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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>55.7. Message Formats</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="protocol-message-types.html" title="55.6. Message Data Types" /><link rel="next" href="protocol-error-fields.html" title="55.8. Error and Notice Message Fields" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">55.7. Message Formats</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="protocol-message-types.html" title="55.6. Message Data Types">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="protocol.html" title="Chapter 55. Frontend/Backend Protocol">Up</a></td><th width="60%" align="center">Chapter 55. Frontend/Backend Protocol</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="protocol-error-fields.html" title="55.8. Error and Notice Message Fields">Next</a></td></tr></table><hr /></div><div class="sect1" id="PROTOCOL-MESSAGE-FORMATS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">55.7. Message Formats</h2></div></div></div><p>
This section describes the detailed format of each message. Each is marked to
indicate that it can be sent by a frontend (F), a backend (B), or both
(F & B).
Notice that although each message includes a byte count at the beginning,
the message format is defined so that the message end can be found without
reference to the byte count. This aids validity checking. (The CopyData
message is an exception, because it forms part of a data stream; the contents
of any individual CopyData message cannot be interpretable on their own.)
</p><div class="variablelist"><dl class="variablelist"><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONOK"><span class="term">AuthenticationOk (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32(8)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(0)</span></dt><dd><p>
Specifies that the authentication was successful.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONKERBEROSV5"><span class="term">AuthenticationKerberosV5 (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32(8)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(2)</span></dt><dd><p>
Specifies that Kerberos V5 authentication is required.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONCLEARTEXTPASSWORD"><span class="term">AuthenticationCleartextPassword (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32(8)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(3)</span></dt><dd><p>
Specifies that a clear-text password is required.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONMD5PASSWORD"><span class="term">AuthenticationMD5Password (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32(12)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(5)</span></dt><dd><p>
Specifies that an MD5-encrypted password is required.
</p></dd><dt><span class="term">Byte4</span></dt><dd><p>
The salt to use when encrypting the password.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONSCMCREDENTIAL"><span class="term">AuthenticationSCMCredential (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32(8)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(6)</span></dt><dd><p>
Specifies that an SCM credentials message is required.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONGSS"><span class="term">AuthenticationGSS (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32(8)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(7)</span></dt><dd><p>
Specifies that GSSAPI authentication is required.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONGSSCONTINUE"><span class="term">AuthenticationGSSContinue (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(8)</span></dt><dd><p>
Specifies that this message contains GSSAPI or SSPI data.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
GSSAPI or SSPI authentication data.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONSSPI"><span class="term">AuthenticationSSPI (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32(8)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(9)</span></dt><dd><p>
Specifies that SSPI authentication is required.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONSASL"><span class="term">AuthenticationSASL (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(10)</span></dt><dd><p>
Specifies that SASL authentication is required.
</p></dd></dl></div><p>
The message body is a list of SASL authentication mechanisms, in the
server's order of preference. A zero byte is required as terminator after
the last authentication mechanism name. For each mechanism, there is the
following:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">String</span></dt><dd><p>
Name of a SASL authentication mechanism.
</p></dd></dl></div><p>
</p></dd><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONSASLCONTINUE"><span class="term">AuthenticationSASLContinue (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(11)</span></dt><dd><p>
Specifies that this message contains a SASL challenge.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
SASL data, specific to the SASL mechanism being used.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-AUTHENTICATIONSASLFINAL"><span class="term">AuthenticationSASLFinal (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('R')</span></dt><dd><p>
Identifies the message as an authentication request.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(12)</span></dt><dd><p>
Specifies that SASL authentication has completed.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
SASL outcome "additional data", specific to the SASL mechanism
being used.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-BACKENDKEYDATA"><span class="term">BackendKeyData (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('K')</span></dt><dd><p>
Identifies the message as cancellation key data.
The frontend must save these values if it wishes to be
able to issue CancelRequest messages later.
