1 files changed, 207 insertions, 0 deletions
diff --git a/src/lib-mail/message-snippet.c b/src/lib-mail/message-snippet.c
new file mode 100644
index 0000000..2982e2e
--- /dev/null
+++ b/src/lib-mail/message-snippet.c
@@ -0,0 +1,207 @@
+/* Copyright (c) 2015-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "buffer.h"
+#include "str.h"
+#include "istream.h"
+#include "mail-html2text.h"
+#include "message-parser.h"
+#include "message-decoder.h"
+#include "message-snippet.h"
+
+#include <ctype.h>
+
+enum snippet_state {
+	/* beginning of the line */
+	SNIPPET_STATE_NEWLINE = 0,
+	/* within normal text */
+	SNIPPET_STATE_NORMAL,
+	/* within quoted text - skip until EOL */
+	SNIPPET_STATE_QUOTED
+};
+
+struct snippet_data {
+	string_t *snippet;
+	unsigned int chars_left;
+};
+
+struct snippet_context {
+	struct snippet_data snippet;
+	struct snippet_data quoted_snippet;
+	enum snippet_state state;
+	bool add_whitespace;
+	struct mail_html2text *html2text;
+	buffer_t *plain_output;
+};
+
+static void snippet_add_content(struct snippet_context *ctx,
+				struct snippet_data *target,
+				const unsigned char *data, size_t size,
+				size_t *count_r)
+{
+	i_assert(target != NULL);
+	if (size == 0)
+		return;
+	if (size >= 3 &&
+	     ((data[0] == 0xEF && data[1] == 0xBB && data[2] == 0xBF) ||
+	      (data[0] == 0xBF && data[1] == 0xBB && data[2] == 0xEF))) {
+		*count_r = 3;
+		return;
+	}
+	if (data[0] == '\0') {
+		/* skip NULs without increasing snippet size */
+		return;
+	}
+	if (i_isspace(*data)) {
+		/* skip any leading whitespace */
+		if (str_len(target->snippet) > 0)
+			ctx->add_whitespace = TRUE;
+		if (data[0] == '\n')
+			ctx->state = SNIPPET_STATE_NEWLINE;
+		return;
+	}
+	if (target->chars_left == 0)
+		return;
+	target->chars_left--;
+	if (ctx->add_whitespace) {
+		if (target->chars_left == 0) {
+			/* don't add a trailing whitespace */
+			return;
+		}
+		str_append_c(target->snippet, ' ');
+		ctx->add_whitespace = FALSE;
+		target->chars_left--;
+	}
+	*count_r = uni_utf8_char_bytes(data[0]);
+	i_assert(*count_r <= size);
+	str_append_data(target->snippet, data, *count_r);
+}
+
+static bool snippet_generate(struct snippet_context *ctx,
+			     const unsigned char *data, size_t size)
+{
+	size_t i, count;
+	struct snippet_data *target;
+
+	if (ctx->html2text != NULL) {
+		buffer_set_used_size(ctx->plain_output, 0);
+		mail_html2text_more(ctx->html2text, data, size,
+				    ctx->plain_output);
+		data = ctx->plain_output->data;
+		size = ctx->plain_output->used;
+	}
+
+	if (ctx->state == SNIPPET_STATE_QUOTED)
+		target = &ctx->quoted_snippet;
+	else
+		target = &ctx->snippet;
+
+	/* message-decoder should feed us only valid and complete
+	   UTF-8 input */
+
+	for (i = 0; i < size; i += count) {
+		count = 1;
+		switch (ctx->state) {
+		case SNIPPET_STATE_NEWLINE:
+			if (data[i] == '>') {
+				ctx->state = SNIPPET_STATE_QUOTED;
+				i++;
+				target = &ctx->quoted_snippet;
+			} else {
+				ctx->state = SNIPPET_STATE_NORMAL;
+				target = &ctx->snippet;
+			}
+			/* fallthrough */
+		case SNIPPET_STATE_NORMAL:
+		case SNIPPET_STATE_QUOTED:
+			snippet_add_content(ctx, target, CONST_PTR_OFFSET(data, i),
+					    size-i, &count);
+			/* break here if we have enough non-quoted data,
+			   quoted data does not need to break here as it's
+			   only used if the actual snippet is left empty. */
+			if (ctx->snippet.chars_left == 0)
+				return FALSE;
+			break;
+		}
+	}
+	return TRUE;
+}
+
+static void snippet_copy(const char *src, string_t *dst)
+{
+	while (*src != '\0' && i_isspace(*src)) src++;
+	str_append(dst, src);
+}
+
+int message_snippet_generate(struct istream *input,
+			     unsigned int max_snippet_chars,
+			     string_t *snippet)
+{
+	const struct message_parser_settings parser_set = { .flags = 0 };
+	struct message_parser_ctx *parser;
+	struct message_part *parts;
+	struct message_part *skip_part = NULL;
+	struct message_decoder_context *decoder;
+	struct message_block raw_block, block;
+	struct snippet_context ctx;
+	pool_t pool;
+	int ret;
+
+	i_zero(&ctx);
+	pool = pool_alloconly_create("message snippet", 2048);
+	ctx.snippet.snippet = str_new(pool, max_snippet_chars);
+	ctx.snippet.chars_left = max_snippet_chars;
+	ctx.quoted_snippet.snippet = str_new(pool, max_snippet_chars);
+	ctx.quoted_snippet.chars_left = max_snippet_chars - 1; /* -1 for '>' */
+	parser = message_parser_init(pool_datastack_create(), input, &parser_set);
+	decoder = message_decoder_init(NULL, 0);
+	while ((ret = message_parser_parse_next_block(parser, &raw_block)) > 0) {
+		if (raw_block.part == skip_part)
+			continue;
+		if (!message_decoder_decode_next_block(decoder, &raw_block, &block))
+			continue;
+		if (block.size == 0) {
+			const char *ct;
+
+			if (block.hdr != NULL)
+				continue;
+
+			/* We already have a snippet, don't look for more in
+			   subsequent parts. */
+			if (ctx.snippet.snippet->used != 0 ||
+			    ctx.quoted_snippet.snippet->used != 0)
+				break;
+
+			skip_part = NULL;
+
+			/* end of headers - verify that we can use this
+			   Content-Type. we get here only once, because we
+			   always handle only one non-multipart MIME part. */
+			ct = message_decoder_current_content_type(decoder);
+			if (ct == NULL)
+				/* text/plain */ ;
+			else if (mail_html2text_content_type_match(ct)) {
+				mail_html2text_deinit(&ctx.html2text);
+				ctx.html2text = mail_html2text_init(0);
+				if (ctx.plain_output == NULL) {
+					ctx.plain_output =
+						buffer_create_dynamic(pool, 1024);
+				}
+			} else if (strncasecmp(ct, "text/", 5) != 0)
+				skip_part = raw_block.part;
+		} else if (!snippet_generate(&ctx, block.data, block.size))
+			break;
+	}
+	i_assert(ret != 0);
+	message_decoder_deinit(&decoder);
+	message_parser_deinit(&parser, &parts);
+	mail_html2text_deinit(&ctx.html2text);
+	if (ctx.snippet.snippet->used != 0)
+		snippet_copy(str_c(ctx.snippet.snippet), snippet);
+	else if (ctx.quoted_snippet.snippet->used != 0) {
+		str_append_c(snippet, '>');
+		snippet_copy(str_c(ctx.quoted_snippet.snippet), snippet);
+	}
+	pool_unref(&pool);
+	return input->stream_errno == 0 ? 0 : -1;
+}