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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →In Mule 4, HTTP headers are metadata on a message, not part of its payload. Read incoming Listener headers from attributes.headers, define headers for an outbound HTTP Request in that operation’s <http:headers> element, and configure headers returned by an HTTP Listener in its <http:response> element. Save the original attributes before a processor replaces the current message if later steps still need them.
Where HTTP headers live in Mule 4
A Mule message has a payload and attributes. The payload carries the content being processed; attributes hold metadata associated with that message. Mule 4 uses typed attributes instead of Mule 3 inbound properties. For an HTTP Listener, received request headers are available at attributes.headers, alongside request details such as method, path, and query parameters. MuleSoft’s Mule message documentation explains the message model.
#[attributes.headers.'x-correlation-id']Header names and expression syntax depend on the connector and DataWeave context. MuleSoft’s Mule 3 migration guide specifically maps Mule 3’s inboundProperties.'host' to Mule 4’s attributes.headers.'host'.
Read headers from an HTTP Listener request
Use the Listener’s current attributes when you need a value from the incoming request. For example, an expression can read a correlation ID from the request header map:
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#[attributes.headers.'x-correlation-id']This is request metadata for the message currently produced by the Listener. It is distinct from headers returned by a downstream HTTP Request, even though both can be accessed through attributes.headers.
Preserve request metadata when an operation replaces the message
Mule messages are immutable. An operation that produces a new message replaces the current payload and attributes with its output. For example, after a JMS publish-consume operation, the current attributes may be JMS attributes rather than the original HTTP Listener attributes. Do not assume the incoming HTTP headers remain available as the current attributes.
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If a later step needs the original request metadata, save it before the replacing operation:
<set-variable variableName="requestAttributes" value="#[attributes]" />Later, read the saved value through vars.requestAttributes. The attributes expression still refers to the current message. When appropriate, an operation’s target parameter can also store its result in a variable rather than replacing the current message; see MuleSoft’s message documentation. Decide whether downstream logic needs the original HTTP metadata, the new connector’s attributes, or both.
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Set headers on an outbound HTTP Request
Configure headers on the HTTP Request operation using a DataWeave map in <http:headers>. Keep query parameters and URI parameters in their separate connector configuration elements. MuleSoft documents this configuration in its HTTP migration guidance.
<http:request config-ref="requestConfig" path="issues" method="GET">
<http:headers>#[{'x-client': vars.clientName}]</http:headers>
</http:request>The example sends x-client with the value stored in vars.clientName. Build the map from the header values the called service requires. The migration guide also advises encoding characters such as { and } in HTTP request paths and URLs to avoid malformed URIs.
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Read headers from an HTTP Request response
An HTTP Request operation returns HTTP Response Attributes. In the resulting message, use attributes.headers for response headers, attributes.statusCode for the status code, and attributes.reasonPhrase for the reason phrase. MuleSoft lists this mapping in its HTTP migration guide.
The meaning of attributes.headers depends on which operation produced the current message: after an HTTP Listener it represents incoming request headers; after an HTTP Request it represents the called service’s response headers.
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Return headers from an HTTP Listener
Set Listener response headers in the <http:response> element. MuleSoft’s HTTP Listener documentation shows the response configuration pattern. A variable containing a map lets flow logic supply headers; the default below makes the map empty when the variable is unset.
<http:listener config-ref="api-httpListenerConfig" path="/api/*">
<http:response statusCode="#[vars.httpStatus default 200]">
<http:headers>#[vars.outboundHeaders default {}]</http:headers>
</http:response>
<http:error-response statusCode="#[vars.httpStatus default 500]">
<http:body>#[payload]</http:body>
<http:headers>#[vars.outboundHeaders default {}]</http:headers>
</http:error-response>
</http:listener>The normal and error responses are configured separately. Include required headers in the error-response configuration too when errors must return them. MuleSoft’s APIkit header documentation demonstrates adding a header to an outboundHeaders map with Set Variable.
Choose the right layer for header handling
| Need | Where to handle it | What to watch |
|---|---|---|
| Inspect headers on an incoming HTTP request | HTTP Listener message attributes: attributes.headers |
Attributes may be replaced when a later operation returns a new message. |
| Send headers to a downstream HTTP service | HTTP Request operation’s <http:headers> map |
Configure query and URI parameters separately. |
| Inspect headers returned by a downstream HTTP service | HTTP Request response attributes: attributes.headers |
These are response headers, not the original Listener request headers. |
| Return headers to the caller | HTTP Listener’s <http:response><http:headers> |
Configure <http:error-response> headers separately when needed. |
| Apply headers at an API gateway policy layer | MuleSoft Header Injection policy | Use for gateway-level request or response handling, not as a requirement for ordinary flow configuration. |
MuleSoft’s Header Injection policy documentation describes configured inbound and outbound key-value maps for adding HTTP headers. The policy is available starting with Mule version 4.1.0, according to that documentation.
Translate Mule 3 inbound properties
When migrating a flow, translate Mule 3 inbound HTTP properties to the typed attributes supplied by the relevant Mule 4 source or operation. For headers, the mapping is from the inbound-property namespace to attributes.headers. The HTTP migration guide also covers metadata such as method, listener path, relative path, request URI, query string, query parameters, URI parameters, HTTP version, scheme, remote address, and client certificate. HTTP Request response metadata maps to HTTP Response Attributes, including headers, status code, and reason phrase. Consult MuleSoft’s migration mapping for the specific property you are translating.