</p></dd><dt><span class="term">Int32(12)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
The process ID of this backend.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
The secret key of this backend.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-BIND"><span class="term">Bind (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('B')</span></dt><dd><p>
Identifies the message as a Bind command.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The name of the destination portal
(an empty string selects the unnamed portal).
</p></dd><dt><span class="term">String</span></dt><dd><p>
The name of the source prepared statement
(an empty string selects the unnamed prepared statement).
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The number of parameter format codes that follow
(denoted <em class="replaceable"><code>C</code></em> below).
This can be zero to indicate that there are no parameters
or that the parameters all use the default format (text);
or one, in which case the specified format code is applied
to all parameters; or it can equal the actual number of
parameters.
</p></dd><dt><span class="term">Int16[<em class="replaceable"><code>C</code></em>]</span></dt><dd><p>
The parameter format codes. Each must presently be
zero (text) or one (binary).
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The number of parameter values that follow (possibly zero).
This must match the number of parameters needed by the query.
</p></dd></dl></div><p>
Next, the following pair of fields appear for each parameter:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int32</span></dt><dd><p>
The length of the parameter value, in bytes (this count
does not include itself). Can be zero.
As a special case, -1 indicates a NULL parameter value.
No value bytes follow in the NULL case.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
The value of the parameter, in the format indicated by the
associated format code.
<em class="replaceable"><code>n</code></em> is the above length.
</p></dd></dl></div><p>
After the last parameter, the following fields appear:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int16</span></dt><dd><p>
The number of result-column format codes that follow
(denoted <em class="replaceable"><code>R</code></em> below).
This can be zero to indicate that there are no result columns
or that the result columns should all use the default format
(text);
or one, in which case the specified format code is applied
to all result columns (if any); or it can equal the actual
number of result columns of the query.
</p></dd><dt><span class="term">Int16[<em class="replaceable"><code>R</code></em>]</span></dt><dd><p>
The result-column format codes. Each must presently be
zero (text) or one (binary).
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-BINDCOMPLETE"><span class="term">BindComplete (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('2')</span></dt><dd><p>
Identifies the message as a Bind-complete indicator.
</p></dd><dt><span class="term">Int32(4)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-CANCELREQUEST"><span class="term">CancelRequest (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int32(16)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(80877102)</span></dt><dd><p>
The cancel request code. The value is chosen to contain
<code class="literal">1234</code> in the most significant 16 bits, and <code class="literal">5678</code> in the
least significant 16 bits. (To avoid confusion, this code
must not be the same as any protocol version number.)
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
The process ID of the target backend.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
The secret key for the target backend.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-CLOSE"><span class="term">Close (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('C')</span></dt><dd><p>
Identifies the message as a Close command.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Byte1</span></dt><dd><p>
'<code class="literal">S</code>' to close a prepared statement; or
'<code class="literal">P</code>' to close a portal.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The name of the prepared statement or portal to close
(an empty string selects the unnamed prepared statement
or portal).
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-CLOSECOMPLETE"><span class="term">CloseComplete (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('3')</span></dt><dd><p>
Identifies the message as a Close-complete indicator.
</p></dd><dt><span class="term">Int32(4)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-COMMANDCOMPLETE"><span class="term">CommandComplete (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('C')</span></dt><dd><p>
Identifies the message as a command-completed response.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The command tag. This is usually a single
word that identifies which SQL command was completed.
</p><p>
For an <code class="command">INSERT</code> command, the tag is
<code class="literal">INSERT <em class="replaceable"><code>oid</code></em>
<em class="replaceable"><code>rows</code></em></code>, where
<em class="replaceable"><code>rows</code></em> is the number of rows
inserted. <em class="replaceable"><code>oid</code></em> used to be the object ID
of the inserted row if <em class="replaceable"><code>rows</code></em> was 1
and the target table had OIDs, but OIDs system columns are
not supported anymore; therefore <em class="replaceable"><code>oid</code></em>
is always 0.
