST was 1 in the OSSL_HTTP_REQ_CTX_new() call.

OSSL_HTTP_REQ_CTX_nbio() attempts to send the request prepared rctx and gathering the response via HTTP, using the rbio and wbio that were given when calling OSSL_HTTP_REQ_CTX_new(). When successful, the contents of the internal memory BIO contains the contents of the HTTP response, without the response headers. It 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_sendreq_d2i() calls OSSL_HTTP_REQ_CTX_nbio(), possibly several times until a timeout is reached, and DER decodes the received response using the ASN.1 template it.

OSSL_HTTP_REQ_CTX_get0_mem_bio() returns the internal memory BIO. Before sending the request, this could used to modify the HTTP request text. Use with caution! After receiving a response via HTTP, the BIO represents the current state of reading the response headers and contents.

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 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.

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:

Calling OSSL_HTTP_REQ_CTX_set_request_line(). This must be done exactly once.
Adding extra headers with OSSL_HTTP_REQ_CTX_add1_header(). This is optional and may be done multiple times with different names.
Add POST data with OSSL_HTTP_REQ_CTX_i2d(). This may only be done if method_POST was 1 in the OSSL_HTTP_REQ_CTX_new() call, and must be done exactly once in that case.

When the request context is fully prepared, the HTTP exchange may be performed with OSSL_HTTP_REQ_CTX_nbio() or OSSL_HTTP_REQ_CTX_sendreq_d2i().

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_i2d() and OSSL_HTTP_REQ_CTX_nbio return 1 for success and 0 for failure.

OSSL_HTTP_REQ_CTX_sendreq_d2i() returns a pointer to an ASN1_VALUE for success and NULL for failure.

OSSL_HTTP_REQ_CTX_get0_mem_bio() returns the internal memory BIO.

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