. Update the Copyright year (only) when changing content.
. /////////////////////////////////////////////////////////////////////////////
-.set previousversion "4.92"
+.set previousversion "4.93"
.include ./local_params
.set ACL "access control lists (ACLs)"
.set I " "
.macro copyyear
-2018, 2019
+2019
.endmacro
. /////////////////////////////////////////////////////////////////////////////
OpenSSL or GnuTLS library. There is no cryptographic code in Exim itself for
implementing SSL.
-.new
If you do not want TLS support you should set
.code
DISABLE_TLS=yes
.endd
in &_Local/Makefile_&.
-.wen
-.new
If OpenSSL is installed, you should set
.code
USE_OPENSL=yes
USE_OPENSSL=yes
USE_OPENSSL_PC=openssl
.endd
-.wen
.cindex "USE_GNUTLS"
If GnuTLS is installed, you should set
.code
Bounce messages are just discarded. This option can be used only by an admin
user.
-.new
.vitem &%-MG%&&~<&'queue&~name'&>&~<&'message&~id'&>&~<&'message&~id'&>&~...
.oindex "&%-MG%&"
.cindex queue named
string to define the default queue.
If the messages are not currently located in the default queue,
a &%-qG<name>%& option will be required to define the source queue.
-.wen
.vitem &%-Mmad%&&~<&'message&~id'&>&~<&'message&~id'&>&~...
.oindex "&%-Mmad%&"
without &%-bd%&, this is the only way of causing Exim to write a pid file,
because in those cases, the normal pid file is not used.
+.new
+.vitem &%-oPX%&
+.oindex "&%-oPX%&"
+.cindex "pid (process id)" "of daemon"
+.cindex "daemon" "process id (pid)"
+This option is not intended for general use.
+The daemon uses it when terminating due to a SIGTEM, possibly in
+combination with &%-oP%&&~<&'path'&>.
+It causes the pid file to be removed.
+.wen
+
.vitem &%-or%&&~<&'time'&>
.oindex "&%-or%&"
.cindex "timeout" "for non-SMTP input"
the implicit key is the host's IP address rather than its name (see section
&<<SECThoslispatsikey>>&).
-.new
&*Warning 3*&: Do not use an IPv4-mapped IPv6 address for a key; use the
IPv4, in dotted-quad form. (Exim converts IPv4-mapped IPv6 addresses to this
notation before executing the lookup.)
-.wen
.next
-.new
.cindex lookup json
.cindex json "lookup type"
.cindex JSON expansions
or array; for the latter two a string-representation os the JSON
is returned.
For elements of type string, the returned value is de-quoted.
-.wen
.next
.cindex "linear search"
.cindex "lookup" "lsearch"
With &"strict"& a response from the DNS resolver that
is not labelled as authenticated data
is treated as equivalent to a temporary DNS error.
-.new
The default is &"lax"&.
-.wen
See also the &$lookup_dnssec_authenticated$& variable.
(notated using the quoting facility) so as to distinguish them from IPv4 keys.
For this reason, when the lookup type is &(iplsearch)&, IPv6 addresses are
converted using colons and not dots.
-.new
In all cases except IPv4-mapped IPv6, full, unabbreviated IPv6
addresses are always used.
The latter are converted to IPv4 addresses, in dotted-quad form.
-.wen
Ideally, it would be nice to tidy up this anomalous situation by changing to
colons in all cases, given that quoting is now available for &(lsearch)&.
the data type. ACL rules always expand strings. A couple of expansion
conditions do not expand some of the brace-delimited branches, for security
reasons,
-.new
.cindex "tainted data" expansion
.cindex expansion "tainted data"
and expansion of data deriving from the sender (&"tainted data"&)
is not permitted.
-.wen
There may be from zero to eight arguments to the function.
-.new
When compiling
a local function that is to be called in this way,
first &_DLFUNC_IMPL_& should be defined,
and second &_local_scan.h_& should be included.
-.wen
The Exim variables and functions that are defined by that API
are also available for dynamically loaded functions. The function itself
must have the following type:
For the &"json"& variant,
if a returned value is a JSON string, it retains its leading and
trailing quotes.
-.new
For the &"jsons"& variant, which is intended for use with JSON strings, the
leading and trailing quotes are removed from the returned value.
