--- /dev/null
+/* MIT (BSD) license - see LICENSE file for details */
+#ifndef CCAN_JSON_OUT_H
+#define CCAN_JSON_OUT_H
+#include <ccan/compiler/compiler.h>
+#include <ccan/tal/tal.h>
+#include <ccan/typesafe_cb/typesafe_cb.h>
+#include <stddef.h>
+
+struct json_out;
+
+/**
+ * json_out_new - allocate a json_out stream.
+ * @ctx: the tal_context to allocate from, or NULL
+ */
+struct json_out *json_out_new(const tal_t *ctx);
+
+/**
+ * json_out_call_on_move - callback for when buffer is reallocated.
+ * @jout: the json_out object to attach to.
+ * @cb: the callback to call.
+ * @arg: the argument to @cb (must match type).
+ *
+ * A NULL @cb disables. You can't currently have more than one callback.
+ * The @delta argument to @cb is the difference between the old location
+ * and the new one, and is never zero.
+ */
+#define json_out_call_on_move(jout, cb, arg) \
+ json_out_call_on_move_((jout), \
+ typesafe_cb_preargs(void, void *, \
+ (cb), (arg), \
+ struct json_out *, \
+ ptrdiff_t), \
+ (arg))
+
+void json_out_call_on_move_(struct json_out *jout,
+ void (*cb)(struct json_out *jout, ptrdiff_t delta,
+ void *arg),
+ void *arg);
+
+/**
+ * json_out_dup - duplicate a json_out stream.
+ * @ctx: the tal_context to allocate from, or NULL
+ * @src: the json_out to copy.
+ */
+struct json_out *json_out_dup(const tal_t *ctx, const struct json_out *src);
+
+/**
+ * json_out_start - start an array or object.
+ * @jout: the json_out object to write into.
+ * @fieldname: the fieldname, if inside an object, or NULL if inside an array.
+ * @type: '[' or '{' to start an array or object, respectively.
+ *
+ * Literally writes '"@fieldname": @type' or '@type ' if fieldname is NULL.
+ * @fieldname must not need JSON escaping.
+ */
+void json_out_start(struct json_out *jout, const char *fieldname, char type);
+
+/**
+ * json_out_end - end an array or object.
+ * @jout: the json_out object to write into.
+ * @type: '}' or ']' to end an array or object, respectively.
+ *
+ * Literally writes ']' or '}', keeping track of whether we need to append
+ * a comma.
+ */
+void json_out_end(struct json_out *jout, char type);
+
+/**
+ * json_out_add - add a formatted member.
+ * @jout: the json_out object to write into.
+ * @fieldname: optional fieldname to prepend (must not need escaping).
+ * @quote: if true, surround fmt by " and ".
+ * @fmt...: the printf-style format
+ *
+ * If you're in an array, @fieldname must be NULL. If you're in an
+ * object, @fieldname must be non-NULL. This is checked if
+ * CCAN_JSON_OUT_DEBUG is defined.
+ * @fieldname must not need JSON escaping.
+ *
+ * If the resulting string requires escaping, we call json_escape().
+ */
+PRINTF_FMT(4,5)
+void json_out_add(struct json_out *jout,
+ const char *fieldname,
+ bool quote,
+ const char *fmt, ...);
+
+/**
+ * json_out_addv - add a formatted member (vararg variant)
+ * @jout: the json_out object to write into.
+ * @fieldname: optional fieldname to prepend.
+ * @quote: if true, surround fmt by " and ".
+ * @fmt: the printf-style format
+ * @ap: the argument list.
+ *
+ * See json_out_add() above.
+ */
+void json_out_addv(struct json_out *jout,
+ const char *fieldname,
+ bool quote,
+ const char *fmt,
+ va_list ap);
+
+/**
+ * json_out_addstr - convenience helper to add a string field.
+ * @jout: the json_out object to write into.
+ * @fieldname: optional fieldname to prepend.
+ * @str: the string to add (must not be NULL).
+ *
+ * Equivalent to json_out_add(@jout, @fieldname, true, "%s", @str);
+ */
+void json_out_addstr(struct json_out *jout,
+ const char *fieldname,
+ const char *str);
+
+/**
+ * json_out_member_direct - add a field, with direct access.
+ * @jout: the json_out object to write into.
+ * @fieldname: optional fieldname to prepend.
+ * @extra: how many bytes to allocate.
+ *
+ * @fieldname must not need JSON escaping. Returns a direct pointer into
+ * the @extra bytes.
+ *
+ * This allows you to write your own efficient type-specific helpers.
+ */
+char *json_out_member_direct(struct json_out *jout,
+ const char *fieldname, size_t extra);
+
+/**
+ * json_out_direct - make room in output and access directly.
+ * @jout: the json_out object to write into.
+ * @len: the length to allocate.
+ *
+ * This lets you access the json_out stream directly, to save a copy,
+ * if you know exactly how much you will write.
+ *
+ * Returns a pointer to @len bytes at the end of @jout.
+ *
+ * This is dangerous, since it doesn't automatically prepend a ","
+ * like the internal logic does, but can be used (carefully) to add
+ * entire objects, or whitespace.
+ */
+char *json_out_direct(struct json_out *jout, size_t extra);
+
+/**
+ * json_out_add_splice - copy a field from another json_out.
+ * @jout: the json_out object to write into.
+ * @fieldname: optional fieldname to prepend.
+ * @src: the json_out object to copy from.
+ *
+ * This asserts that @src is well-formed (as per json_out_finished()),
+ * then places it into @jout with optional @fieldname prepended. This
+ * can be used to assemble sub-objects for your JSON and then copy
+ * them in.
+ *
+ * Note that it will call json_out_contents(@src), so it expects that
+ * object to be unconsumed.
+ */
+void json_out_add_splice(struct json_out *jout,
+ const char *fieldname,
+ const struct json_out *src);
+
+/**
+ * json_out_finished - assert that the json buffer is finished.
+ * @jout: the json_out object written to.
+ *
+ * This simply causes internal assertions that all arrays and objects are
+ * finished. It needs CCAN_JSON_OUT_DEBUG defined to have any effect.
+ */
+void json_out_finished(const struct json_out *jout);
+
+/**
+ * json_out_contents - read contents from json_out stream.
+ * @jout: the json_out object we want to read from.
+ * @len: set to the length of the buffer returned.
+ *
+ * This returns a pointer into the JSON written so far. Returns NULL
+ * and sets @len to 0 if there's nothing left in the buffer.
+ */
+const char *json_out_contents(const struct json_out *jout, size_t *len);
+
+/**
+ * json_out_consume - discard contents from json_out stream.
+ * @jout: the json_out object we read from.
+ * @len: the length to consume (must be <= @len from json_out_contents)
+ */
+void json_out_consume(struct json_out *jout, size_t len);
+#endif /* CCAN_JSON_OUT_H */
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