[PATCH v2 2/3] show: indicate length, encoding of omitted body content

[Peter Wang <novalazy@gmail.com>]

If a leaf part's body content is omitted, return the encoded length and
transfer encoding in --format=json output.  This information may be used
by the consumer, e.g. to decide whether to download a large attachment
over a slow link.

Returning the _encoded_ content length is more efficient than returning
the _decoded_ content length.  Returning the transfer encoding allows
the consumer to estimate the decoded content length.
---
 devel/schemata |    9 ++++++++-
 notmuch-show.c |   14 ++++++++++++++
 2 files changed, 22 insertions(+), 1 deletions(-)

diff --git a/devel/schemata b/devel/schemata
index 9cb25f5..094b9a5 100644
--- a/devel/schemata
+++ b/devel/schemata
@@ -69,7 +69,14 @@ part = {
     # A leaf part's body content is optional, but may be included if
     # it can be correctly encoded as a string.  Consumers should use
     # this in preference to fetching the part content separately.
-    content?:       string
+    content?:       string,
+    # If a leaf part's body content is not included, the length of
+    # the encoded content (in bytes) may be given instead.
+    content-length?: int,
+    # If a leaf part's body content is not included, its transfer encoding
+    # may be given.  Using this and the encoded content length, it is
+    # possible for the consumer to estimate the decoded content length.
+    content-transfer-encoding?: string
 }
 
 # The headers of a message or part (format_headers_json with reply = FALSE)
diff --git a/notmuch-show.c b/notmuch-show.c
index 3556293..83535c7 100644
--- a/notmuch-show.c
+++ b/notmuch-show.c
@@ -664,6 +664,20 @@ format_part_json (const void *ctx, sprinter_t *sp, mime_node_t *node,
 	    sp->map_key (sp, "content");
 	    sp->string_len (sp, (char *) part_content->data, part_content->len);
 	    g_object_unref (stream_memory);
+	} else {
+	    GMimeDataWrapper *wrapper = g_mime_part_get_content_object (GMIME_PART (node->part));
+	    GMimeStream *stream = g_mime_data_wrapper_get_stream (wrapper);
+	    ssize_t length = g_mime_stream_length (stream);
+	    const char *cte = g_mime_object_get_header (meta, "content-transfer-encoding");
+
+	    if (length >= 0) {
+		sp->map_key (sp, "content-length");
+		sp->integer (sp, length);
+	    }
+	    if (cte) {
+		sp->map_key (sp, "content-transfer-encoding");
+		sp->string (sp, cte);
+	    }
 	}
     } else if (GMIME_IS_MULTIPART (node->part)) {
 	sp->map_key (sp, "content");
-- 
1.7.4.4