</p><p>
For a <code class="command">DELETE</code> command, the tag is
<code class="literal">DELETE <em class="replaceable"><code>rows</code></em></code> where
<em class="replaceable"><code>rows</code></em> is the number of rows deleted.
</p><p>
For an <code class="command">UPDATE</code> command, the tag is
<code class="literal">UPDATE <em class="replaceable"><code>rows</code></em></code> where
<em class="replaceable"><code>rows</code></em> is the number of rows updated.
</p><p>
For a <code class="command">MERGE</code> command, the tag is
<code class="literal">MERGE <em class="replaceable"><code>rows</code></em></code> where
<em class="replaceable"><code>rows</code></em> is the number of rows inserted,
updated, or deleted.
</p><p>
For a <code class="command">SELECT</code> or <code class="command">CREATE TABLE AS</code>
command, the tag is <code class="literal">SELECT <em class="replaceable"><code>rows</code></em></code>
where <em class="replaceable"><code>rows</code></em> is the number of rows retrieved.
</p><p>
For a <code class="command">MOVE</code> command, the tag is
<code class="literal">MOVE <em class="replaceable"><code>rows</code></em></code> where
<em class="replaceable"><code>rows</code></em> is the number of rows the
cursor's position has been changed by.
</p><p>
For a <code class="command">FETCH</code> command, the tag is
<code class="literal">FETCH <em class="replaceable"><code>rows</code></em></code> where
<em class="replaceable"><code>rows</code></em> is the number of rows that
have been retrieved from the cursor.
</p><p>
For a <code class="command">COPY</code> command, the tag is
<code class="literal">COPY <em class="replaceable"><code>rows</code></em></code> where
<em class="replaceable"><code>rows</code></em> is the number of rows copied.
(Note: the row count appears only in
<span class="productname">PostgreSQL</span> 8.2 and later.)
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-COPYDATA"><span class="term">CopyData (F & B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('d')</span></dt><dd><p>
Identifies the message as <code class="command">COPY</code> data.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
Data that forms part of a <code class="command">COPY</code> data stream. Messages sent
from the backend will always correspond to single data rows,
but messages sent by frontends might divide the data stream
arbitrarily.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-COPYDONE"><span class="term">CopyDone (F & B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('c')</span></dt><dd><p>
Identifies the message as a <code class="command">COPY</code>-complete indicator.
</p></dd><dt><span class="term">Int32(4)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-COPYFAIL"><span class="term">CopyFail (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('f')</span></dt><dd><p>
Identifies the message as a <code class="command">COPY</code>-failure indicator.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">String</span></dt><dd><p>
An error message to report as the cause of failure.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-COPYINRESPONSE"><span class="term">CopyInResponse (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('G')</span></dt><dd><p>
Identifies the message as a Start Copy In response.
The frontend must now send copy-in data (if not
prepared to do so, send a CopyFail message).
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int8</span></dt><dd><p>
0 indicates the overall <code class="command">COPY</code> format is textual (rows
separated by newlines, columns separated by separator
characters, etc.).
1 indicates the overall copy format is binary (similar
to DataRow format).
See <a class="xref" href="sql-copy.html" title="COPY"><span class="refentrytitle">COPY</span></a>
for more information.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The number of columns in the data to be copied
(denoted <em class="replaceable"><code>N</code></em> below).
</p></dd><dt><span class="term">Int16[<em class="replaceable"><code>N</code></em>]</span></dt><dd><p>
The format codes to be used for each column.
Each must presently be zero (text) or one (binary).
All must be zero if the overall copy format is textual.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-COPYOUTRESPONSE"><span class="term">CopyOutResponse (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('H')</span></dt><dd><p>
Identifies the message as a Start Copy Out response.