-.wen
. XXX should be a UTF-8 compare
The results of matching are handled as above.
For the &"json"& variant,
if a returned value is a JSON string, it retains its leading and
trailing quotes.
-.new
For the &"jsons"& variant, which is intended for use with JSON strings, the
leading and trailing quotes are removed from the returned value.
-.wen
.vitem &*${filter{*&<&'string'&>&*}{*&<&'condition'&>&*}}*&
If the string is a single variable of type certificate,
returns the SHA-256 hash fingerprint of the certificate.
-.new
The operator can also be spelled &%sha2%& and does the same as &%sha256%&
(except for certificates, which are not supported).
Finally, if an underbar
and a number is appended it specifies the output length, selecting a
member of the SHA-2 family of hash functions.
Values of 256, 384 and 512 are accepted, with 256 being the default.
-.wen
.vitem &*${sha3:*&<&'string'&>&*}*& &&&
To scan a named list, expand it with the &*listnamed*& operator.
-.new
.vitem "&*forall_json{*&<&'a JSON array'&>&*}{*&<&'a condition'&>&*}*&" &&&
"&*forany_json{*&<&'a JSON array'&>&*}{*&<&'a condition'&>&*}*&" &&&
"&*forall_jsons{*&<&'a JSON array'&>&*}{*&<&'a condition'&>&*}*&" &&&
The array separator is not changeable.
For the &"jsons"& variants the elements are expected to be JSON strings
and have their quotes removed before the evaluation of the condition.
-.wen
.vindex "&$config_file$&"
The name of the main configuration file Exim is using.
-.new
.vitem &$dmarc_domain_policy$& &&&
&$dmarc_status$& &&&
&$dmarc_status_text$& &&&
&$dmarc_used_domains$&
Results of DMARC verification.
For details see section &<<SECDMARC>>&.
-.wen
.vitem &$dkim_verify_status$&
Results of DKIM verification.
.cindex queues named
The name of the spool queue in use; empty for the default queue.
-.new
.vitem &$r_...$&
.vindex &$r_...$&
.cindex router variables
They can be given any name that starts with &$r_$&.
The values persist for the address being handled through subsequent routers
and the eventual transport.
-.wen
.vitem &$rcpt_count$&
.vindex "&$rcpt_count$&"
&*Note*&: Under versions of OpenSSL preceding 1.1.1,
when a list of more than one
file is used for &%tls_certificate%&, this variable is not reliable.
-.new
The macro "_TLS_BAD_MULTICERT_IN_OURCERT" will be defined for those versions.
-.wen
.vitem &$tls_in_peercert$&
.vindex "&$tls_in_peercert$&"
but in the context of an outward SMTP delivery taking place via the &(smtp)& transport
becomes the same as &$tls_out_cipher$&.
-.new
.vitem &$tls_in_cipher_std$&
.vindex "&$tls_in_cipher_std$&"
As above, but returning the RFC standard name for the cipher suite.
-.wen
.vitem &$tls_out_cipher$&
.vindex "&$tls_out_cipher$&"
&<<CHAPTLS>>& for details of TLS support and chapter &<<CHAPsmtptrans>>& for
details of the &(smtp)& transport.
-.new
.vitem &$tls_out_cipher_std$&
.vindex "&$tls_out_cipher_std$&"
As above, but returning the RFC standard name for the cipher suite.
-.wen
.vitem &$tls_out_dane$&
.vindex &$tls_out_dane$&
.vindex &$tls_out_tlsa_usage$&
Bitfield of TLSA record types found. See section &<<SECDANE>>&.
-.new
.vitem &$tls_in_ver$&
.vindex "&$tls_in_ver$&"
When a message is received from a remote host over an encrypted SMTP connection
.vindex "&$tls_out_ver$&"
When a message is being delivered to a remote host over an encrypted SMTP connection
this variable is set to the protocol version.
-.wen
.vitem &$tod_bsdinbox$&
UTF-8 multicharacters to appear in domain name components, in addition to
letters, digits, and hyphens.
-.new
If Exim is built with internationalization support
and the SMTPUTF8 ESMTP option is in use (see chapter &<<CHAPi18n>>&)
this option can be left as default.
