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Using the new structured printer support in sprinter.h, implement
sprinter_json_create, which returns a new JSON structured output
formatter. The formatter prints output similar to the existing JSON, but
with differences in whitespace (mostly newlines, --output=summary prints
the entire message summary on one line, not split across multiple lines).
Also implement a "structured" formatter for plain text that prints
prefixed strings, to be used with notmuch-search.c plain text output.
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This patch adds a new struct type sprinter_t, which is used for
structured formatting, e.g. JSON or S-Expressions. The structure printer
is heavily based on code from Austin Clements
(id:87d34hsdx8.fsf@awakening.csail.mit.edu).
It includes the following functions:
/* 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 *);
/* 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 *);
/* Set the current string prefix. This only affects the text
* printer, which will print this string, followed by a colon,
* before any string. For other printers, this does nothing.
*/
void (*set_prefix) (struct sprinter *, const char *);
To support the plain text format properly, the following additional
function must also be implemented:
/* Set the current string prefix. This only affects the text
* printer, which will print this string, followed by a colon,
* before any string. For other printers, this does nothing.
*/
void (*set_prefix) (struct sprinter *, const char *);
The structure also contains a flag that should be set to FALSE in all
custom printers and to TRUE in the plain text formatter.
/* True if this is the special-cased plain text printer.
*/
notmuch_bool_t is_text_printer;
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"}}
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