MINOR: http-htx: Add functions to read a raw error file and convert it in HTX

http_parse_errorfile() may now be used to parse a raw HTTP message from a
file. A status code is passed as parameter. It must be one of the supported HTTP
error codes to be valid. Otherwise an error is returned. It aims to be used to
parse "errorfile" directives. It relies on http_load_errorfile() to do most of
the job, ie reading the file content and converting it in HTX.

include/proto/http_htx.h

@@ -49,4 +49,7 @@ unsigned int http_get_htx_fhdr(const struct htx *htx, const struct ist hdr,
 			       int occ, struct http_hdr_ctx *ctx, char **vptr, size_t *vlen);
 int http_str_to_htx(struct buffer *buf, struct ist raw);
 
+int http_load_errorfile(const char *file, struct buffer *buf, char **errmsg);
+int http_parse_errorfile(int status, const char *file, struct buffer *buf, char **errmsg);
+
 #endif /* _PROTO_HTTP_HTX_H */

src/http_htx.c

@@ -9,6 +9,12 @@
  * 2 of the License, or (at your option) any later version.
  *
  */
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <types/global.h>
 
 #include <common/config.h>
 #include <common/debug.h>
@@ -832,6 +838,81 @@ end:
 
 REGISTER_CONFIG_POSTPARSER("http_htx", http_htx_init);
 
+/* Reads content of an error file and convert it in an HTX message. On success,
+ * the result is stored in <buf> and 1 is returned. On error, 0 is returned and
+ * an error message is written into the <errmsg> buffer. It is this function
+ * responsibility to allocate <buf> and to release it if an error occurred.
+ */
+int http_load_errorfile(const char *file, struct buffer *buf, char **errmsg)
+{
+	struct stat stat;
+	char *err = NULL;
+	int errnum, errlen;
+	int fd = -1;
+	int ret = 0;
+
+	fd = open(file, O_RDONLY);
+	if ((fd < 0) || (fstat(fd, &stat) < 0)) {
+		memprintf(errmsg, "error opening file '%s'.", file);
+		goto out;
+	}
+
+	if (stat.st_size <= global.tune.bufsize)
+		errlen = stat.st_size;
+	else {
+		ha_warning("custom error message file '%s' larger than %d bytes. Truncating.\n",
+			   file, global.tune.bufsize);
+		errlen = global.tune.bufsize;
+	}
+
+	err = malloc(errlen);
+	if (!err) {
+		memprintf(errmsg, "out of memory.");
+		goto out;
+	}
+
+	errnum = read(fd, err, errlen);
+	if (errnum != errlen) {
+		memprintf(errmsg, "error reading file '%s'.", file);
+		goto out;
+	}
+
+	if (!http_str_to_htx(buf, ist2(err, errlen))) {
+		memprintf(errmsg, "unable to convert custom error message file '%s' in HTX.", file);
+		goto out;
+	}
+
+	ret = 1;
+  out:
+	if (fd >= 0)
+		close(fd);
+	free(err);
+	return ret;
+}
+
+
+/* This function parses the raw HTTP error file <file> for the status code
+ * <status>. On success, it returns the HTTP_ERR_* value corresponding to the
+ * specified status code and it allocated and fills the buffer <buf> with the
+ * HTX message. On error, it returns -1 and nothing is allocated.
+ */
+int http_parse_errorfile(int status, const char *file, struct buffer *buf, char **errmsg)
+{
+	int rc, ret = -1;
+
+	for (rc = 0; rc < HTTP_ERR_SIZE; rc++) {
+		if (http_err_codes[rc] == status) {
+			if (http_load_errorfile(file, buf, errmsg))
+				ret = rc;
+			break;
+		}
+	}
+
+	if (rc >= HTTP_ERR_SIZE)
+		memprintf(errmsg, "status code '%d' not handled.", status);
+	return ret;
+}
+
 /************************************************************************/
 /*                             HTX sample fetches                       */
 /************************************************************************/