[PATCH 1/3] Adding an S-expression structured output printer.

[Peter Feigl]

This commit adds an sprinter for Lisp S-Expressions. Later commits will
use this printer.

The structure is the same as json, but:
- arrays are written as lists: ("foo" "bar" "baaz" 1 2 3)
- maps are written as a-lists: ((key "value") (other-key "other-value"))
- true is written as t
- false is written as nil
- null is written as nil
---
 Makefile.local  |   1 +
 sprinter-sexp.c | 235 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 236 insertions(+)
 create mode 100644 sprinter-sexp.c

diff --git a/Makefile.local b/Makefile.local
index 2b91946..0db1713 100644
--- a/Makefile.local
+++ b/Makefile.local
@@ -270,6 +270,7 @@ notmuch_client_srcs =		\
 	notmuch-tag.c		\
 	notmuch-time.c		\
 	sprinter-json.c		\
+	sprinter-sexp.c		\
 	sprinter-text.c		\
 	query-string.c		\
 	mime-node.c		\
diff --git a/sprinter-sexp.c b/sprinter-sexp.c
new file mode 100644
index 0000000..8401c52
--- /dev/null
+++ b/sprinter-sexp.c
@@ -0,0 +1,235 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <talloc.h>
+#include "sprinter.h"
+
+struct sprinter_sexp {
+    struct sprinter vtable;
+    FILE *stream;
+    /* Top of the state stack, or NULL if the printer is not currently
+     * inside any aggregate types. */
+    struct sexp_state *state;
+
+    /* A flag to signify that a separator should be inserted in the
+     * output as soon as possible.
+     */
+    notmuch_bool_t insert_separator;
+};
+
+struct sexp_state {
+    struct sexp_state *parent;
+
+    /* True if nothing has been printed in this aggregate yet.
+     * Suppresses the space before a value. */
+    notmuch_bool_t first;
+
+    /* True if the state is a map state.
+       Used to add a space between key/value pairs. */
+    notmuch_bool_t in_map;
+
+    /* 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 space. */
+static struct sprinter_sexp *
+sexp_begin_value (struct sprinter *sp)
+{
+    struct sprinter_sexp *sps = (struct sprinter_sexp *) sp;
+
+    if (sps->state) {
+        if (! sps->state->first) {
+            if (sps->insert_separator) {
+                fputc ('\n', sps->stream);
+                sps->insert_separator = FALSE;
+            } else {
+                if( ! sps->state->in_map)
+                    fputc (' ', sps->stream);
+            }
+        } else {
+            sps->state->first = FALSE;
+        }
+    }
+    return sps;
+}
+
+/* Helper function to begin an aggregate type.  Prints the open
+ * character and pushes a new state frame. */
+static void
+sexp_begin_aggregate (struct sprinter *sp, char open, char close)
+{
+    struct sprinter_sexp *sps = sexp_begin_value (sp);
+    struct sexp_state *state = talloc (sps, struct sexp_state);
+    fputc (open, sps->stream);
+    state->parent = sps->state;
+    state->first = TRUE;
+    state->in_map = FALSE;
+    state->close = close;
+    sps->state = state;
+}
+
+static void
+sexp_begin_map (struct sprinter *sp)
+{
+    struct sprinter_sexp *sps = (struct sprinter_sexp *) sp;
+    sexp_begin_aggregate (sp, '(', ')');
+    sps->state->in_map = TRUE;
+}
+
+static void
+sexp_begin_list (struct sprinter *sp)
+{
+    sexp_begin_aggregate (sp, '(', ')');
+}
+
+static void
+sexp_end (struct sprinter *sp)
+{
+    struct sprinter_sexp *sps = (struct sprinter_sexp *) sp;
+    struct sexp_state *state = sps->state;
+
+    if (sps->state->in_map)
+        fputc (')', sps->stream);
+    fputc (sps->state->close, sps->stream);
+    sps->state = state->parent;
+    talloc_free (state);
+    if (sps->state == NULL)
+        fputc ('\n', sps->stream);
