KHTTP_TEMPLATEX(3)

NAME
khttp_templatex, khttp_templatex_buf, khttp_templatex_fd - emit filled-in templates for kcgi

LIBRARY
libkcgi

SYNOPSIS
#include <sys/types.h>
#include <stdarg.h>
#include <stdint.h>
#include <kcgi.h>
enum kcgi_err
khttp_templatex(const struct ktemplate *t, const char *filename, const struct ktemplatex *x, void *arg);
enum kcgi_err
khttp_templatex_buf(const struct ktemplate *t, const char *buf, size_t sz, const struct ktemplatex *x, void *arg);
enum kcgi_err
khttp_templatex_fd(const struct ktemplate *t, int fd, const char *filename, const struct ktemplatex *x, void *arg);

DESCRIPTION
Modify input by replacing keys in a template. This generalises the khttp_template(3) family of functions with generic writing functions. All functions accept a template t consisting of the following fields:

const char *const *key
    An array of keys to be replaced in the template.

size_t keysz
    The number of keys in t->key.

void *arg
    An optional argument passed to t->cb.

int (*cb)(size_t index, void *arg)
    The callback function invoked when a key at position index, which is always less than t->keysz, is found in t->key. The optional arg is passed the function. The function must return zero on failure, non-zero on success.

They further accept an extension x consisting of the following:

writer
    A writing function for writing input that does not match key sequences. If it is invoked and the return value is not KCGI_OK, templating stops and the return value is returned to the caller.

fbk A fall-back function invoked if a key sequences was not found in the c->key array. This accepts the key sequence, length of the sequence, and arg. If NULL, key sequences not found are passed to writer.

If t is NULL, the input is passed through to x->writer without any processing.

Otherwise, the input is passed to x->writer until a key sequence in encountered matching a key in t->key. The callback t->cb is then invoked instead of printing the key sequence. If there are multiple matching keys in t->key, only one is used (which is not yet fixed). If the key sequence is not found in t->key, it is passed to x->fbk, if not NULL, or passed directly to x->writer otherwise.

The different input types are khttpx_template(), which reads input from the file filename; khttpx_template_buf(), which reads from a binary buffer buf of length sz; and khttpx_template_fd(), which reads from a file descriptor fd with optional file-name fname used only for logging purposes.

SYNTAX
Each substring of the input beginning and ending with a pair of “at” signs, @@key@@, is called a "key sequence". Zero-length keys @@@@ are allowed and match empty template keys. If the @@ pair is escaped with a single backslash, \@@, the backslash is removed and it's emitted as @@.

A key sequence may not contain an escaped pair: this is parsed as a backslash followed by the trailing pair.

RETURN VALUES
These return an enum kcgi_err indicating the error state:

KCGI_OK
    No error occurred.

KCGI_ENOMEM
    Memory allocation failed.

KCGI_SYSTEM
    A system call failed. For example, writing to the output stream failed, or khttp_template() failed to open(2) filename.

KCGI_FORM
    t->cb returned 0.

If the x->writer function returns anything but KCGI_OK, the return code is passed as the return value.

EXAMPLES
The following simple example takes a buffer buf and applies the replacement template of two values, writing it to the current context req. It stores the result in the given buffer out.

    static int writer(size_t idx, void *arg)
    {
      struct kcgi_buf *p = arg;
      if (idx == 0)
        kcgi_buf_puts(p, "foo-value");
      else if (idx == 1)
        kcgi_buf_puts(p, "bar-value");
      return 1;
    }
    enum kcgi_err format(struct kcgi_buf *out)
    {
      const char *const keys[] = { "foo", "bar" };
      struct ktemplate t = {
        .key = keys,
        .keysz = 2,
        .arg = out,
        .cb = writer
      };
      struct ktemplatex x = {
        .writer = kcgi_buf_write,
        .fbk = NULL
      };
      const char *in = "foo=@@foo@@, bar=@@bar@@";
      memset(&out, 0, sizeof(struct kcgi_buf));
      return khttp_templatex_buf
        (&t, in, strlen(in), &x, out);
    }

The function will produce "foo=foo-value, bar=bar-value".

SEE ALSO
kcgi(3), khttp_body(3), khttp_parse(3), khttp_template(3), khttp_write(3)

AUTHORS
Written by Kristaps Dzonsons <kristaps@bsd.lv>.