[PATCH v4 2/3] Add structured output formatter for JSON.

[craven at gmx.net]

Using the new structured printer support in sprinter.h, implement
sprinter_json_new, which returns a new JSON structured output
formatter.

The formatter prints output similar to the existing JSON, but with
differences in whitespace (mostly newlines).
---
 Makefile.local |   1 +
 sprinter.c     | 172 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 173 insertions(+)
 create mode 100644 sprinter.c

diff --git a/Makefile.local b/Makefile.local
index a890df2..8baf0c2 100644
--- a/Makefile.local
+++ b/Makefile.local
@@ -290,6 +290,7 @@ notmuch_client_srcs =		\
 	notmuch-show.c		\
 	notmuch-tag.c		\
 	notmuch-time.c		\
+	sprinter.c		\
 	query-string.c		\
 	mime-node.c		\
 	crypto.c		\
diff --git a/sprinter.c b/sprinter.c
new file mode 100644
index 0000000..649f79a
--- /dev/null
+++ b/sprinter.c
@@ -0,0 +1,172 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <talloc.h>
+#include "sprinter.h"
+
+#define ARRAY_SIZE(arr) (sizeof (arr) / sizeof (arr[0]))
+
+struct sprinter *
+sprinter_text = NULL;
+
+/*
+ * Every below here is the implementation of the JSON printer.
+ */
+
+struct sprinter_json
+{
+    struct sprinter vtable;
+    FILE *stream;
+    /* Top of the state stack, or NULL if the printer is not currently
+     * inside any aggregate types. */
+    struct json_state *state;
+};
+
+struct json_state
+{
+    struct json_state *parent;
+    /* True if nothing has been printed in this aggregate yet.
+     * Suppresses the comma before a value. */
+    notmuch_bool_t first;
+    /* The character that closes the current aggregate. */
+    char close;
+};
+
+/* Helper function to set up the stream to print a value.  If this
+ * value follows another value, prints a comma. */
+static struct sprinter_json *
+json_begin_value(struct sprinter *sp)
+{
+    struct sprinter_json *spj = (struct sprinter_json*)sp;
+    if (spj->state) {
+	if (!spj->state->first)
+	    fputs (", ", spj->stream);
+	else
+	    spj->state->first = false;
+    }
+    return spj;
+}
+
+/* Helper function to begin an aggregate type.  Prints the open
+ * character and pushes a new state frame. */
+static void
+json_begin_aggregate(struct sprinter *sp, char open, char close)
+{
+    struct sprinter_json *spj = json_begin_value (sp);
+    struct json_state *state = talloc (spj, struct json_state);
+
+    fputc (open, spj->stream);
+    state->parent = spj->state;
+    state->first = true;
+    state->close = close;
+    spj->state = state;
+}
+
+static void
+json_begin_map(struct sprinter *sp)
+{
+    json_begin_aggregate (sp, '{', '}');
+}
+
+static void
+json_begin_list(struct sprinter *sp)
+{
+    json_begin_aggregate (sp, '[', ']');
+}
+
+static void
+json_end(struct sprinter *sp)
+{
+    struct sprinter_json *spj = (struct sprinter_json*)sp;
+    struct json_state *state = spj->state;
+
+    fputc (spj->state->close, spj->stream);
+    spj->state = state->parent;
+    talloc_free (state);
+    if(spj->state == NULL)
+	fputc ('\n', spj->stream);
+}
+
+static void
+json_string(struct sprinter *sp, const char *val)
+{
+    static const char * const escapes[] = {
+	['\"'] = "\\\"", ['\\'] = "\\\\", ['\b'] = "\\b",
+	['\f'] = "\\f",  ['\n'] = "\\n",  ['\t'] = "\\t"
+    };
+    struct sprinter_json *spj = json_begin_value (sp);
+    fputc ('"', spj->stream);
+    for (; *val; ++val) {
+	unsigned char ch = *val;
+	if (ch < ARRAY_SIZE(escapes) && escapes[ch])
+	    fputs (escapes[ch], spj->stream);
+	else if (ch >= 32)
+	    fputc (ch, spj->stream);
+	else
+	    fprintf (spj->stream, "\\u%04x", ch);
+    }
+    fputc ('"', spj->stream);
+}
+
+static void
+json_integer(struct sprinter *sp, int val)
+{
+    struct sprinter_json *spj = json_begin_value (sp);
+    fprintf (spj->stream, "%d", val);
+}
+
+static void
+json_boolean(struct sprinter *sp, notmuch_bool_t val)
+{
+    struct sprinter_json *spj = json_begin_value (sp);
+    fputs (val ? "true" : "false", spj->stream);
+}
+
+static void
+json_null(struct sprinter *sp)
+{
+    struct sprinter_json *spj = json_begin_value (sp);
+    fputs ("null", spj->stream);
+}
+
+static void
+json_map_key(struct sprinter *sp, const char *key)
+{
+    struct sprinter_json *spj = (struct sprinter_json*)sp;
+    json_string (sp, key);
+    fputs (": ", spj->stream);
+    spj->state->first = true;
+}
+
+static void
+json_frame(struct sprinter *sp)
+{
+    struct sprinter_json *spj = (struct sprinter_json*)sp;
+    fputc ('\n', spj->stream);
+}
+
+struct sprinter *
+sprinter_json_new(const void *ctx, FILE *stream)
+{
+    static const struct sprinter_json template = {
+	.vtable = {
+	    .begin_map = json_begin_map,
+	    .begin_list = json_begin_list,
+	    .end = json_end,
+	    .string = json_string,
+	    .integer = json_integer,
+	    .boolean = json_boolean,
+	    .null = json_null,
+	    .map_key = json_map_key,
+	    .frame = json_frame,
+	}
+    };
+    struct sprinter_json *res;
+
+    res = talloc (ctx, struct sprinter_json);
+    if (!res)
+	return NULL;
+
+    *res = template;
+    res->stream = stream;
+    return &res->vtable;
+}
-- 
1.7.11.1