This message will be followed by copy-out data.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int8</span></dt><dd><p>
0 indicates the overall <code class="command">COPY</code> format
is textual (rows separated by newlines, columns
separated by separator characters, etc.). 1 indicates
the overall copy format is binary (similar to DataRow
format). See <a class="xref" href="sql-copy.html" title="COPY"><span class="refentrytitle">COPY</span></a> for more information.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The number of columns in the data to be copied
(denoted <em class="replaceable"><code>N</code></em> below).
</p></dd><dt><span class="term">Int16[<em class="replaceable"><code>N</code></em>]</span></dt><dd><p>
The format codes to be used for each column.
Each must presently be zero (text) or one (binary).
All must be zero if the overall copy format is textual.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-COPYBOTHRESPONSE"><span class="term">CopyBothResponse (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('W')</span></dt><dd><p>
Identifies the message as a Start Copy Both response.
This message is used only for Streaming Replication.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int8</span></dt><dd><p>
0 indicates the overall <code class="command">COPY</code> format
is textual (rows separated by newlines, columns
separated by separator characters, etc.). 1 indicates
the overall copy format is binary (similar to DataRow
format). See <a class="xref" href="sql-copy.html" title="COPY"><span class="refentrytitle">COPY</span></a> for more information.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The number of columns in the data to be copied
(denoted <em class="replaceable"><code>N</code></em> below).
</p></dd><dt><span class="term">Int16[<em class="replaceable"><code>N</code></em>]</span></dt><dd><p>
The format codes to be used for each column.
Each must presently be zero (text) or one (binary).
All must be zero if the overall copy format is textual.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-DATAROW"><span class="term">DataRow (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('D')</span></dt><dd><p>
Identifies the message as a data row.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The number of column values that follow (possibly zero).
</p></dd></dl></div><p>
Next, the following pair of fields appear for each column:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int32</span></dt><dd><p>
The length of the column value, in bytes (this count
does not include itself). Can be zero.
As a special case, -1 indicates a NULL column value.
No value bytes follow in the NULL case.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
The value of the column, in the format indicated by the
associated format code.
<em class="replaceable"><code>n</code></em> is the above length.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-DESCRIBE"><span class="term">Describe (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('D')</span></dt><dd><p>
Identifies the message as a Describe command.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Byte1</span></dt><dd><p>
'<code class="literal">S</code>' to describe a prepared statement; or
'<code class="literal">P</code>' to describe a portal.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The name of the prepared statement or portal to describe
(an empty string selects the unnamed prepared statement
or portal).
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-EMPTYQUERYRESPONSE"><span class="term">EmptyQueryResponse (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('I')</span></dt><dd><p>
Identifies the message as a response to an empty query string.
(This substitutes for CommandComplete.)
</p></dd><dt><span class="term">Int32(4)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-ERRORRESPONSE"><span class="term">ErrorResponse (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('E')</span></dt><dd><p>
Identifies the message as an error.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div><p>
The message body consists of one or more identified fields,
followed by a zero byte as a terminator. Fields can appear in
any order. For each field there is the following:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1</span></dt><dd><p>
A code identifying the field type; if zero, this is
the message terminator and no string follows.
The presently defined field types are listed in
<a class="xref" href="protocol-error-fields.html" title="55.8. Error and Notice Message Fields">Section 55.8</a>.
Since more field types might be added in future,
frontends should silently ignore fields of unrecognized
type.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The field value.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-EXECUTE"><span class="term">Execute (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('E')</span></dt><dd><p>
Identifies the message as an Execute command.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The name of the portal to execute
(an empty string selects the unnamed portal).
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Maximum number of rows to return, if portal contains
a query that returns rows (ignored otherwise). Zero
denotes <span class="quote">“<span class="quote">no limit</span>”</span>.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-FLUSH"><span class="term">Flush (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('H')</span></dt><dd><p>
Identifies the message as a Flush command.
</p></dd><dt><span class="term">Int32(4)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-FUNCTIONCALL"><span class="term">FunctionCall (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('F')</span></dt><dd><p>
Identifies the message as a function call.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Specifies the object ID of the function to call.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The number of argument format codes that follow
(denoted <em class="replaceable"><code>C</code></em> below).