-.wen
Without that,
if you want to look up such domain names in the DNS, you must also
adjust the value of &%dns_check_names_pattern%& to match the extended form. A
.new
-.option dkim_verify_hashes main "string list" "sha256 : sha512 : sha1"
+.option dkim_verify_hashes main "string list" "sha256 : sha512"
.cindex DKIM "selecting signature algorithms"
This option gives a list of hash types which are acceptable in signatures,
+.wen
and an order of processing.
Signatures with algorithms not in the list will be ignored.
-Note that the presence of sha1 violates RFC 8301.
-Signatures using the rsa-sha1 are however (as of writing) still common.
-The default inclusion of sha1 may be dropped in a future release.
+Acceptable values include:
+.code
+sha1
+sha256
+sha512
+.endd
+
+Note that the acceptance of sha1 violates RFC 8301.
.option dkim_verify_keytypes main "string list" "ed25519 : rsa"
This option gives a list of key types which are acceptable in signatures,
.option dkim_verify_minimal main boolean false
If set to true, verification of signatures will terminate after the
first success.
-.wen
.option dkim_verify_signers main "domain list&!!" $dkim_signers
.cindex DKIM "controlling calls to the ACL"
This is a fudge to help with name servers that give big delays or otherwise do
not work for the AAAA record type. In due course, when the world's name
servers have all been upgraded, there should be no need for this option.
-.new
Note that all lookups, including those done for verification, are affected;
this will result in verify failure for IPv6 connections or ones using names
only valid for IPv6 addresses.
-.wen
.option dns_retrans main time 0s
used. See chapter &<<CHAPsecurity>>& for a discussion of security issues.
-.new
.option exim_version main string "current version"
.cindex "Exim version"
.cindex customizing "version number"
.cindex "version number of Exim" override
This option overrides the &$version_number$&/&$exim_version$& that Exim reports in
various places. Use with care; this may fool stupid security scanners.
-.wen
.option extra_local_interfaces main "string list" unset
name. If no specific path is set for the log files at compile or runtime,
or if the option is unset at runtime (i.e. &`log_file_path = `&)
they are written in a sub-directory called &_log_& in Exim's spool directory.
-.new
A path must start with a slash.
To send to syslog, use the word &"syslog"&.
-.wen
Chapter &<<CHAPlog>>& contains further details about Exim's logging, and
section &<<SECTwhelogwri>>& describes how the contents of &%log_file_path%& are
used. If this string is fixed at your installation (contains no expansion
that clients will use it; &"out of order"& commands that are &"expected"& do
not count as protocol errors (see &%smtp_max_synprot_errors%&).
-.new
.option pipelining_connect_advertise_hosts main "host list&!!" *
.cindex "pipelining" "early connection"
.cindex "pipelining" PIPE_CONNECT
See also the &%hosts_pipe_connect%& smtp transport option.
Currently the option name &"X_PIPE_CONNECT"& is used.
-.wen
.option prdr_enable main boolean false
added to the message. Otherwise, the string should start with the text
&"Received:"& and conform to the RFC 2822 specification for &'Received:'&
header lines.
-.new
The default setting is:
.code
id $message_exim_id\
${if def:received_for {\n\tfor $received_for}}
.endd
-.wen
The reference to the TLS cipher is omitted when Exim is built without TLS
support. The use of conditional expansions ensures that this works for both
&*Note*&: Under versions of OpenSSL preceding 1.1.1,
when a list of more than one
file is used, the &$tls_in_ourcert$& variable is unreliable.
-.new
The macro "_TLS_BAD_MULTICERT_IN_OURCERT" will be defined for those versions.
-.wen
If the option contains &$tls_out_sni$& and Exim is built against OpenSSL, then
if the OpenSSL build supports TLS extensions and the TLS client sends the
The value of this option is expanded and indicates the source of DH parameters
to be used by Exim.
-.new
This option is ignored for GnuTLS version 3.6.0 and later.
The library manages parameter negotiation internally.
-.wen
&*Note: The Exim Maintainers strongly recommend,
for other TLS library versions,
Certificate Authority.
Usable for GnuTLS 3.4.4 or 3.3.17 or OpenSSL 1.1.0 (or later).
-.new
The macro "_HAVE_TLS_OCSP" will be defined for those versions.
-.wen
-.new
For OpenSSL 1.1.0 or later, and
-.wen
for GnuTLS 3.5.6 or later the expanded value of this option can be a list
of files, to match a list given for the &%tls_certificate%& option.
