[PATCH v5 1/3] Add support for structured output formatters.

[Peter Feigl]

From: <craven at gmx.net>

This patch adds a new type sprinter_t, which is used for structured
formatting, e.g. JSON or S-Expressions. The structure printer is the
code from Austin Clements (id:87d34hsdx8.fsf at awakening.csail.mit.edu)
with minor modifications.

The structure printer contains the following function pointers:

/* Start a new map/dictionary structure. This should be followed by
 * a sequence of alternating calls to map_key and one of the
 * value-printing functions until the map is ended by end.
 */
void (*begin_map)(struct sprinter *);

/* Start a new list/array structure.
 */
void (*begin_list)(struct sprinter *);

/* End the last opened list or map structure.
 */
void (*end)(struct sprinter *);

/* Set the prefix of the next component. This is purely for
 * debugging purposes and for the unstructured text formatter.
 */
void (*set_prefix)(struct sprinter *, const char *);

/* Print one string/integer/boolean/null element (possibly inside a
 * list or map, followed or preceded by separators).
 * For string, the char * must be UTF-8 encoded.
 */
void (*string)(struct sprinter *, const char *);
void (*integer)(struct sprinter *, int);
void (*boolean)(struct sprinter *, notmuch_bool_t);
void (*null)(struct sprinter *);

/* Print the key of a map's key/value pair. The char * must be UTF-8
 * encoded.
 */
void (*map_key)(struct sprinter *, const char *);

/* Insert a separator (usually extra whitespace) for improved
 * readability without affecting the abstract syntax of the
 * structure being printed.
 * For JSON, this could simply be a line break.
 */
void (*separator)(struct sprinter *);

The printer can (and should) use internal state to insert delimiters and
syntax at the correct places.

Example:

format->begin_map(format);
format->map_key(format, "foo");
format->begin_list(format);
format->integer(format, 1);
format->integer(format, 2);
format->integer(format, 3);
format->end(format);
format->map_key(format, "bar");
format->begin_map(format);
format->map_key(format, "baaz");
format->string(format, "hello world");
format->end(format);
format->end(format);

would output JSON as follows:

{"foo": [1, 2, 3], "bar": { "baaz": "hello world"}}
---
 sprinter.h | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 sprinter.h

diff --git a/sprinter.h b/sprinter.h
new file mode 100644
index 0000000..c9cd6a6
--- /dev/null
+++ b/sprinter.h
@@ -0,0 +1,50 @@
+#ifndef NOTMUCH_SPRINTER_H
+#define NOTMUCH_SPRINTER_H
+
+/* Necessary for notmuch_bool_t */
+#include "notmuch-client.h"
+
+/* Structure printer interface */
+typedef struct sprinter {
+    /* Start a new map/dictionary structure. This should be followed by
+     * a sequence of alternating calls to map_key and one of the
+     * value-printing functions until the map is ended by end.
+     */
+    void (*begin_map)(struct sprinter *);
+
+    /* Start a new list/array structure.
+     */
+    void (*begin_list)(struct sprinter *);
+
+    /* End the last opened list or map structure.
+     */
+    void (*end)(struct sprinter *);
+
+    /* Set the prefix of the next component. This is purely for
+     * debugging purposes and for the unstructured text formatter.
+     */
+    void (*set_prefix)(struct sprinter *, const char *);
+
+    /* Print one string/integer/boolean/null element (possibly inside a
+     * list or map, followed or preceded by separators).
+     * For string, the char * must be UTF-8 encoded.
+     */
+    void (*string)(struct sprinter *, const char *);
+    void (*integer)(struct sprinter *, int);
+    void (*boolean)(struct sprinter *, notmuch_bool_t);
+    void (*null)(struct sprinter *);
+
+    /* Print the key of a map's key/value pair. The char * must be UTF-8
+     * encoded.
+     */
+    void (*map_key)(struct sprinter *, const char *);
+
+    /* Insert a separator (usually extra whitespace) for improved
+     * readability without affecting the abstract syntax of the
+     * structure being printed.
+     * For JSON, this could simply be a line break.
+     */
+    void (*separator)(struct sprinter *);
+} sprinter_t;
+
+#endif // NOTMUCH_SPRINTER_H
-- 
1.7.11.1