From: Timo Sirainen <timo.sirainen@open-xchange.com>
Date: Fri, 17 Apr 2026 14:55:05 +0000 (+0200)
Subject: [PATCH 02/14] imap: Stream BODYSTRUCTURE to client without ostream memory duplication
X-Git-Tag: archive/raspbian/1%2.4.1+dfsg1-6+rpi1+deb13u7^2~62
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=d0adf60476b521447ece50a5a7d3e95dee66e9f9;p=dovecot.git

[PATCH 02/14] imap: Stream BODYSTRUCTURE to client without ostream memory duplication

For huge BODYSTRUCTURE responses (messages with many MIME parts),
o_stream_send_str() caused the ostream to copy the entire string into
its ring buffer when the stream was corked, doubling memory usage.

Use the same o_stream_set_max_buffer_size(0) + o_stream_send_istream()
pattern as fetch_stream_continue() so the ostream buffer stays at 0
bytes and the I/O loop handles flow control via WAIT_OUTPUT.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Gbp-Pq: Name 0002-imap-Stream-BODYSTRUCTURE-to-client-without-ostream-.patch
---

diff --git a/src/imap/imap-fetch.c b/src/imap/imap-fetch.c
index ca4b321..b4a8a46 100644
--- a/src/imap/imap-fetch.c
+++ b/src/imap/imap-fetch.c
@@ -732,6 +732,34 @@ static bool fetch_body_init(struct imap_fetch_init_context *ctx)
 	return imap_fetch_body_section_init(ctx);
 }
 
+static int fetch_bodystructure_stream_continue(struct imap_fetch_context *ctx)
+{
+	struct imap_fetch_state *state = &ctx->state;
+	enum ostream_send_istream_result res;
+
+	o_stream_set_max_buffer_size(ctx->client->output, 0);
+	res = o_stream_send_istream(ctx->client->output, state->cur_input);
+	o_stream_set_max_buffer_size(ctx->client->output, SIZE_MAX);
+
+	switch (res) {
+	case OSTREAM_SEND_ISTREAM_RESULT_FINISHED:
+		i_stream_unref(&state->cur_input);
+		state->cont_handler = NULL;
+		if (o_stream_send(ctx->client->output, ")", 1) < 0)
+			return -1;
+		return 1;
+	case OSTREAM_SEND_ISTREAM_RESULT_WAIT_INPUT:
+		i_unreached();
+	case OSTREAM_SEND_ISTREAM_RESULT_WAIT_OUTPUT:
+		return 0;
+	case OSTREAM_SEND_ISTREAM_RESULT_ERROR_INPUT:
+		i_unreached();
+	case OSTREAM_SEND_ISTREAM_RESULT_ERROR_OUTPUT:
+		return -1;
+	}
+	i_unreached();
+}
+
 static int fetch_bodystructure(struct imap_fetch_context *ctx,
 			       struct mail *mail, void *context ATTR_UNUSED)
 {
@@ -748,12 +776,13 @@ static int fetch_bodystructure(struct imap_fetch_context *ctx,
 			return -1;
 	}
 
-	if (o_stream_send(ctx->client->output, "BODYSTRUCTURE (", 15) < 0 ||
-	    o_stream_send_str(ctx->client->output, bodystructure) < 0 ||
-	    o_stream_send(ctx->client->output, ")", 1) < 0)
+	if (o_stream_send(ctx->client->output, "BODYSTRUCTURE (", 15) < 0)
 		return -1;
 
-	return 1;
+	ctx->state.cur_input =
+		i_stream_create_from_data(bodystructure, strlen(bodystructure));
+	ctx->state.cont_handler = fetch_bodystructure_stream_continue;
+	return fetch_bodystructure_stream_continue(ctx);
 }
 
 static bool fetch_bodystructure_init(struct imap_fetch_init_context *ctx)