This can be zero to indicate that there are no arguments
or that the arguments all use the default format (text);
or one, in which case the specified format code is applied
to all arguments; or it can equal the actual number of
arguments.
</p></dd><dt><span class="term">Int16[<em class="replaceable"><code>C</code></em>]</span></dt><dd><p>
The argument format codes. Each must presently be
zero (text) or one (binary).
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
Specifies the number of arguments being supplied to the
function.
</p></dd></dl></div><p>
Next, the following pair of fields appear for each argument:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int32</span></dt><dd><p>
The length of the argument value, in bytes (this count
does not include itself). Can be zero.
As a special case, -1 indicates a NULL argument value.
No value bytes follow in the NULL case.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
The value of the argument, in the format indicated by the
associated format code.
<em class="replaceable"><code>n</code></em> is the above length.
</p></dd></dl></div><p>
After the last argument, the following field appears:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int16</span></dt><dd><p>
The format code for the function result. Must presently be
zero (text) or one (binary).
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-FUNCTIONCALLRESPONSE"><span class="term">FunctionCallResponse (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('V')</span></dt><dd><p>
Identifies the message as a function call result.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
The length of the function result value, in bytes (this count
does not include itself). Can be zero.
As a special case, -1 indicates a NULL function result.
No value bytes follow in the NULL case.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
The value of the function result, in the format indicated by
the associated format code.
<em class="replaceable"><code>n</code></em> is the above length.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-GSSENCREQUEST"><span class="term">GSSENCRequest (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int32(8)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(80877104)</span></dt><dd><p>
The <acronym class="acronym">GSSAPI</acronym> Encryption request code. The value is chosen to contain
<code class="literal">1234</code> in the most significant 16 bits, and <code class="literal">5680</code> in the
least significant 16 bits. (To avoid confusion, this code
must not be the same as any protocol version number.)
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-GSSRESPONSE"><span class="term">GSSResponse (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('p')</span></dt><dd><p>
Identifies the message as a GSSAPI or SSPI response. Note that
this is also used for SASL and password response messages.
The exact message type can be deduced from the context.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
GSSAPI/SSPI specific message data.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-NEGOTIATEPROTOCOLVERSION"><span class="term">NegotiateProtocolVersion (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('v')</span></dt><dd><p>
Identifies the message as a protocol version negotiation
message.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Newest minor protocol version supported by the server
for the major protocol version requested by the client.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Number of protocol options not recognized by the server.
</p></dd></dl></div><p>
Then, for protocol option not recognized by the server, there
is the following:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">String</span></dt><dd><p>
The option name.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-NODATA"><span class="term">NoData (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('n')</span></dt><dd><p>
Identifies the message as a no-data indicator.
</p></dd><dt><span class="term">Int32(4)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-NOTICERESPONSE"><span class="term">NoticeResponse (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('N')</span></dt><dd><p>
Identifies the message as a notice.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div><p>
The message body consists of one or more identified fields,
followed by a zero byte as a terminator. Fields can appear in
any order. For each field there is the following:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1</span></dt><dd><p>
A code identifying the field type; if zero, this is
the message terminator and no string follows.
The presently defined field types are listed in
<a class="xref" href="protocol-error-fields.html" title="55.8. Error and Notice Message Fields">Section 55.8</a>.
Since more field types might be added in future,
frontends should silently ignore fields of unrecognized
type.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The field value.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-NOTIFICATIONRESPONSE"><span class="term">NotificationResponse (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('A')</span></dt><dd><p>
Identifies the message as a notification response.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
The process ID of the notifying backend process.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The name of the channel that the notify has been raised on.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The <span class="quote">“<span class="quote">payload</span>”</span> string passed from the notifying process.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-PARAMETERDESCRIPTION"><span class="term">ParameterDescription (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('t')</span></dt><dd><p>
Identifies the message as a parameter description.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The number of parameters used by the statement
(can be zero).