The ordering of the two lists must match.
-.new
The macro "_HAVE_TLS_OCSP_LIST" will be defined for those versions.
-.wen
-.new
The file(s) should be in DER format,
except for GnuTLS 3.6.3 or later
or for OpenSSL,
PEM blobs (ie. separate OCSP responses), it sends them in the
TLS Certificate record interleaved with the certificates of the chain;
although a GnuTLS client is happy with that, an OpenSSL client is not.
-.wen
.option tls_on_connect_ports main "string list" unset
.cindex SSMTP
This makes the configuration file less messy, and also reduces the number of
lookups (though Exim does cache lookups).
-.new
See also the &%set%& option below.
-.wen
.vindex "&$sender_address_data$&"
.vindex "&$address_data$&"
This option controls whether the local part is used to form the key for retry
hints for addresses that suffer temporary errors while being handled by this
-.new
router. The default value is true for any router that has any of
&%check_local_user%&,
&%local_parts%&,
&%local_part_suffix%&,
&%senders%& or
&%require_files%&
-.wen
set, and false otherwise. Note that this option does not apply to hints keys
for transport delays; they are controlled by a generic transport option of the
same name.
matters.
-.new
.option set routers "string list" unset
.cindex router variables
This option may be used multiple times on a router;
This is similar to the &%address_data%& option, except that
many independent variables can be used, with choice of naming.
-.wen
.option translate_ip_address routers string&!! unset
Section &<<SECID136>>& contains further information.
-.new
This option should not be used when other message-handling software
may duplicate messages by making hardlinks to the files. When that is done Exim
will count the message size once for each filename, in contrast with the actual
disk usage. When the option is not set, calculating total usage requires
a system-call per file to get the size; the number of links is then available also
as is used to adjust the effective size.
-.wen
.option quota_warn_message appendfile string&!! "see below"
Exim will not use the SMTP PIPELINING extension when delivering to any host
that matches this list, even if the server host advertises PIPELINING support.
-.new
.option hosts_pipe_connect smtp "host list&!!" unset
.cindex "pipelining" "early connection"
.cindex "pipelining" PIPE_CONNECT
presence of a &"def:"& test on it, but suitably complex coding
can avoid the check and produce unexpected results.
You have been warned.
-.wen
.option hosts_avoid_tls smtp "host list&!!" unset
message on the same connection. See section &<<SECTmulmessam>>& for an
explanation of when this might be needed.
-.new
.option hosts_noproxy_tls smtp "host list&!!" unset
.cindex "TLS" "passing connection"
.cindex "multiple SMTP deliveries"
For any host that matches this list, a TLS session which has
been started will not be passed to a new delivery process for sending another
message on the same session.
-.wen
The traditional implementation closes down TLS and re-starts it in the new
process, on the same open TCP connection, for each successive message
.cindex "RFC 3030" "CHUNKING"
This option provides a list of servers to which, provided they announce
CHUNKING support, Exim will attempt to use BDAT commands rather than DATA.
+.new
+Unless DKIM signing is being done,
+.wen
BDAT will not be used in conjunction with a transport filter.
.option hosts_try_dane smtp "host list&!!" *
the Cyrus SASL authentication library.
The third is an interface to Dovecot's authentication system, delegating the
work via a socket interface.
-.new
The fourth provides for negotiation of authentication done via non-SMTP means,
as defined by RFC 4422 Appendix A.
-.wen
The fifth provides an interface to the GNU SASL authentication library, which
provides mechanisms but typically not data sources.
The sixth provides direct access to Heimdal GSSAPI, geared for Kerberos, but
use unencrypted plain text, you should not use the same passwords for SMTP
connections as you do for login accounts.
-.new
.section "Avoiding cleartext use" "SECTplain_TLS"
The following generic option settings will disable &(plaintext)& authenticators when
TLS is not being used:
&*Note*&: a plaintext SMTP AUTH done inside TLS is not vulnerable to casual snooping,
but is still vulnerable to a Man In The Middle attack unless certificates
(including their names) have been properly verified.
-.wen
.section "Plaintext server options" "SECID171"
.cindex "options" "&(plaintext)& authenticator (server)"
non-issue, as a man-in-the-middle attack will cause the correct client and
server to see different identifiers and authentication will fail.