+}
+
+/* This implementation supports embedded NULs as allowed by the JSON
+ * specification and Unicode.  Support for *parsing* embedded NULs
+ * varies, but is generally not a problem outside of C-based parsers
+ * (Python's json module and Emacs' json.el take embedded NULs in
+ * stride). */
+static void
+sexp_string_len_internal (struct sprinter *sp, const char *val, size_t len, notmuch_bool_t quote)
+{
+    static const char *const escapes[] = {
+        ['\"'] = "\\\"", ['\\'] = "\\\\", ['\b'] = "\\b",
+        ['\f'] = "\\f",  ['\n'] = "\\n",  ['\t'] = "\\t"
+    };
+    struct sprinter_sexp *sps = sexp_begin_value (sp);
+
+    if(quote)
+        fputc ('"', sps->stream);
+    for (; len; ++val, --len) {
+        unsigned char ch = *val;
+        if (ch < ARRAY_SIZE (escapes) && escapes[ch])
+            fputs (escapes[ch], sps->stream);
+        else if (ch >= 32)
+            fputc (ch, sps->stream);
+        else
+            fprintf (sps->stream, "\\u%04x", ch);
+    }
+    if(quote)
+        fputc ('"', sps->stream);
+}
+
+static void
+sexp_string_len (struct sprinter *sp, const char *val, size_t len)
+{
+    sexp_string_len_internal (sp, val, len, TRUE); /* print quoted */
+}
+
+static void
+sexp_symbol_len (struct sprinter *sp, const char *val, size_t len)
+{
+    sexp_string_len_internal (sp, val, len, FALSE); /* print unquoted */
+}
+
+static void
+sexp_string (struct sprinter *sp, const char *val)
+{
+    if (val == NULL)
+        val = "";
+    sexp_string_len (sp, val, strlen (val));
+}
+
+static void
+sexp_symbol (struct sprinter *sp, const char *val)
+{
+    if (val == NULL)
+        val = "";
+    sexp_symbol_len (sp, val, strlen (val));
+}
+
+static void
+sexp_integer (struct sprinter *sp, int val)
+{
+    struct sprinter_sexp *sps = sexp_begin_value (sp);
+
+    fprintf (sps->stream, "%d", val);
+}
+
+static void
+sexp_boolean (struct sprinter *sp, notmuch_bool_t val)
+{
+    struct sprinter_sexp *sps = sexp_begin_value (sp);
+
+    fputs (val ? "t" : "nil", sps->stream);
+}
+
+static void
+sexp_null (struct sprinter *sp)
+{
+    struct sprinter_sexp *sps = sexp_begin_value (sp);
+
+    fputs ("nil", sps->stream);
+}
+
+static void
+sexp_map_key (struct sprinter *sp, const char *key)
+{
+    struct sprinter_sexp *sps = (struct sprinter_sexp *) sp;
+
+    if( sps->state->in_map && ! sps->state->first)
+        fputs (") ", sps->stream);
+    fputc ('(', sps->stream);
+    sexp_symbol (sp, key);
+    fputc (' ', sps->stream);
+}
+
+static void
+sexp_set_prefix (unused (struct sprinter *sp), unused (const char *name))
+{
+}
+
+static void
+sexp_separator (struct sprinter *sp)
+{
+    struct sprinter_sexp *sps = (struct sprinter_sexp *) sp;
+
+    sps->insert_separator = TRUE;
+}
+
+struct sprinter *
+sprinter_sexp_create (const void *ctx, FILE *stream)
+{
+    static const struct sprinter_sexp template = {
+        .vtable = {
+            .begin_map = sexp_begin_map,
+            .begin_list = sexp_begin_list,
+            .end = sexp_end,
+            .string = sexp_string,
+            .string_len = sexp_string_len,
+            .integer = sexp_integer,
+            .boolean = sexp_boolean,
+            .null = sexp_null,
+            .map_key = sexp_map_key,
+            .separator = sexp_separator,
+            .set_prefix = sexp_set_prefix,
+            .is_text_printer = FALSE,
+        }
+    };
+    struct sprinter_sexp *res;
+
+    res = talloc (ctx, struct sprinter_sexp);
+    if (! res)
+        return NULL;
+
+    *res = template;
+    res->stream = stream;
+    return &res->vtable;
+}
-- 
1.8.0