</p></dd></dl></div><p>
Then, for each parameter, there is the following:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int32</span></dt><dd><p>
Specifies the object ID of the parameter data type.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-PARAMETERSTATUS"><span class="term">ParameterStatus (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('S')</span></dt><dd><p>
Identifies the message as a run-time parameter status report.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The name of the run-time parameter being reported.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The current value of the parameter.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-PARSE"><span class="term">Parse (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('P')</span></dt><dd><p>
Identifies the message as a Parse command.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The name of the destination prepared statement
(an empty string selects the unnamed prepared statement).
</p></dd><dt><span class="term">String</span></dt><dd><p>
The query string to be parsed.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The number of parameter data types specified
(can be zero). Note that this is not an indication of
the number of parameters that might appear in the
query string, only the number that the frontend wants to
prespecify types for.
</p></dd></dl></div><p>
Then, for each parameter, there is the following:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int32</span></dt><dd><p>
Specifies the object ID of the parameter data type.
Placing a zero here is equivalent to leaving the type
unspecified.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-PARSECOMPLETE"><span class="term">ParseComplete (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('1')</span></dt><dd><p>
Identifies the message as a Parse-complete indicator.
</p></dd><dt><span class="term">Int32(4)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-PASSWORDMESSAGE"><span class="term">PasswordMessage (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('p')</span></dt><dd><p>
Identifies the message as a password response. Note that
this is also used for GSSAPI, SSPI and SASL response messages.
The exact message type can be deduced from the context.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The password (encrypted, if requested).
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-PORTALSUSPENDED"><span class="term">PortalSuspended (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('s')</span></dt><dd><p>
Identifies the message as a portal-suspended indicator.
Note this only appears if an Execute message's row-count limit
was reached.
</p></dd><dt><span class="term">Int32(4)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-QUERY"><span class="term">Query (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('Q')</span></dt><dd><p>
Identifies the message as a simple query.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The query string itself.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-READYFORQUERY"><span class="term">ReadyForQuery (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('Z')</span></dt><dd><p>
Identifies the message type. ReadyForQuery is sent
whenever the backend is ready for a new query cycle.
</p></dd><dt><span class="term">Int32(5)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Byte1</span></dt><dd><p>
Current backend transaction status indicator.
Possible values are '<code class="literal">I</code>' if idle (not in
a transaction block); '<code class="literal">T</code>' if in a transaction
block; or '<code class="literal">E</code>' if in a failed transaction
block (queries will be rejected until block is ended).
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-ROWDESCRIPTION"><span class="term">RowDescription (B)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('T')</span></dt><dd><p>
Identifies the message as a row description.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
Specifies the number of fields in a row (can be zero).
</p></dd></dl></div><p>
Then, for each field, there is the following:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">String</span></dt><dd><p>
The field name.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
If the field can be identified as a column of a specific
table, the object ID of the table; otherwise zero.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
If the field can be identified as a column of a specific
table, the attribute number of the column; otherwise zero.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
The object ID of the field's data type.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The data type size (see <code class="varname">pg_type.typlen</code>).
Note that negative values denote variable-width types.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
The type modifier (see <code class="varname">pg_attribute.atttypmod</code>).
The meaning of the modifier is type-specific.
</p></dd><dt><span class="term">Int16</span></dt><dd><p>
The format code being used for the field. Currently will
be zero (text) or one (binary). In a RowDescription
returned from the statement variant of Describe, the
format code is not yet known and will always be zero.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-SASLINITIALRESPONSE"><span class="term">SASLInitialResponse (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('p')</span></dt><dd><p>
Identifies the message as an initial SASL response. Note that
this is also used for GSSAPI, SSPI and password response messages.
The exact message type is deduced from the context.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">String</span></dt><dd><p>
Name of the SASL authentication mechanism that the client
selected.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of SASL mechanism specific "Initial Client Response" that
follows, or -1 if there is no Initial Response.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
SASL mechanism specific "Initial Response".