-This is currently only supported when using the GnuTLS library. This is
+.new
+This is
only usable by mechanisms which support "channel binding"; at time of
writing, that's the SCRAM family.
+.wen
This defaults off to ensure smooth upgrade across Exim releases, in case
this option causes some clients to start failing. Some future release
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
-.new
.chapter "The external authenticator" "CHAPexternauth"
.scindex IIDexternauth1 "&(external)& authenticator"
.scindex IIDexternauth2 "authenticators" "&(external)&"
.ecindex IIDexternauth1
.ecindex IIDexternauth2
-.wen
.section "OpenSSL vs GnuTLS" "SECTopenvsgnu"
.cindex "TLS" "OpenSSL &'vs'& GnuTLS"
TLS is supported in Exim using either the OpenSSL or GnuTLS library.
-.new
To build Exim to use OpenSSL you need to set
.code
USE_OPENSSL=yes
.endd
in Local/Makefile.
-.wen
To build Exim to use GnuTLS, you need to set
.code
if it requests it. If the server is Exim, it will request a certificate only if
&%tls_verify_hosts%& or &%tls_try_verify_hosts%& matches the client.
-.new
&*Note*&: Do not use a certificate which has the OCSP-must-staple extension,
for client use (they are usable for server use).
As the TLS protocol has no means for the client to staple before TLS 1.3 it will result
in failed connections.
-.wen
If the &%tls_verify_certificates%& option is set on the &(smtp)& transport, it
specifies a collection of expected server certificates.
the operation and configuration of DKIM, see section &<<SECDKIM>>&.
+.vitem &*control&~=&~dmarc_disable_verify*&
+.cindex "disable DMARC verify"
+.cindex "DMARC" "disable verify"
+This control turns off DMARC verification processing entirely. For details on
+the operation and configuration of DMARC, see section &<<SECDMARC>>&.
+
+
.vitem &*control&~=&~dscp/*&<&'value'&>
.cindex "&ACL;" "setting DSCP value"
.cindex "DSCP" "inbound"
&'Resent-Cc:'& header lines exist, they are also checked. This condition can be
used only in a DATA or non-SMTP ACL.
-.new
There is one possible option, &`case_insensitive`&. If this is present then
local parts are checked case-insensitively.
-.wen
There are, of course, many legitimate messages that make use of blind (bcc)
recipients. This check should not be used on its own for blocking messages.
specialized interfaces for &"daemon"& type virus scanners, which are resident
in memory and thus are much faster.
-.new
Since message data needs to have arrived,
the condition may be only called in ACL defined by
&%acl_smtp_data%&,
&%acl_smtp_data_prdr%&,
&%acl_smtp_mime%& or
&%acl_smtp_dkim%&
-.wen
A timeout of 2 minutes is applied to a scanner call (by default);
if it expires then a defer action is taken.
This function is used in conjunction with &'smtp_printf()'&, as described
below.
-.new
.vitem &*void&~smtp_printf(char&~*,BOOL,&~...)*&
The arguments of this function are almost like &[printf()]&; it writes to the SMTP
-.wen
output stream. You should use this function only when there is an SMTP output
stream, that is, when the incoming message is being received via interactive
SMTP. This is the case when &%smtp_input%& is TRUE and &%smtp_batched_input%&
If an SMTP TLS connection is established, &'smtp_printf()'& uses the TLS
output function, so it can be used for all forms of SMTP connection.
-.new
The second argument is used to request that the data be buffered
(when TRUE) or flushed (along with any previously buffered, when FALSE).
This is advisory only, but likely to save on system-calls and packets
The argument was added in Exim version 4.90 - changing the API/ABI.
Nobody noticed until 4.93 was imminent, at which point the
ABI version number was incremented.
-.wen
Strings that are written by &'smtp_printf()'& from within &[local_scan()]&
must start with an appropriate response code: 550 if you are going to return
The &'smtp_printf()'& function does not return any error indication, because it
does not
-.new
guarantee a flush of
-.wen
pending output, and therefore does not test
the state of the stream. (In the main code of Exim, flushing and error
detection is done when Exim is ready for the next SMTP input command.) If
&%millisec%&: Timestamps have a period and three decimal places of finer granularity
appended to the seconds value.
