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cl_hp_get_field(3) canlock-hp 3.3.0 manual cl_hp_get_field(3)


cl_hp_get_field - Execute header parser


#include <libcanlock-3/canlock-hp.h>

char *cl_hp_get_field(const char *data, size_t data_len,
                      const char *field);


Note: Consider the function cl_hp_unfold_field() if the header field was already extracted by another header parser (but may still contain folding).

The cl_hp_get_field() function executes the header parser to extract and unfold a single header field.
This implementation executes the canlock-mhp utility in a separate process.

The parameter data should point to the beginning of the input data.
Specify the length of the input data with the data_len parameter.
The name of a single header field must be specified with the field parameter.

The input data must be a message in canonical format (with US-ASCII encoded CRLF line breaks). If the message is in some local format (e.g. EBCDIC encoded or with LF line breaks), it must be converted to canonical format before it can be used as input.

The input data may be a naked header without message body, but the empty line separator after the header must always be present. The syntax of the extracted header field is not checked beyond the folding. The rest of the message need not be fully RFC 5536 conformant too, as long as all header fields start on new lines (and are correctly folded, so that there is no ambiguity). Common syntax errors (like 8-bit characters in the header) are ignored.


If the parser reports success, a pointer to the NUL-terminated output data is returned. Otherwise, NULL is returned.

On success, the caller is responsible to free() the memory block allocated for the output data.


Michael Baeuerle


Report bugs to <>.


cl_hp_get_field() tries to comply with the following standards:

RFC 5322, RFC 5536


free(3), cl_hp_parse_field(3), cl_hp_unfold_field(3), canlock-hfp(1), canlock-mhp(1), canlock(1)

2021-11-24 Unix