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-SASLRESPONSE"><span class="term">SASLResponse (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('p')</span></dt><dd><p>
Identifies the message as a SASL response. Note that
this is also used for GSSAPI, SSPI and password response messages.
The exact message type can be deduced from the context.
</p></dd><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Byte<em class="replaceable"><code>n</code></em></span></dt><dd><p>
SASL mechanism specific message data.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-SSLREQUEST"><span class="term">SSLRequest (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int32(8)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(80877103)</span></dt><dd><p>
The <acronym class="acronym">SSL</acronym> request code. The value is chosen to contain
<code class="literal">1234</code> in the most significant 16 bits, and <code class="literal">5679</code> in the
least significant 16 bits. (To avoid confusion, this code
must not be the same as any protocol version number.)
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-STARTUPMESSAGE"><span class="term">StartupMessage (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Int32</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd><dt><span class="term">Int32(196608)</span></dt><dd><p>
The protocol version number. The most significant 16 bits are
the major version number (3 for the protocol described here).
The least significant 16 bits are the minor version number
(0 for the protocol described here).
</p></dd></dl></div><p>
The protocol version number is followed by one or more pairs of
parameter name and value strings. A zero byte is required as a
terminator after the last name/value pair.
Parameters can appear in any
order. <code class="literal">user</code> is required, others are optional.
Each parameter is specified as:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">String</span></dt><dd><p>
The parameter name. Currently recognized names are:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">user</code></span></dt><dd><p>
The database user name to connect as. Required;
there is no default.
</p></dd><dt><span class="term"><code class="literal">database</code></span></dt><dd><p>
The database to connect to. Defaults to the user name.
</p></dd><dt><span class="term"><code class="literal">options</code></span></dt><dd><p>
Command-line arguments for the backend. (This is
deprecated in favor of setting individual run-time
parameters.) Spaces within this string are
considered to separate arguments, unless escaped with
a backslash (<code class="literal">\</code>); write <code class="literal">\\</code> to
represent a literal backslash.
</p></dd><dt><span class="term"><code class="literal">replication</code></span></dt><dd><p>
Used to connect in streaming replication mode, where
a small set of replication commands can be issued
instead of SQL statements. Value can be
<code class="literal">true</code>, <code class="literal">false</code>, or
<code class="literal">database</code>, and the default is
<code class="literal">false</code>. See
<a class="xref" href="protocol-replication.html" title="55.4. Streaming Replication Protocol">Section 55.4</a> for details.
</p></dd></dl></div><p>
In addition to the above, other parameters may be listed.
Parameter names beginning with <code class="literal">_pq_.</code> are
reserved for use as protocol extensions, while others are
treated as run-time parameters to be set at backend start
time. Such settings will be applied during backend start
(after parsing the command-line arguments if any) and will
act as session defaults.
</p></dd><dt><span class="term">String</span></dt><dd><p>
The parameter value.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-SYNC"><span class="term">Sync (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('S')</span></dt><dd><p>
Identifies the message as a Sync command.
</p></dd><dt><span class="term">Int32(4)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div></dd><dt id="PROTOCOL-MESSAGE-FORMATS-TERMINATE"><span class="term">Terminate (F)</span></dt><dd><div class="variablelist"><dl class="variablelist"><dt><span class="term">Byte1('X')</span></dt><dd><p>
Identifies the message as a termination.
</p></dd><dt><span class="term">Int32(4)</span></dt><dd><p>
Length of message contents in bytes, including self.
</p></dd></dl></div></dd></dl></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="protocol-message-types.html" title="55.6. Message Data Types">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="protocol.html" title="Chapter 55. Frontend/Backend Protocol">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="protocol-error-fields.html" title="55.8. Error and Notice Message Fields">Next</a></td></tr><tr><td width="40%" align="left" valign="top">55.6. Message Data Types </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 55.8. Error and Notice Message Fields</td></tr></table></div></body></html>
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