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+From: Austin Clements <amdragon@mit.edu>\r
+To: notmuch@notmuchmail.org\r
+Subject: [PATCH v4 09/11] lib: Support empty header values in database\r
+Date: Mon, 25 Aug 2014 13:26:07 -0400\r
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+\r
+Commit 567bcbc2 introduced support for storing various headers in\r
+document values. However, doing so in a backwards-compatible way\r
+meant that genuinely empty header values could not be distinguished\r
+from the old behavior of not storing the headers at all, so these\r
+required parsing the original message.\r
+\r
+Now that we have database features, new databases can declare that all\r
+messages have header values, so if we have this feature flag, we can\r
+use the stored header value even if it's the empty string.\r
+\r
+This requires slight cleanup to notmuch_message_get_header, since the\r
+code previously couldn't distinguish between empty headers and headers\r
+that are never stored in the database (previously this distinction\r
+didn't matter).\r
+---\r
+ lib/message.cc | 45 +++++++++++++++++++++++++++------------------\r
+ 1 file changed, 27 insertions(+), 18 deletions(-)\r
+\r
+diff --git a/lib/message.cc b/lib/message.cc\r
+index 3f93426..ed8c59e 100644\r
+--- a/lib/message.cc\r
++++ b/lib/message.cc\r
+@@ -414,26 +414,35 @@ _notmuch_message_ensure_message_file (notmuch_message_t *message)\r
+ const char *\r
+ notmuch_message_get_header (notmuch_message_t *message, const char *header)\r
+ {\r
+- try {\r
+- std::string value;\r
+-\r
+- /* Fetch header from the appropriate xapian value field if\r
+- * available */\r
+- if (strcasecmp (header, "from") == 0)\r
+- value = message->doc.get_value (NOTMUCH_VALUE_FROM);\r
+- else if (strcasecmp (header, "subject") == 0)\r
+- value = message->doc.get_value (NOTMUCH_VALUE_SUBJECT);\r
+- else if (strcasecmp (header, "message-id") == 0)\r
+- value = message->doc.get_value (NOTMUCH_VALUE_MESSAGE_ID);\r
+-\r
+- if (!value.empty())\r
++ Xapian::valueno slot = Xapian::BAD_VALUENO;\r
++\r
++ /* Fetch header from the appropriate xapian value field if\r
++ * available */\r
++ if (strcasecmp (header, "from") == 0)\r
++ slot = NOTMUCH_VALUE_FROM;\r
++ else if (strcasecmp (header, "subject") == 0)\r
++ slot = NOTMUCH_VALUE_SUBJECT;\r
++ else if (strcasecmp (header, "message-id") == 0)\r
++ slot = NOTMUCH_VALUE_MESSAGE_ID;\r
++\r
++ if (slot != Xapian::BAD_VALUENO) {\r
++ try {\r
++ std::string value = message->doc.get_value (slot);\r
++\r
++ /* If we have NOTMUCH_FEATURE_FROM_SUBJECT_ID_VALUES, then\r
++ * empty values indicate empty headers. If we don't, then\r
++ * it could just mean we didn't record the header. */\r
++ if ((message->notmuch->features &\r
++ NOTMUCH_FEATURE_FROM_SUBJECT_ID_VALUES) ||\r
++ ! value.empty())\r
+ return talloc_strdup (message, value.c_str ());\r
+ \r
+- } catch (Xapian::Error &error) {\r
+- fprintf (stderr, "A Xapian exception occurred when reading header: %s\n",\r
+- error.get_msg().c_str());\r
+- message->notmuch->exception_reported = TRUE;\r
+- return NULL;\r
++ } catch (Xapian::Error &error) {\r
++ fprintf (stderr, "A Xapian exception occurred when reading header: %s\n",\r
++ error.get_msg().c_str());\r
++ message->notmuch->exception_reported = TRUE;\r
++ return NULL;\r
++ }\r
+ }\r
+ \r
+ /* Otherwise fall back to parsing the file */\r
+-- \r
+2.0.0\r
+\r