.next
-.new
.cindex "log" "message id"
&%msg_id%&: The value of the Message-ID: header.
.next
This will be either because the message is a bounce, or was submitted locally
(submission mode) without one.
The field identifier will have an asterix appended: &"id*="&.
-.wen
.next
.cindex "log" "outgoing interface"
.cindex "log" "local interface"
On accept lines, where PIPELINING was offered but not used by the client,
the field has a minus appended.
-.new
.cindex "pipelining" "early connection"
If Exim is built with the SUPPORT_PIPE_CONNECT build option
accept "L" fields have a period appended if the feature was
offered but not used, or an asterisk appended if used.
Delivery "L" fields have an asterisk appended if used.
-.wen
.next
.cindex "log" "queue run"
.vitem &*-x*&
Match only non-frozen messages.
-.new
.vitem &*-G*&&~<&'queuename'&>
Match only messages in the given queue. Without this, the default queue is searched.
-.wen
.endlist
The following options control the format of the output:
certificate.
.endlist
-.new
Any of the above may have an extra hyphen prepended, to indicate the the
corresponding data is untrusted.
-.wen
Following the options there is a list of those addresses to which the message
is not to be delivered. This set of addresses is initialized from the command
The domain(s) you want to sign with.
After expansion, this can be a list.
Each element in turn,
-.new
lowercased,
-.wen
is put into the &%$dkim_domain%& expansion variable
while expanding the remaining signing options.
If it is empty after expansion, DKIM signing is not done,
Signers SHOULD use RSA keys of at least 2048 bits.
.endd
-.new
EC keys for DKIM are defined by RFC 8463.
-.wen
They are considerably smaller than RSA keys for equivalent protection.
As they are a recent development, users should consider dual-signing
(by setting a list of selectors, and an expansion for this option)
certtool --load_privkey=dkim_ed25519.private --pubkey_info --outder | tail -c +13 | base64
.endd
-.new
Exim also supports an alternate format
of Ed25519 keys in DNS which was a candidate during development
of the standard, but not adopted.
A future release will probably drop that support.
-.wen
.option dkim_hash smtp string&!! sha256
Can be set to any one of the supported hash methods, which are:
Verification of DKIM signatures in SMTP incoming email is done for all
messages for which an ACL control &%dkim_disable_verify%& has not been set.
-.new
.cindex DKIM "selecting signature algorithms"
Individual classes of signature algorithm can be ignored by changing
the main options &%dkim_verify_hashes%& or &%dkim_verify_keytypes%&.
The &%dkim_verify_minimal%& option can be set to cease verification
processing for a message once the first passing signature is found.
-.wen
.cindex authentication "expansion item"
Performing verification sets up information used by the
&%authresults%& expansion item.
-.new
For most purposes the default option settings suffice and the remainder
of this section can be ignored.
-.wen
The results of verification are made available to the
&%acl_smtp_dkim%& ACL, which can examine and modify them.
If a domain or identity is listed several times in the (expanded) value of
&%dkim_verify_signers%&, the ACL is only called once for that domain or identity.
-.new
Note that if the option is set using untrustworthy data
(such as the From: header)
care should be taken to force lowercase for domains
and for the domain part if identities.
The default setting can be regarded as trustworthy in this respect.
-.wen
If multiple signatures match a domain (or identity), the ACL is called once
for each matching signature.
To enforce this you must either have a DKIM ACL which checks this variable
and overwrites the &$dkim_verify_status$& variable as discussed above,
-.new
or have set the main option &%dkim_verify_hashes%& to exclude
processing of such signatures.
-.wen
.vitem &%$dkim_canon_body%&
The body canonicalization method. One of 'relaxed' or 'simple'.
.cindex lookup spf
A lookup expansion is also available. It takes an email
address as the key and an IP address
-.new
(v4 or v6)
-.wen
as the database:
.code
-.new
.section DMARC SECDMARC
.cindex DMARC verification
warn add_header = :at_start:${authresults {$primary_hostname}}
.endd
-.wen
The name is placed in the variable &$event_name$& and the event action
expansion must check this, as it will be called for every possible event type.
-.new
The current list of events is:
-.wen
.display
&`dane:fail after transport `& per connection
&`msg:complete after main `& per message
git://git.exim.org / users / heiko / exim.git / blobdiff